1. Anatomy of the heart I:
location and structure of heart, anatomy of chambers. Systemic and pulmonary
circulation
2. Anatomy of the heart II: structure of heart wall, blood supplying
and innervation of the heart. Pericardium. Projection of heart on the front
thoracic wall
3.
Thoracic part of aorta: topography, parietal and visceral branches. System of superior vena cava
Lesson # 28
Theme 1. Anatomy of the heart I: location and structure
of heart, anatomy of chambers. Systemic and pulmonary circulation
THE VASCULAR system is divided for
descriptive purposes into (a) the blood vascular system, which comprises
the heart and bloodvessels for the circulation of the blood; and (b) the lymph vascular system, consisting of lymph glands and lymphatic
vessels, through which a colorless fluid, the lymph, circulates. It must be noted, however, that the two systems
communicate with each other and are intimately associated developmentally.
The heart is the central organ of the
blood vascular system, and consists of a hollow muscle; by its contraction the
blood is pumped to all parts of the body through a complicated series of tubes,
termed arteries. The arteries
undergo enormous ramification in their course throughout the body, and end in
minute vessels, called arterioles,
which in their turn open into a close-meshed network of microscopic vessels,
termed capillaries. After the blood
has passed through the capillaries it is collected into a series of larger
vessels, called veins, by which it
is returned to the heart. The passage of the blood through the heart and
blood-vessels constitutes what is termed the circulation of the blood, of which the following is an outline.
The HEART is a hollow
muscular organ, which is situated in thoracic cavity in middle mediastinum. It
has a heart apex, which is directed down to the left and heart base.
Heart has a sternocostal (anterior) surface, diaphragmatic
(posterior) surface, right/left pulmonary surfaces. Coronal
sulcus passes on diaphragmatic and partially on sternоcostal surfaces,
which marks the border between ventricles and atriums. Anterior
interventricular sulcus and posterior interventricular sulcus
pass from coronal sulcus downward and project borders between right and left
ventricles. On heart base right and left auricles are situated, which
envelop the great vessels. On heart base at the anterior from right ventricle pulmonary
trunk passes, which subdivides into two pulmonary arteries. Aorta
passes
behind pulmonary trunk; behind from aorta from right side superior vena cava
and inferior vena cava, and to the left four pulmonary veins.
Front view of heart and lungs.
Heart
cavity subdivides on right and left atriums and right and left ventricles.
Left chambers of heart are arterial and in adult do not communicate with right
venous half of heart. Exist two blood circles.
Big
circle or systemic circulation of the blood starts in left ventricle by
aorta and terminates in right atrium by vena cava superior and inferior.
Systemic circulation of the blood provides by arterial blood all of organs and
tissues.
The
small circle or pulmonary circulation of the blood begins by pulmonary
trunk from right ventricle and terminates in left atrium by 4 pulmonary veins.
Venous blood flows in arteries of pulmonary circulation of which and arterial
(oxygenated) blood - in veins.
VIDEO
Right
atrium consists of
own atrium and right auricle.
Internal
wall is smooth, but in auricle pectinate muscles are situated. Right
atrium receives the superior and inferior venae cavae, which open by foramen
of inferior vena cava and foramen of superior vena cava. Intervensus
tubercle is situated between these foramens. Broadened posterior area,
where two venae cavae fall is called as sinus venae cavae. Right atrium
is separated from left by interatrial septum, where oval fossa is
situated. It is limited by limbus of oval fossa. Atrium
communicates by right ventricle through the right atrioventricular ostium.
Foramen of coronal sinus situated between last and foramen of inferior
vena cava. Alongside are contained foramens of venarum minimarum.
Right
ventricle consists of
own ventricle and conus arteriosus - superior part, which continues
through the ostium of pulmonary trunk into pulmonary trunk. The right
and left ventricles are separated by interventricular septum, which has
muscular part (greater) and membranous part (lesser). On internal surface of
right ventricle are situated the trabeculi carneae, which carry
cone-shaped anterior, posterior and septal pappillar muscles.
From top of these muscles chordae tendineae start and terminate at cusps
of right atrioventricular valve.
Right
atrioventricular ostium closes by right
atrioventricular (tricuspidal) valve, which consists of anterior
cusp, posterior cusp and septal cusp edges of which attach to chordae
tendineae. During contraction of atria blood stream presses the cusps to
the wall of ventricle. During contraction of ventricles free edges of cusps
close up but do not pull out because they are kept by chordae tendineae from
ventricle. Ostium of pulmonary trunk closes by valve of pulmonary
trunk, which consists of right, left and anterior semilunar valvulae,
which have on superior margin the nodules of semilunar valvulae. Nodules
assist to compact closing up. Between each semilunar valvula and
pulmonary trunk wall sinuses of pulmonary trunk are situated.
Base and diaphragmatic surface of heart.
Left
atrium has an
irregular cube shape; anterior wall forms a left auricle. Internal wall
surfaces of left atrium is smooth and only in auricle area pectinate muscles
are situated. The ostia of 4 pulmonary veins open into left atrium. Left
atrium communicates with left ventricle by the means of left
atrioventricular ostium. Oval fossa makes a mark poorly on interatrial
septum.
Left
ventricle is the
largest heart chamber, its wall forms larger part of diaphragmatic surface. Internal
surface containes the trabeculi carneae, which attach anterior
papillary muscle and posterior papillary muscle. The tops of these
muscles by means of cordae tendineae hold the cusps of mitral valve.
Left atrioventricular ostium
closes by left atrioventricular (bicuspidal) valve [valve mitralis],
which consists of anterior cusp and posterior cusp edges of which
attach to chordae tendineae. From left ventricle aorta starts. Aortic
ostium closes by aortic valve, which consists of right,
left and posterior semilunar valvulae, which have on superior margin the nodules
of semilunar valvulae. Between each semilunar valvula and aorta walls are
situated aortic sinuses.
Base of ventricles exposed by removal of the atria.
Size.—The heart, in the adult, measures
about 12 cm.
in length, 8 to 9 cm.
in breadth at the broadest part, and 6 cm. in thickness. Its weight, in the
male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. The
heart continues to increase in weight and size up to an advanced period of
life; this increase is more marked in men than in women.
Component Parts.—As has already been
stated (page 497), the heart is subdivided by septa into right and left halves,
and a constriction subdivides each half of the organ into two cavities, the
upper cavity being called the atrium, the lower the ventricle.
The heart therefore consists of four chambers, viz., right and left atria, and
right and left ventricles.
The division of the heart into four cavities is indicated on its surface
by grooves. The atria are separated from the ventricles by the coronary
sulcus (auriculoventricular groove); this contains the trunks of the
nutrient vessels of the heart, and is deficient in front, where it is crossed
by the root of the pulmonary artery. The interatrial groove, separating
the two atria, is scarcely marked on the posterior surface, while anteriorly it
is hidden by the pulmonary artery and aorta. The ventricles are separated by
two grooves, one of which, the anterior longitudinal sulcus, is situated
on the sternocostal surface of the heart, close to its left margin, the other posterior
longitudinal sulcus, on the diaphragmatic surface near the right margin;
these grooves extend from the base of the ventricular portion to a notch, the incisura
apicis cordis, on the acute margin of the heart just to the right of the
apex.
The base (basis cordis) (491), directed upward, backward, and to the right, is separated from the
fifth, sixth, seventh, and eighth thoracic vertebræ by the esophagus,
aorta, and thoracic duct. It is formed mainly by the left atrium, and, to a
small extent, by the back part of the right atrium. Somewhat quadrilateral in
form, it is in relation above with the bifurcation of the pulmonary artery, and
is bounded below by the posterior part of the coronary sulcus, containing the
coronary sinus. On the right it is limited by the sulcus terminalis of the
right atrium, and on the left by the ligament of the left vena cava and the
oblique vein of the left atrium. The four pulmonary veins, two on either side,
open into the left atrium, while the superior vena cava opens into the upper,
and the anterior vena cava into the lower, part of the right atrium.
VIDEO
The Apex (apex cordis).—The
apex is directed downward, forward, and to the left, and is overlapped by the
left lung and pleura: it lies behind the fifth left intercostal space, 8 to 9 cm. from the
mid-sternal line, or about 4
cm. below and 2 mm. to the medial side of the left
mammary papilla.
The sternocostal surface (492) is directed forward, upward, and to the left. Its lower part is convex,
formed chiefly by the right ventricle, and traversed near its left margin by
the anterior longitudinal sulcus. Its upper part is separated from the lower by
the coronary sulcus, and is formed by the atria; it presents a deep concavity (494), occupied by the ascending aorta and the pulmonary artery.
The diaphragmatic surface (491), directed downward and slightly backward, is formed by the ventricles,
and rests upon the central tendon and a small part of the left muscular portion
of the diaphragm. It is separated from the base by the posterior part of the
coronary sulcus, and is traversed obliquely by the posterior longitudinal
sulcus.
The right margin of the heart is long, and is formed by the right
atrium above and the right ventricle below. The atrial portion is rounded and
almost vertical; it is situated behind the third, fourth, and fifth right
costal cartilages about 1.25
cm. from the margin of the sternum. The ventricular
portion, thin and sharp, is named the acute margin; it is nearly
horizontal, and extends from the sternal end of the sixth right costal
cartilage to the apex of the heart.
The left or obtuse margin is shorter, full, and rounded:
it is formed mainly by the left ventricle, but to a slight extent, above, by
the left atrium. It extends from a point in the second left intercostal space,
about 2.5 mm.
from the sternal margin, obliquely downward, with a convexity to the left, to
the apex of the heart.
Right Atrium (atrium dextrum; right auricle).—The right atrium is larger than the left, but its walls are somewhat
thinner, measuring about 2
mm.; its cavity is capable of containing about 57 c.c.
It consists of two parts: a principal cavity, or sinus venarum, situated
posteriorly, and an anterior, smaller portion, the auricula.
Sinus Venarum (sinus venosus).—The
sinus venarum is the large quadrangular cavity placed between the two
venæ cavæ. Its walls, which are extremely thin, are connected below
with the right ventricle, and medially with the left atrium, but are free in
the rest of their extent.
Auricula (auricula dextra; right auricular appendix).—The auricula is a small conical muscular pouch, the margins of which
present a dentated edge. It projects from the upper and front part of the sinus
forward and toward the left side, overlapping the root of the aorta.
Sternocostal
surface of heart.
The separation of the auricula from the sinus venarum is indicated
externally by a groove, the terminal sulcus, which extends from the
front of the superior vena cava to the front of the inferior vena cava, and
represents the line of union of the sinus venosus of the embryo with the
primitive atrium. On the inner wall of the atrium the separation is marked by a
vertical, smooth, muscular ridge, the terminal crest. Behind the crest
the internal surface of the atrium is smooth, while in front of it the muscular
fibers of the wall are raised into parallel ridges resembling the teeth of a
comb, and hence named the musculi pectinati.
Its interior presents the following parts for examination:
Openings »
Superior vena cava.
Inferior vena cava.
Coronary sinus.
Valves »
Valve of the inferior vena cava.
Foramina venarum minimarum.
Valve of the coronary sinus.
Atrioventricular.
Fossa ovalis.
Limbus fossæ ovalis.
Intervenous tubercle.
Musculi pectinati.
Crista terminalis.
VIDEO
The superior vena cava returns the blood from the upper half of the
body, and opens into the upper and back part of the atrium, the direction of
its orifice being downward and forward. Its opening has no valve.
The inferior vena cava, larger than the superior, returns the
blood from the lower half of the body, and opens into the lowest part of the
atrium, near the atrial septum, its orifice being directed upward and backward,
and guarded by a rudimentary valve, the valve of the inferior vena cava
(Eustachian valve). The blood entering the atrium through the superior
vena cava is directed downward and forward, i.e., toward the
atrioventricular orifice, while that entering through the inferior vena cava is
directed upward and backward, toward the atrial septum. This is the normal
direction of the two currents in fetal life.
The coronary sinus opens into the atrium, between the orifice of
the inferior vena cava and the atrioventricular opening. It returns blood from
the substance of the heart and is protected by a semicircular valve, the valve
of the coronary sinus (valve of Thebesius).
Interior
of right side of heart.
The foramina venarum minimarum (foramina Thebesii) are the
orifices of minute veins (venœ cordis minimœ), which return
blood directly from the muscular substance of the heart.
The atrioventricular opening (tricuspid orifice) is the
large oval aperture of communication between the atrium and the ventricle; it
will be described with the right ventricle.
The valve of the inferior vena cava (valvula venœ
cavœ inferioris [Eustachii]; Eustachian valve) is
situated in front of the orifice of the inferior vena cava. It is semilunar in
form, its convex margin being attached to the anterior margin of the orifice;
its concave margin, which is free, ends in two cornua, of which the left is
continuous with the anterior edge of the limbus fossæ ovalis while the
right is lost on the wall of the atrium. The valve is formed by a duplicature
of the lining membrane of the atrium, containing a few muscular fibers. In
the fetus this valve is of large size, and serves to direct the blood from
the inferior vena cava, through the foramen ovale, into the left atrium. In
the adult it occasionally persists, and may assist in preventing the reflux
of blood into the inferior vena cava; more commonly it is small, and may
present a cribriform or filamentous appearance; sometimes it is altogether
wanting.
The valve of the coronary sinus (valvula sinus coronarii [Thebesii];
Thebesian valve) is a semicircular fold of the lining membrane of the
atrium, at the orifice of the coronary sinus. It prevents the regurgitation of
blood into the sinus during the contraction of the atrium. This valve may be
double or it may be cribriform.
The fossa ovalis is an oval depression on the septal wall of the
atrium, and corresponds to the situation of the foramen ovale in the fetus. It
is situated at the lower part of the septum, above and to the left of the
orifice of the inferior vena cava.
The limbus fossæ ovalis (annulus ovalis) is the
prominent oval margin of the fossa ovalis. It is most distinct above and at the
sides of the fossa; below, it is deficient. A small slit-like valvular opening
is occasionally found, at the upper margin of the fossa, leading upward beneath
the limbus, into the left atrium; it is the remains of the fetal aperture
between the two atria.
The intervenous tubercle (tuberculum intervenosum; tubercle of
Lower) is a small projection on the posterior wall of the atrium, above the
fossa ovalis. It is distinct in the hearts of quadrupeds, but in man is
scarcely visible. It was supposed by Lower to direct the blood from the
superior vena cava toward the atrioventricular opening.
Right Ventricle (ventriculus dexter).—The
right ventricle is triangular in form, and extends from the right atrium to
near the apex of the heart. Its anterosuperior surface is rounded and convex,
and forms the larger part of the sternocostal surface of the heart. Its under
surface is flattened, rests upon the diaphragm, and forms a small part of the
diaphragmatic surface of the heart. Its posterior wall is formed by the
ventricular septum, which bulges into the right ventricle, so that a transverse
section of the cavity presents a semilunar outline. Its upper and left angle
forms a conical pouch, the conus arteriosus, from which the pulmonary
artery arises. A tendinous band, which may be named the tendon of the conus
arteriosus, extends upward from the right atrioventricular fibrous ring and
connects the posterior surface of the conus arteriosus to the aorta. The wall
of the right ventricle is thinner than that of the left, the proportion between
them being as 1 to 3; it is thickest at the base, and gradually becomes thinner
toward the apex. The cavity equals in size that of the left ventricle, and is
capable of containing about 85 c.c.
Its interior (493) presents the following parts for examination:
Openings »
Right atrioventricular.
Valves »
Tricuspid.
Pulmonary artery.
Pulmonary.
Trabeculæ carneæ
Chordæ tendineæ
The right atrioventricular orifice is the large oval aperture of
communication between the right atrium and ventricle. Situated at the base of
the ventricle, it measures about 4 cm. in diameter and is surrounded by a
fibrous ring, covered by the lining membrane of the heart; it is considerably
larger than the corresponding aperture on the left side, being sufficient to
admit the ends of four fingers. It is guarded by the tricuspid valve.
The opening of the pulmonary artery is circular in form, and
situated at the summit of the conus arteriosus, close to the ventricular
septum. It is placed above and to the left of the atrioventricular opening, and
is guarded by the pulmonary semilunar valves.
VIDEO
The tricuspid valve (valvula tricuspidalis) (493,
495) consists of three somewhat triangular cusps or segments. The largest
cusp is interposed between the atrioventricular orifice and the conus
arteriosus and is termed the anterior or infundibular cusp. A
second, the posterior or marginal cusp, is in relation to the
right margin of the ventricle, and a third, the medial or septal
cusp, to the ventricular septum. They are formed by duplicatures of the
lining membrane of the heart, strengthened by intervening layers of fibrous
tissue: their central parts are thick and strong, their marginal portions thin
and translucent, and in the angles between the latter small intermediate
segments are sometimes seen. Their bases are attached to a fibrous ring
surrounding the atrioventricular orifice and are also joined to each other so
as to form a continuous annular membrane, while their apices project into the
ventricular cavity. Their atrial surfaces, directed toward the blood current
from the atrium, are smooth; their ventricular surfaces, directed toward the
wall of the ventricle, are rough and irregular, and, together with the apices
and margins of the cusps, give attachment to a number of delicate tendinous
cords, the chordæ tendineæ.
Heart
seen from above.
The trabeculæ carneæ (columnœ carneœ)
are rounded or irregular muscular columns which project from the whole of the
inner surface of the ventricle, with the exception of the conus arteriosus.
They are of three kinds: some are attached along their entire length on one
side and merely form prominent ridges, others are fixed at their extremities
but free in the middle, while a third set (musculi papillares) are continuous
by their bases with the wall of the ventricle, while their apices give origin
to the chordæ tendineæ which pass to be attached to the segments of
the tricuspid valve. There are two papillary muscles, anterior and posterior:
of these, the anterior is the larger, and its chordæ tendineæ are
connected with the anterior and posterior cusps of the valve: the posterior
papillary muscle sometimes consists of two or three parts; its chordæ
tendineæ are connected with the posterior and medial cusps. In addition
to these, some chordæ tendineæ spring directly from the ventricular
septum, or from small papillary eminences on it, and pass to the anterior and
medial cusps. A muscular band, well-marked in sheep and some other animals,
frequently extends from the base of the anterior papillary muscle to the
ventricular septum. From its attachments it may assist in preventing
overdistension of the ventricle, and so has been named the moderator band.
The pulmonary semilunar valves (494) are three in number, two in front and one behind, formed by
duplicatures of the lining membrane, strengthened by fibrous tissue. They are
attached, by their convex margins, to the wall of the artery, at its junction
with the ventricle, their free borders being directed upward into the lumen of
the vessel. The free and attached margins of each are strengthened by tendinous
fibers, and the former presents, at its middle, a thickened nodule (corpus
Arantii). From this nodule tendinous fibers radiate through the segment to
its attached margin, but are absent from two narrow crescentic portions, the lunulæ,
placed one on either side of the nodule immediately adjoining the free margin.
Between the semilunar valves and the wall of the pulmonary artery are three pouches
or sinuses (sinuses of Valsalva).
Left Atrium (atrium sinistum; left auricle).—The left atrium is rather smaller than the right, but its walls are
thicker, measuring about 3
mm.; it consists, like the right, of two parts, a principal
cavity and an auricula.
The principal cavity is cuboidal in form, and concealed, in
front, by the pulmonary artery and aorta; in front and to the right it is
separated from the right atrium by the atrial septum; opening into it on either
side are the two pulmonary veins.
Auricula (auricula sinistra; left auricular appendix).—The auricula is somewhat constricted at its junction with the principal
cavity; it is longer, narrower, and more curved than that of the right side,
and its margins are more deeply indented. It is directed forward and toward the
right and overlaps the root of the pulmonary artery.
Interior
of left side of heart.
The interior of the left atrium (496)
presents the following parts for examination:
Openings of the four pulmonary veins.
Left atrioventricular opening.
Musculi pectinati.
The pulmonary veins, four in number, open into the upper part of
the posterior surface of the left atrium—two on either side of its middle line:
they are not provided with valves. The two left veins frequently end by a
common opening.
The left atrioventricular opening is the aperture between the
left atrium and ventricle, and is rather smaller than the corresponding opening
on the right side.
The musculi pectinati, fewer and smaller than in the right
auricula, are confined to the inner surface of the auricula.
On the atrial septum may be seen a lunated impression, bounded below by
a crescentic ridge, the concavity of which is turned upward. The depression is
just above the fossa ovalis of the right atrium.
Left Ventricle (ventriculus sinister).—The left ventricle is longer and more conical in shape than the right,
and on transverse section its concavity presents an oval or nearly circular
outline. It forms a small part of the sternocostal surface and a considerable
part of the diaphragmatic surface of the heart; it also forms the apex of the
heart. Its walls are about three times as thick as those of the right
ventricle.
Its interior (496) presents the following parts for examination:
Openings »
Left atrioventricular.
Valves »
Bicuspid or Mitral.
Aortic.
Aortic.
Trabeculæ carneæ.
Chordæ tendineæ
The left atrioventricular opening (mitral orifice) is
placed below and to the left of the aortic orifice. It is a little smaller than
the corresponding aperture of the opposite side, admitting only two fingers. It
is surrounded by a dense fibrous ring, covered by the lining membrane of the
heart, and is guarded by the bicuspid or mitral valve.
Aorta
laid open to show the semilunar valves.
The aortic opening is a circular aperture, in front and to the
right of the atrioventricular, from which it is separated by the anterior cusp
of the bicuspid valve. Its orifice is guarded by the aortic semilunar valves.
The portion of the ventricle immediately below the aortic orifice is termed the
aortic vestibule, and possesses fibrous instead of muscular walls.
VIDEO
The bicuspid or mitral valve (valvula bicuspidalis
[metralis]) (495,
496) is attached to the circumference of the left atrioventricular orifice
in the same way that the tricuspid valve is on the opposite side. It consists
of two triangular cusps, formed by duplicatures of the lining membrane,
strengthened by fibrous tissue, and containing a few muscular fibers. The cusps
are of unequal size, and are larger, thicker, and stronger than those of the
tricuspid valve. The larger cusp is placed in front and to the right between
the atrioventricular and aortic orifices, and is known as the anterior or
aortic cusp; the smaller or posterior cusp is placed behind and
to the left of the opening. Two smaller cusps are usually found at the angles
of junction of the larger. The cusps of the bicuspid valve are furnished with
chordæ tendineæ, which are attached in a manner similar to those on
the right side; they are, however, thicker, stronger, and less numerous.
The aortic semilunar valves (494,
497) are three in number, and surround the orifice of the aorta; two are
anterior (right and left) and one posterior. They are similar in structure, and
in their mode of attachment, to the pulmonary semilunar valves, but are larger,
thicker, and stronger; the lunulæ are more distinct, and the noduli or
corpora Arantii thicker and more prominent. Opposite the valves the aorta
presents slight dilatations, the aortic sinuses (sinuses of Valsalva),
which are larger than those at the origin of the pulmonary artery.
The trabeculæ carneæ are of three kinds, like those
upon the right side, but they are more numerous, and present a dense
interlacement, especially at the apex, and upon the posterior wall of the
ventricle. The musculi papillares are two in number, one being connected
to the anterior, the other to the posterior wall; they are of large size, and
end in rounded extremities from which the chordæ tendineæ arise.
The chordæ tendineæ from each papillary muscle are connected to
both cusps of the bicuspid valve.
The course of the blood from
the left ventricle through the body generally to the right side of the heart
constitutes the greater or systemic
circulation, while its passage from the right ventricle through the lungs
to the left side of the heart is termed the lesser or pulmonary circulation.
It is necessary, however, to state
that the blood which circulates through the spleen, pancreas, stomach, small
intestine, and the greater part of the large intestine is not returned directly
from these organs to the heart, but is conveyed by the portal vein to the liver. In the liver this vein divides, like an
artery, and ultimately ends in capillary-like vessels (sinusoids), from which the rootlets of a series of veins, called
the hepatic veins, arise; these
carry the blood into the inferior vena cava, whence it is conveyed to the right
atrium. From this it will be seen that the blood contained in the portal vein
passes through two sets of vessels: (1) the capillaries in the spleen,
pancreas, stomach, etc., and (2) the sinusoids in the liver. The blood in the
portal vein carries certain of the products of digestion: the carbohydrates,
which are mostly taken up by the liver cells and stored as glycogen, and the
protein products which remain in solution and are carried into the general
circulation to the various tissues and organs of the body.
Speaking generally, the arteries may
be said to contain pure and the veins impure blood. This is true of the
systemic, but not of the pulmonary vessels, since it has been seen that the
impure blood is conveyed from the heart to the lungs by the pulmonary arteries,
and the pure blood returned from the lungs to the heart by the pulmonary veins.
Arteries, therefore, must be defined as vessels which convey blood from the heart, and veins as vessels
which return blood to the heart.
Section
of the heart showing the ventricular septum.
Ventricular Septum (septum ventriculorum; interventricular septum)
(498).
—The
ventricular septum is directed obliquely backward and to the right, and is
curved with the convexity toward the right ventricle: its margins correspond
with the anterior and posterior longitudinal sulci. The greater portion of it
is thick and muscular and constitutes the muscular ventricular septum,
but its upper and posterior part, which separates the aortic vestibule from the
lower part of the right atrium and upper part of the right ventricle, is thin
and fibrous, and is termed the membranous ventricular septum. An
abnormal communication may exist between the ventricles at this part owing to
defective development of the membranous septum.
THE
DISTRIBUTION of the systematic arteries is like a highly ramified tree, the
common trunk of which, formed by the aorta, commences at the left ventricle,
while the smallest ramifications extend to the peripheral parts of the body and
the contained organs. Arteries are found in all parts of the body, except in
the hairs, nails, epidermis, cartilages, and cornea; the larger trunks usually
occupy the most protected situations, running, in the limbs, along the flexor
surface, where they are less exposed to injury.
There
is considerable variation in the mode of division of the arteries: occasionally
a short trunk subdivides into several branches at the same point, as may be
observed in the celiac artery and the thyrocervical trunk: the vessel may give
off several branches in succession, and still continue as the main trunk, as is
seen in the arteries of the limbs; or the division may be dichotomous, as, for
instance, when the aorta divides into the two common iliacs.
A
branch of an artery is smaller than the trunk from which it arises; but if an
artery divides into two branches, the combined sectional area of the two
vessels is, in nearly every instance, somewhat greater than that of the trunk;
and the combined sectional area of all the arterial branches greatly exceeds
that of the aorta; so that the arteries collectively may be regarded as a cone,
the apex of which corresponds to the aorta, and the base to the capillary
system.
The
arteries, in their distribution, communicate with one another, forming what are
called anastomoses, and these
communications are very free between the large as well as between the smaller
branches. The anastomosis between trunks of equal size is found where great
activity of the circulation is requisite, as in the brain; here the two
vertebral arteries unite to form the basilar, and the two anterior cerebral
arteries are connected by a short communicating trunk; it is also found in the
abdomen, where the intestinal arteries have very ample anastomoses between
their larger branches. In the limbs the anastomoses are most numerous and of
largest size around the joints, the branches of an artery above uniting with
branches from the vessels below. These anastomoses are of considerable interest
to the surgeon, as it is by their enlargement that a collateral circulation is established after the application of a
ligature to an artery. The smaller branches of arteries anastomose more
frequently than the larger; and between the smallest twigs these anastomoses
become so numerous as to constitute a close network that pervades nearly every
tissue of the body.
Throughout
the body generally the larger arterial branches pursue a fairly straight
course, but in certain situations they are tortuous. Thus the external
maxillary artery in its course over the face, and the arteries of the lips, are
extremely tortuous to accommodate themselves to the movements of the parts. The
uterine arteries are also tortuous, to accommodate themselves to the increase
of size which the uterus undergoes during pregnancy.
The
pulmonary artery conveys the venous
blood from the right ventricle of the heart to the lungs. It is a short, wide
vessel, about 5 cm. in length and 3 cm. in diameter, arising from the conus arteriosus of the right ventricle. It
extends obliquely upward and backward, passing at first in front and then to
the left of the ascending aorta, as far as the under surface of the aortic
arch, where it divides, about the level of the fibrocartilage between the fifth
and sixth thoracic vertebræ, into right and left branches of nearly equal
size.
Relations.—The whole of this vessel is contained within the
pericardium. It is enclosed with the ascending aorta in a single tube of the
visceral layer of the serous pericardium, which is continued upward upon them
from the base of the heart. The fibrous layer of the pericardium is gradually
lost upon the external coats of the two branches of the artery. In front, the pulmonary artery is separated
from the anterior end of the second left intercostal space by the pleura and
left lung, in addition to the pericardium; it rests at first upon the ascending
aorta, and higher up lies in front of the left atrium on a plane posterior to
the ascending aorta. On either side
of its origin is the auricula of the corresponding atrium and a coronary
artery, the left coronary artery passing, in the first part of its course,
behind the vessel. The superficial part of the cardiac plexus lies above its
bifurcation, between it and the arch of the aorta.
The
right branch of the pulmonary artery
(ramus dexter a. pulmonalis), longer
and larger than the left, runs horizontally to the right, behind the ascending
aorta and superior vena cava and in front of the right bronchus, to the root of
the right lung, where it divides into two branches. The lower and larger of
these goes to the middle and lower lobes of the lung; the upper and smaller is
distributed to the upper lobe.
The
left branch of the pulmonary artery
(ramus sinister a. pulmonalis),
shorter and somewhat smaller than the right, passes horizontally in front of
the descending aorta and left bronchus to the root of the left lung, where it
divides into two branches, one for each lobe of the lung. Above, it is connected to the concavity of the aortic arch by the
ligamentum arteriosum, on the left of which is the left recurrent nerve, and on
the right the superficial part of the cardiac plexus. Below, it is joined to the upper left pulmonary vein by the
ligament of the left vena cava.
The
terminal branches of the pulmonary arteries will be described with the anatomy
of the lungs.
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Theme 2. Anatomy of the
heart II: structure of heart wall, blood supplying and innervation of the
heart. Pericardium. Projection of heart on the front thoracic wall
Wall
of heart consists of
internal layer - endocardium, muscular layer - myocardium and external layer -
epicardium.
Endocardium covers heart cavity from within. Its double sheets
forms aortic and pulmonary trunk valves, cusps right and left atrioventricular
valves.
Myocardium
(middle layer) is formed by muscular tissue,
which consists of cardiomyocytes. Muscular fibbers of atria and ventricles
start from fibrous tissue, which enters to composition of soft heart
skeleton. Last includes right and left
fibrous rings, that are situated around right and left atrioventricular
ostia, right fibrous triangle and left fibrous triangle, that are
situated around valve of aorta and valve of pulmonary trunk, and membranous
part of interventricular septum.
Myocardium
of atria consists of two
layers: superficial, which is common for both of atria and consists of circulation fibres, and deep layer, which consists
of longitudinal bundles and is separate each from other.
Myocardium
of ventricles consists of
three layers: external, middle and internal. External (oblique) layer origins from fibrous annuli, continues downward till apex
cordis where forms vortex cordis and passes into internal layer
of opposite side with longitudinal
fibres. So, external
and internal layers are common for both ventricles and middle (circular) layer separate for each ventricle.
External
heart membrane epicardium is visceral sheet of serous
pericardium. Epicardium covers a heart, initial departments of aorta and
pulmonary trunk, and also terminal departments of venae cavae and pulmonary
veins. Visceral sheet passes into parietal sheet of serous pericardium on these
vessels.
Strucutre.—The heart consists of muscular fibers, and of
fibrous rings which serve for their attachment. It is covered by the visceral
layer of the serous pericardium (epicardium), and lined by the endocardium.
Between these two membranes is the muscular wall or myocardium.
The
endocardium is a thin, smooth membrane which lines and gives the
glistening appearance to the inner surface of the heart; it assists in forming
the valves by its reduplications, and is continuous with the lining membrane of
the large bloodvessels. It consists of connective tissue and elastic fibers,
and is attached to the muscular structure by loose elastic tissue which
contains bloodvessels and nerves; its free surface is covered by endothelial
cells.
The
fibrous rings surround the atrioventricular and arterial orifices, and
are stronger upon the left than on the right side of the heart. The
atrioventricular rings serve for the attachment of the muscular fibers of the
atria and ventricles, and for the attachment of the bicuspid and tricuspid
valves. The left atrioventricular ring is closely connected, by its right
margin, with the aortic arterial ring; between these and the right
atrioventricular ring is a triangular mass of fibrous tissue, the trigonum
fibrosum, which represents the os cordis seen in the heart of some
of the larger animals, as the ox and elephant. Lastly, there is the tendinous
band, already referred to, the posterior surface of the conus arteriosus.
The
fibrous rings surrounding the arterial orifices serve for the attachment of the
great vessels and semilunar valves. Each ring receives, by its ventricular
margin, the attachment of some of the muscular fibers of the ventricles; its
opposite margin presents three deep semicircular notches, to which the middle
coat of the artery is firmly fixed. The attachment of the artery to its fibrous
ring is strengthened by the external coat and serous membrane externally, and
by the endocardium internally. From the margins of the semicircular notches the
fibrous structure of the ring is continued into the segments of the valves. The
middle coat of the artery in this situation is thin, and the vessel is dilated
to form the sinuses of the aorta and pulmonary artery.
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Anastomosing
muscular fibers of the heart seen in a longitudinal section. On the right the
limits of the separate cells with their nuclei are exhibited somewhat
diagrammatically
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Purkinje’s
fibers from the sheep’s heart. A. In longitudinal section. B. In
transverse section.
Cardiac
Muscular Tissue.—The fibers of the heart
differ very remarkably from those of other striped muscles. They are smaller by
one-third, and their transverse striæ are by no means so well-marked.
They show faint longitudinal striation. The fibers are made up of distinct quadrangular
cells, joined end to end so as to form a syncytium (499). Each cell contains a clear oval nucleus, situated
near its center. The extremities of the cells have a tendency to branch or
divide, the subdivisions uniting with offsets from other cells, and thus
producing an anastomosis of the fibers. The connective tissue between the
bundles of fibers is much less than in ordinary striped muscle, and no
sarcolemma has been proved to exist.
Purkinje
Fibers (500).—Between the endocardium and the ordinary cardiac
muscle are found, imbedded in a small amount of connective tissue, peculiar fibers
known as Purkinje fibers. They are found in certain mammals and in birds, and
can be best seen in the sheep’s heart, where they form a considerable portion
of the moderator band and also appear as gelatinous-looking strands on the
inner walls of the atria and ventricles. They also occur in the human heart
associated with the terminal distributions of the bundle of His. The fibers are
very much larger in size than the cardiac cells and differ from them in several
ways. In longitudinal section they are quadrilateral in shape, being about
twice as long as they are broad. The central portion of each fiber contains one
or more nuclei and is made up of granular protoplasm, with no indication of
striations, while the peripheral portion is clear and has distinct transverse
striations. The fibers are intimately connected with each other, possess no
definite sarcolemma, and do not branch.
The
muscular structure of the heart consists of bands of fibers, which
present an exceedingly intricate interlacement. They comprise (a) the
fibers of the atria, (b) the fibers of the ventricles, and (c)
the atrioventricular bundle of His.
The
fibers of the atria are arranged in two layers—a superficial, common to
both cavities, and a deep, proper to each. The superficial fibers are
most distinct on the front of the atria, across the bases of which they run in
a transverse direction, forming a thin and incomplete layer. Some of these
fibers run into the atrial septum. The deep fibers consist of looped and
annular fibers. The looped fibers pass upward over each atrium, being
attached by their two extremities to the corresponding atrioventricular ring,
in front and behind. The annular fibers surround the auriculæ, and
form annular bands around the terminations of the veins and around the fossa
ovalis.
The
fibers of the ventricles are arranged in a complex manner, and various
accounts have been given of their course and connections; the following
description is based on the work of McCallum. 94 They
consist of superficial and deep layers, all of which, with the exception of
two, are inserted into the papillary muscles of the ventricles. The superficial
layers consist of the following: (a) Fibers which spring from the
tendon of the conus arteriosus and sweep downward and toward the left across
the anterior longitudinal sulcus and around the apex of the heart, where they
pass upward and inward to terminate in the papillary muscles of the left
ventricle; those arising from the upper half of the tendon of the conus
arteriosus pass to the anterior papillary muscle, those from the lower half to
the posterior papillary muscle and the papillary muscles of the septum. (b)
Fibers which arise from the right atrioventricular ring and run diagonally
across the diaphragmatic surface of the right ventricle and around its right
border on to its costosternal surface, where they dip beneath the fibers just
described, and, crossing the anterior longitudinal sulcus, wind around the apex
of the heart and end in the posterior papillary muscle of the left ventricle. (c)
Fibers which spring from the left atrioventricular ring, and, crossing the
posterior longitudinal sulcus, pass successively into the right ventricle and
end in its papillary muscles. The deep layers are three in number; they
arise in the papillary muscles of one ventricle and, curving in an S-shaped
manner, turn in at the longitudinal sulcus and end in the papillary muscles of
the other ventricle. The layer which is most superficial in the right ventricle
lies next the lumen of the left, and vice versa. Those of the first
layer almost encircle the right ventricle and, crossing in the septum to the
left, unite with the superficial fibers from the right atrioventricular ring to
form the posterior papillary muscle. Those of the second layer have a less
extensive course in the wall of the right ventricle, and a correspondingly
greater course in the left, where they join with the superficial fibers from
the anterior half of the tendon of the conus arteriosus to form the papillary
muscles of the septum. Those of the third layer pass almost entirely around the
left ventricle and unite with the superficial fibers from the lower half of the
tendon of the conus arteriosus to form the anterior papillary muscle. Besides
the layers just described there are two bands which do not end in papillary
muscles. One springs from the right atrioventricular ring and crosses in the
atrioventricular septum; it then encircles the deep layers of the left
ventricle and ends in the left atrioventricular ring. The second band is
apparently confined to the left ventricle; it is attached to the left
atrioventricular ring, and encircles the portion of the ventricle adjacent to
the aortic orifice.
The
atrioventricular bundle of His (501),
is the only direct muscular connection known to exist between the atria and the
ventricles. Its cells differ from ordinary cardiac muscle cells in being more
spindle-shaped. They are, moreover, more loosely arranged and have a richer
vascular supply than the rest of the heart muscle. It arises in connection with
two small collections of spindle-shaped cells, the sinoatrial and
atrioventricular nodes. The sinoatrial node is situated on the anterior
border of the opening of the superior vena cava; from its strands of fusiform
fibers run under the endocardium of the wall of the atrium to the
atrioventricular node. The atrioventricular node lies near the orifice
of the coronary sinus in the annular and septal fibers of the right atrium;
from it the atrioventricular bundle passes forward in the lower part of the
membranous septum, and divides into right and left fasciculi. These run down in
the right and left ventricles, one on either side of the ventricular septum,
covered by endocardium. In the lower parts of the ventricles they break up into
numerous strands which end in the papillary muscles and in the ventricular
muscle generally. The greater portion of the atrioventricular bundle consists
of narrow, somewhat fusiform fibers, but its terminal strands are composed of
Purkinje fibers.
Dr.
A. Morison 95
has shown that in the sheep and pig the atrioventricular bundle “is a great
avenue for the transmission of nerves from the auricular to the ventricular
heart; large and numerous nerve trunks entering the bundle and coursing with
it.” From these, branches pass off and form plexuses around groups of Purkinje
cells, and from these plexuses fine fibrils go to innervate individual cells.
Clinical
and experimental evidence go to prove that this bundle conveys the impulse to
systolic contraction from the atrial septum to the ventricles.
Schematic
representation of the atrioventricular bundle of His. The bundle, represented
in red originates near the orifice of the coronary sinus, undergoes slight
enlargement to form a node, passes forward to the ventricular septum, and
divides into two limbs. The ultimate distribution cannot be completely shown in
this diagram.
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Vessels
and Nerves.—The arteries supplying the heart are the right and left coronary
from the aorta; the veins end in the
right atrium.
Structure
of Arteries—The arteries are composed of three coats: an internal or
endothelial coat (tunica intima of
Kölliker); a middle or muscular coat (tunica
media); and an external or connective-tissue coat (tunica adventitia). The two inner coats together are very easily
separated from the external, as by the ordinary operation of tying a ligature
around an artery. If a fine string be tied forcibly upon an artery and then
taken off, the external coat will be found undivided, but the two inner coats
are divided in the track of the ligature and can easily be further dissected
from the outer coat.
The
arteries, in their distribution throughout the body, are included in thin
fibro-areolar investments, which form their sheaths. The vessel is loosely connected with its sheath by
delicate areolar tissue; and the sheath usually encloses the accompanying
veins, and sometimes a nerve. Some arteries, as those in the cranium, are not
included in sheaths.
All
the larger arteries, like the other organs of the body, are supplied with
bloodvessels. These nutrient vessels, called the vasa vasorum, arise from
a branch of the artery, or from a neighboring vessel, at some considerable
distance from the point at which they are distributed; they ramify in the loose
areolar tissue connecting the artery with its sheath, and are distributed to
the external coat, but do not, in man, penetrate the other coats; in some of
the larger mammals a few vessels have been traced into the middle coat. Minute
veins return the blood from these vessels; they empty themselves into the vein
or veins accompanying the artery. Lymphatic vessels are also present in the
outer coat.
Arteries
are also supplied with nerves, which are derived from the sympathetic, but may
pass through the cerebrospinal nerves. They form intricate plexuses upon the
surfaces of the larger trunks, and run along the smaller arteries as single
filaments, or bundles of filaments which twist around the vessel and unite with
each other in a plexiform manner. The branches derived from these plexuses
penetrate the external coat and are distributed principally to the muscular
tissue of the middle coat, and thus regulate, by causing the contraction and
relaxation of this tissue the amount of blood sent to any part.
The
Capillaries.—The smaller arterial branches
(excepting those of the cavernous structure of the sexual organs, of the
splenic pulp, and of the placenta) terminate in net-works of vessels which
pervade nearly every tissue of the body. These vessels, from their minute size,
are termed capillaries. They are interposed between the smallest branches of
the arteries and the commencing veins, constituting a net-work, the branches of
which maintain the same diameter throughout; the meshes of the net-work are
more uniform in shape and size than those formed by the anastomoses of the
small arteries and veins.
The
diameters of the capillaries vary in
the different tissues of the body, the usual size being about 8μ. The smallest are those of the brain
and the mucous membrane of the intestines; and the largest those of the skin
and the marrow of bone, where they are stated to be as large as 20μ in diameter. The form of the capillary net varies in the
different tissues, the meshes being generally rounded or elongated.
The
rounded form of mesh is most common, and
prevails where there is a dense network, as in the lungs, in most glands and
mucous membranes, and in the cutis; the meshes are not of an absolutely
circular outline, but more or less angular, sometimes nearly quadrangular, or
polygonal, or more often irregular.
Elongated
meshes are observed in the muscles and nerves,
the meshes resembling parallelograms in form, the long axis of the mesh running
parallel with the long axis of the nerve or muscle. Sometimes the capillaries
have a looped arrangement; a single
vessel projecting from the common net-work and returning after forming one or
more loops, as in the papillæ of the tongue and skin.
The
number of the capillaries and the size of the meshes determine the degree of
vascularity of a part. The closest network and the smallest interspaces are
found in the lungs and in the choroid coat of the eye. In these situations the
interspaces are smaller than the capillary vessels themselves. In the
intertubular plexus of the kidney, in the conjunctiva, and in the cutis, the
interspaces are from three to four times as large as the capillaries which form
them; and in the brain from eight to ten times as large as the capillaries in
their long diameters, and from four to six times as large in their transverse diameters.
In the adventitia of arteries the width of the meshes is ten times that of the
capillary vessels. As a general rule, the more active the function of the
organ, the closer is its capillary net and the larger its supply of blood; the
meshes of the network are very narrow in all growing parts, in the glands, and
in the mucous membranes, wider in bones and ligaments which are comparatively
inactive; bloodvessels are nearly altogether absent in tendons, in which very
little organic change occurs after their formation. In the liver the
capillaries take a more or less radial course toward the intralobular vein, and
their walls are incomplete, so that the blood comes into direct contact with
the liver cells. These vessels in the liver are not true capillaries but
“sinusoids;” they are developed by the growth of columns of liver cells into
the blood spaces of the embryonic organ.
Structure.—The wall of a capillary consists of a fine
transparent endothelial layer, composed of cells joined edge to edge by an
interstitial cement substance, and continuous with the endothelial cells which
line the arteries and veins. When stained with nitrate of silver the edges
which bound the epithelial cells are brought into view. These cells are of
large size and of an irregular polygonal or lanceolate shape, each containing
an oval nucleus which may be displayed by carmine or hematoxylin. Between their
edges, at various points of their meeting, roundish dark spots are sometimes
seen, which have been described as stomata, though they are closed by
intercellular substance. They have been believed to be the situations through
which the colorless corpuscles of the blood, when migrating from the
bloodvessels, emerge; but this view, though probable, is not universally
accepted.
The
lymphatics end in the thoracic and right lymphatic ducts.
The
nerves are derived from the cardiac plexus, which are formed partly from
the vagi, and partly from the sympathetic trunks. They are freely distributed
both on the surface and in the substance of the heart, the separate nerve
filaments being furnished with small ganglia.
The
Cardiac Cycle and the Actions of the Valves.—By
the contractions of the heart the blood is pumped through the arteries to all
parts of the body. These contractions occur regularly and at the rate of about
seventy per minute. Each wave of contraction or period of activity is
followed by a period of rest, the two periods constituting what is known
as a cardiac cycle.
Each
cardiac cycle consists of three phases, which succeed each other as follows:
(1) a short simultaneous contraction of both atria, termed the atrial
systole, followed, lowed, after a slight pause, by (2) a simultaneous, but
more prolonged, contraction of both ventricles, named the ventricular
systole, and (3) a period of rest, during which the whole heart is
relaxed. The atrial contraction commences around the venous openings, and
sweeping over the atria forces their contents through the atrioventricular
openings into the ventricles, regurgitation into the veins being prevented by
the contraction of their muscular coats. When the ventricles contract, the
tricuspid and bicuspid valves are closed, and prevent the passage of the blood
back into the atria; the musculi papillares at the same time are shortened,
and, pulling on the chordæ tendineæ, prevent the inversion of the
valves into the atria. As soon as the pressure in the ventricles exceeds that
in the pulmonary artery and aorta, the valves guarding the orifices of these
vessels are opened and the blood is driven from the right ventricle into the
pulmonary artery and from the left into the aorta. The moment the systole of
the ventricles ceases, the pressure of the blood in the pulmonary artery and
aorta closes the pulmonary and aortic semilunar valves to prevent regurgitation
of blood into the ventricles, the valves remaining shut until reopened by the
next ventricular systole. During the period of rest the tension of the
tricuspid and bicuspid valves is relaxed, and blood is flowing from the veins
into the atria, being aspirated by negative intrathoracic pressure, and
slightly also from the atria into the ventricles. The average duration of a
cardiac cycle is about 8/10 of a second, made up as follows:
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The
rhythmical action of the heart is muscular in origin—that is to say, the
heart muscle itself possesses the inherent property of contraction apart from
any nervous stimulation. The more embryonic the muscle the better is it able to
initiate and propagate the contraction wave; this explains why the normal
systole of the heart starts at the entrance of the veins, for there the muscle
is most embryonic in nature. At the atrioventricular junction there is a slight
pause in the wave of muscular contraction. To obviate this so far as possible a
peculiar band of marked embryonic type passes across the junction and so
carries on the contraction wave to the ventricles. This band, composed of
special fibers, is the atrioventricular bundle of His (p. 537). The nerves, although
not concerned in originating the contractions of the heart muscle, play an
important role in regulating their force and frequency in order to subserve the
physiological needs of the organism.
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Conducting
heart system consists of atypical muscular fibres, which have
ability to carry impulses from nerves of heart to myocardium of atria and
ventricles. Centre of conducting heart system includes two ganglia:
1.
Sinoatrial
ganglion (Kiss-Fleck) disposed in wall of right
atrium between foramen of superior vena cava and right auricle. This ganglion
gives off the branches to myocardium of atria and directs a heart contraction
rhythm.
2.
Atrioventricular
ganglion (Ashoff-Tavar) lies in thickness of
inferior department of interatrial septum. This ganglion continues in atrioventricular
fascicle (Giss) which communicates myocardium
of atria and ventricles. Fascicle subdivides on right leg and left leg
in muscular part of interventricular septum, the terminal branches of which
(Purkinje fibres) terminate in ventricles myocardium.
Blood
supplying of the heart realizes by means of right
coronal artery and left coronal
artery, which take its beginning from aorta
bulb in suitable its sinuses. Right coronal artery passes to
the right under right auricle, lies into coronal sulcus and passes on posterior
interventricular sulcus, where anastomose with circumflex branch of left
coronal artery. Branches of right coronal artery supply wall of right ventricle
and atrium, back portion of interventricular septum, papillary muscles of right
ventricle and ganglia of conducting heart system. Left coronal artery
passes under left auricle where divides into two branches: anterior
interventricular branch and circumflex
branch. Last rounds a heart in
coronal sulcus and passes on posterior surface where anastomoses with right
coronal artery, forming circular arterial anastomose of arterial heart vessels. Anterior interventricular branch passes on same name heart sulcus to the apex, where
anastomoses with terminal portion of right coronal artery, forming longitudinal
arterial heart anastomose. Left
coronal artery supplies wall of left ventricle, anterior wall of right
ventricle, wall of left atrium and larger half of interventricular septum.
VIDEO
Venous
system of the heart carries largest part of
deoxygenated blood into coronal sinus. Some veins empty in it:
-
greater
cardiac vein [vena cordis magna], which passes
in anterior interventricular sulcus and coronal sulcus;
-
lesser
cardiac vein [vena cordis parva], which passes
in right part of coronal sulcus;
-
middle
cardiac vein [vena cordis media] passes in posterior interventricular sulcus;
-
posterior
vein of left ventricle;
-
oblique
vein of left atrium.
There
are venae minimae (Tebezia) and anterior venae, positioned in
myocardium of right atrium.
Innervation
of the Heart. Sympathetic fibres pass from sympathetic trunk and form the
superior, middle and inferior cervical cardiac nerves. Also thoracic department
of sympathetic trunk gives off the thoracic cardiac sympathetic nerves. They
hasten cardiac contractions and add their amplitude, broaden the coronal
vessels. The parasympathetic
fibres pass in composition of superior, inferior and thoracic cardiac branches
of vagus nerve. They slow a rhythm of cardiac contractions, reduce their
amplitude and narrow space of coronal arteries. The sensory fibres from heart wall receptor pass in composition
of cardiac nerves and cardiac branches to spinal cord.
The
heart nerves form superficial extraorgan cardiac plexus and deep
extraorgan cardiac plexus. The branches of extraorgan cardiac plexus
continue into one intraorgan cardiac plexus, which conventionally
subdivides on subepicardial plexus, intramuscular plexus and subendocardial
plexus. Subepicardial plexus is reach developed.
Topography
of the heart. Heart is situated in thoracic cavity; two thirds are
disposed to the left from middle line and one third on the right side. From
sides a heart is covered by pleural sacs, and lesser its front surface adjoins
to sternum and costal cartilages.
Superior
heart border passes on line, which connects
upper margins of third costal cartilages. Right heart boundary path passes from ІІІ right costal superior margin to V
right costal cartilage. Inferior heart border passes on line, which passes from right V right costal cartilage to
apex cordis. Apex cordis projects into
left V intercostal space 1-1,5 cm medially from medioclavicular line. Left
heart boundary path lies through superior
margin of left ІІІ costal cartilage to apex cordis. Palpitation sound of
bicuspidal valve is listened in
apex cordis area. Aortic valve is
listened into second intercostal space to the right from sternum. Valve
of pulmonary trunk - into ІІ intercostal
space to the left from sternum. Right atrioventricular (tricuspidal)
valve is listened by base xyphoid process
of sternum to the right (joint of ІV costal cartilage with sternum).
Heart
is enveloped by pericardium, which consists of fibrous and serous
portions. Fibrous pericardium near base of big vessels passes into their
external membrane. Serous pericardium has parietal lamina that
covers fibrous pericardium from within and visceral lamina that covers
surface of the heart and is known as epicardium. Parietal lamina passes
into visceral lamina closely the base of heart. There is space like fissure
between two laminae – pericardial cavity with small amount of serous
liquid that prevents friction during palpitation. There are two deepening in
pericardial cavity: transverse sinus and oblique sinus. Transverse sinus
is bordered in front by aorta and pulmonary trunk, behind by superior vena cava.
Oblique pericardial sinus is situated on the diaphragmatic surface between
pulmonary veins on the left and inferior vena cava on the right.
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Theme 3. Thoracic aorta: topography,
parietal and visceral branches. System of superior vena cava
AORTA
is the largest arterial vessel of systemic circulation. It subdivides on
ascending part of aorta, aortic arch and descending part of aorta, which has
thoracic and abdominal portions of aorta.
Ascending part of aorta
leave the left ventricle behind left margin of sternum on level III intercostal
space. In initial department it has expansion is aorta bulb, in which three
aortic sinuses are contained. Ascending part of aorta lies behind and a little
to the right from pulmonary trunk, rises
up and to level of second right costal cartilage passes into arc.
The
Arch of the Aorta turns posteriorly to the left from second costal
cartilage to left side of fourth thoracic vertebral body, where passes into
descending aorta. Between concave aortic arch surface and pulmonary trunk on
beginning of left pulmonary artery is situated obliterated arterial Botali
duct. From convex aortic arch surface starts to from the right to the left:
brachiocephalic trunk, left common carotid and left subclavian artery.
The
arch of the aorta, and its branches.
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The
Arch of the Aorta (Arcus AortÆ; Transverse Aorta) (505).—The arch of the aorta begins at the level of the upper border of the second sternocostal
articulation of the right side, and runs at first upward, backward, and to the left
in front of the trachea; it is then directed backward on the left side of the
trachea and finally passes downward on the left side of the body of the fourth
thoracic vertebra, at the lower border of which it becomes continuous with the
descending aorta. It thus forms two curvatures: one with its convexity upward,
the other with its convexity forward and to the left. Its upper border is
usually about 2.5 cm. below the superior border to the manubrium sterni.
Relations.—The arch of the aorta is covered anteriorly
by the pleuræ and anterior margins of the lungs, and by the remains of
the thymus. As the vessel runs backward its left side is in contact with
the left lung and pleura. Passing downward on the left side of this part of the
arch are four nerves; in order from before backward these are, the left
phrenic, the lower of the superior cardiac branches of the left vagus, the
superior cardiac branch of the left sympathetic, and the trunk of the left
vagus. As the last nerve crosses the arch it gives off its recurrent branch,
which hooks around below the vessel and then passes upward on its right side.
The highest left intercostal vein runs obliquely upward and forward on the left
side of the arch, between the phrenic and vagus nerves. On the right are
the deep part of the cardiac plexus, the left recurrent nerve, the esophagus,
and the thoracic duct; the trachea lies behind and to the right of the vessel. Above
are the brachiocephalic, left common carotid, and left subclavian arteries,
which arise from the convexity of the arch and are crossed close to their origins
by the left brachiocephalic vein. Below are the bifurcation of the
pulmonary artery, the left bronchus, the ligamentum arteriosum, the superficial
part of the cardiac plexus, and the left recurrent nerve. As already stated,
the ligamentum arteriosum connects the commencement of the left pulmonary
artery to the aortic arch.
Between
the origin of the left subclavian artery and the attachment of the ductus
arteriosus the lumen of the fetal aorta is considerably narrowed, forming what
is termed the aortic isthmus, while immediately beyond the ductus
arteriosus the vessel presents a fusiform dilation which His has named the aortic
spindle—the point of junction of the two parts being marked in the
concavity of the arch by an indentation or angle. These conditions persist, to
some extent, in the adult, where His found that the average diameter of the
spindle exceeded that of the isthmus by 3 mm.
Distinct
from this diffuse and moderate stenosis at the isthmus is the condition known
as coarctation of the aorta, or marked stenosis often amounting to
complete obliteration of its lumen, seen in adults and occuring at or near,
oftenest a little below, the insertion of the ligamentum arteriosum into the
aorta. According to Bonnet 96
this coarctation is never found in the fetus or at birth, and is due to an
abnormal extension of the peculiar tissue of the ductus into the aortic wall,
which gives rise to a simultaneous stenosis of both vessels as it contracts
after birth—the ductus is usually obliterated in these cases. An extensive
collateral circulation is set up, by the costocervicals, internal mammaries,
and the descending branches of the transverse cervical above the stenosis, and
below it by the first four aortic intercostals, the pericardiaco-phrenics, and
the superior and inferior epigastrics.
Peculiarities.—The height to which the aorta rises in the thorax
is usually about 2.5 cm. below the upper border of the sternum; but it may
ascend nearly to the top of the bone. Occasionally it is found 4 cm., more
rarely from 5 to 8 cm. below this point. Sometimes the aorta arches over the
root of the right lung (right aortic arch) instead of over that of the left,
and passes down on the right side of the vertebral column, a condition which is
found in birds. In such cases all the thoracic and abdominal viscera are
transposed. Less frequently the aorta, after arching over the root of the right
lung, is directed to its usual position on the left side of the vertebral
column; this peculiarity is not accompanied by transposition of the viscera.
The aorta occasionally divides, as in some quadrupeds, into an ascending and a
descending trunk, the former of which is directed vertically upward, and
subdivides into three branches, to supply the head and upper extremities.
Sometimes the aorta subdivides near its origin into two branches, which soon
reunite. In one of these cases the esophagus and trachea were found to pass
through the interval between the two branches; this is the normal condition of
the vessel in the reptilia.
Branches
(505, 506).—The branches given off from the arch of the aorta
are three in number: the brachiocephalic,
the left common carotid, and the left
subclavian.
Peculiarities.—Position of the Branches.—The branches,
instead of arising from the highest part of the arch, may spring from the
commencement of the arch or upper part of the ascending aorta; or the distance
between them at their origins may be increased or diminished, the most frequent
change in this respect being the approximation of the left carotid toward the
brachiocephalic artery.
The
number of the primary branches may be reduced to one, or more commonly
two; the left carotid arising from the brachiocephalic artery; or (more rarely)
the carotid and subclavian arteries of the left side arising from a left
brachiocephalic artery. But the number may be increased to four, from the right
carotid and subclavian arteries arising directly from the aorta, the
brachiocephalic being absent. In most of these latter cases the right
subclavian has been found to arise from the left end of the arch; in other cases
it is the second or third branch given off, instead of the first. Another
common form in which there are four primary branches is that in which the left
vertebral artery arises from the arch of the aorta between the left carotid and
subclavian arteries. Lastly, the number of trunks from the arch may be
increased to five or six; in these instances, the external and internal
carotids arise separately from the arch, the common carotid being absent on one
or both sides. In some few cases six branches have been found, and this
condition is associated with the origin of both vertebral arteries from the
arch.
Number
Usual, Arrangement Different.—When the aorta
arches over to the right side, the three branches have an arrangement the
reverse of what is usual; the brachiocephalic artery is a left, one, and the
right carotid and subclavian arise separately. In other cases, where the aorta
takes its usual course, the two carotids may be joined in a common trunk, and
the subclavians arise separately from the arch, the right subclavian generally
arising from the left end of the arch.
In
some instances other arteries spring from the arch of the aorta. Of these the
most common are the bronchial, one or both, and the thyreoidea ima; but the
internal mammary and the inferior thyroid have been seen to arise from this
vessel.
The
Brachiocephalic Artery (A. Anonyma; Brachiocephalic Artery) (505).—The brachiocephalic artery is the largest branch of the arch of the aorta, and
is from 4 to 5 cm. in length. It arises, on a level with the upper
border of the second right costal cartilage, from the commencement of the arch
of the aorta, on a plane anterior to the origin of the left carotid; it ascends
obliquely upward, backward, and to the right to the level of the upper border
of the right sternoclavicular articulation, where it divides into the right
common carotid and right subclavian arteries.
Relations.—Anteriorly, it is separated from the
manubrium sterni by the Sternohyoideus and Sternothyreoideus, the remains of
the thymus, the left brachiocephalic and right inferior thyroid veins which
cross its root, and sometimes the superior cardiac branches of the right vagus.
Posterior to it is the trachea, which it crosses obliquely. On the right
side are the right brachiocephalic vein, the superior vena cava, the right
phrenic nerve, and the pleura; and on the left side, the remains of the
thymus, the origin of the left common carotid artery, the inferior thyroid
veins, and the trachea.
Branches.—The brachiocephalic artery usually gives off no
branches; but occasionally a small branch, the thyreoidea ima, arises from it. Sometimes it gives off a thymic or bronchial branch.
The
thyreoidea ima (a. thyreoidea ima) ascends in front of the
trachea to the lower part of the thyroid gland, which it supplies. It varies
greatly in size, and appears to compensate for deficiency or absence of one of
the other thyroid vessels. It occasionally arises from the aorta, the right
common carotid, the subclavian or the internal mammary.
Point
of Division.—The brachiocephalic artery
sometimes divides above the level of the sternoclavicular joint, less
frequently below it.
Position.—When the aortic arch is on the right side, the
brachiocephalic is directed to the left side of the neck.
Collateral
Circulation.—Allan Burns demonstrated, on the
dead subject, the possibility of the establishment of the collateral
circulation after ligature of the brachiocephalic artery, by tying and dividing
that artery. He then found that “Even coarse injection, impelled into the
aorta, passed freely by the anastomosing branches into the arteries of the
right arm, filling them and all the vessels of the head completely.” 97 The branches by which this circulation would be carried
on are very numerous; thus, all the communications across the middle line
between the branches of the carotid arteries of opposite sides would be
available for the supply of blood to the right side of the head and neck; while
the anastomosis between the costocervical of the subclavian and the first
aortic intercostal (see infra on the collateral circulation after
obliteration of the thoracic aorta) would bring the blood, by a free and direct
course, into the right subclavian. The numerous connections, also, between the
intercostal arteries and the branches of the axillary and internal mammary
arteries would, doubtless, assist in the supply of blood to the right arm,
while the inferior epigastric from the external iliac would, by means of its
anastomosis with the internal mammary, compensate for any deficiency in the
vascularity of the wall of the chest.
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Descending
aorta has thoracic part of aorta, which
passes in posterior mediastinum and lies to the left from bodies of thoracic
vertebrae and abdominal part of aorta, which starts on level of ХІІ thoracic
vertebra, passes through aortic hiatus of diaphragm, and extends to
level of ІV lumbar vertebra. Abdominal part of aorta is disposed front
of anterior surface of lumbar vertebrae to the left from midiane line. Here
abdominal aorta gives off the pair parietal branches, pair and odd visceral
branches and finishes in bifurcation, dividing into two common iliac arteries.
Branches
of thoracic part of aorta
Parietal
branches and visceral branches there distinguish in thoracic part of aorta.
Follow
arteries belong to parietal branches of thoracic part of aorta:
-
superior
phrenic arteries are pair, pass to lumbar part
of diaphragm;
-
posterior
intercostal arteries are 10 pairs in number,
which pass in ІІІ-XІ intercostal spaces and supply intercostal muscles, ribs,
skin, breasts. Lower posterior intercostal arteries supply also muscles of
anterior abdominal wall. X posterior intercostal artery is situated under
posterior margin of XІІ rib and has a name of subcostal artery. From each posterior intercostal artery move away
the sprigs to muscles and posterior skin, to membranes of spinal cord and lateral
and medial cutaneі branches to breasts skin and
abdominal, sprigs to mammary gland.
Follow
arteries belong to visceral branches of thoracic part of aorta:
-
bronchial
branches - to trachea, bronchі and lung;
-
esophageal
branches to esophagus;
-
pericardial
branches to posterior part of pericardium;
-
mediastinal
branches supply connective tissue and lymphatic
nodes in posterior mediastinum.
The
thoracic aorta (530)
is contained in the posterior mediastinal cavity. It begins at the lower
border of the fourth thoracic vertebra where it is continuous with the aortic
arch, and ends in front of the lower border of the twelfth at the aortic hiatus
in the diaphragm. At its commencement, it is situated on the left of the
vertebral column; it approaches the median line as it descends; and, at its
termination, lies directly in front of the column. The vessel describes a curve
which is concave forward, and as the branches given off from it are small, its
diminution in size is inconsiderable.
The
thoracic aorta, viewed from the left side.
Relations.—It is in relation, anteriorly, from above
downward, with the root of the left lung, the pericardium, the esophagus, and
the diaphragm; posteriorly, with the vertebral column and the hemiazygos
veins; on the right side, with the azygos vein and thoracic duct; on the
left side, with the left pleura and lung. The esophagus, with its
accompanying plexus of nerves, lies on the right side of the aorta above; but
at the lower part of the thorax it is placed in front of the aorta, and, close
to the diaphragm, is situated on its left side.
Peculiarities.—The aorta is occasionally found to be obliterated
at the junction of the arch with the thoracic aorta, just below the ductus
arteriosus. Whether this is the result of disease, or of congenital
malformation, is immaterial to our present purpose; it affords an interesting
opportunity of observing the resources of the collateral circulation. The
course of the anastomosing vessels, by which the blood is brought from the
upper to the lower part of the artery, will be found well described in an
account of two cases in the Pathological Transactions, vols. viii and x.
In the former, Sydney Jones thus sums up the detailed description of the
anastomosing vessels: The principal communications by which the circulation was
carried on were: (1) The internal mammary, anastomosing with the intercostal
arteries, with the inferior phrenic of the abdominal aorta by means of the
musculophrenic and pericardiacophrenic, and largely with the inferior
epigastric. (2) The costocervical trunk, anastomosing anteriorly by means of a
large branch with the first aortic intercostal, and posteriorly with the
posterior branch of the same artery. (3) The inferior thyroid, by means of a
branch about the size of an ordinary radial, forming a communication with the
first aortic intercostal. (4) The transverse cervical, by means of very large
communications with the posterior branches of the intercostals. (5) The
branches (of the subclavian and axillary) going to the side of the chest were
large, and anastomosed freely with the lateral branches of the intercostals. In
the second case Wood describes the anastomoses in a somewhat similar manner,
adding the remark that “the blood which was brought into the aorta through the
anastomosis of the intercostal arteries appeared to be expended principally in
supplying the abdomen and pelvis; while the supply to the lower extremities had
passed through the internal mammary and epigastrics.”
In
a few cases an apparently double descending thoracic aorta has been found, the
two vessels lying side by side, and eventually fusing to form a single tube in
the lower part of the thorax or in the abdomen. One of them is the aorta, the
other represents a dissecting aortic aneurism which has become canalized;
opening above and below into the true aorta, and at first sight presenting the
appearances of a proper bloodvessel.
Branches
of the Thoracic Aorta.—
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The
pericardial branches (rami pericardiaci) consist of a few small
vessels which are distributed to the posterior surface of the pericardium.
The
bronchial arteries (aa. bronchiales) vary in number, size, and
origin. There is as a rule only one right bronchial artery, which arises
from the first aortic intercostal, or from the upper left bronchial artery. The
left bronchial arteries are usually two in number, and arise from
the thoracic aorta. The upper left bronchial arises opposite the fifth thoracic
vertebra, the lower just below the level of the left bronchus. Each vessel runs
on the back part of its bronchus, dividing and subdividing along the bronchial
tubes, supplying them, the areolar tissue of the lungs, the bronchial lymph
glands, and the esophagus.
The
esophageal arteries (aa. æsophageæ) four or five in
number, arise from the front of the aorta, and pass obliquely downward
to the esophagus, forming a chain of anastomoses along that tube, anastomosing
with the esophageal branches of the inferior thyroid arteries above, and with
ascending branches from the left inferior phrenic and left gastric arteries
below.
The
mediastinal branches (rami mediastinales) are numerous small
vessels which supply the lymph glands and loose areolar tissue in the posterior
mediastinum.
Intercostal
Arteries (aa. intercostales).—There are
usually nine pairs of aortic intercostal arteries. They arise from the
back of the aorta, and a redistributed to the lower nine intercostal spaces,
the first two spaces being supplied by the highest intercostal artery, a branch
of the costocervical trunk of the subclavian. The right aortic intercostals are longer than the left, on
account of the position of the aorta on the left side of the vertebral column;
they pass across the bodies of the vertebræ behind the esophagus,
thoracic duct, and vena azygos, and are covered by the right lung and pleura.
The left aortic intercostals run
backward on the sides of the vertebræ and are covered by the left lung
and pleura; the upper two vessels are crossed by the highest left intercostal
vein, the lower vessels by the hemiazygos veins. The further course of the
intercostal arteries is practically the same on both sides. Opposite the heads
of the ribs the sympathetic trunk passes downward in front of them, and the
splanchnic nerves also descend in front by the lower arteries. Each artery then
divides into an anterior and a posterior
ramus.
The
Anterior Ramus crosses the corresponding intercostal space obliquely
toward the angle of the upper rib, and thence is continued forward in the
costal groove. It is placed at first between the pleura and the posterior
intercostal membrane, then it pierces this membrane, and lies between it and
the Intercostalis externus as far as the angle of the rib; from this onward it
runs between the Intercostales externus and internus, and anastomoses in front
with the intercostal branch of the internal mammary or musculophrenic. Each
artery is accompanied by a vein and a nerve, the former being above and the
latter below the artery, except in the upper spaces, where the nerve is at
first above the artery. The first aortic intercostal artery anastomoses with
the intercostal branch of the costocervical trunk, and may form the chief
supply of the second intercostal space. The lower two intercostal arteries are
continued anteriorly from the intercostal spaces into the abdominal wall, and
anastomose with the subcostal, superior epigastric, and lumbar arteries.
Branches.—The anterior rami give off the following branches:
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The
collateral intercostal branch comes off from the intercostal artery near
the angle of the rib, and descends to the upper border of the rib below, along
which it courses to anastomose with the intercostal branch of the internal
mammary.
Muscular
branches are given to the Intercostales and Pectorales and to the Serratus
anterior; they anastomose with the highest and lateral thoracic branches of the
axillary artery.
The
lateral cutaneous branches accompany the lateral cutaneous branches of
the thoracic nerves.
Mammary
branches are given off by the vessels in the third, fourth, and fifth
spaces. They supply the mamma, and increase considerably in size during the
period of lactation.
The
Posterior Ramus runs backward through a space which is bounded above and
below by the necks of the ribs, medially by the body of a vertebra, and
laterally by an anterior costotransverse ligament. It gives off a spinal
branch which enters the vertebral canal through the intervertebral foramen
and is distributed to the medulla spinalis and its membranes and the
vertebræ. It then courses over the transverse process with the posterior
division of the thoracic nerve, supplies branches to the muscles of the back and
cutaneous branches which accompany the corresponding cutaneous branches of the
posterior division of the nerve.
The
subcostal arteries, so named because they lie below the last ribs,
constitute the lowest pair of branches derived from the thoracic aorta, and are
in series with the intercostal arteries. Each passes along the lower border of
the twelfth rib behind the kidney and in front of the Quadratus lumborum
muscle, and is accompanied by the twelfth thoracic nerve. It then pierces the
posterior aponeurosis of the Transversus abdominis, and, passing forward
between this muscle and the Obliquus internus, anastomoses with the superior
epigastric, lower intercostal, and lumbar arteries. Each subcostal artery gives
off a posterior branch which has a similar distribution to the posterior ramus
of an intercostal artery.
The
superior phrenic branches are small and arise from the lower part
of the thoracic aorta; they are distributed to the posterior part of the upper
surface of the diaphragm, and anastomose with the musculophrenic and
pericardiacophrenic arteries.
A
small aberrant artery is sometimes found arising from the right
side of the thoracic aorta near the origin of the right bronchial. It passes
upward and to the right behind the trachea and the esophagus, and may
anastomose with the highest right intercostal artery. It represents the remains
of the right dorsal aorta, and in a small proportion of cases is enlarged to
form the first part of the right subclavian artery.
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Superior
vena cava is generated by reason of
confluence of right and left brachiocephalic veins behind joint of cartilage of
first right rib with sternum. Superior vena cava on level of third right
cartilage empties into right atrium. Azygos vein empties into superior vena
cava from right side.
Brachiocephalic
veins form by the confluence of subclavian
vein, internal jugular and sometimes External jugular vein. This place is
called as venous angle, where
thoracic lymphatic duct empties (left side), and right lymphatic duct (right
side). Inferior thyroid veins from thyroid plexus, inferior laryngeal
vein and thymic vein, pericardial veins from pericardium, bronchic
veins and esophageal veins from esophagus fall into brachiocephalic
veins.
Azygos
vein continues into thoracic cavity from right
ascending lumbar vein. Azygos vein receives posterior intercostal veins,
esophageal veins, bronchic veins, pericardial veins and mediastinal
veins, also hemizygos vein.
The
Veins of the Thorax The brachiocephalic veins (vv. anonymæ;
brachiocephalic veins) are two large trunks, placed one on either side of
the root of the neck, and formed by the union of the internal jugular and
subclavian veins of the corresponding side; they are devoid of valves.
The
Right Brachiocephalic Vein (v. anonyma dextra) is a short vessel,
about 2.5 cm. in length, which begins behind the sternal end of the clavicle,
and, passing almost vertically downward, joins with the left brachiocephalic
vein just below the cartilage of the first rib, close to the right border of
the sternum, to form the superior vena cava. It lies in front and to the right
of the brachiocephalic artery; on its right side are the phrenic nerve and the
pleura, which are interposed between it and the apex of the lung. This vein, at
its commencement, receives the right vertebral vein; and, lower down, the right
internal mammary and right inferior thyroid veins, and sometimes the vein from
the first intercostal space.
The
venæ cavæ and azygos veins, with their tributaries.
The
Left Brachiocephalic Vein (v. anonyma sinistra), about 6 cm. in
length, begins behind the sternal end of the clavicle and runs obliquely
downward and to the right behind the upper half of the manubrium sterni to the
sternal end of the first right costal cartilage, where it unites with the right
brachiocephalic vein to form the superior vena cava. It is separated
from the manubrium sterni by the Sternohyoideus and Sternothyreoideus, the
thymus or its remains, and some loose areolar tissue. Behind it are the three
large arteries, brachiocephalic, left common carotid, and left subclavian,
arising from the aortic arch, together with the vagus and phrenic nerves. The
left brachiocephalic vein may occupy a higher level, crossing the jugular notch
and lying directly in front of the trachea.
Tributaries.—Its tributaries are the left vertebral, left
internal mammary, left inferior thyroid, and the left highest intercostal
veins, and occasionally some thymic and pericardiac veins.
Peculiarities.—Sometimes the brachiocephalic veins open separately
into the right atrium; in such cases the right vein takes the ordinary course
of the superior vena cava; the left vein—left superior vena cava, as it is
then termed—which may communicate by a small branch with the right one, passes
in front of the root of the left lung, and, turning to the back of the heart,
ends in the right atrium. This occasional condition in the adult is due to the
persistence of the early fetal condition, and is the normal state of things in
birds and some mammalia.
The
internal mammary veins (vv. mammariæ internæ) are
venæ comitantes to the lower half of the internal mammary artery, and
receive tributaries corresponding to the branches of the artery. They then
unite to form a single trunk, which runs up on the medial side of the artery
and ends in the corresponding brachiocephalic vein. The superior phrenic
vein, i.e., the vein accompanying the pericardiacophrenic artery,
usually opens into the internal mammary vein.
The
inferior thyroid veins (vv. thyreoideæ inferiores) two,
frequently three or four, in number, arise in the venous plexus on the
thyroid gland, communicating with the middle and superior thyroid veins. They
form a plexus in front of the trachea, behind the Sternothyreoidei. From this plexus,
a left vein descends and joins the left brachiocephalic trunk, and a right vein
passes obliquely downward and to the right across the brachiocephalic artery to
open into the right brachiocephalic vein, just at its junction with the
superior vena cava; sometimes the right and left veins open by a common trunk
in the latter situation. These veins receive esophageal tracheal, and inferior
laryngeal veins, and are provided with valves at their terminations in the
brachiocephalic veins.
The
highest intercostal vein (v. intercostalis suprema; superior
intercostal veins) (right and left) drain the blood from the upper three or
four intercostal spaces. The right vein (v. intercostalis suprema
dextra) passes downward and opens into the vena azygos; the left vein
(v. intercostalis suprema sinistra) runs across the arch of the aorta
and the origins of the left subclavian and left common carotid arteries and opens
into the left brachiocephalic vein. It usually receives the left bronchial
vein, and sometimes the left superior phrenic vein, and communicates below with
the accessory hemiazygos vein.
The
superior vena cava (v. cava superior) drains the blood from the
upper half of the body. It measures about 7 cm. in length, and is formed by the
junction of the two brachiocephalic veins. It begins immediately below
the cartilage of the right first rib close to the sternum, and, descending
vertically behind the first and second intercostal spaces, ends in the upper
part of the right atrium opposite the upper border of the third right costal
cartilage: the lower half of the vessel is within the pericardium. In its
course it describes a slight curve, the convexity of which is to the right
side.
Relations.—In front are the anterior margins of the
right lung and pleura with the pericardium intervening below; these separate it
from the first and second intercostal spaces and from the second and third
right costal cartilages; behind it are the root of the right lung and
the right vagus nerve. On its right side are the phrenic nerve and right
pleura; on its left side, the commencement of the brachiocephalic artery
and the ascending aorta, the latter overlapping it. Just before it pierces the
pericardium, it receives the azygos vein and several small veins from the
pericardium and other contents of the mediastinal cavity. The portion contained
within the pericardium is covered, in front and laterally, by the serous layer
of the membrane. The superior vena cava has no valves.
The
azygos vein (v. azygos; vena azygos major) begins opposite
the first or second lumbar vertebra, by a branch, the ascending lumbar vein
(page 678); sometimes by a branch from the right renal vein, or from the
inferior vena cava. It enters the thorax through the aortic hiatus in the
diaphragm, and passes along the right side of the vertebral column to the
fourth thoracic vertebra, where it arches forward over the root of the right
lung, and ends in the superior vena cava, just before that vessel pierces the
pericardium. In the aortic hiatus, it lies with the thoracic duct on the right
side of the aorta; in the thorax it lies upon the intercostal arteries, on the
right side of the aorta and thoracic duct, and is partly covered by pleura.
Tributaries.—It receives the right subcostal and intercostal
veins, the upper three or four of these latter opening by a common stem, the
highest superior intercostal vein. It receives the hemiazygos veins, several
esophageal, mediastinal, and pericardial veins, and, near its termination, the
right bronchial vein. A few imperfect valves are found in the azygos vein; but
its tributaries are provided with complete valves.
The
intercostal veins on the left side, below the upper three intercostal spaces,
usually form two trunks, named the hemiazygos and accessory
hemiazygos veins.
The
Hemiazygos Vein (v. hemiazygos; vena azygos minor inferior) begins
in the left ascending lumbar or renal vein. It enters the thorax, through the
left crus of the diaphragm, and, ascending on the left side of the vertebral
column, as high as the ninth thoracic vertebra, passes across the column,
behind the aorta, esophagus, and thoracic duct, to end in the azygos vein. It
receives the lower four or five intercostal veins and the subcostal vein of the
left side, and some esophageal and mediastinal veins.
The
Accessory Hemiazygos Vein (v. hemiazygos accessoria; vena azygos
minor superior) descends on the left side of the vertebral column, and
varies inversely in size with the highest left intercostal vein. It receives
veins from the three or four intercostal spaces between the highest left
intercostal vein and highest tributary of the hemiazygos; the left bronchial
vein sometimes opens into it. It either crosses the body of the eighth thoracic
vertebra to join the azygos vein or ends in the hemiazygos. When this vein is
small, or altogether wanting, the left highest intercostal vein may extend as
low as the fifth or sixth intercostal space.
In
obstruction of the superior vena cava, the azygos and hemiazygos veins are one
of the principal means by which the venous circulation is carried on,
connecting as they do the superior and inferior venæ cavæ, and
communicating with the common iliac veins by the ascending lumbar veins and
with many of the tributaries of the inferior vena cava.
The
Bronchial Veins (vv. bronchiales) return the blood from the
larger bronchi, and from the structures at the roots of the lungs; that of the
right side opens into the azygos vein, near its termination; that of the left
side, into the highest left intercostal or the accessory hemiazygos vein. A
considerable quantity of the blood which is carried to the lungs through the
bronchial arteries is returned to the left side of the heart through the
pulmonary veins.
The
Veins of the Vertebral Column
The
veins which drain the blood from the vertebral column, the neighboring muscles,
and the meninges of the medulla spinalis form intricate plexuses extending
along the entire length of the column; these plexuses may be divided into two
groups, external and internal, according to their positions inside or outside
the vertebral canal. The plexuses of the two groups anastomose freely with each
other and end in the intervertebral veins.
The
external vertebral venous plexuses (plexus venosi vertebrales
externi; extraspinal veins) best marked in the cervical region, consist of
anterior and posterior plexuses which anastomose freely with each other. The anterior
external plexuses lie in front of the bodies of the vertebræ,
communicate with the basivertebral and intervertebral veins, and receive
tributaries from the vertebral bodies. The posterior external plexuses
are placed partly on the posterior surfaces of the vertebral arches and their
processes, and partly between the deep dorsal muscles. They are best developed
in the cervical region, and there anastomose with the vertebral, occipital, and
deep cervical veins.
Transverse
section of a thoracic vertebra, showing the vertebral venous plexuses.
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Median
sagittal section of two thoracic vertebræ, showing the vertebral venous
plexuses.
The
internal vertebral venous plexuses (plexus venosi vertebrales
interni; intraspinal veins) lie within the vertebral canal between the dura
mater and the vertebræ, and receive tributaries from the bones and from the
medulla spinalis. They form a closer net-work than the external plexuses, and,
running mainly in a vertical direction, form four longitudinal veins, two in
front and two behind; they therefore may be divided into anterior and posterior
groups. The anterior internal plexuses consist of large veins which lie
on the posterior surfaces of the vertebral bodies and intervertebral
fibrocartilages on either side of the posterior longitudinal ligament; under
cover of this ligament they are connected by transverse branches into which the
basivertebral veins open. The posterior internal plexuses are placed,
one on either side of the middle line in front of the vertebral arches and
ligamenta flava, and anastomose by veins passing through those ligaments with
the posterior external plexuses. The anterior and posterior plexuses
communicate freely with one another by a series of venous rings (retia
venosa vertebrarum), one opposite each vertebra. Around the foramen magnum
they form an intricate net-work which opens into the vertebral veins and is
connected above with the occipital sinus, the basilar plexus, the condyloid
emissary vein, and the rete canalis hypoglossi.
The
basivertebral veins (vv. basivertebrales) emerge from the
foramina on the posterior surfaces of the vertebral bodies. They are contained
in large, tortuous channels in the substance of the bones, similar in every
respect to those found in the diploë of the cranial bones. They
communicate through small openings on the front and sides of the bodies of the
vertebræ with the anterior external vertebral plexuses, and converge
behind to the principal canal, which is sometimes double toward its posterior
part, and open by valved orifices into the transverse branches which unite the
anterior internal vertebral plexuses. They become greatly enlarged in advanced
age.
The
intervertebral veins (vv. intervertebrales) accompany the spinal
nerves through the intervertebral foramina; they receive the veins from the
medulla spinalis, drain the internal and external vertebral plexuses and end in
the vertebral, intercostal, lumbar, and lateral sacral veins, their orifices
being provided with valves.
The
veins of the medulla spinalis (vv. spinales; veins of the spinal cord)
are situated in the pia mater and form a minute, tortuous, venous plexus. They
emerge chiefly from the median fissures of the medulla spinalis and are largest
in the lumbar region. In this plexus there are (1) two median longitudinal
veins, one in front of the anterior fissure, and the other behind the posterior
sulcus of the cord, and (2) four lateral longitudinal veins which run behind
the nerve roots. They end in the intervertebral veins. Near the base of the
skull they unite, and form two or three small trunks, which communicate with
the vertebral veins, and then end in the inferior cerebellar veins, or in the
inferior petrosal sinuses.
Prepared
byAssistant Galytsa-Harhalis
O.Ya.