Lecture
Genital Glands. The
first appearance of the genital gland is essentially the same in the two sexes,
and consists in a thickening of the epithelial layer which lines the peritoneal
cavity on the medial side of the urogenital fold. The thick plate of epithelium
extends deeply, pushing before it the mesoderm and forming a distinct
projection. This is termed the genital
ridge, and from it the testis in the male and the ovary in the female are
developed. At first the mesonephros and genital ridge are suspended by a common
mesentery, but as the embryo grows the genital ridge gradually becomes pinched
off from the mesonephros, with which it is at first continuous, though it still
remains connected to the remnant of this body by a fold of peritoneum, the mesorchium or mesovarium. About the seventh week the distinction of sex in the
genital ridge begins to be perceptible.
The Ovary.—The ovary,
thus formed from the genital ridge, is at first a mass of cells derived from
the celomic epithelium; later the mass is differentiated into a central part or
medulla covered by a surface layer, the germinal
epithelium. Between the cells of the germinal epithelium a number of larger
cells, the primitive ova, are found,
and these are carried into the subjacent stroma by bud-like ingrowths (genital cords) of the germinal
epithelium. The surface epithelium ultimately forms the permanent epithelial
covering of this organ; it soon loses its connection with the central mass, and
a tunica albuginea develops between them. The ova are chiefly derived from the
cells of the central mass; these are separated from one another by the growth
of connective tissue in an irregular manner; each ovum assumes a covering of
connective tissue (follicle) cells, and in this way the rudiments of the
ovarian follicles are formed. According to Beard the primitive ova are early
set apart during the segmentation of the ovum and migrate into the germinal
ridge.
Waldeyer taught that the primitive
germ cells are derived from the “germinal epithelium,” covering the genital
ridge. Beard, on the other hand, maintains that in the skate they are not
derived from this epithelium, but are probably formed during the later stages
of cell cleavage, before there is any trace of an embryo; and a similar view
was advanced by Nussbaum as to their origin in amphibia. Beard says: “At the
close of segmentation many of the future germ cells lie in the segmentation
cavity just beneath the site of the future embryo, and there is no doubt they
subsequently wander into it.” The germ cells, “after they enter the resting
phase, are sharply marked off from the cells of the embryo by entire absence of
mitoses among them.” They can be further recognized by their irregular form and
ameboid processes, and by the fact that their cytoplasm has no affinity for
ordinary stains, but assumes a brownish tinge when treated by osmic acid. The
path along which they travel into the embryo is a very definite one, viz.,
“from the yolk sac upward between the splanchnopleure and gut in the hinder
portion of the embryo.” This pathway, named by Beard the germinal path, “leads them directly to the position which they
ought finally to take up in the `germinal ridge' or nidus.” A considerable
number apparently never reach their proper destination, since “vagrant germ
cells are found in all sorts of places, but more particularly on the
mesentery.” Some of these may possibly find their way into the germinal ridge;
some probably undergo atrophy, while others may persist and become the seat of
dermoid tumors.
Descent of the Ovaries. In
the female there is also a gubernaculum, which effects a considerable change in
the position of the ovary, though not so extensive a change as in that of the
testis. The gubernaculum in the female lies in contact with the fundus of the
uterus and contracts adhesions to this organ, and thus the ovary is prevented
from descending below this level. The part of the gubernaculum between the
ovary and the uterus becomes ultimately the proper ligament of the ovary, while
the part between the uterus and the labium majus forms the round ligament of
the uterus. A pouch of peritoneum analogous to the saccus vaginalis in the male
accompanies it along the inguinal canal: it is called the
Fallopian tubes. The fallopian tubes are about
Uterus
The uterus is a hollow cavity about the size of a pear (in women who have never
been pregnant) that exists to house a developing fertilised egg. The main part
of the uterus (which sits in the pelvic cavity) is called the body of the
uterus, while the rounded region above the entrance of the fallopian tubes is
the fundus and its narrow outlet, which protrudes into the vagina, is the
cervix.
The thick wall of the uterus is
composed of 3 layers. The inner layer is known as the endometrium. If an egg
has been fertilised it will burrow into the endometrium, where it will stay for
the rest of its growth. The uterus will expand during a pregnancy to make room
for the growing fetus. A part of the wall of the fertilised egg, which has
burrowed into the endometrium, develops into the placenta. If an egg has not been
fertilised, the endometrial lining is shed at the end of each menstrual cycle.
The myometrium is the large middle
layer of the uterus, which is made up of interlocking groups of muscle. It
plays an important role during the birth of a baby, contracting rhythmically to
move the baby out of the body via the birth canal (vagina).
"Hystera" and "Uterine" redirect here.
For the state of mind, see hysteria. "Womb"
The uterus (from Latin
"uterus", plural uteri) or womb is a major female
hormone-responsive reproductive sex organ of most mammals including humans.
One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species.
Two uteri usually form initially in a female fetus, and in placental mammals
they may partially or completely fuse into a single uterus depending on the
species. In many species with two uteri, only one is functional. Humans and
other higher primates usually have a single completely
fused uterus, although in some individuals the uteri may not have completely
fused. In English, the term uterus is
used consistently within the medical and related professions, while the Germanic-derived
term womb is more common in everyday usage.
The uterus consists of a body and a cervix. The cervix protrudes into the vagina. The uterus is held in position within the pelvis
by condensations of endopelvic fascia, which are called ligaments. These
ligaments include the pubocervical, transverse. cervical ligaments cardinal ligaments,
and the uterosacral
ligaments. It is covered by a sheet-like fold of peritoneum, the broad ligament.[2]
The uterus is essential in sexual response by directing blood flow to
the pelvis and to the external genitalia, including the ovaries, vagina, labia, and
clitoris.
The reproductive function of the uterus
is to accept a fertilized ovum which passes through
the utero-tubal
junction from the fallopian tube. It implants into the endometrium, and derives nourishment from
blood vessels which develop exclusively for this purpose. The fertilized ovum
becomes an embryo, attaches to a wall of the uterus, creates a placenta, and
develops into a fetus (gestates) until childbirth. Due to anatomical barriers such
as the pelvis, the uterus is pushed partially into
the abdomen due to its expansion during pregnancy. Even during pregnancy the
mass of a human uterus amounts to only about a kilogram (
Humans may have a bicornuate
uterus, a uterine malformation where the two parts of
the uterus fail to fuse completely during fetal development.
The uterus is located inside the pelvis immediately dorsal
(and usually somewhat rostral)
to the urinary bladder
and ventral to the rectum. The human uterus is pear-shaped and about
From outside to inside, the path to the uterus is as
follows:
·
Cervix uteri - "neck of uterus"
o
External
orifice of the uterus
o
Internal
orifice of the uterus
·
corpus uteri - "Body of
uterus"
o
Cavity
of the body of the uterus
The three layers, from innermost to outermost, are as
follows:
The lining of the uterine cavity is called the
"endometrium". It consists of the functional endometrium and the
basal endometrium from which the former arises. Damage to the basal endometrium
results in adhesion formation and/or fibrosis (Asherman's syndrome).
In all placental mammals, including humans, the endometrium builds a lining
periodically which is shed or reabsorbed if no pregnancy occurs. Shedding of the
functional endometrial lining is responsible for menstrual bleeding (known colloquially as a
"period" in humans, with a cycle of approximately 28 days, +/-7 days
of flow and +/-21 days of progression) throughout the fertile years of a female
and for some time beyond. Depending on the species and attributes of physical
and psychological health, weight, environmental factors of circadian rhythm, photoperiodism (the physiological reaction
of organisms to the length of day or night), the effect of menstrual cycles to
the reproductive function of the uterus is subject to hormone production, cell
regeneration and other biological activities. The menstrual cycles may vary
from a few days to six months, but can vary widely even in the same individual,
often stopping for several cycles before resuming. Marsupials and monotremes do
not have menstruation.
The uterus mostly consists of smooth muscle, known as
"myometrium." The innermost layer of myometrium is known as the junctional
zone, which becomes thickened in adenomyosis.
The loose connective tissue around the uterus.
The uterus is primarily supported by the
pelvic diaphragm, perineal body and the urogenital
diaphragm. Secondarily, it is supported by ligaments and the
peritoneum (broad ligament
of uterus)
Normally the uterus lies in anteversion &
anteflexion. Anteversion is a forward angle between the axis of the cervix and
that of the vagina measuring about 90 degrees, provided the urinary bladder and
the rectum are empty. Anteflexion is a forward angle between the body and
cervix at the isthmus measuring about 125 degrees, provided the bladder and
rectum are empty.
It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each):
Name |
From |
To |
Posterior cervix |
Anterior face of sacrum |
|
Side of the cervix |
||
Side of the cervix |
The uterus is in the middle of the
pelvic cavity in frontal plane
(due to ligamentum latum
uteri). The fundus does not surpass the linea terminalis, while the vaginal part of
the cervix does not extend below interspinal
line. The uterus is mobile and
moves under the pressure of the full bladder or full rectum anteriorly, whereas
if both are full it moves upwards. Increased intraabdominal pressure pushes it
downwards. The mobility is conferred to it by musculo-fibrous apparatus that
consists of suspensory and sustentacular part. Under normal circumstances the
suspensory part keeps the uterus in anteflexion and anteversion (in 90% of
women) and keeps it "floating" in the pelvis. The meaning of these
terms are described below:
Distinction |
More common |
Less common |
Position tipped |
"Anteverted":
Tipped forward |
"Retroverted":
Tipped backwards |
Position of fundus |
"Anteflexed": Fundus is pointing forward relative to the
cervix |
"Retroflexed": Fundus is pointing backwards |
Sustentacular part supports the pelvic
organs and comprises the larger pelvic diaphragm in the back and the
smaller urogenital
diaphragm in the front.
The pathological changes of the position
of the uterus are:
·
retroversion/retroflexion, if it is
fixed
·
hyperanteflexion - tipped too forward;
most commonly congenital, but may be caused by tumors
·
anteposition, retroposition,
lateroposition - the whole uterus is moved; caused by parametritis or tumors
·
elevation, descensus, prolapse
·
rotation (the whole uterus rotates
around its longitudinal axis), torsion (only the body of the uterus rotates
around)
·
inversion
In cases where the uterus is
"tipped", also known as retroverted uterus, women may have symptoms of pain during sexual
intercourse, pelvic pain during menstruation, minor incontinence, urinary tract
infections, difficulty conceiving, and difficulty using tampons. A pelvic
examination by a doctor can determine if a uterus is tipped.
Schematic diagram of uterine arterial vasculature seen as a cross-section through
the myometrium and endometrium.
The uterus is supplied by arterial blood
both from the uterine artery
and the ovarian artery.
The nerves are derived from the hypogastric and ovarian
plexuses, and from the third and fourth sacral nerves.
The bilateral Müllerian ducts form during early
fetal life. In males, MIF
secreted from the testes leads to their regression. In females these ducts give
rise to the Fallopian tubes
and the uterus. In humans the lower segments of the two ducts fuse to form a
single uterus, however, in cases of uterine malformations
this development may be disturbed. The different uterine forms in various
mammals are due to various degrees
of fusion of the two Müllerian ducts.
Vagina
The vagina is a fibromuscular tube that extends from the cervix to the
vestibule of the vulva. The vagina receives the penis and semen during sexual
intercourse and also provides a passageway for menstrual blood flow to leave
the body.
The Metanephros and the Permanent
Kidney.—The rudiments of the permanent kidneys make their
appearance about the end of the first or the beginning of the second month.
Each kidney has a two-fold origin, part arising from the metanephros, and part
as a diverticulum from the hind-end of the Wolffian duct, close to where the
latter opens into the cloaca. The metanephros arises in the intermediate cell
mass, caudal to the mesonephros, which it resembles in structure. The
diverticulum from the Wolffian duct grows dorsalward and forward along the
posterior abdominal wall, where its blind extremity expands and subsequently
divides into several buds, which form the rudiments of the pelvis and calyces of
the kidney; by continued growth and subdivision it gives rise to the collecting
tubules of the kidney. The proximal portion of the diverticulum becomes the
ureter. The secretory tubules are developed from the metanephros, which is
moulded over the growing end of the diverticulum from the Wolffian duct. The
tubules of the metanephros, unlike those of the pronephros and mesonephros, do
not open into the Wolffian duct. One end expands to form a glomerulus, while
the rest of the tubule rapidly elongates to form the convoluted and straight
tubules, the loops of Henle, and the connecting tubules; these last join and
establish communications with the collecting tubules derived from the ultimate
ramifications of the diverticulum from the Wolffian duct. The mesoderm around
the tubules becomes condensed to form the connective tissue of the kidney. The
ureter opens at first into the hind-end of the Wolffian duct; after the sixth
week it separates from the Wolffian duct, and opens independently into the part
of the cloaca which ultimately becomes the bladder.
The
secretory tubules of the kidney become arranged into pyramidal masses or
lobules, and the lobulated condition of the kidneys exists for some time after
birth, while traces of it may be found even in the adult. The kidney of the ox
and many other animals remains lobulated throughout life.
The External Organs of Generation—As
already stated, the cloacal membrane, composed of ectoderm and entoderm,
originally reaches from the umbilicus to the tail. The mesoderm extends to the
midventral line for some distance behind the umbilicus, and forms the lower
part of the abdominal wall; it ends below in a prominent swelling, the cloacal tubercle. Behind this tubercle
the urogenital part of the cloacal membrane separates the ingrowing sheets of
mesoderm.
The
first rudiment of the penis (or clitoris) is a structure termed the phallus; it is derived from the phallic
portion of the cloaca which has extended on to the end and sides of the under
surface of the cloacal tubercle. The terminal part of the phallus representing
the future glans becomes solid; the remainder, which is hollow, is converted
into a longitudinal groove by the absorption of the urogenital membrane.
In the female a deep groove forms around
the phallus and separates it from the rest of the cloacal tubercle, which is
now termed the genital tubercle. The
sides of the genital tubercle grow backward as the genital swellings, which ultimately form the labia majora; the tubercle
itself becomes the mons pubis. The labia minora arise by the continued growth
of the lips of the groove on the under surface of the phallus; the remainder of
the phallus forms the clitoris.
In the male the early changes are
similar, but the pelvic portion of the cloaca undergoes much greater
development, pushing before it the phallic portion. The genital swellings
extend around between the pelvic portion and the anus, and form a scrotal area;
during the changes associated with the descent of the testes this area is drawn
out to form the scrotal sacs. The penis is developed from the phallus. As in
the female, the urogenital membrane undergoes absorption, forming a channel on
the under surface of the phallus; this channel extends only as far forward as
the corona glandis.
The
corpora cavernosa of the penis (or
clitoris) and of the urethra arise from the mesodermal tissue in the phallus;
they are at first dense structures, but later vascular spaces appear in them,
and they gradually become cavernous.
The
prepuce in both sexes is formed by
the growth of a solid plate of ectoderm into the superficial part of the
phallus; on coronal section this plate presents the shape of a horseshoe. By
the breaking down of its more centrally situated cells the plate is split into
two lamellæ, and a cutaneous fold, the prepuce, is liberated and forms a
hood over the glans. “Adherent prepuce is not an adhesion really, but a
hindered central desquamation” (Berry Hart).
The Urethra.—As
already described, in both sexes the phallic portion of the cloaca extends on
to the under surface of the cloacal tubercle as far forward as the apex. At
the apex the walls of the phallic portion come together and fuse, the lumen
is obliterated, and a solid plate, the urethral
plate, is formed. The remainder of the phallic portion is for a time
tubular, and then, by the absorption of the urogenital membrane, it
establishes a communication with the exterior; this opening is the primitive urogenital ostium, and it
extends forward to the corona glandis. In the female this condition is
largely retained; the portion of the groove on the clitoris broadens out
while the body of the clitoris enlarges, and thus the adult urethral opening
is situated behind the base of the clitoris. In the male, by the
greater growth of the pelvic portion of the cloaca a longer urethra is
formed, and the primitive ostium is carried forward with the phallus, but it
still ends at the corona glandis. Later it closes from behind forward.
Meanwhile the urethral plate of the glans breaks down centrally to form a
median groove continuous with the primitive ostium. This groove also closes
from behind forward, so that the external urethral opening is shifted forward
to the end of the glans. |
The Mammæ (Mammary Gland; Breasts)
The mammæ secrete the milk, and are accessory glands of the
generative system. They exist in the male as well as in the female; but in the
former only in the rudimentary state, unless their growth is excited by
peculiar circumstances. In the female they are two large hemispherical
eminences lying within the superficial fascia and situated on the front and
sides of the chest; each extends from the second rib above to the sixth rib
below, and from the side of the sternum to near the midaxillary line. Their
weight and dimensions differ at different periods of life, and in different
individuals. Before puberty they are of small size, but enlarge as the
generative organs become more completely developed. They increase during
pregnancy and especially after delivery, and become atrophied in old age. The
left mamma is generally a little larger than the right. The deep surface of
each is nearly circular, flattened, or slightly concave, and has its long
diameter directed upward and lateralward toward the axilla; it is separated
from the fascia covering the Pectoralis major, Serratus anterior, and Obliquus
externus abdominis by loose connective tissue. The subcutaneous surface of the
mamma is convex, and presents, just below the center, a small conical
prominence, the papilla.
The Mammary Papilla or Nipple (papilla mammæ) is a
cylindrical or conical eminence situated about the level of the fourth
intercostal space. It is capable of undergoing a sort of erection from
mechanical excitement, a change mainly due to the contraction of its muscular
fibers. It is of a pink or brownish hue, its surface wrinkled and provided with
secondary papillæ; and it is perforated by from fifteen to twenty
orifices, the apertures of the lactiferous ducts. The base of the mammary
papilla is surrounded by an areola. In the virgin the areola is of a delicate
rosy hue; about the second month after impregnation it enlarges and acquires a
darker tinge, and as pregnancy advances it may assume a dark brown or even
black color. This color diminishes as soon as lactation is over, but is never
entirely lost throughout life. These changes in the color of the areola are of
importance in forming a conclusion in a case of suspected first pregnancy. Near
the base of the papilla, and upon the surface of the areola, are numerous large
sebaceous glands, the areolar glands, which become much enlarged during
lactation, and present the appearance of small tubercles beneath the skin.
These glands secrete a peculiar fatty substance, which serves as a protection
to the integument of the papilla during the act of sucking. The mammary papilla
consists of numerous vessels, intermixed with plain muscular fibers, which are
principally arranged in a circular manner around the base: some few fibers radiating
from base to apex.
Development.—The mamma is developed partly from mesoderm and partly from
ectoderm—its bloodvessels and connective tissue being derived from the former,
its cellular elements from the latter. Its first rudiment is seen about the
third month, in the form of a number of small inward projections of the
ectoderm, which invade the mesoderm; from these, secondary tracts of cellular
elements radiate and subsequently give rise to the epithelium of the glandular
follicles and ducts. The development of the follicles, however, remains
imperfect, except in the parous female.
Structure—The mamma consists of gland tissue; of fibrous tissue,
connecting its lobes; and of fatty tissue in the intervals between the lobes.
The gland tissue, when freed from fibrous tissue and fat, is of a pale reddish
color, firm in texture, flattened from before backward and thicker in the
center than at the circumference. The subcutaneous surface of the mamma
presents numerous irregular processes which project toward the skin and are
joined to it by bands of connective tissue. It consists of numerous lobes, and
these are composed of lobules, connected together by areolar tissue,
bloodvessels, and ducts. The smallest lobules consist of a cluster of rounded
alveoli, which open into the smallest branches of the lactiferous ducts; these
ducts unite to form larger ducts, and these end in a single canal,
corresponding with one of the chief subdivisions of the gland. The number of
excretory ducts varies from fifteen to twenty; they are termed the tubuli
lactiferi. They converge toward the areola, beneath which they form dilatations
or ampullæ, which serve as reservoirs for the milk, and, at the base of
the papillæ, become contracted, and pursue a straight course to its summit,
perforating it by separate orifices considerably narrower than the ducts
themselves. The ducts are composed of areolar tissue containing longitudinal
and transverse elastic fibers; muscular fibers are entirely absent; they are
lined by columnar epithelium resting on a basement membrane. The epithelium of
the mamma differs according to the state of activity of the organ. In the gland
of a woman who is not pregnant or suckling, the alveoli are very small and
solid, being filled with a mass of granular polyhedral cells. During pregnancy
the alveoli enlarge, and the cells undergo rapid multiplication. At the
commencement of lactation, the cells in the center of the alveolus undergo
fatty degeneration, and are eliminated in the first milk, as colostrum corpuscles.
The peripheral cells of the alveolus remain, and form a single layer of
granular, short columnar cells, with spherical nuclei, lining the basement
membrane. The cells, during the state of activity of the gland, are capable of
forming, in their interior, oil globules, which are then ejected into the lumen
of the alveolus, and constitute the milk globules. When the acini are distended
by the accumulation of the secretion the lining epithelium becomes flattened.
The fibrous tissue invests the entire surface of the mamma,
and sends down septa between its lobes, connecting them together.
The fatty tissue covers the surface of the gland, and
occupies the interval between its lobes. It usually exists in considerable
abundance, and determines the form and size of the gland. There is no fat
immediately beneath the areola and papilla.
Vessels and Nerves.—The arteries supplying the mammæ are derived
from the thoracic branches of the axillary, the intercostals, and the internal
mammary. The veins describe an anastomotic circle around the base of the
papilla, called by Haller the circulus venosus. From this, large branches
transmit the blood to the circumference of the gland, and end in the axillary
and internal mammary veins. The nerves are derived from the anterior and
lateral cutaneous branches of the fourth, fifth, and sixth thoracic nerves.