LESSON 16
Topography and
structure of female reproductive organs
A woman's reproductive
system must produce sex hormones and functional gametes and also be able to
protect and support a developing embryo and nourish the newborn infant. The
principal organs of the female reproductive system (Figure 28-13 ) are the ovaries, the uterine tubes (Fallopian tubes or oviducts),
the uterus, the vagina, and the components of the external
genitalia. As in males, a variety of accessory glands secrete into the female
reproductive tract.
The ovaries, uterine
tubes, and uterus are enclosed within an extensive mesentery known as the broad
ligament (Figure 28-14 ). The uterine tubes run along the superior border of the broad ligament
and open into the pelvic cavity lateral to the ovaries. The mesovarium,
a thickened fold of mesentery, supports and stabilizes the position of each
ovary. The broad ligament attaches to the sides and floor of the pelvic cavity,
where it becomes continuous with the parietal peritoneum. The broad ligament
thus subdivides this part of the peritoneal cavity. The pocket formed between
the posterior wall of the uterus and the anterior surface of the colon is the rectouterine pouch; that formed between the
uterus and the posterior wall of the bladder is the vesicouterine
pouch. These subdivisions are most apparent in sagittal section (Figure 28-13 ).
a
Several other ligaments
assist the broad ligament in supporting and stabilizing the position of the
uterus and associated reproductive organs. These ligaments lie within the
mesentery sheet of the broad ligament and are connected to the ovaries or
uterus. The broad ligament limits side-to-side movement and rotation, and the
other ligaments (described with the ovaries and uterus) prevent
superior-inferior movement.
The Ovaries
The paired ovaries are
small, almond-shaped organs located near the lateral walls of the pelvic cavity
(Figures 28-13 and 28-14 ). The ovaries (1) produce immature female gametes, or oocytes; (2)
secrete female sex hormones, including estrogens
and progestins; and (3) secrete inhibin, involved in the feedback control of pituitary FSH
production.
The position of each
ovary is stabilized by the mesovarium and by a pair
of supporting ligaments: the ovarian ligament and the suspensory
ligament (Figure 28-14 ). The ovarian ligament extends from the uterus, near the attachment of
the uterine tube, to the medial surface of the ovary. The suspensory ligament
extends from the lateral surface of the ovary past the open end of the uterine
tube to the pelvic wall. The suspensory ligament contains the major blood
vessels of the ovary, the ovarian artery and ovarian vein. These vessels are
connected to the ovary at the ovarian hilum, where the ovary attaches to the mesovarium.
A typical ovary is a
flattened oval that is about
Oogenesis
Ovum production, or oogenesis, begins before a woman's birth, accelerates at puberty, and ends at menopause.
Between puberty and menopause, oogenesis occurs on a monthly basis as part of
the ovarian cycle.
Unlike the situation in
the male gonads, the oogonia, or stem cells of females, complete their mitotic divisions before
birth. Between the third and seventh months of fetal
development, the daughter cells, or primary oocytes, prepare to undergo
meiosis. They proceed as far as prophase of meiosis I,
but at that time the process comes to a halt. The primary oocytes then remain
in a state of suspended development until the individual reaches puberty. At
that time, rising levels of FSH trigger the start of the ovarian cycle. Each
month thereafter, some of the primary oocytes will be stimulated to undergo
further development. Not all primary oocytes produced in development survive
until puberty. There are roughly 2 million primordial follicles in the
ovaries at birth, each containing a primary oocyte. By the time of puberty,
that number has dropped to about 400,000. The rest of the primordial follicles
degenerate in a process called atresia.
Although the nuclear
events under way during meiosis in the ovaries are the same as those in the
testes, the process differs in two important details:
1.
The cytoplasm of the
primary oocyte is unevenly distributed during the two meiotic divisions.
Oogenesis produces one functional ovum, which contains most of the original
cytoplasm, and two or three nonfunctional polar bodies that later disintegrate (Figure 28-15 ).
2.
3.
The ovary releases a
secondary oocyte rather than a mature ovum. The secondary oocyte is suspended
in metaphase of meiosis II; meiosis will not be completed unless and until
fertilization occurs.
Ovarian follicles are
specialized structures in which oocyte growth and meiosis I occur. The ovarian
follicles are located in the cortex of the ovaries. Primary oocytes are located
in the outer portion of the ovarian cortex near the tunica albuginea,
in clusters called egg nests. Each primary oocyte within an egg nest is
surrounded by a single squamous layer of follicular cells. The primary
oocyte and its follicular cells form a primordial follicle. After sexual maturation, a different group of primordial follicles is
activated each month. This monthly process is known as the ovarian cycle.
The ovarian cycle can be
divided into a follicular phase, or preovulatory
phase, and a luteal phase, or postovulatory phase. Important steps
in the ovarian cycle can be summarized as follows:
STEP 1: Formation of primary follicles.
Follicle formation is stimulated by FSH from the anterior pituitary. The
ovarian cycle begins as activated primordial follicles develop into primary
follicles. In a primary follicle, the follicular cells enlarge and undergo repeated
cell divisions. The divisions create several layers of follicular cells around
the oocyte. These follicle cells are now called granulosa
cells.
As layers of granulosa cells develop around the primary oocyte,
microvilli from the surrounding granulosa cells
intermingle with those of the primary oocyte. The microvilli are surrounded by
a layer of glycoproteins, and the entire region is called the zona pellucida. The microvilli increase the surface area available for the transfer of
materials from the granulosa cells to the rapidly
enlarging oocyte.
The conversion from
primordial to primary follicles and subsequent follicular development occurs
under FSH stimulation. As the granulosa cells enlarge
and multiply, adjacent cells in the ovarian stroma form
a layer of thecal cells around the follicle. Thecal cells and granulosa cells
work together to produce sex hormones called estrogens.
STEP 2: Formation of secondary follicles.
Although many primordial follicles develop into primary follicles, only a few
will proceed to the next step. The transformation begins as the wall of the
follicle thickens and the granulosa cells begin
secreting small amounts of fluid. This follicular fluid, or liquor folliculi, accumulates in small pockets that gradually
expand and separate the inner and outer layers of the follicle. At this stage,
the complex is known as a secondary follicle. Although the primary oocyte continues to grow at a steady pace, the
follicle as a whole now enlarges rapidly because follicular fluid accumulates.
STEP 3: Formation of a tertiary follicle.
Eight to ten days after the start of the ovarian cycle, the ovaries generally
contain only a single secondary follicle destined for further development. By
the tenth to fourteenth day of the cycle, that follicle has formed a tertiary
follicle, or mature Graafian follicle, roughly
Until this time, the
primary oocyte has been suspended in prophase of the first meiotic division, a
state it achieved before birth. As the tertiary follicle completes its
development, LH levels begin rising, and the primary oocyte completes meiosis
I. Instead of producing two secondary oocytes, the first meiotic division
yields a secondary oocyte and a small, nonfunctional
polar body. The secondary oocyte then enters meiosis II but stops once again on
reaching metaphase. Meiosis II will not be completed unless fertilization
occurs.
As the time of ovulation approaches, the secondary oocyte and the surrounding
granulosa cells lose their connections with the
follicular wall and drift free within the antrum.
This event generally occurs on day 14 of a 28-day cycle. The granulosa cells immediately surrounding the secondary
oocyte are now known as the corona radiata.
STEP 4: Ovulation.
At ovulation, the tertiary follicle releases the secondary oocyte. The distended
follicular wall ruptures, releasing the follicular contents, including the
secondary oocyte and corona radiata, into the pelvic
cavity. The sticky follicular fluid keeps the corona radiata
attached to the surface of the ovary, where direct contact with projections of
the uterine tube or with fluid currents established by their ciliated
epithelium can transfer the secondary oocyte to the uterine tube.
STEP 5: Formation and degeneration of the corpus luteum.
The empty tertiary follicle initially collapses, and ruptured vessels bleed
into the antrum. The remaining granulosa
cells then invade the area, proliferating to create an endocrine structure
known as the corpus luteum, named for its yellow color (lutea,
yellow). This process occurs under LH stimulation.
The lipids contained in
the corpus luteum are used to manufacture steroid
hormones known as progestins, principally the steroid
progesterone. Although moderate amounts of estrogens are also secreted by the
corpus luteum, levels are not as high as they were at
ovulation, and progesterone is the principal hormone in the interval after
ovulation. Its primary function is to prepare the uterus for pregnancy by
stimulating the maturation of the uterine lining and the secretions of uterine
glands.
STEP 6: Unless pregnancy occurs, the corpus luteum begins to degenerate roughly 12 days after
ovulation.
Progesterone and estrogen levels then fall markedly.
Fibroblasts invade the nonfunctional corpus luteum, producing a knot of pale scar tissue called a
corpus albicans. The disintegration, or involution,
of the corpus luteum marks the end of the ovarian
cycle. A new cycle then begins with the activation of another group of
primordial follicles.
Age and Oogenesis
Although many primordial
follicles may have developed into primary follicles, and several primary
follicles may have been converted to secondary follicles, generally only a
single oocyte will be released into the pelvic cavity at ovulation. The rest
undergo atresia. At puberty, there are about 200,000 primordial follicles in
each ovary. Forty years later, few if any follicles remain, although only about
500 will have been ovulated during the interim.
The Uterine Tubes
Each uterine tube is a
hollow, muscular tube measuring roughly
1.
The infundibulum. The end closest to the ovary forms an expanded funnel, or infundibulum,
with numerous fingerlike projections that extend into
the pelvic cavity. The projections are called fimbriae. The inner surfaces of the infundibulum are lined with cilia that beat
toward the middle segment of the uterine tube, the ampulla.
2.
The ampulla. The thickness of the smooth muscle layers in the wall of the middle
segment, or ampulla, of the uterine tube gradually increases as it approaches
the uterus.
3.
The isthmus. The ampulla leads to the isthmus (Figure 28-17b ), a short segment connected to the uterine wall.
Histology of the Uterine Tube
The epithelium lining the
uterine tube is composed of ciliated columnar epithelial cells with scattered mucin-secreting cells. The mucosa is surrounded by
concentric layers of smooth muscle (Figure 28-17b ). Oocyte transport involves a combination of ciliary
movement and peristaltic contractions in the walls of the uterine tube. A few
hours before ovulation, sympathetic and parasympathetic nerves from the hypogastric plexus "turn on" this beating
pattern. The uterine tubes transport a secondary oocyte for final maturation
and fertilization. It normally takes 3-4 days for an oocyte to travel from the
infundibulum to the uterine cavity. If fertilization is to occur, the
secondary oocyte must encounter spermatozoa during the first 12-24 hours of its
passage. Fertilization typically occurs near the boundary between the
ampulla and isthmus of the uterine tube.
Along with its transport
function, the uterine tube also provides a nutrient-rich environment that
contains lipids and glycogen. This mixture provides nutrients to both
spermatozoa and a developing pre-embryo (the cell cluster produced by
the initial divisions that follow fertilization). Unfertilized oocytes degenerate
in the terminal portions of the uterine tubes or within the uterus.
The Uterus
The uterus provides
mechanical protection, nutritional support, and waste removal for the
developing embryo (weeks 1-8) and fetus
(from week 9 to delivery). In addition, contractions in the muscular wall of
the uterus are important in ejecting the fetus at the
time of birth.
The uterus is a small,
pear-shaped organ about
Suspensory Ligaments of the Uterus
In addition to the broad
ligament, three pairs of suspensory ligaments stabilize the position of the
uterus and limit its range of movement (Figure 28-18a,b
). The uterosacral ligaments extend from the
lateral surfaces of the uterus to the anterior face of the sacrum, keeping the
body of the uterus from moving inferiorly and anteriorly. The round ligaments
arise on the lateral margins of the uterus just posterior and inferior to the
attachments of the uterine tubes. These ligaments extend through the inguinal
canal and end in the connective tissues of the external genitalia. The round
ligaments restrict primarily posterior movement of the uterus. The lateral
(cardinal) ligaments extend from the base of the uterus and vagina to the
lateral walls of the pelvis. These ligaments tend to prevent inferior movement
of the uterus. Additional mechanical support is provided by the skeletal
muscles and fascia of the pelvic floor.
Internal Anatomy of the Uterus
We can divide the uterus
into two anatomical regions (Figure 28-18c ): the body and the cervix. The uterine body, or corpus,
is the largest region of the uterus. The fundus is the rounded portion of the
body superior to the attachment of the uterine tubes. The body ends at a
constriction known as the uterine isthmus. The cervix is the inferior portion of the uterus that extends from the isthmus to
the vagina.
The tubular cervix
projects about
The uterus receives blood
from branches of the uterine arteries, which arise from branches of the internal
iliac arteries, and the ovarian arteries, which arise from the
abdominal aorta inferior to the renal arteries. There are extensive
interconnections among the arteries to the uterus. This arrangement helps
ensure a reliable flow of blood to the organ despite changes in position and
the changes in uterine shape that accompany pregnancy. Numerous veins and lymphatic
vessels also supply each portion of the uterus. The uterus is innervated by
autonomic fibers from the hypogastric
plexus (sympathetic) and from sacral segments S3 and S4
(parasympathetic). Sensory information reaches the CNS within the dorsal roots
of spinal nerves T11 and T12. The most delicate anesthetic procedures used during labor
and delivery, known as segmental blocks, target only spinal nerves T10-L1.
The Uterine Wall
The dimensions of the
uterus are highly variable. In adult women of reproductive age who have not
given birth, the uterine wall is about
.
The endometrium
contributes about 10 percent to the mass of the uterus. The glandular and
vascular tissues of the endometrium support the physiological demands of the
growing fetus. Vast numbers of uterine glands open
onto the endometrial surface. These glands extend deep into the lamina propria almost all the way to the myometrium. Under the
influence of estrogen, the uterine glands, blood
vessels, and epithelium change with the various phases of the monthly uterine
cycle.
The myometrium, the
thickest portion of the uterine wall, forms almost 90 percent of the mass of
the uterus. Smooth muscle in the myometrium is arranged into longitudinal,
circular, and oblique layers. The smooth muscle tissue of the myometrium
provides much of the force needed to move a large fetus
out of the uterus and into the vagina.
The Ovary
is a pair organ, is situated in cavity of lesser pelvis. It has medial
surface and lateral surface, free margin and mesenteric margin,
uterine extremity and tubarius
extremity. Ovary is situated in peritoneal cavity,
it is covered by embryonic epithelium (not by peritoneum). Ovary attaches to
uterus by proper ovaric ligament, and
to pelvis walls - by the medium of suspensory ovaric
ligament. Ovaric mesentery approaches to
anterior margin, through which the vessels and nerves get into ovary hilus. Ovary parenchyma consists of cortex and medulla.
Ovule ripens in cortex, where primary folliculi
are situated, which then transforms into Graaf
vesicle. After that as vesicle blowes up, an oocyte
gets out from the ovary and gets into uterine tube. Vesicle becomes as corpus
luteum [yellow body]. If there is not
fecundation, then corpus luteum transform into corpus
albicans. In case of fecundation corpus luteum grows up and turns into corpus luteum verum, which functions
during pregnancy.
Uterus and right broad ligament, seen
from behind. The broad ligament has been spread
out and the ovary drawn downward.
The ovaries are homologous with the testes in the male. They are
two nodular bodies, situated one on either side of the uterus in relation to
the lateral wall of the pelvis, and attached to the back of the broad ligament
of the uterus, behind and below the uterine tubes. The ovaries are of a grayish-pink color, and present
either a smooth or a puckered uneven surface. They are each about
Adult ovary, epoöphoron,
and uterine tube. (From
Farre, after Kobelt.)
a, a. Epoöphoron
formed from the upper part of the Wolffian body. b.
Remains of the uppermost tubes sometimes forming hydatids.
c. Middle set of tubes. d. Some lower atrophied tubes. e.
Atrophied remains of the Wolffian duct. f. The
terminal bulb or hydatid. h. The uterine tube.
i. Hydatid
attached to the extremity. l. The ovary.
Epoöphoron (parovarium; organ of Rosenmüller) lies
in the mesosalpinx between the ovary and the uterine
tube, and consists of a few short tubules (ductuli
transversi) which converge toward the ovary while
their opposite ends open into a rudimentary duct, the ductus
longitudinalis epoöphori
(duct of Gärtner).
Paroöphoron.—The paroöphoron consists of a few scattered rudimentary
tubules, best seen in the child, situated in the broad ligament between the epoöphoron and the uterus.
The ductuli transversi
of the epoophoron and the tubules of the paroophoron are remnants of the tubules of the Wolffian body or mesonephros; the
ductus longitudinalis epoöphori is a persistent portion of the Wolffian duct.
In the fetus the ovaries are
situated, like the testes, in the lumbar region, near the kidneys, but they
gradually descend into the pelvis.
Section of the ovary. (After Schrön.)
1. Outer covering.
Structure. The surface of the ovary is covered by a
layer of columnar cells which constitutes the germinal epithelium of Waldeyer. This epithelium gives to the ovary a dull gray color as compared with the
shining smoothness of the peritoneum; and the transition between the squamous
epithelium of the peritoneum and the columnar cells which cover the ovary is
usually marked by a line around the anterior border of the ovary. The ovary
consists of a number of vesicular ovarian follicles imbedded in the meshes of a
stroma or frame-work.
The stroma is a peculiar
soft tissue, abundantly supplied with bloodvessels,
consisting for the most part of spindle-shaped cells with a small amount of
ordinary connective tissue. These cells have been regarded by some anatomists
as unstriped muscle cells, which, indeed, they most
resemble; by others as connective-tissue cells. On the surface of the organ this
tissue is much condensed, and forms a layer (tunica albuginea)
composed of short connective-tissue fibers, with
fusiform cells between them. The stroma of the ovary
may contain interstitial cells resembling those of the testis.
Vesicular Ovarian Follicles (Graafian
follicles).—Upon making a section of an ovary,
numerous round transparent vesicles of various sizes are to be seen; they are
the follicles, or ovisacs containing the ova.
Immediately beneath the superficial covering is a layer of stroma,
in which are a large number of minute vesicles, of uniform size, about
The larger follicles consist of an external fibrovascular coat, connected with the surrounding stroma of the ovary by a net-work of bloodvessels;
and an internal coat, which consists of several layers of nucleated cells,
called the membrana granulosa.
At one part of the mature follicle the cells of the membrana
granulosa are collected into a mass which projects
into the cavity of the follicle. This is termed the discus proligerus, and in it the ovum is imbedded. The follicle contains a transparent albuminous
fluid.
The development and maturation of the follicles and ova
continue uninterruptedly from puberty to the end of the fruitful period of
woman’s life, while their formation commences before birth. Before puberty the
ovaries are small and the follicles contained in them are disposed in a
comparatively thick layer in the cortical substance; here they present the
appearance of a large number of minute closed vesicles, constituting the early
condition of the follicles; many, however, never attain full development, but
shrink and disappear. At puberty the ovaries enlarge and become more vascular,
the follicles are developed in greater abundance, and their ova are capable of
fecundation.
Section of vesicular ovarian follicle
Discharge of the Ovum.—The follicles, after
attaining a certain stage of development, gradually approach the surface of the
ovary and burst; the ovum and fluid contents of the follicle are liberated on
the exterior of the ovary, and carried into the uterine tube by currents set up
by the movements of the cilia covering the mucous membrane of the fimbriae.
Corpus Luteum.—After the discharge of the ovum the lining of the follicle
is thrown into folds, and vascular processes grow inward from the surrounding
tissue. In this way the space is filled up and the corpus luteum
formed. It consists at first of a radial arrangement of yellow cells with bloodvessels and lymphatic spaces, and later it merges with
the surrounding stroma.
Vessels and Nerves.—The
arteries of the ovaries and uterine tubes are the ovarian from the
aorta. Each anastomoses freely in the mesosalpinx,
with the uterine artery, giving some branches to the uterine tube, and others
which traverse the mesovarium and enter the hilum of
the ovary. The veins emerge from the hilum in the form of a plexus, the pampiniform plexus; the ovarian vein is
formed from this plexus, and leaves the pelvis in company with the artery. The nerves
are derived from the hypogastric or pelvic plexus,
and from the ovarian plexus, the uterine tube receiving a branch from one of
the uterine nerves.
The Uterine tube
is a pair organ is situated in area of superior margin of ligamentum
latum uteri. Length of each tube is 8-
§ uterine
part runs in wall of uterus and opens into uterine cavity
by uterine ostium;
§ isthmus
of uterine tube lies closely to uterus;
§ ampulla of
uterine tube is greater part of uterine tube;
§ infundibulum of uterine
tube - is broadened part, which opens by abdominal foramen of uterine
tube into abdominal (peritoneal) cavity and covered by fimbria, one of
which - ovaric fimbria is longer then other.
Uterine
tube is covered from all sides by peritoneum and has its own mesentery.
Tube has also muscular membrane (longitudinal and circular layers) and mucous
membrane. Fecundation realizes in uterine tube normally, than fertilized
ovule passes into uterus.
Female pelvis and its contents, seen
from above and in front.
The Uterus
is an odd hollow organ, pear-shaped object, which is situated in cavity of
lesser pelvis. It has a fundus, body and neck of uterus, which
opens into vagina by uterine ostium, limited
by anterior labium and posterior labium. Uterine neck divided
into supravaginal portion and
vaginal portion. Uterine body has vesical surface
(anterior) and intestinal surface (posterior). Place of transition body of
uterus into neck is called as isthmus. Anterior uterus surface adjoins to
urinary bladder, and posterior - to rectum. Attached to empty urinary bladder
body of uterus is tilted forward. Such position is called anteversio.
Attached to full urinary bladder a fundus and uterus body displaces posteriorly
– this is retroversio. Also between body and
uterus neck is formed a
angle, open forward. Such position is called anteflexio.
Triangle-shaped cavity of uterus above communicate
with uterine tubes, and vagina through the cervical canal and ostium uteri.
Wall of uterus
consists of three layers:
• mucous membrane (endometrium), submucous stratum is absent ,so there is no folds on
internal surface of uterus;
• muscular membrane (myometrium) is
formed by smooth muscle and consists of internal, middle and external layers;
• serous membrane (perimetrium)
is a peritoneum, which covers an uterus from all sides, except part of front
surface and lateral margins and supravaginal portion
of neck (mesoperitoneal position). Serous
membrane forms ligamentum uteri latum, which forms mesentery of uterus, mesentery of
ovary and mesentery of uterine tube. Between sheets of ligamentum
latum uteri the vessels, nerves, adipose tissue (parametrium) and ligamentum teres uteri are contained. Ligamentum
teres [round] uteri passes through the
inguinal canal to pubis. Also uterus is fixed to pelvic walls by cardinal
ligament.
The uterus is a hollow, thick-walled, muscular organ situated
deeply in the pelvic cavity between the bladder and rectum. Into its upper part
the uterine tubes open, one on either side, while below, its cavity communicates
with that of the vagina. When the ova are discharged from the ovaries they are
carried to the uterine cavity through the uterine tubes. If an ovum be
fertilized it imbeds itself in the uterine wall and is normally retained in the
uterus until prenatal development is completed, the uterus undergoing changes
in size and structure to accommodate itself to the needs of the growing embryo
(see page 59). After parturition the uterus returns almost to its former
condition, but certain traces of its enlargement remains. It is necessary,
therefore, to describe as the type-form the adult virgin uterus, and then to
consider the modifications which are effected as a result of pregnancy.
Sagittal section of the lower part of a
female trunk, right segment. SM. INT.
Small intestine
In the virgin state the uterus is flattened antero-posteriorly and is pyriform
in shape, with the apex directed downward and backward. It lies between the
bladder in front and the pelvic or sigmoid colon and rectum behind, and is
completely within the pelvis, so that its base is below the level of the
superior pelvic aperture. Its upper part is suspended by the broad and the
round ligaments, while its lower portion is imbedded in the fibrous tissue of
the pelvis.
The long axis of the uterus usually lies approximately in
the axis of the superior pelvic aperture, but as the organ is freely movable
its position varies with the state of distension of the bladder and rectum.
Except when much displaced by a fully distended bladder, it forms a forward
angle with the vagina, since the axis of the vagina corresponds to the axes of
the cavity and inferior aperture of the pelvis.
The uterus measures about
Body (corpus uteri).—The body gradually narrows from the fundus to the isthmus.
The vesical or anterior
surface (facies vesicalis)
is flattened and covered by peritoneum, which is reflected on to the bladder to
form the vesicouterine excavation. The surface lies
in apposition with the bladder.
The intestinal or posterior surface (facies intestinalis)
is convex transversely and is covered by peritoneum, which is continued down on
to the cervix and vagina. It is in relation with the sigmoid colon, from which
it is usually separated by some coils of small intestine.
The fundus (fundus uteri) is convex in all
directions, and covered by peritoneum continuous with that on the vesical and intestinal surfaces. On it rest some coils of
small intestine, and occasionally the distended sigmoid colon.
The lateral margins (margo lateralis)
are slightly convex. At the upper end of each the uterine tube pierces the
uterine wall. Below and in front of this point the round ligament of the uterus
is fixed, while behind it is the attachment of the ligament of the ovary. These
three structures lie within a fold of peritoneum which is reflected from the
margin of the uterus to the wall of the pelvis, and is named the broad
ligament.
Cervix (cervix uteri; neck).—The cervix is the lower constricted segment of the uterus.
It is somewhat conical in shape, with its truncated apex directed downward and
backward, but is slightly wider in the middle than either above or below. Owing
to its relationships, it is less freely movable than the body, so that the
latter may bend on it. The long axis of the cervix is therefore seldom in the
same straight line as the long axis of the body. The long axis of the uterus as
a whole presents the form of a curved line with its concavity forward, or in
extreme cases may present an angular bend at the region of the isthmus.
The cervix projects through the anterior wall of the vagina,
which divides it into an upper, supravaginal portion,
and a lower, vaginal portion.
The supravaginal portion
(portio supravaginalis
[cervicis]) is separated in front from
the bladder by fibrous tissue (parametrium),
which extends also on to its sides and lateralward
between the layers of the broad ligaments. The uterine arteries reach the
margins of the cervix in this fibrous tissue, while on either side the ureter
runs downward and forward in it at a distance of about
The vaginal portion (portio
vaginalis [cervicis])
of the cervix projects free into the anterior wall of the vagina between the
anterior and posterior fornices. On its rounded
extremity is a small, depressed, somewhat circular aperture, the external
orifice of the uterus, through which the cavity of the cervix communicates
with that of the vagina. The external orifice is bounded by two lips, an
anterior and a posterior, of which the anterior is the shorter and thicker,
although, on account of the slope of the cervix, it projects lower than the
posterior. Normally, both lips are in contact with the posterior vaginal wall.
Interior of the Uterus—The
cavity of the uterus is small in comparison with the size of the organ.
The Cavity of the Body (cavum
uteri) is a mere slit, flattened antero-posteriorly.
It is triangular in shape, the base being formed by the internal surface of the
fundus between the orifices of the uterine tubes, the apex by the internal
orifice of the uterus through which the cavity of the body communicates with
the canal of the cervix.
The Canal of the Cervix (canalis
cervicis uteri) is somewhat fusiform, flattened
from before backward, and broader at the middle than
at either extremity. It communicates above through the internal orifice with
the cavity of the body, and below through the external orifice with the vaginal
cavity. The wall of the canal presents an anterior and a posterior longitudinal
ridge, from each of which proceed a number of small oblique columns, the palmate
folds, giving the appearance of branches from the stem of a tree; to this
arrangement the name arbor vitae uterina is applied. The folds on the two walls are not
exactly opposed, but fit between one another so as to close the cervical canal.
Posterior half of uterus and upper part
of vagina.
The total length of the uterine cavity from the external
orifice to the fundus is about
Ligaments.—The ligaments of the
uterus are eight in number: one anterior; one posterior; two lateral
or broad; two uterosacral; and
two round ligaments.
The anterior ligament consists of the vesicouterine fold of peritoneum, which is reflected on to
the bladder from the front of the uterus, at the junction of the cervix and
body.
The posterior ligament consists of the rectovaginal fold of peritoneum, which is reflected from
the back of the posterior fornix of the vagina on to the front of the rectum.
It forms the bottom of a deep pouch called the rectouterine
excavation, which is bounded in front by the posterior wall of the uterus,
the supravaginal cervix, and the posterior fornix of
the vagina; behind, by the rectum; and laterally by two crescentic
folds of peritoneum which pass backward from the cervix uteri on either side of
the rectum to the posterior wall of the pelvis. These folds are named the sacrogenital or rectouterine
folds. They contain a considerable amount of fibrous tissue and non-striped
muscular fibers which are attached to the front of
the sacrum and constitute the uterosacral
ligaments.
The two lateral or broad ligaments (ligamentum latum uteri)
pass from the sides of the uterus to the lateral walls of the pelvis. Together
with the uterus they form a septum across the female pelvis, dividing that
cavity into two portions. In the anterior part is contained the bladder; in the
posterior part the rectum, and in certain conditions some coils of the small
intestine and a part of the sigmoid colon. Between the two layers of each broad
ligament are contained: (1) the uterine tube superiorly; (2) the round ligament
of the uterus; (3) the ovary and its ligament; (4) the epoöphoron
and paroöphoron; (5) connective tissue; (6) unstriped muscular fibers; and
(7) bloodvessels and nerves. The portion of the broad
ligament which stretches from the uterine tube to the level of the ovary is
known by the name of the mesosalpinx.
Between the fimbriated extremity of the tube and the
lower attachment of the broad ligament is a concave rounded margin, called the infundibulopelvic ligament.
The round ligaments (ligamentum
teres uteri) are two flattened bands between 10
and
In addition to the ligaments just described, there is a band
named the ligamentum transversalis
colli (Mackenrodt) on
either side of the cervix uteri. It is attached to the side of the cervix uteri
and to the vault and lateral fornix of the vagina, and is continuous externally
with the fibrous tissue which surrounds the pelvic bloodvessels.
The form, size, and situation of the uterus vary at
different periods of life and under different circumstances.
Sagittal section through the pelvis of a
newly born female.
In the fetus the uterus is
contained in the abdominal cavity, projecting beyond the superior aperture of
the pelvis. The cervix is considerably larger than the body.
At puberty the uterus is pyriform
in shape, and weighs from 14 to
The position of the uterus in the adult is liable to
considerable variation, depending chiefly on the condition of the bladder and
rectum. When the bladder is empty the entire uterus is directed forward, and is
at the same time bent on itself at the junction of the body and cervix, so that
the body lies upon the bladder. As the latter fills, the uterus gradually
becomes more and more erect, until with a fully distended bladder the fundus may
be directed backward toward the sacrum.
During menstruation the organ is enlarged, more
vascular, and its surfaces rounder; the external orifice is rounded, its labia
swollen, and the lining membrane of the body thickened, softer, and of a darker
color. According to Sir J. Williams, at each
recurrence of menstruation, a molecular disintegration of the mucous membrane
takes place, which leads to its complete removal, only the bases of the glands
imbedded in the muscle being left. At the cessation of menstruation, a fresh
mucous membrane is formed by a proliferation of the remaining structures.
During pregnancy the uterus becomes enormously
enlarged, and in the eighth month reaches the epigastric
region. The increase in size is partly due to growth of preëxisting
muscle, and partly to development of new fibers.
After parturition the uterus nearly regains its usual
size, weighing about
In old age the uterus becomes atrophied, and paler
and denser in texture; a more distinct constriction separates the body and
cervix. The internal orifice is frequently, and the external orifice
occasionally, obliterated, while the lips almost entirely disappear.
Structure.—The
uterus is composed of three coats: an external or serous, a middle
or muscular, and an internal or mucous.
The serous coat (tunica serosa) is derived
from the peritoneum; it invests the fundus and the whole of the intestinal
surface of the uterus; but covers the vesical surface
only as far as the junction of the body and cervix. In the lower fourth of the
intestinal surface the peritoneum, though covering the uterus, is not closely
connected with it, being separated from it by a layer of loose cellular tissue
and some large veins.
The muscular coat (tunica muscularis)
forms the chief bulk of the substance of the uterus. In the virgin it is dense,
firm, of a grayish color,
and cuts almost like cartilage. It is thick opposite the middle of the body and
fundus, and thin at the orifices of the uterine tubes. It consists of bundles
of unstriped muscular fibers,
disposed in layers, intermixed with areolar tissue, bloodvessels,
lymphatic vessels, and nerves. The layers are three in number: external,
middle, and internal. The external and middle layers constitute the muscular
coat proper, while the inner layer is a greatly
hypertrophied muscularis mucosae. During pregnancy
the muscular tissue becomes more prominently developed, the fibers
being greatly enlarged.
The external layer, placed beneath the peritoneum, is
disposed as a thin plane on the vesical and
intestinal surfaces. It consists of fibers which pass
transversely across the fundus, and, converging at each lateral angle of the
uterus, are continued on to the uterine tube, the round ligament, and the
ligament of the ovary: some passing at each side into the broad ligament, and
others running backward from the cervix into the sacrouterine
ligaments. The middle layer of fibers presents no
regularity in its arrangement, being disposed longitudinally, obliquely, and
transversely. It contains more bloodvessels than
either of the other two layers. The internal or deep layer consists of circular
fibers arranged in the form of two hollow cones, the
apices of which surround the orifices of the uterine tubes, their bases
intermingling with one another on the middle of the body of the uterus. At the
internal orifice these circular fibers form a
distinct sphincter.
The mucous membrane (tunica mucosa) is smooth,
and closely adherent to the subjacent tissue. It is continuous through the fimbriated extremity of the uterine tubes, with the
peritoneum; and, through the external uterine orifice, with the lining of the
vagina.
In the body of the uterus the mucous membrane is smooth,
soft, of a pale red color, lined by columnar ciliated
epithelium, and presents, when viewed with a lens, the orifices of numerous
tubular follicles, arranged perpendicularly to the surface. The structure of
the corium differs from that of ordinary mucous membranes, and consists of an
embryonic nucleated and highly cellular form of connective tissue in which run
numerous large lymphatics. In it are the tube-like uterine
glands, lined by ciliated columnar epithelium. They are of small size in
the unimpregnated uterus, but shortly after
impregnation become enlarged and elongated, presenting a contorted or waved
appearance (see page 60).
In the cervix the mucous membrane is sharply differentiated
from that of the uterine cavity. It is thrown into numerous oblique ridges,
which diverge from an anterior and posterior longitudinal raphé.
In the upper two-thirds of the canal, the mucous membrane is provided with
numerous deep glandular follicles, which secrete a clear
viscid alkaline mucus; and, in addition, extending through the whole length of
the canal is a variable number of little cysts, presumably follicles which have
become occluded and distended with retained secretion. They are called the ovula Nabothi. The
mucous membrane covering the lower half of the cervical canal presents numerous
papillae. The epithelium of the upper two-thirds is cylindrical and ciliated,
but below this it loses its cilia, and gradually changes to stratified squamous
epithelium close to the external orifice. On the vaginal surface of the cervix
the epithelium is similar to that lining the vagina, viz., stratified squamous.
The arteries of the internal organs of
generation of the female, seen from behind.
Vessels and
Nerves.—The arteries
of the uterus are the uterine, from the hypogastric;
and the ovarian, from the abdominal aorta.
They are remarkable for their tortuous course in the substance of the
organ, and for their frequent anastomoses. The termination of the ovarian
artery meets that of the uterine artery, and forms an anastomotic trunk from
which branches are given off to supply the uterus, their disposition being circular.
Histology of the Uterus
We can divide the endometrium into (1) a functional zone, the layer closest to
the uterine cavity, and (2) an outer basilar zone adjacent to the myometrium.
The functional zone contains most of the uterine glands and contributes most of
the endometrial thickness. The basilar zone attaches the endometrium to the
myometrium and contains the terminal branches of the tubular glands.
Within the myometrium,
branches of the uterine arteries form arcuate
arteries that encircle the endometrium. Radial arteries supply straight
arteries that deliver blood to the basilar zone of the endometrium and spiral
arteries that supply the functional zone (Figure 28-19 ).
The structure of the
basilar zone remains relatively constant over time, but that of the functional
zone undergoes cyclical changes in response to sex hormone levels. These
cyclical changes produce the characteristic histological features of the
uterine cycle.
The Uterine Cycle
The uterine cycle, or menstrual
cycle, is a repeating series of changes in the structure of the
endometrium. The uterine cycle averages 28 days in length, but it can range
from 21 to 35 days in healthy women of reproductive age. We can divide the
cycle into three phases: (1) menses, (2) the proliferative phase,
and (3) the secretory phase. The histological appearance of the
endometrium during each phase is shown in Figure 28-20 . The phases occur in response to hormones associated with the
regulation of the ovarian cycle. Menses and the proliferative phase occur
during the follicular phase of the ovarian cycle. The secretory phase
corresponds to the luteal phase of the ovarian cycle. We shall consider the
regulatory mechanism in a later section.
Menses
The uterine cycle begins with the onset of menses, an interval marked by the degeneration of the functional zone of the
endometrium. The deterioration occurs in patches. It is caused by the
constriction of the spiral arteries, which reduces blood flow to areas of
endometrium. Deprived of oxygen and nutrients, the secretory glands and other
tissues in the functional zone begin to deteriorate. Eventually, the weakened
arterial walls rupture, and blood pours into the connective tissues of the
functional zone. Blood cells and degenerating tissues then break away and enter
the uterine lumen, to be lost by passage through the cervical os and into the vagina. Only the functional zone is
affected, because the deeper, basilar zone is provided with blood from the
straight arteries, which remain unconstricted.
The sloughing of tissue
is gradual, and at each site, repairs begin almost at once. Nevertheless,
before menses has ended, the entire functional zone has been lost (Figure 28-20a ). This process of endometrial sloughing is called menstruation.
Menstruation generally lasts from 1 to 7 days, and over this period roughly 35
to 50 ml of blood is lost. The process can be relatively painless. Painful
menstruation, or dysmenorrhea, can result from uterine inflammation and contraction or from
conditions involving adjacent pelvic structures.
The Proliferative Phase
The basilar zone, including the basal portions of the uterine glands, survives
menses intact. In the days following the completion of menses, the epithelial
cells of the glands multiply and spread across the endometrial surface,
restoring the integrity of the uterine epithelium (Figure 28-20b
). Further growth and vascularization result in the complete restoration
of the functional zone. As this reorganization proceeds, the endometrium is
said to be in the proliferative
phase. This restoration occurs at the same
time as the enlargement of primary and secondary follicles in the ovary. The
proliferative phase is stimulated and sustained by estrogens secreted by the
developing ovarian follicles.
By the time ovulation
occurs, the functional zone is several millimeters
thick, and prominent mucous glands extend to the border with the basilar zone.
At this time, the endometrial glands are manufacturing a mucus rich in
glycogen. The entire functional zone is highly vascularized, with small
arteries spiraling toward the inner surface from
larger arteries in the myometrium.
The Secretory Phase
During the secretory phase of the uterine cycle, the endometrial glands
enlarge, accelerating their rates of secretion, and the arteries elongate and
spiral through the tissues of the functional zone .
This activity occurs under the combined stimulatory effects of progestins and estrogens from the
corpus luteum. This phase begins at the time of
ovulation and persists as long as the corpus luteum
remains intact.
Secretory activities peak
about 12 days after ovulation. Over the next day or two, the glandular activity
declines, and the uterine cycle comes to a close as the corpus luteum stops producing stimulatory hormones. A new cycle
then begins with the onset of menses and the disintegration of the functional
zone. The secretory phase generally lasts 14 days. As a result, you can
determine the date of ovulation after the fact, by counting backward 14 days
from the first day of menses.
Menarche and Menopause
The uterine cycle begins with the menarche, or first menstrual period at puberty, typically at age 11-12. The
cycles continue until age 45-55, when menopause, the last uterine cycle,
occurs. Over the intervening three and a half to four decades, the regular
appearance of uterine cycles is interrupted only by unusual circumstances, such
as illness, stress, starvation, or pregnancy.
If menarche does not
appear by age 16, or if the normal uterine cycle of an adult woman becomes
interrupted for 6 months or more, the condition of amenorrhea exists. Primary amenorrhea is the failure to initiate menses.
This condition may indicate developmental abnormalities, such as nonfunctional ovaries, the absence of a uterus, or an endocrine
or genetic disorder. Transient secondary amenorrhea may be caused by
severe physical or emotional stresses. In effect, the reproductive system gets
"switched off" under these conditions. Examples of factors that can
cause amenorrhea include drastic weight-reduction programs, anorexia nervosa,
and severe depression or grief. Amenorrhea has also been observed in marathon
runners and other women engaged in training programs that require sustained
high levels of exertion and severely reduce body lipid reserves.
The vagina is an elastic,
muscular tube. It extends between the cervix of the uterus and the vestibule,
a space bounded by the female external genitalia (Figures 28-13 and 28-14 ). The vagina has an average length of 7.5-
At the proximal end of
the vagina, the cervix projects into the vaginal canal. The shallow recess
surrounding the cervical protrusion is known as the fornix. The vagina lies
parallel to the rectum, and the two are in close contact posteriorly.
Anteriorly, the urethra extends along the superior wall of the vagina from the
urinary bladder to the external urethral meatus, which opens into the
vestibule. The primary blood supply of the vagina is via the vaginal branches
of the internal iliac (or uterine) arteries and veins. Innervation is from the hypogastric plexus, sacral nerves S2-S4,
and branches of the pudendal nerve.
The vagina has three
major functions:
1.
It serves as a passageway
for the elimination of menstrual fluids.
2.
It receives the penis
during sexual intercourse and holds spermatozoa prior to their passage into the
uterus.
3.
It forms the lower
portion of the birth canal, through which the fetus
passes during delivery.
4.
Histology of the
Vagina
In sectional view, the
lumen of the vagina appears constricted, forming a rough H. The vaginal walls
contain a network of blood vessels and layers of smooth muscle. The lining is
moistened by the secretions of the cervical glands and by the movement of water
across the permeable epithelium. The vagina and vestibule are separated by the
hymen, an elastic epithelial fold that partially or completely blocks the
entrance to the vagina before the onset of sexual intercourse. The two bulbospongiosus muscles extend along either
side of the vaginal entrance, and their contractions constrict the entrance,
(Figure 11-13a ). These muscles cover the vestibular bulbs, masses of erectile
tissue on either side of the vaginal entrance. The vestibular bulbs have the
same embryological origins as the corpus spongiosum
of the penis in the male.
The vaginal lumen is
lined by a nonkeratinized stratified squamous
epithelium that in the relaxed state is thrown into folds called rugae. The underlying lamina propria is thick and elastic, and it contains small blood
vessels, nerves, and lymph nodes. The vaginal mucosa is surrounded by an
elastic muscularis layer, with layers of smooth
muscle fibers arranged in circular and longitudinal
bundles continuous with the uterine myometrium. The portion of the vagina
adjacent to the uterus has a serosal covering
continuous with the pelvic peritoneum. Along the rest of the vagina, the muscularis layer is surrounded by an adventitia of
fibrous connective tissue.
The vagina contains a
population of resident bacteria, usually harmless, supported by nutrients in
the cervical mucus. The metabolic activity of these bacteria creates an acidic
environment, which restricts the growth of many pathogens. An inflammation of
the vaginal canal, known as vaginitis, is caused by fungi, bacteria, or
parasites. In addition to any discomfort that may result, the condition may
affect the survival of sperm and thereby reduce fertility.
An acidic environment
also inhibits sperm motility; for this reason, the buffers in semen are
important to successful fertilization.
The hormonal changes
associated with the ovarian cycle also have an effect on the vaginal
epithelium. A vaginal smear is a sample of epithelial cells shed at the
vaginal surface. By examining these cells, a clinician can estimate the
corresponding stage in the ovarian and uterine cycles. This technique is an
example of exfoliative cytology.
The External Genitalia
The region containing the
female external genitalia is the vulva, or pudendum (Figure 28-22 ). The vagina opens into the vestibule, a central space bounded by small
folds known as the labia minora (singular, labium
minus). The labia minora are covered with a
smooth, hairless skin. The urethra opens into the vestibule just anterior to
the vaginal entrance. The paraurethral glands, or Skene's glands, discharge into the urethra
near the external urethral opening. Anterior to the urethral opening, the clitoris projects into the vestibule. The clitoris, a small, rounded tissue
projection, is the female equivalent of the penis; it is derived from the same
embryonic structures. Internally, it contains erectile tissue comparable to the
corpora cavernosa of the penis. The clitoris engorges
with blood during sexual arousal. A small erectile glans sits atop the
organ; extensions of the labia minora encircle the
body of the clitoris, forming the prepuce, or hood, of the clitoris.
A variable number of
small lesser vestibular glands discharge their secretions onto the exposed
surface of the vestibule, keeping it moistened. During arousal, a pair of ducts
discharges the secretions of the greater vestibular glands (Bartholin's glands) into the vestibule near the posterolateral margins of the vaginal entrance. These
mucous glands have the same embryological origins as the bulbourethral glands
of males.
The outer limits of the
vulva are established by the mons pubis
and the labia majora. The bulge of the mons pubis is created by adipose tissue beneath the skin
anterior to the pubic symphysis. Adipose tissue also
accumulates within the labia majora (singular, labium
majus), prominent folds of skin that encircle and
partially conceal the labia minora and adjacent
structures. The outer margins of the labia majora and
the mons pubis are covered with coarse hair, but the
inner surfaces of the labia majora are relatively hairless.
Sebaceous glands and scattered apocrine sweat glands secrete onto the inner
surface of the labia majora, moistening them and
providing lubrication.
The Mammary Glands
A newborn infant cannot
fend for itself, and several of its key systems have yet to complete their
development. Over the initial period of adjustment to an independent existence,
the infant gains nourishment from the milk secreted by the maternal mammary
glands. Milk production, or lactation, occurs in these glands, which in females are specialized organs of the
integumentary system that are controlled primarily by hormones of the
reproductive system and the placenta, a temporary structure that provides
the embryo or fetus with nutrients.
On each side, a mammary
gland lies in the subcutaneous tissue of the pectoral fat pad beneath the skin
of the chest (Figure 28-23). Each breast bears a small conical projection, the nipple, where the ducts of underlying mammary gland opens onto the body
surface. The reddish-brown region of skin around each nipple is the areola. Large sebaceous glands beneath the areolar surface give it a grainy texture.
The glandular tissue of
the mammary gland consists of separate lobes, each containing several secretory
lobules. Ducts leaving the lobules converge, giving rise to a single lactiferous duct in each lobe (Figure 28-23 ). Near the nipple, that lactiferous duct enlarges, forming an expanded
chamber called a lactiferous
sinus. Typically, 15-20 lactiferous
sinuses open onto the surface of each nipple.
Dense connective tissue
surrounds the duct system and forms partitions that extend between the lobes
and the lobules. These bands of connective tissue, known as the suspensory
ligaments of the breast, originate in the dermis of the overlying skin. A layer
of loose connective tissue separates the mammary complex from the underlying pectoralis muscles. Branches of the internal thoracic
artery supply blood to each mammary gland (Figure 21-23 ).
Development of the Mammary Glands during Pregnancy
There are two types of
mammary glands: inactive and active. The inactive, or resting, mammary
gland is dominated by a duct system rather than by active glandular cells. The
size of the mammary glands in a nonpregnant woman
reflects primarily the amount of adipose tissue present, not the amount of
glandular tissue. The secretory apparatus does not complete its development
until pregnancy occurs. The active mammary gland is a tubuloalveolar
gland, consisting of multiple glandular tubes that end in secretory
alveoli. We shall discuss the hormonal mechanisms involved in the control of
mammary gland function in Chapter 29.
CONCEPT CHECK QUESTIONS
1.
As the result of
infections such as gonorrhea, scar tissue can block
the lumen of each uterine tube. How would this blockage affect a woman's
ability to conceive?
2.
What is the advantage of
the normally acidic pH of the vagina?
3.
Which layer of the uterus
is sloughed off during menstruation?
4.
Would blockage of a
single lactiferous sinus interfere with delivery of milk to the nipple? Explain.