28. ANATOMY OF FEMALE REPRODUCTIVE SYSTEM B. FEMALE INTERNAL REPRODUCTIVE ORGANS

B. FEMALE INTERNAL REPRODUCTIVE ORGANS


include 

1. Ovaries (female gonads);
2. Uterine (fallopian) tubes, or oviducts; 
3. Uterus; 
4. Vagina; 




1. Ovaries

• The ovaries ( egg receptacles), 
• which are the female gonads,
• are paired glands 
• that resemble unshelled almonds in size and shape; 

• they are homologous to the testes. (Here homologous means that two organs have the same embryonic origin.) 

• The ovaries produce 

        (1) gametes, 

                    - secondary oocytes that develop into mature ova (eggs) after fertilization, and 

        (2) hormones, including
               - progesterone 
               - and estrogens (the female sex hormones),
               - inhibin, 
               - and relaxin.

• The ovaries, one on either side of the uterus,

• descend to the brim of the superior portion of the pelvic cavity during the third month of development. 

• A series of ligaments holds them in position. 

1. The broad ligament of the uterus , which is itself part of the parietal peritoneum, attaches to the ovaries by a double-layered fold of peritoneum called the mesovarium. 


2. The ovarian ligament anchors the ovaries to the uterus, and 

3. The suspensory ligament attaches them to the pelvic wall. 

• Each ovary contains a hilum, 

           - the point of entrance and exit for blood vessels and nerves along which the mesovarium is attached.



Histology of the Ovary


Each ovary consists of the following parts :


1.  The germinal epithelium (germen sprout or bud)

•  is a layer of simple epithelium (low cuboidal or squamous) that covers the surface of the ovary. 

(We now know that the term germinal epithelium in humans is not accurate because it does not give rise to ova; the name came about because, at one time, people believed that it did. We have since learned

that the cells that produce ova arise from the yolk sac and migrate to the ovaries during embryonic development.)


2.  The tunica albuginea 

• is a whitish capsule of dense irregular connective tissue 
• located immediately deep to the germinal epithelium.

3.  The ovarian cortex 

• is a region just deep to the tunica albuginea.
• It consists of ovarian follicles 
• surrounded by dense irregular connective tissue that contains

            - collagen fibers and 
            - fibroblast-like cells called stromal cells.



4. The ovarian medulla 

• is deep to the ovarian cortex. 
• The border between the cortex and medulla is indistinct, 
• but the medulla consists of more loosely arranged connective tissue 
• and contains

• blood vessels,
• lymphatic vessels, and 
• nerves.

5.  Ovarian follicles 

• (folliculus little bag) 
• are in the cortex 
• and consist of oocytes in various stages of development, 
• plus the cells surrounding them. 

• When the surrounding cells form a single layer, they are called follicular cells; 
• later in development, when they form several layers, they are referred to as granulosa cells. 

• The surrounding cells nourish the developing oocyte and 
• begin to secrete estrogens as the follicle grows larger.

6.  A mature (graafian) follicle 

• is a large, fluid-filled follicle
• that is ready to rupture and expel its secondary oocyte, a process known as ovulation.

7.  A corpus luteum 

• ( yellow body) 
• contains the remnants of a mature follicle after ovulation. 

• The corpus luteum produces

             - progesterone, 

             - estrogens, 
             - relaxin, and 
             - inhibin 

• until it degenerates into fibrous scar tissue called the corpus albicans ( white body).

2. Uterine Tubes

• Females have two uterine (fallopian) tubes, or oviducts, 
• that extend laterally from the uterus . 

• The tubes, which measure about 10 cm (4 in.) long, 
• lie between the folds of the broad ligaments of the uterus. 

•  They provide a route for sperm to reach an ovum and transport secondary oocytes and fertilized ova from the ovaries to the uterus. 

• The funnel-shaped portion of each tube, called the infundibulum, 
• is close to the ovary 
• but is open to the pelvic cavity. 

• From the infundibulum the uterine tube extends medially and eventually inferiorly and attaches to the superior lateral angle of the uterus.

 

• It ends in a fringe of fingerlike projections called fimbriae (FIM-bre¯ -e¯ fringe), 

• one of which is attached to the lateral end of the ovary. 

The ampulla of the uterine tube 

• is the widest, longest portion, 
• making up about the lateral two-thirds of its length. 

The isthmus of the uterine tube 

• is the more medial, 
• short, narrow, thick-walled portion that joins the uterus.

HISTOLOGY 


Histologically, 

The uterine tubes are composed of three layers:

1. mucosa, 
2. muscularis, and 
3. serosa. 

The mucosa 

•  consists of epithelium and lamina propria (areolar connective tissue). 
• The epithelium contains 

a. ciliated simple columnar cells, 

          - which function as a “ciliary conveyor belt” to help move a fertilized ovum (or secondary
oocyte) within the uterine tube toward the uterus, and

b. nonciliated cells called peg cells, 
     
             - which have microvilli and
            -  secrete a fluid that provides nutrition for the ovum . 


The middle layer, the muscularis,

•  is composed of 

      a. an inner,thick,circular ring of smooth muscle 

      b. an outer, thin region of longitudinal smooth muscle. 

• 1. Peristaltic contractions of the muscularis and 2. the ciliary action of the mucosa 

                     - help move the oocyte or fertilized ovum toward the uterus. 

• The outer layer of the uterine tubes is a serous membrane, the serosa. 
• Local currents produced by movements of the fimbriae,

              - which surround the ovary during ovulation, 
             - sweep the ovulated secondary oocyte from the pelvic cavity into the uterine tube.

•  A sperm cell usually encounters and fertilizes a secondary oocyte in the ampulla of the uterine tube, although fertilization in the pelvic cavity is not uncommon. 

• Fertilization can occur at any time up to about 24 hours after ovulation. 
• Some hours after fertilization, the nuclear materials of the haploid ovum and sperm unite.

•  The diploid fertilized ovum is now called a zygote and 
• begins to undergo cell divisions while moving toward the uterus.
•  It arrives at the uterus 6 to 7 days after ovulation.

3. Uterus

• The uterus (womb) serves as part of the pathway for sperm deposited in the vagina to reach the uterine tubes. 
• It is also the site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor. 

• During reproductive cycles when implantation does not occur, the uterus is the source of menstrual flow.

Anatomy of the Uterus

• Situated between the urinary bladder and the rectum, 

• the uterus is the size and shape of an inverted pear .

•  In females who have never been pregnant, it is about 
• 7.5 cm (3 in.) long, 
• 5 cm (2 in.) wide, and 
• 2.5 cm (1 in.) thick. 

• The uterus is larger in females who have recently been pregnant, 
• and smaller (atrophied) when sex hormone levels are low, as occurs after menopause.

Anatomical subdivisions of the uterus 

include: 

(1) a domeshaped portion superior to the uterine tubes called the fundus,
(2) a tapering central portion called the body, and (3) an inferior narrow portion called the cervix that opens into the vagina.

• Between the body of the uterus and the cervix is the isthmus
• (IS-mus), 
• a constricted region 
• about 1 cm (0.5 in.) long. 

• The interior of the body of the uterus is called the uterine cavity, and
• the interior of the cervix is called the cervical canal. 

The cervical canal 

• opens into the uterine cavity at the internal os (os mouthlike opening) 
• and into the vagina at the external os.

Normally, 

• the body of the uterus projects anteriorly and superiorly over the urinary bladder in a position called anteflexion.

• The cervix projects inferiorly and posteriorly and enters the anterior wall of the vagina at nearly a right angle.

•  Several ligaments that are either extensions of the parietal peritoneum or fibromuscular cords maintain the position of the uterus. 

1. The paired broad ligaments are double folds of peritoneum attaching the uterus to either side of the pelvic cavity. 

2. The paired uterosacral ligaments, also
peritoneal extensions, lie on either side of the rectum and connect the uterus to the sacrum. 

3. The cardinal (lateral cervical) ligaments 

• are located inferior to the bases of the broad ligaments and 
• extend from the pelvic wall to the cervix and vagina.

4. The round ligaments 

• are bands of fibrous connective tissue between the layers of the broad ligament; 
• they extend from a point on the uterus just inferior to the uterine tubes to a portion of the labia majora of the external genitalia. 

• Although the ligaments normally maintain the anteflexed position of the uterus,
•  they also allow the uterine body enough movement such that the uterus may become malpositioned. 

• A posterior tilting of the uterus, called retroflexion (retro- backward or behind), 
• is a harmless variation of the normal position of the uterus. 
• There is often no cause for the condition, but it may occur after childbirth.

Histology of the Uterus


Histologically, 

• the uterus consists of three layers of tissue:

1. perimetrium, 
2. myometrium, and
3. endometrium 


The outer layer—the perimetrium (peri- around; -metrium uterus) or serosa—

• is part of the visceral peritoneum;
• it is composed of simple squamous epithelium and areolar connective tissue.

• Laterally, it becomes the broad ligament.

• Anteriorly, it covers the urinary bladder and forms a shallow pouch, the vesicouterine pouch (ves -i-ko¯-U¯ -ter-in; vesico- bladder; . 

• Posteriorly, it covers the rectum and forms a deep pouch between the uterus and urinary bladder, the rectouterine pouch (rek-to¯-U¯ -ter-in; recto- rectum) or pouch of Douglas
• — the most inferior point in the pelvic cavity.

The middle layer of the uterus, the myometrium (myo- muscle), 

• consists of three layers of smooth muscle fibers that are

1. thickest in the fundus and 
2. thinnest in the cervix. 

• The thicker middle layer is circular; 
• the inner and outer layers are longitudinal or oblique. 

• During labor and childbirth, coordinated contractions of the myometrium in response to oxytocin from the posterior pituitary help expel the fetus from the uterus.

• The inner layer of the uterus, the endometrium (endo- within), 
• is highly vascularized 

• and has three components: 

• (1) An innermost layer composed of simple columnar epithelium (ciliated secretory cells) lines the lumen.
• (2) An underlying endometrial stroma is a very thick region of lamina propria (areolar connective tissue). 
• (3) Endometrial (uterine) glands develop as invaginations of the luminal epithelium and extend almost to the myometrium. 

• The endometrium is divided into two layers.

A. The stratum functionalis (functional layer) 

• lines the uterine cavity 
• and sloughs off during menstruation. 

B. The deeper layer, the stratum basalis (basal layer), 

• is permanent 
• and gives rise to a new stratum functionalis after each menstruation.

Blood supply 

• Branches of the internal iliac artery called uterine arteries supply blood to the uterus. 

• Uterine arteries give off branches called arcuate arteries ( shaped like a bow) that
•  are arranged in a circular fashion in the myometrium. 

• These arteries branch into radial arteries that penetrate deeply into the myometrium. 

• Just before the branches enter the endometrium, they divide into two kinds of arterioles: 

a. Straight arterioles 

• supply the stratum basalis with the materials needed to regenerate the stratum functionalis; 

b. Spiral arterioles 

• supply the stratum functionalis 
• and change markedly during the menstrual cycle.

Venous drainage

Blood leaving the uterus is drained 

• by the uterine veins into the internal iliac veins. 

• The extensive blood supply of the uterus is essential to support regrowth of a new stratum functionalis after
• menstruation,
•  implantation of a fertilized ovum, and 
• development of the placenta.

Cervical Mucus

• The secretory cells of the mucosa of the cervix produce a secretion called cervical mucus, 
• a mixture of 

                 - water, 
                 - glycoproteins,
                 - lipids,
                 - enzymes, and
                 - inorganic salts.

• During their reproductive years, females secrete 20–60 mL of cervical mucus per day.

• Cervical mucus is more hospitable to sperm at or near the time of ovulation because 

a. it is then less viscous and
b.  more alkaline (pH 8.5). 

• At other times, a more viscous mucus forms a cervical plug that physically impedes sperm penetration. 

1. Cervical mucus

• supplements the energy needs of sperm, and

2.  both the cervix and cervical mucus 

• protect sperm from phagocytes and the hostile environment of the vagina and uterus. 

3. Cervical mucus may also play a role in capacitation

•    —a series of functional changes that sperm undergo in the female reproductive tract before they are able to fertilize a secondary oocyte. 

• Capacitation causes a sperm cell’s tail to beat even more vigorously, and it prepares the sperm cell’s plasma membrane to fuse with the oocyte’s plasma membrane.

4. Vagina


The vagina ( sheath) is 

• a tubular, 
• 10-cm (4-in.) 
• long fibromuscular canal 
• lined with mucous membrane 
• that extends from the exterior of the body to the uterine cervix . 

• It is the receptacle for the penis during sexual intercourse,
• the outlet for menstrual flow, 
• and the passageway for childbirth.

•  Situated between the urinary bladder and the rectum,
• the vagina is directed superiorly and posteriorly, where it attaches to the uterus. 

• A recess called the fornix ( arch or vault) surrounds the vaginal attachment to the cervix. 
• When properly inserted, a contraceptive diaphragm rests in the fornix, where it is held in place as it covers the cervix.

• The mucosa of the vagina is continuous with that of the uterus.

HISTOLOGY

 Histologically,

•  it consists of

•  nonkeratinized stratified squamous epithelium and 
• areolar connective tissue

            -that lies in a series of transverse folds called rugae (ROO-ge¯). 

• Dendritic cells in the mucosa are antigen-presenting cells . 
• Unfortunately, they also participate in the transmission of viruses—for example, HIV (the virus that causes AIDS)—to a female during intercourse with an infected male. 

• The mucosa of he vagina contains large stores of glycogen, the decomposition of which produces organic acids. 
• The resulting acidic environment retards microbial growth, but it also is harmful to sperm.

• Alkaline components of semen, mainly from the seminal vesicles,

                - raise the pH of fluid in the vagina and                     - increase viability of the sperm.


The muscularis is composed of 

A. an outer circular layer and
B. an inner longitudinal layer of smooth muscle
     - that can stretch considerably 

• to accommodate the penis during sexual intercourse and
•  a child during birth.

The adventitia, the superficial layer of the vagina, consists of
                - areolar connective tissue. 
It anchors the vagina to adjacent organs 

• such as the urethra and urinary bladder anteriorly and 
• the rectum and anal canal posteriorly.

• A thin fold of vascularized mucous membrane, called the hymen ( membrane), 
• forms a border around 
• and partially closes the inferior end of the vaginal opening to the exterior, the vaginal orifice . 

• After its rupture, usually following the first sexual intercourse, only remnants of the hymen remain. 
• Sometimes the hymen completely covers the orifice, a condition called imperforate hymen (im-PER-fo¯-ra¯t). 
• Surgery may be needed to open the orifice and permit the discharge of menstrual flow.