Neurobiology 104                                        Read Chap 20

November 17, 2003

 

 

                                       Female reproductive system

 

 

See FIGURE 20-1

 

  Relationship between the male and female reproductive systems.

 

 

The ducts of the male and female reproductive systems develop

from separate, parallel systems of ducts in the embryo.  

One system develops and the other degenerates.

 

             Male:     Wollfian and mesonephric duct

             Female:   Mullerian duct

 

Ovaries and testes are homologous, from the same embryonic primordium.

 

   1. Development

      Testes and ovaries arise from an indifferent gonad in the embryo.

      Germ line cells migrate into it from the yolk sac.

      The gonad migrates from the back of the body wall into the

         abdominal cavity or scrotum, carrying the peritoneum with it.

 

   2. Functions are 2-fold:

      To produce sex steroids; testosterone or estrogen + progesterone.

      To produce gametes; haploid sperm and haploid egg.

 

   3. Regulation:

      Both gonads are regulated by FSH (follicle stimulating

      hormone) and LH (luteinizing hormone) from the gonadotroph

      cells (basophils) of the anterior pituitary.

 

   4. Terminology of homologous cells:

 

          CELLS                     MALE              FEMALE

 

   Germline stem cells           spermatogonium       oogonium

 

   Germline in meiosis I         1  spermatocyte      1  oocyte

   Germline in meiosis II        2  spermatocyte      2  oocyte

   Haploid meiotic product       spermatid            mature egg

 

   Supporting epithelial cells   Sertoli cells        follicular/

   around the germ-line cells                         granulosa cells

 

   Steroid-producing cells       interstitial =       thecal cells

   outside the epithelium        Leydig cells

 

The main differences between male and female gonad functions are:

     1. Sperm and testosterone are produced continuously.

     2. Testosterone production can be divorced form sperm formation.

 

 

 

 

 

                             Ovary

 

  See FIGURE 20-2 A

 

      Histologically, the ovary has four components:

 

1. Germinal epithelium: a (misnamed) covering epithelium,                                    corresponding to a mesothelium.

  

2. Tunica albuginea: a nondescript capsule of dense C.T.

 

3. A loose connective tissue matrix.

 

4. Follicles consist of an egg = ovum =oocyte (in prophase I of meiosis)

   surrounded by layer of follicular cells (later called granulosa

   cells).  The follicles are located in the outer cortical region of

   the ovary.

 

                     FOLLICULAR STAGES

 

                             ­Primordial­ ­follicles­ are present from birth

                                  Their follicular cells are squamous.

 

                             Growing ­follicles­:  At each ovarian cycle

                                  a number of follicles become active,

                                  grow and start to mature as follows:

 

                              The ­follicular­ ­cells­ become cuboidal,

                                  divide, and form a stratified                                             epithelium.  Their name then

                                  changes to ­granulosa­ ­cells­.

See FIGURE 20-2 B

                              A ­zona­ ­pellucida­ forms around oocyte.

 

                              An ­antrum­ ­cavity­ forms.

 

                              A ­cumulus­ ­oophorus­ forms around the egg.

 

                              The follicle greatly enlarges.

 

                              Surrounding fibroblasts organize into

                              a ­theca­ ­interna­ and ­theca­ ­externa­.

 

                              The cells of the theca interna and the

                              follicular cells cooperate to produce

                              estrogen.

 

                              The follicle becomes ready to ovulate.

    
                          

                              Terminology for stages of growth

 

                              Primordial follicles are inactive.

 

                              Follicles are called ­primary until they                                   develop an antrum space after which they                              are called secondary follicles.

                                

                              ­Graafian­ = tertiary = mature follicle are

                              defined physiologically: A Graafian

                              follicle will ovulate in response to a

                              surge of LH from the pituitary.

 

                              Graafian follicles are ~ 1 cm across.

 

After ovulation

 

    When the egg is released it is accompanied by a surrounded

       layer of granulosa cells, the ­corona­ ­radiata­.

    The remains of the follicle become luteinized under the

       influence of LH to form a ­corpus­ ­luteum­.

    Granulosa cells become ­granulosa­ ­lutein­ ­cells­.

    Theca interna cells become ­theca­ ­lutein­ ­cells­.

    The basement membrane degenerates and blood vessels grow in

       amongst the granulosa lutein cells.

    The corpus luteum secretes ­estrogen­ and ­progesterone­.

    The corpus luteum grows for about 10-14 days and then

       degenerates unless pregnancy occurs. 

    During pregnancy it lasts for 6 months, supported by the hormone

       ­chorionic­ ­gonadotropin­ secreted by the placenta.

    The scar tissue that replaces a corpus luteum is called a

            ­corpus­ ­albicans­ ("white body").

 

­Atresia­ is the death and degeneration of growing follicles.

 

       Most follicles degenerate before reaching maturation.

            2,000,000 follicles are present at birth.

              400,000 follicles are present at puberty (menarche).

                < 400 follicles ovulate (1 per month until menopause).

 

       ­Atretic­ ­follicles­ look diverse because:

           1. follicles progressively degenerate.

           2. atresia may start at any stage of follicular development.

 

       All of the other mottlings and patterns seen in a mature

       ovary are scars and the traces of follicles undergoing the

       degenerative process of atresia. 

 

 

  ­Ovarian­ ­cycle­ (hormone relationships)

 

 

 

 

 

See FIGURE 20-8

 

Further tidbits:

 

   The maturation cycle of follicles does not coincide with the ovarian

     cycle.  Growing follicles can persist through the luteal phase.

 

   Ovulation usually alternates between ovaries.

 

   Birth control pills work by suppressing FSH secretion.

      Therefore they must replace the estrogen and progesterone that

      the follicles normally would have produced.

 

 

                            Oviduct

 

A. Four segments are distinguished (names not important)

 

B. Histology:

The mucosa has: -  a simple columnar epithelium with ciliated and                               mucus-secreting (peg) cells.

                     -  elaborate folds running longitudinally.

                     -  a lamina propria of loose C.T.

 

     The smooth muscle layers are inner circular and outer longitudinal.

 

C. Physiology:

     1. At ovulation the fimbriae move closer to the surface of the                ovary to recover the ovum by ciliary movement

 

     2. The smooth muscle contracts rhythmically towards the uterus.

 

     3. the sperm fertilizes the ovum in about the middle of the oviduct.

 

     4. the zygote moves down the oviduct to reach the uterus in 5-6 days.

 

 

                                Uterus

 

Structure (from outside inwards)

1. Epimetrium: The outer surface of the uterus is covered in part by a serosa and in part by an adventitia.

 

2. Myometrium: Smooth muscle running in various directions makes            up the main part of the wall.  The amount increases greatly during pregnancy.

   Large blood vessels run in the middle layer of the myometrium.

 

3. Endometrium: The lumen is covered with a specialized mucosa.


 

 

 

See FIGURE 20-11

 

The simple columnar epithelium of the endometrium extends as simple glands through its full thickness.  Special arterioles supply the tissue with blood as shown in the diagram.

 

Physiologically, the endometrium is divided into an upper functional layer and a lower basal layer.  During menstruation the functional layer is shed.  It is then replaced by growth on the basal layer.  The basal layer undergoes relatively little change in structure during the menstrual cycle.

 

The menstrual cycle.

 

The cyclic changes in hormones from the ovarian cycle causes a corresponding menstrual cycle of changes in the endometrium.

 

 

See FIGURE 20-12

 

 

  1. Menstrual phase (days 1-5)

 

Because it is the only part of the cycle that is visible externally the first day of menstruation is taken as day 1 of the cycle.  The next four days are defined as the menstrual phase.  The connective tissue, epithelium, glands and blood vessels of the functional layer disintegrate and are lost.

 

  2. Proliferative (= follicular = estrogenic) phase (days 6-14)

 

The epithelial cells in the tips of the glands remaining in the basal layer divide and grow out over the bare connective tissue surface of the endometrium to reestablish its surface epithelium.  The stromal cells (fibroblasts) divide to reconstitute the lamina propria of the functional layer.  As the functional layer becomes deeper the glands elongate and become corkscrew shaped.

 

  3. Secretory (= luteal = progestational) phase (days 15-28)

 

The glands secrete under the influence of progesterone.  Much of the secretion stays within the glands dilating them into large complex cavities.  If implantation does not occur secretion of progesterone stops by day 28.  This causes the spiral arteries to constrict, depriving the functional layer of its blood supply and kills the tissue.

 

 

 

 

 

                               Cervix

 

                     See FIGURE 20-1

 

The cervix is the lower, cylindrical part of the uterus.  Its lumen, the cervical canal communicates with the outer portion protruding in the vagina by a small opening, the os.

 

The inner surface is lined by a modified endometrium with permanent columnar epithelium and permanent, branched, mucous glands.

 

The glands provide lubrication for the vagina and block the passage of bacteria into the uterus.  At the time of ovulation       the mucus becomes watery instead of viscous.

 

The outer mucosa is a continuation of that of the vagina, with stratified squamous nonkeratinized epithelium.

 

 

Vagina

 

The vagina is a fibromuscular tube to receive the penis and ejaculate.

 

Its wall consists of: 

 

     Epithelium, stratified squamous unkeratinized.

The upper cells store glycogen, which makes them seem plump and empty.  The bacteria in the vagina ferment the glycogen in the desquamated cells to keep the pH low. 

 

Lamina propria, rich in blood vessels but without glands or

    nerve endings.

Some fluid seeps into the lumen from the blood vessels of the lamina propria during sexual stimulation.

 

Smooth muscle layers

These are oriented mainly longitudinally and are continuous with the outer muscle layer of the uterus.

 

     Adventitia containing many veins, elastic fibers and nerve bundles

Distention of the vaginal lumen and cervix during intercourse can cause release of oxytocin and prolactin.

 

The vaginal wall has transverse ridges (which, of course, are not visible in cross-sections.)

 

 

 

 

Clitoris

 

The clitoris is the female­ ­homologue­ ­of­ ­the­ ­penis­.  It is composed of columns of erectile tissue but does not enclose the urethra.  We will defer its description until the lecture on the male penis.

 

 

Breast

 

The breast has unusual structure, physiology and development.  The pages, by Dr. Lu, summarize some of its most important histology and development.

 

           Read the section in your text book PP 483-486