Female Reproductive System

1. Ovaries (gonads). Produce gametes (secondary oocytes) and hormones (estrogens, progesterone, inhibin, relaxin).
2. Uterine (fallopian) tubes. Transport secondary oocytes from ovaries to uterus. Site of fertilization.
3. Uterus. Site of implantation, fetal development, and labor.
4. Vagina. Receptacle for the penis during intercourse, outlet for menstrual flow, and passageway for childbirth.
5. External organs (vulva or pudendum). Protective structures and sensory organs for sexual response.
6. Mammary glands. Synthesize, secrete, and eject milk for nourishment of the newborn.

From superficial to deep:

1. Germinal epithelium. Single layer of simple cuboidal or squamous epithelium. Important: despite the name, this layer does NOT give rise to ova. The cells that produce ova arise from the yolk sac and migrate to the ovaries during embryonic development.
2. Tunica albuginea. Whitish capsule of dense irregular CT immediately deep to the germinal epithelium.
3. Ovarian cortex. Just deep to the tunica albuginea. Contains ovarian follicles surrounded by dense irregular CT with collagen fibers and fibroblast-like stromal cells.
4. Ovarian medulla. Deep to the cortex (indistinct border between them). More loose CT. Contains blood vessels, lymphatic vessels, and nerves.
5. Ovarian follicles. Found in the cortex. Contain oocytes in various stages of development. Surrounding cells start as a single layer of follicular cells; later development produces several layers of granulosa cells. These cells nourish the developing oocyte and begin to secrete estrogens as the follicle grows.
6. Mature follicle. Large fluid-filled follicle ready to rupture and expel its secondary oocyte (ovulation).
7. Corpus luteum (yellow body). Remnants of a mature follicle after ovulation. Produces progesterone, estrogens, relaxin, and inhibin until it degenerates into the corpus albicans (white body), a fibrous scar.

Each month, FSH and LH from the anterior pituitary stimulate development of several primordial follicles. Typically only one reaches maturity needed for ovulation.

Stage 1: Primordial Follicle

Primary oocyte arrested in prophase I, surrounded by a single layer of flattened follicular cells.

Stage 2: Primary Follicle

• Primary oocyte at a later stage of development.
• Surrounded by several layers of cuboidal and low-columnar cells called granulosa cells.
• Outermost granulosa cells rest on a basement membrane.
• Forms a clear glycoprotein layer called the zona pellucida between the primary oocyte and granulosa cells.
• Stromal cells around the basement membrane organize into the theca folliculi.

Stage 3: Secondary Follicle

• Theca differentiates into two layers:
  • Theca interna: highly vascular, cuboidal secretory cells. Secrete estrogens.
  • Theca externa: outer layer of stromal cells and collagen fibers.
• Granulosa cells secrete follicular fluid that builds up in a cavity called the antrum.
• The innermost layer of granulosa cells firmly attaches to the zona pellucida and is now called the corona radiata.

Stage 4: Mature (Graafian) Follicle

• Large fluid-filled follicle just prior to ovulation.
• The primary oocyte completes Meiosis I, producing two haploid (n) cells of unequal size:
  • First polar body: the smaller cell, a packet of disorganized material.
  • Secondary oocyte: larger cell, receives most of the cytoplasm. Begins Meiosis II and stops in metaphase.
• The mature follicle ruptures and releases the secondary oocyte. This is ovulation.

What Comes Out of the Mature Follicle

The secondary oocyte is expelled into the pelvic cavity along with the first polar body and the corona radiata. Fimbriae sweep it into the uterine tube.

If Fertilization Does NOT Occur

The cells degenerate. The cycle ends. Menstruation will follow.

If Sperm Are Present

1. One sperm penetrates the secondary oocyte.
2. This resumes meiosis II in the secondary oocyte.
3. The secondary oocyte splits into two haploid cells of unequal size:
   • Larger cell = ovum (mature egg).
   • Smaller cell = second polar body.
4. The nuclei of sperm and ovum unite to form a diploid zygote.
5. The first polar body undergoes another division into two polar bodies.

Final Tally

One primary oocyte yields 1 ovum + 3 polar bodies (all of which degenerate). Compare to males: 1 primary spermatocyte yields 4 functional sperm.

1. After ovulation, currents from the fimbriae surround the mature follicle.
2. Currents sweep the ovulated secondary oocyte from the peritoneal cavity into the uterine tube.
3. A sperm cell typically encounters and fertilizes the secondary oocyte in the ampulla of the uterine tube. (Fertilization in the peritoneal cavity is not uncommon.)
4. Fertilization can occur up to 24 hours after ovulation.
5. Hours after fertilization, the haploid nuclei unite.
6. The diploid fertilized ovum is now a zygote. It begins cell divisions while moving toward the uterus.
7. Arrives in the uterus 6 to 7 days after ovulation.
8. Unfertilized secondary oocytes disintegrate.

1. Mucosa

• Ciliated simple columnar cells. Form a "ciliary conveyor belt" that helps move the fertilized ovum or secondary oocyte toward the uterus.
• Non-ciliated cells (peg cells). Have microvilli. Secrete fluid that nourishes the ovum and supports sperm.
• Lamina propria. Areolar CT.

2. Muscularis

Function: peristalsis (wave-like contractions) that move the ovum or secondary oocyte toward the uterus.

• Inner layer: thick circular ring of smooth muscle.
• Outer layer: thin region of longitudinal smooth muscle.

3. Serosa

Outer layer of serous membrane.

Functions

1. Part of the pathway for sperm deposited in the vagina (to reach the uterine tubes).
2. Site of implantation of a fertilized ovum.
3. Development of the fetus during pregnancy.
4. Assists in labor.
5. Source of menstrual flow during cycles when implantation has not occurred.

Characteristics

Inverted pear shape. Variable size depending on pregnancy (much larger). Smaller (atrophied) without hormone influence (menopause).

Location

Between the urinary bladder (anterior) and the rectum (posterior).

1. Perimetrium (Outer Layer / Serosa)

Part of the visceral peritoneum. Made of simple squamous epithelium and areolar CT.

• Laterally: becomes the broad ligament.
• Anteriorly: covers the urinary bladder, forms a shallow pouch.
• Posteriorly: covers the rectum and forms a deep pouch (the rectouterine pouch or pouch of Douglas). This is the most inferior point in the pelvic cavity.

2. Myometrium (Middle Layer)

Three layers of smooth muscle. Thickest in the fundus, thinnest in the cervix.

• Inner and outer layers: longitudinal.
• Middle layer: oblique.

Function: coordinated contractions during childbirth. Responds to oxytocin from the posterior pituitary to expel the fetus from the uterus.

3. Endometrium (Inner Layer)

Highly vascular. Three components:

1. Innermost layer: simple columnar epithelium with cilia and secretory cells.
2. Underlying stroma: very thick region of lamina propria (areolar CT).
3. Uterine (endometrial) glands: invaginations of the luminal epithelium that extend almost into the myometrium.

Two Arterioles into the Endometrium

• Straight arterioles. Supply the stratum basalis. They survive each menstrual cycle and enable regeneration of the functionalis.
• Spiral arterioles. Supply the stratum functionalis. They change during the menstrual cycle and constrict to drive sloughing.

Drainage

Uterine veins drain into the internal iliac veins.

Why Such an Extensive Blood Supply

1. Support the growth of a new stratum functionalis after menstruation.
2. Implantation of a fertilized ovum.
3. Development of the placenta.

Produced by: secretory cells of the mucosa of the cervix.

Composition: water, glycoproteins, lipids, enzymes, inorganic salts.

Volume: 20 to 60 mL/day during reproductive age.

Consistency Changes Across the Cycle

• Near ovulation: less viscous, more alkaline, hospitable to sperm.
• Other times: can impede sperm penetration.

Functions

1. Supplements sperm with energy.
2. Protects sperm from phagocytes and the hostile environment of the vagina/uterus.
3. Supports capacitation: a series of functional changes sperm undergo in the female reproductive tract prior to fertilization.
   • Sperm tail beats more vigorously.
   • Plasma membrane is prepared to fuse with the oocyte.

Mucosa

Continuous with the uterus.

• Tissue: non-keratinized stratified squamous epithelium and areolar CT. Creates transverse folds called rugae.
• Antigen-presenting (dendritic) cells found here participate in transmission of viruses (HIV).
• Large stores of glycogen, which can be decomposed into organic acids.
• Acidic environment inhibits microbial growth. This is protective, but the same acidity is hostile to sperm. (Hence the alkaline buffering provided by semen.)

Muscularis

• Composed of an outer circular layer and an inner longitudinal layer of smooth muscle.
• Function: stretches to accommodate the penis during intercourse and a baby during childbirth.

Adventitia

• Superficial layer.
• Made of areolar CT.
• Anchors the vagina to adjacent organs: urethra and urinary bladder anteriorly, rectum posteriorly.

Hymen

Thin fold of vascularized mucous membrane that forms a border or partially closes the inferior end of the vaginal opening (vaginal orifice).

Ruptures following first sexual intercourse.

1. Mons Pubis

Elevation of adipose tissue covered by skin and coarse pubic hair. Function: cushions the pubic symphysis.

2. Labia Majora

Two large longitudinal folds of skin covered by pubic hair. Contain adipose tissue, sebaceous (oil) glands, and apocrine (sweat) glands.

Homologous to the scrotum.

3. Labia Minora

Smaller folds. No hair, no fat. Few sudoriferous glands but many sebaceous glands.

Homologous to the spongy urethra.

4. Clitoris

Small cylindrical mass containing two erectile bodies (corpora cavernosa), numerous nerves, and blood vessels.

• Location: anterior junction of the labia minora.
• Prepuce of the clitoris: point where the labia minora unite and cover the clitoris with skin.
• Glans clitoris: the exposed part.
• Function: responds to tactile stimulation. Plays a role in sexual excitement.

Homologous to the penis.

5. Vestibule

Region between the labia minora.

Contains: hymen, vaginal orifice, external urethral orifice, and several duct/gland openings.

Homologous to the male intermediate (membranous) urethra.

Vaginal Orifice

Opening of the vagina to the exterior.

External Urethral Orifice

Opening of the urethra to the exterior.

Paraurethral Glands (Skene's Glands)

On either side of the external urethral orifice. Secrete mucus. Embedded in the wall of the urethra.

Homologous to the prostate.

Greater Vestibular Glands (Bartholin's Glands)

On either side of the vaginal orifice. Produce a small amount of mucus during sexual arousal to aid lubrication.

Homologous to the bulbourethral (Cowper's) glands in males.

Bulb of the Vestibule

Two elongated masses of erectile tissue deep to the vaginal orifice. Becomes engorged with blood during sexual arousal. Narrows and puts pressure on the penis during intercourse.

Homologous to the corpus spongiosum and bulb of the penis in males.

Project anteriorly from two muscles: pectoralis major and serratus anterior. A layer of fascia (dense irregular CT) attaches the breast to these muscles.

Specialized Structures

1. Nipple. Pigmented projection containing a series of openings of lactiferous ducts where milk emerges.
   • Areola: circular pigmented area surrounding the nipple. Contains modified sebaceous (oil) glands.
2. Suspensory ligaments of the breast (Cooper's ligaments). Between skin and fascia. Support the breast. Become looser with age or excessive strain (jogging, high impact aerobics, sports).
3. Mammary gland. A modified sudoriferous (sweat) gland that produces milk.
4. Lobes: 25 to 50 lobes or compartments. Lobes divide into lobules containing alveoli (milk-producing structures).
5. Lactiferous ducts. Drain milk from the alveoli and transport it to the nipple.
6. Myoepithelial cells. Contracting cells that propel milk toward the nipple.

Function: Lactation

Milk production and ejection. Stimulus: baby suckling on the nipple stimulates the release of oxytocin from the posterior pituitary, which triggers milk ejection.

Blood Supply

Internal thoracic artery, lateral thoracic artery, and intercostal arteries.