Female Reproductive System: Anatomy and Physiology (Seeley's Anatomy & Physiology, Ch. 28)

Anatomy of the Female Reproductive System

Main Organs and Structures

The female reproductive system consists of several specialized organs responsible for gamete production, fertilization, and supporting embryonic development.

• Ovaries: Produce oocytes and hormones.

• Uterine tubes (Fallopian tubes, oviducts): Transport oocytes and are the site of fertilization.

• Uterus: Supports fetal development.

• Vagina: Organ of copulation and birth canal.

• External genital organs: Include vulva, labia, clitoris, and vestibule.

• Mammary glands: Produce milk for nourishment of offspring.

Ovaries

The ovaries are paired organs attached to the uterus by several ligaments and are the site of oocyte production and hormone secretion.

• Broad ligament: Extension of peritoneum supporting ovaries and uterine tubes.

• Mesovarium: Peritoneal fold attaching ovary to broad ligament.

• Suspensory ligament: Connects ovary to body wall; contains ovarian vessels and nerves.

• Ovarian ligament: Connects ovary to uterus; passage for vessels and nerves.

Ovarian Histology

The ovary is composed of distinct layers and tissues that support oocyte development.

• Ovarian (germinal) epithelium: Outermost layer, visceral peritoneum.

• Tunica albuginea: Dense fibrous capsule beneath epithelium.

• Cortex: Outer region containing follicles with oocytes.

• Medulla: Inner region with blood vessels, nerves, lymphatics.

• Stroma: Connective tissue framework.

Oogenesis and Follicle Development

Oogenesis

Oogenesis is the process by which female gametes (oocytes) are produced in the ovaries.

• Oogonia: Stem cells that divide to form primary oocytes.

• By the fourth month of prenatal life, ~5 million oocytes are present; ~2 million begin meiosis but arrest until puberty.

• Primary oocytes are surrounded by granulosa cells forming primordial follicles.

• Primordial follicle → primary follicle (oocyte and granulosa cells enlarge).

• Primary follicle → secondary follicle → mature (Graafian) follicle.

• Usually only one follicle ovulates; others degenerate (atresia).

Ovulation, Fertilization, and Follicle Fate

Ovulation is the release of a secondary oocyte, followed by possible fertilization and changes in follicle structure.

• Ovulation: Secondary oocyte released from ovary.

• Meiosis produces one large oocyte and small polar bodies (unequal cytokinesis).

• Graafian follicle becomes corpus luteum after ovulation.

• Fertilization: Sperm binds and penetrates oocyte; oocyte completes meiosis II, forming a zygote.

• Corpus luteum persists if fertilization occurs; otherwise, it degenerates into corpus albicans.

Uterine Tubes (Fallopian Tubes)

Structure and Function

The uterine tubes transport oocytes and are the site of fertilization.

• Mesosalpinx: Broad ligament portion associated with uterine tube.

• Opens into peritoneal cavity to receive oocyte.

• Fimbriae: Ciliated projections from infundibulum, help capture oocyte.

• Ampulla: Widest part, typical site of fertilization.

• Three layers: serosa (outer), muscular layer (middle), mucosa (inner, ciliated columnar epithelium).

• Cilia and secretions aid movement and nourishment of oocyte/embryo.

Uterus

Structure and Layers

The uterus is a muscular organ supporting fetal development and menstruation.

• Parts: body, isthmus, cervix, fundus.

• Ligaments: broad, round (to labia majora), uterosacral (to sacrum).

• Layers:

  • Perimetrium: Serous membrane (outer).

  • Myometrium: Smooth muscle (middle).

  • Endometrium: Mucous membrane (inner).

    • Functional layer: Sheds during menstruation.

    • Basal layer: Deepest, regenerates functional layer.

• Cervix: More rigid, less contractile; contains cervical canal with mucous glands.

Vagina

Structure and Function

The vagina serves as the organ of copulation, birth canal, and passage for menstrual flow.

• Hymen: Thin membrane covering vaginal opening.

• Walls: Muscular, lined with moist stratified squamous epithelium.

• Features: Longitudinal columns and transverse rugae for expansion.

• Fornix: Superior portion attached to cervix.

Female External Genitalia

Vulva (Pudendum)

The external genitalia protect internal structures and facilitate sexual function.

• Vestibule: Space surrounded by labia minora.

• Labia minora: Inner folds bordering vestibule.

• Clitoris: Erectile organ; contains corpora cavernosa and corpora spongiosa.

• Labia majora: Outer folds, unite to form mons pubis.

• Vaginal orifice: Opening surrounded by erectile tissue (bulb of vestibule).

Glands and Additional Structures

• Greater vestibular gland, lesser vestibular glands, paraurethral glands: Secrete fluids for lubrication.

• Labia majora: Contains sebaceous and sweat glands; pudendal cleft is the space between them.

• Mons pubis: Fatty elevation over symphysis pubis.

Perineum

Structure and Clinical Significance

The perineum is the region between the vagina and anus, important in childbirth.

• Divided into urogenital triangle (anterior) and anal triangle (posterior).

• Clinical perineum: Area prone to tearing during childbirth.

• Episiotomy: Surgical incision to aid delivery.

Mammary Glands

Structure and Function

Mammary glands are specialized for milk production and consist of glandular and adipose tissue.

• Located within breasts (mammae).

• Composed of glandular lobes and adipose tissue.

• Cooper ligaments: Support breast structure.

Physiology of Female Reproduction

Puberty

Puberty marks the onset of reproductive capability in females.

• Begins with menarche (first menstrual bleeding).

• Triggered by increased GnRH (gonadotropin-releasing hormone) levels.

Menstrual Cycle

The menstrual cycle averages 28 days and consists of ovarian and uterine changes.

• Ovarian cycle: Follicular and luteal phases in the ovary.

• Uterine cycle: Changes in endometrial lining.

• Amenorrhea: Absence of menstruation.

• Menopause: Permanent cessation of menstruation.

Ovarian Cycle Phases

• Follicular phase (days 1-14):

  • Primordial follicle matures; oocyte undergoes meiosis I.

  • FSH stimulates follicle development; estrogen release leads to LH surge and ovulation.

  • Estrogen also stimulates endometrial proliferation.

• Luteal phase (days 15-28):

  • Corpus luteum forms, secretes estrogen and progesterone.

  • Progesterone thickens endometrium and stimulates secretion.

  • If no fertilization, corpus luteum degenerates, hormone levels drop, and menstruation occurs.

  • If fertilization, hCG maintains corpus luteum.

Female Sexual Behavior and Sex Act

Hormonal and Psychological Factors

Female sexual behavior is influenced by hormones and psychological factors.

• Androgens and steroids play roles in sexual response.

• Parasympathetic stimulation causes blood engorgement, erect nipples, and secretion of mucous-like fluid.

• Orgasm is not required for fertilization.

Female Fertility and Pregnancy

Fertility

• Sperm deposited in vagina, transported to ampulla of uterine tube.

• Sperm undergo capacitation to release acrosomal enzymes for fertilization.

Pregnancy and Fertilization

• Oocyte viable for up to 24 hours post-ovulation; sperm viable up to 6 days.

• Ectopic pregnancy: Implantation outside uterine cavity.

• Fertilization occurs in uterine tube; embryo forms after union of oocyte and sperm nuclei.

• Trophoblast (outer embryonic mass) secretes enzymes for implantation and hCG.

Hormone Changes During Pregnancy

• hCG produced by embryo, maintains corpus luteum in first trimester.

• Placenta produces increasing levels of progesterone and estrogen throughout pregnancy.

Menopause

Definition and Symptoms

Menopause is the permanent cessation of menstrual cycles, typically occurring between ages 40-50.

• Ovaries stop producing estrogen and progesterone.

• Symptoms: hot flashes, irritability, night sweats, fatigue, anxiety, emotional disturbances.

Table: Comparison of Oogenesis and Spermatogenesis

Feature	Oogenesis	Spermatogenesis
Location	Ovary	Testis
Gamete produced	Oocyte	Sperm
Meiotic divisions	Unequal (large oocyte, small polar bodies)	Equal (four sperm cells)
Timing	Begins prenatally, arrests until puberty	Begins at puberty, continues throughout life
Number of gametes per cycle	One (usually)	Millions

Key Equations and Hormonal Pathways

• GnRH stimulates release of FSH and LH from pituitary.

• FSH stimulates follicle development; LH surge triggers ovulation.

• hCG maintains corpus luteum during early pregnancy.

Hormonal Regulation Equation:

$GnRH \rightarrow FSH, LH \rightarrow Estrogen, Progesterone$

Menstrual Cycle Length:

$\text{Average cycle length} = 28 \text{ days}$

Additional info: The notes above expand on the anatomical and physiological details relevant to genetics, especially oogenesis, fertilization, and hormonal regulation, which are foundational for understanding inheritance and reproductive genetics.