Chapter 28 – Comprehensive Reproductive System Study Notes

Functions of the Reproductive System

• Gametogenesis
  • Production of gametes
  • Males: spermatozoa
  • Females: oocytes (eggs)
• Fertilization support
  • Male ducts mature & transport sperm; penis deposits sperm in female tract
  • Female tract receives sperm & conveys them to oocyte
• Development & nourishment of offspring
  • Uterus shelters embryo/fetus until birth
  • Mammary glands supply milk post-natally
• Endocrine control
  • Sex hormones drive development, function, secondary sex traits & behavior

Meiosis

• Human somatic cells: 46 chromosomes ( 23 homologous pairs: 22 autosomes + 1 sex-pair )
  Gametes: 23 chromosomes (haploid)
• Meiosis I – reductional
  • Synapsis → tetrads; crossing-over → genetic variety
  • Homologs separate → 23 duplicated chromosomes per daughter cell
• Meiosis II – equational
  • Sister chromatids split → 4 genetically unique haploid cells
• Both divisions contain prophase, metaphase, anaphase, telophase; cytokinesis follows each

Male Reproductive Anatomy

Gross Structures

• Testes (in scrotum) – exocrine (sperm) & endocrine (testosterone)
• Duct system
  • Seminiferous tubules → tubuli recti → rete testis → efferent ductules → epididymis → ductus deferens → ampulla → ejaculatory duct → urethra (prostatic ➝ membranous ➝ spongy)
• Accessory glands
  • Seminal vesicles, prostate, bulbourethral glands
• Supporting structures
  • Scrotum (dartos & cremaster regulate temperature), penis (corpora cavernosa ×2, corpus spongiosum ×1 – forms glans; prepuce may be removed by circumcision)
• Perineum divided into urogenital & anal triangles; clinical perineum between vagina/penis and anus

Testicular Histology & Descent

• Tunica albuginea → septa → lobules containing seminiferous tubules & interstitial (Leydig) cells
• Sustentacular (Sertoli) cells
  • Nourish germ cells, form blood-testis barrier, convert testosterone → DHT/estradiol, secrete sex-hormone-binding globulin
• Testes develop retro-peritoneally; guided by gubernaculum through inguinal canal (weak spot → hernia)
  • Failure to descend = cryptorchidism (↑temperature → impaired spermatogenesis)
  • Process vaginalis becomes tunica vaginalis (serous sac)

Spermatogenesis & Spermiogenesis

• Sequence
  1. Spermatogonium ( 46 ) divides mitotically
  2. Primary spermatocyte ( 46 duplicated) → meiosis I → secondary spermatocytes ( 23 duplicated)
  3. Secondary spermatocytes → meiosis II → spermatids ( 23 single)
  4. Spermiogenesis: spermatid → spermatozoon
  • Head: nucleus + acrosome (enzymes)
  • Midpiece: mitochondria
  • Tail: flagellum (motility)
• Entire process occurs while cells nestle within Sertoli cells and migrate luminally

Epididymis, Ductus Deferens & Ejaculatory Duct

• Epididymis (head-body-tail)
  • ~15 days transit; site of maturation → motility & oocyte-binding competence
  • Lined by pseudostratified columnar epithelium with stereocilia (↑surface area for fluid resorption)
• Ductus deferens
  • Runs in spermatic cord (testicular vessels, nerves, cremaster, fasciae)
  • Smooth muscle → peristalsis during emission
  • Distal ampulla joins duct of seminal vesicle → ejaculatory duct inside prostate
• Ejaculatory ducts empty into prostatic urethra

Accessory Glands & Semen Composition

• Seminal vesicles (≈60\% volume)
  • Alkaline, fructose (fuel), prostaglandins, fibrinogen
• Prostate (≈30\%)
  • Thin, milky, alkaline; clotting factors + fibrinolysin
• Bulbourethral glands (≈5\%)
  • Mucus pre-ejaculate; neutralizes urethra & vagina
• Testes add small fluid; total mixture = semen

Male Hormonal Regulation

• Hypothalamus releases GnRH → anterior pituitary → LH & FSH
  • LH → Leydig cells → testosterone ↑
  • FSH → Sertoli cells → spermatogenesis + inhibin
• Feedback
  • Testosterone ↓ GnRH & LH/FSH (negative)
  • Inhibin ↓ FSH specifically
• Puberty (≈12–14 yr)
  • Adrenal testosterone inhibition wanes; GnRH pulse amplitude ↑; spermatogenesis begins

Testosterone Effects

• Descent of testes, enlargement of genitalia & ducts, spermatogenesis
• Secondary traits: body & facial hair, rough skin, darkened complexion, sebaceous activity, laryngeal hypertrophy (voice), ↑RBCs, protein synthesis, metabolic & bone growth (epiphyseal closure)

Male Sexual Response

1. Erection – parasympathetic (NO-mediated vasodilation)
2. Emission – sympathetic; peristalsis of ducts; glands secrete; semen accumulates in prostatic urethra
3. Ejaculation – sympathetic (internal sphincter closes) + somatic (rhythmic bulbospongiosus contractions)
4. Orgasm → resolution (sympathetic vasoconstriction/venous drainage)

Female Reproductive Anatomy

Ovaries & Ligaments

• Suspended by
  • Mesovarium (to broad ligament)
  • Suspensory ligament (to lateral wall; houses vessels/nerves)
  • Ovarian ligament (to uterus)
• Surface: germinal epithelium; tunica albuginea
  • Cortex (follicles); medulla (vessels/CT)

Uterine Tubes

• Mesosalpinx anchors to broad ligament
• Regions: fimbriae → infundibulum → ampulla (site of fertilization) → isthmus
• Wall: serosa, smooth muscle, mucosa with ciliated columnar folds – cilia & peristalsis move oocyte/zygote to uterus; secretions nourish

Uterus

• Parts: fundus, body, cervix (rigid; mucus glands)
• Wall
  • Perimetrium (serosa)
  • Myometrium (smooth muscle)
  • Endometrium: basal layer (permanent) + functional layer (cyclic; spiral arteries)
• Ligaments: broad, round (through inguinal canal to labia majora), uterosacral (to sacrum)

Vagina

• Muscular tube; mucosa = moist stratified squamous with rugae & columns; fornices surround cervix; hymen covers orifice (may be perforated)

External Genitalia (Vulva/Pudendum)

• Labia majora (hairy lateral folds) → mons pubis; pudendal cleft between
• Labia minora (hairless medial folds) unite anteriorly → prepuce over clitoris (erectile; homologous to corpora cavernosa)
• Vestibule between labia minora: urethral & vaginal orifices, opening of greater vestibular (Bartholin) glands; bulbs of vestibule flank vaginal orifice (erectile; homologous to corpus spongiosum)
• Perineum divided into urogenital & anal triangles; clinical perineum often incised (episiotomy)

Mammary Glands

• 15–20 lobes → lactiferous ducts → sinus → nipple; areola contains sebaceous areolar glands
• Suspensory (Cooper) ligaments tether to pectoralis major fascia
• Lobules → alveoli lined by secretory epithelium; myoepithelial cells eject milk
• Male hypertrophy = gynecomastia

Oogenesis & Follicular Development

1. Prenatal: oogonia (mitosis) → primary oocytes (enter meiosis I, stall in prophase I)
   \sim 5\,\text{million} at 4 mo. gestation → \sim 2\,\text{million} at birth
2. Childhood: primordial follicles (primary oocyte + flat granulosa) dormant; number declines to \sim 300{,}000 at puberty
3. Follicular phase (responds to FSH)
   • Primordial → primary follicle (cuboidal granulosa, zona pellucida)
   • Primary → secondary follicle (vesicles, theca interna/externa)
   • Vesicles coalesce → antrum → mature/Graafian follicle; oocyte sits in cumulus oophorus; corona radiata surrounds
4. Ovulation: LH surge → prostaglandin/inflammatory changes → follicle ruptures; secondary oocyte (metaphase II) + corona radiata expelled
5. Post-ovulation
   • Follicular cells → corpus luteum (progesterone + estrogen)
   • If no hCG, luteum degenerates ≈10–12 days → corpus albicans (scar)
6. If fertilized (in ampulla)
   • Oocyte completes meiosis II → ovum + second polar body; male & female pronuclei fuse → zygote

Ovarian & Uterine (Menstrual) Cycles (~28 days)

Ovarian Cycle

• Follicular phase (days 1–14)
  • ↑FSH → follicle growth → ↑estrogen
  • Rising estrogen → positive feedback → LH surge & smaller FSH surge → ovulation
• Luteal phase (days 15–28)
  • Corpus luteum secretes progesterone (dominant) + estrogen → prepares endometrium
  • Without fertilization → luteolysis → ↓progesterone → menstruation
  • With fertilization → embryo trophoblast secretes hCG → maintains corpus luteum

Uterine Cycle

• Menses (≈days 1–5): functional layer sloughs; spiral arteries constrict then rupture → bleeding
• Proliferative phase (≈days 6–14): estrogen stimulates regeneration; glands/spiral arteries grow
• Secretory phase (≈days 15–28): progesterone hypertrophies endometrium; glands secrete glycogen; optimum on day \approx 21 for implantation

Hormonal Control in Females

• GnRH (hypothalamus) → LH & FSH (ant. pituitary)
• Follicular estrogen exerts
  • Negative feedback early (↓FSH)
  • Positive feedback mid-cycle (LH/FSH surges)
• Progesterone + estrogen from corpus luteum inhibit GnRH/LH/FSH (negative)
• Inhibin from granulosa/luteal cells selectively inhibits FSH

Pregnancy & Hormonal Shifts

• Fertilization viable window: oocyte ≤24 h post-ovulation; sperm ≤6 days
• hCG
  • Secreted by trophoblast/placenta; peaks 8–9 wk; maintains corpus luteum (progesterone)
  • Basis of urine pregnancy tests
• Placenta assumes steroid production → rising progesterone (plateaus near term) & estrogen (sharp rise pre-parturition)
• Trophoblast enzymes digest endometrium for implantation; ectopic implantation (e.g., uterine tube) = ectopic pregnancy

Menopause

• Cease menses around 40–50 yr; perimenopause = transition phase
• Ovarian follicles exhausted → ↓estrogen/progesterone; ↑LH/FSH (lack feedback)
• Symptoms: hot flashes, night sweats, mood swings, fatigue, anxiety

Female Sexual Response, Fertility & Parturition

• Sexual arousal: parasympathetic vasodilation (clitoral & vestibular bulbs engorge; secretions lubricate)
• Orgasm involves rhythmic uterine & vaginal contractions; not required for fertilization
• Parturition (not detailed in transcript) is triggered by complex fetal & maternal hormonal interplay (oxytocin, prostaglandins, estrogens)

Key Hormones & Actions

• GnRH – stimulates LH & FSH release
• LH – ovulation; luteinization; stimulates testosterone in males
• FSH – follicle growth; spermatogenesis support
• Estrogen – endometrial proliferation; secondary sex traits; feedback modulation; ductal breast growth
• Progesterone – endometrial secretion & hypertrophy; alveolar breast development; negative feedback with estrogen
• Prolactin – milk production postpartum
• Oxytocin – uterine contractions during coitus & labor; milk ejection
• Inhibin – inhibits FSH (both sexes)
• hCG – rescues corpus luteum; stimulates fetal testicular testosterone

Ethical & Clinical Notes

• Cryptorchidism risk: infertility & malignancy; corrected surgically (orchiopexy)
• Inguinal canal weakness → indirect hernias (male risk ↑)
• Circumcision debated ethically/culturally; medical pros & cons
• Episiotomy use declining; current trend favors limited intervention
• Gynecomastia may reflect endocrine disorders or drug effects