Overview
This lecture covers the basic anatomy and physiology of the male and female reproductive systems, including gamete production, hormonal regulation, and the sexual and menstrual cycles.
Introduction to Reproduction
- Reproduction is biparental, requiring male gametes (sperm) and female gametes (eggs).
- Sperm are motile and small; eggs are larger and nutrient-rich.
- Sex can be identified as phenotypic (physical traits), gonadal (ovaries/testes), or genetic (XX/XY chromosomes).
Sex Determination and Development
- Humans have 23 chromosome pairs: 22 autosomes and 1 pair of sex chromosomes (XX=female, XY=male).
- Sex is determined by sperm (X or Y); eggs only contribute X chromosomes.
- Androgens (testosterone, DHT) drive male development; estrogens and progesterone regulate female traits.
Male Reproductive Anatomy and Physiology
- Testes are outside the pelvic cavity in the scrotum to maintain lower temperature for sperm production.
- Seminiferous tubules in testes produce sperm; nurse (Sertoli) cells support sperm development and form the blood-testis barrier.
- Leydig (interstitial) cells between tubules produce testosterone in response to LH.
- Sperm mature in the epididymis and travel via the vas deferens during ejaculation.
Hormonal Regulation in Males
- Hypothalamus releases GnRH, stimulating pituitary release of FSH and LH.
- FSH stimulates Sertoli cells; LH stimulates Leydig cells.
- Sertoli cells produce inhibin (inhibits FSH) and androgen-binding protein (maintains high testosterone for spermatogenesis).
- Testosterone provides negative feedback on GnRH and LH release.
Spermatogenesis
- Spermatogenesis produces four haploid sperm from one diploid stem cell via meiosis.
- Crossing over during meiosis increases genetic diversity.
- Sperm production requires lower testicular temperature regulated by cremaster and dartos muscles and the pampiniform plexus.
Male Accessory Glands and Sexual Response
- Seminal vesicles, prostate gland, and bulbourethral glands produce seminal fluid for sperm transport and survival.
- Erection is mediated by parasympathetic-induced nitric oxide, increasing blood flow to erectile tissues.
- Ejaculation is triggered by sympathetic input, coordinating contraction of ducts and glands.
Female Reproductive Anatomy and Physiology
- Female primary sex organs (ovaries) produce eggs; secondary organs include uterus, fallopian tubes, and vagina.
- Eggs develop in follicles; ovulation is the release of a mature egg.
- After ovulation, the corpus luteum forms and produces hormones to support pregnancy.
Oogenesis and Menstrual (Sexual) Cycle
- Females are born with a finite number of primary oocytes, arrested in meiosis I until puberty.
- Each month, a cohort of follicles matures; usually one completes maturation and is ovulated.
- Only one functional haploid egg is produced; the rest become polar bodies and degenerate.
Hormonal Regulation in Females
- GnRH stimulates FSH and LH release from the pituitary.
- FSH and LH stimulate follicle growth and estrogen production.
- Rising estrogen initially inhibits, then triggers a surge in LH and FSH, resulting in ovulation.
- After ovulation, corpus luteum secretes progesterone and estrogen, inhibiting further GnRH, FSH, and LH.
Ovarian and Uterine Cycles
- Ovarian cycle: follicular phase (follicle development), ovulation, luteal phase (corpus luteum activity).
- Uterine cycle: menstrual (sloughing), proliferative (regeneration), secretory (thickening and secretion) phases.
- If no pregnancy occurs, corpus luteum regresses, hormone levels drop, and menstruation begins.
Key Terms & Definitions
- Gamete — Sperm or egg; reproductive cell.
- Zygote — Fertilized egg cell.
- Spermatogenesis — Production of sperm.
- Oogenesis — Production of eggs.
- Seminiferous tubule — Site of sperm production in testes.
- Leydig cell — Testicular cell producing testosterone.
- Sertoli cell — "Nurse" cell supporting sperm in testes.
- Follicle — Structure in ovary housing an egg.
- Corpus luteum — Hormone-secreting ovarian remnant after ovulation.
- FSH (Follicle Stimulating Hormone) — Stimulates gamete production.
- LH (Luteinizing Hormone) — Triggers ovulation and hormone production.
- GnRH — Gonadotropin-releasing hormone from hypothalamus.
- Estrogen/Progesterone — Key female sex hormones.
- Androgens — Male sex hormones, e.g., testosterone.
Action Items / Next Steps
- Review diagrams of male/female reproductive anatomy and hormone pathways.
- Study the timing and regulation of the menstrual cycle.
- Prepare for discussion on fertilization and early embryonic development.