Chapter 27 - Reproductive System

Introduction

Primary sex organs (gonads):
- Male: Testes
- Female: Ovaries
Gonads produce gametes and secrete sex hormones.
Male function: Manufacture sperm and deliver to female tract for potential fertilization.
Fertilization: Sperm fuses with egg to form a zygote (first cell of new individual).

Occurs in ovaries and testes; process for genetic makeup of eggs and sperm.
Human cells: 46 chromosomes (23 pairs of homologous chromosomes).
Meiosis vs Mitosis:
- Mitosis: 1 DNA replication, 1 division, results in diploid cells.
- Meiosis: 1 DNA replication, 2 divisions, results in 4 haploid cells.
Meiosis Steps:
- Meiosis I: Reduction division, homologous pairs separate (diploid to haploid).
- Meiosis II: Duplicates (sister chromatids) separate, forming 4 cells with 23 chromosomes each.
Genetic Variability:
- Crossing over during Meiosis I.
- Random lining up of homologous chromosomes.

Begins at puberty in testes; stem cells produce primary spermatocytes.
Process:
- Spermatocytes move from outer edge of seminiferous tubule to lumen.
- Meiosis I: Forms secondary spermatocytes.
- Meiosis II: Forms spermatids.
- Spermiogenesis: Spermatids elongate, shed cytoplasm, form a tail.
Sperm Structure:
- Head: Genetic material.
- Midpiece: Contains mitochondria.
- Tail: Flagellum for propulsion.

Testes:
- Located in scrotum (3°C lower than body temp for sperm production).
- Divided into lobules with seminiferous tubules for sperm production.
- Leydig cells produce testosterone.
Pathway of Sperm:
- From seminiferous tubules → epididymis (gain motility) → vas deferens → ejaculatory duct → urethra.
Accessory Glands:
- Seminal vesicles produce alkaline fluid with fructose, enzymes, prostaglandins.
- Prostate gland produces acidic fluid with nutrients and enzymes.
- Bulbourethral glands produce mucus for urethra lubrication.
Erection and Ejaculation:
- Erection: Blood influx into penile tissue, driven by nitric oxide.
- Ejaculation: Sympathetic reflex, ducts contract, bladder sphincter constricts, penile muscles contract.
Hormonal Influence:
- Hypothalamus stimulates FSH and LH production.
- FSH: Stimulates spermatogenesis.
- LH: Causes testosterone secretion.
- Testosterone: Triggers sperm formation, secondary male characteristics.

Ovaries: Produce eggs, estrogen, progesterone.
- Follicles house oocytes.
- Monthly, one follicle develops, releases egg (ovulation).
Pathway of Egg:
- Ovulation: Egg released into peritoneal cavity.
- Fimbriae and cilia move egg into uterine tube (site for potential fertilization).
- Fertilized egg (zygote) or unfertilized egg moves to uterus.
Uterus:
- Layers: Endometrium (inner), myometrium (muscular), perimetrium (outer).
- Function: Receive, nourish, retain fertilized ovum.
Cervix and Vagina:
- Cervix: Produces mucus, changes consistency mid-cycle.
- Vagina: Acidic pH, protective but hostile to sperm.
Egg Supply and Hormonal Effect:
- Females born with egg supply; eggs complete meiosis upon ovulation.
- Estrogen promotes oogenesis, follicle growth, secondary female characteristics.

Before birth, stem cells form primary oocytes in primordial follicles.
Primary oocytes begin meiosis I, stall early.
Monthly, one primary oocyte resumes, ends meiosis I (forms secondary oocyte and first polar body).
Secondary oocyte begins meiosis II, halts at metaphase II.
If fertilized, completes meiosis II (yields ovum and second polar body).

Follicular Phase:
- FSH and LH stimulate follicle growth, estrogen secretion.
- Primordial follicle develops into Graafian follicle.
Ovulation:
- Burst of LH releases oocyte (day 14).
Luteal Phase:
- LH surge forms corpus luteum, secretes progesterone and estrogen.
- If pregnancy: Corpus luteum persists, placenta takes over hormone production.
- If no pregnancy: Corpus luteum degenerates, hormone levels fall.
Cycle Effects:
- Progesterone prepares endometrium for implantation.
- Menstruation occurs if no pregnancy.