Chapter 26: The Reproductive System – Anatomy & Physiology Study Notes

Reproductive System Overview

Introduction to Sexual Reproduction

• Function: The reproductive system ensures the continuation of the species by producing offspring.

• Sexual reproduction involves the production of specialized cells called gametes (sperm in males, eggs in females), each containing half the normal chromosome number.

• During fertilization, a male and female gamete combine to form a zygote with the normal diploid chromosome number.

• This process promotes genetic diversity, increasing a species' evolutionary survival chances.

Cell Division in Reproduction

Meiosis

• Meiosis is a type of cell division that reduces the chromosome number by half, producing haploid gametes.

• All body (somatic) cells are diploid (2n) with 46 chromosomes (23 pairs).

• Gametes are haploid (n) with 23 chromosomes.

• Fertilization restores the diploid number: $n + n \rightarrow 2n$

Male Reproductive System

Anatomy

• Testes: Contain seminiferous tubules (site of sperm production) and interstitial cells (produce testosterone).

• Epididymis: Coiled duct where sperm matures.

• Scrotal sac: Houses testes and epididymis outside the abdomen to maintain a temperature 3°C below body temperature, necessary for sperm viability.

• Ductus deferens: Transports sperm toward the urethra.

• Accessory glands: Include the prostate (activates sperm, produces semen), seminal vesicles (produce nutrient-rich semen), and bulbourethral glands (produce mucus, cleanse urethra).

• External genitalia: Scrotum and penis.

Physiology

Process	Location	Description	Hormonal Control
Spermatogenesis	Seminiferous tubules	Meiosis produces spermatids (haploid gametes)	FSH
Spermiogenesis	Epididymis	Spermatids mature into motile sperm	Testosterone (LH control)
Secondary Sexual Characteristics	Body-wide	Voice deepening, hair growth, muscle and bone changes	Testosterone (LH control)

Female Reproductive System

Anatomy

• Ovaries: Contain follicles (produce estrogen, mature eggs).

• Follicle maturation: Controlled by FSH; one follicle matures monthly.

• Corpus luteum: Formed from the follicle after ovulation; produces progesterone (LH control).

• Fallopian tubes: Transport egg to uterus; site of fertilization.

• Uterus: Composed of fundus, body, and cervix. Layers include endometrium (mucosa), myometrium (muscle), and perimetrium (outer layer).

• Vagina: Birth canal; external genitalia (vulva) includes pubis, labia, clitoris; perineum is the region from pubis to coccyx.

Physiology

• Estrogen: Produced by ovarian follicles; controls secondary sex characteristics and uterine development.

• Progesterone: Produced by corpus luteum; maintains uterine lining.

• FSH & LH: From anterior pituitary; FSH stimulates follicle maturation, LH triggers ovulation.

• Menstrual cycle: If no fertilization, corpus luteum degenerates, hormone levels drop, and endometrium is shed (menstruation). If fertilization occurs, embryo produces hCG, maintaining corpus luteum and pregnancy.

Comparison: No Fertilization vs. Fertilization

Event	No Fertilization	Fertilization
Corpus Luteum	Degenerates	Maintained by hCG
Hormone Levels	Progesterone & Estrogen decline	hCG and placental hormones maintain pregnancy
Endometrium	Sloughs off (menstruation)	Remains intact (supports embryo)

Mammary Glands

• Modified sweat glands; development controlled by estrogens.

• Contain alveolar glands (produce milk) and lactiferous ducts (transport milk), separated by connective tissue and fat.

• Breast cancer: Most common in epithelial ducts; early detection via self-exam and mammography is crucial.

Pregnancy and Childbirth

Pregnancy

• Implanted embryo produces hCG, maintaining corpus luteum and early pregnancy.

• Placenta: Formed by embryo and maternal tissues; nourishes fetus and produces hormones to sustain pregnancy.

Birth Control Pill

• Contains estrogen and synthetic progestins.

• Mimics pregnancy, inhibiting FSH/LH release and preventing ovulation.

• Endometrium matures; withdrawal of pill leads to sloughing (withdrawal bleeding).

Childbirth

• Oxytocin and prostaglandins induce uterine contractions.

• Cervix dilates to 10 cm; amniotic sac ruptures.

• Baby is expelled head-first (vertex position); placenta is delivered after.

Gamete Formation: Mitosis vs. Meiosis

Key Definitions

• Chromosomes: Thread-like structures carrying genetic information.

• Genes: Segments of DNA coding for proteins.

• Somatic cells: All body cells except those forming gametes.

• Germ cells: Cells that give rise to gametes.

• Homologues: Pairs of chromosomes, one from each parent.

Mitosis

• Ensures constant chromosome number (2n) in somatic cells.

• Phases: DNA replication (4n) → Prophase → Metaphase → Anaphase → Telophase → Cytokinesis.

Meiosis

• Reduces chromosome number to haploid (n) in gametes.

• Phases:

  • DNA replication (4n)

  • Prophase I: Homologues pair, synapsis and crossing over occur.

  • Metaphase I: Tetrads align at equator.

  • Anaphase I: Homologues separate.

  • Telophase I: Cells divide (2n).

  • No DNA synthesis between divisions.

  • Prophase II, Metaphase II, Anaphase II, Telophase II: Chromatids separate, resulting in four haploid cells (n).

Spermatogenesis vs. Oogenesis

Process	Stages	Outcome
Spermatogenesis	Spermatogonium (2n) → Primary spermatocyte (Meiosis I) → Secondary spermatocyte (n, Meiosis II) → 4 spermatids (n)	4 functional sperm
Oogenesis	Oogonium (2n) → Primary oocyte (Meiosis I, arrested until puberty) → Secondary oocyte (n, Meiosis II) → Ovum (n, after fertilization)	1 functional ovum, 3 polar bodies

Hormonal Regulation

Male Hormones

• GnRH (from hypothalamus) stimulates anterior pituitary to release:

  • FSH: Stimulates spermatogenesis.

  • LH: Stimulates testosterone production (interstitial cells), which supports spermatogenesis, spermiogenesis, and secondary sexual characteristics.

Female Hormones

• GnRH (from hypothalamus) stimulates anterior pituitary to release:

  • FSH: Stimulates follicle maturation and estrogen production (growth of uterine lining, somatic effects).

  • LH: Triggers ovulation and supports corpus luteum (progesterone production).

• Drop in FSH, LH, estrogen, and progesterone leads to endometrial sloughing (menstruation).

Homeostatic Imbalances and Disorders

• Chlamydia: Most common bacterial STD; can cause pelvic inflammatory disease, sterility, and neonatal complications.

• Gonorrhea: Bacterial STD; causes inflammation, pelvic inflammatory disease, and sterility.

• Syphilis: Bacterial STD; causes systemic symptoms and lesions; treated with penicillin.

• Human papilloma virus (HPV): Causes warts, increases cervical cancer risk.

• Herpes simplex & EBV: Cause blisters, can be dormant or recurrent; may cause fetal malformations if transmitted during pregnancy.

• Non-disjunction genetic defects: Chromosomal distribution errors (e.g., Turner’s syndrome XO, Klinefelter’s XXY).

• Menarche: Onset of menstruation (~age 13); fertility begins ~2 years later.

• Dysmenorrhea: Painful menstruation.

• Endometriosis: Endometrial tissue outside uterus causes pain and adhesions.

• Menopause: Cessation of menstruation (~age 50); associated with hot flashes, increased risk of heart disease and osteoporosis.

• Ovarian cysts: Fluid-filled follicles; usually benign but may become cancerous.

• Inguinal hernia: Protrusion of intestine into groin due to muscle separation.

• Mumps: Viral infection of salivary glands; can cause testicular inflammation and sterility.

Additional info:

• hCG (human chorionic gonadotropin): Hormone produced by embryo; maintains corpus luteum and progesterone production in early pregnancy.

• Placenta: Functions as an endocrine organ, producing hormones (e.g., estrogen, progesterone, hCG) to maintain pregnancy.

• Vertex position: The most common and safest fetal position for childbirth, with the head delivered first.