The Reproductive System: Anatomy, Physiology, and Hormonal Regulation

Reproductive System: Overview

Basics

The reproductive system is not primarily involved in maintaining homeostasis, but rather in ensuring the continuation of the species through sexual reproduction. This process introduces genetic variability, with fertilization and gestation occurring internally in humans. Typically, one offspring is produced per pregnancy.

• Sexual reproduction increases genetic diversity.

• Fertilization and gestation are internal processes.

• Most pregnancies result in a single offspring.

Functions

• Production and support of gametes (sperm in males, ova in females).

• Males: Formation, transport, and delivery of sperm.

• Females: Formation and transport of ova, protection and nourishment of the developing embryo, and delivery of the fetus.

Anatomical Overview

• Reproductive organs (gonads: testes in males, ovaries in females)

• Associated ducts (e.g., vas deferens, uterine tubes)

• Accessory glands (e.g., prostate, seminal vesicles, mammary glands)

• External genitalia (e.g., penis, vulva)

Male Reproductive System

Testes

The testes are the essential male gonads, responsible for sperm production and hormone secretion. They are suspended in the scrotum by the spermatic cord.

• Develop initially in the abdominal cavity (retroperitoneally).

• Descend into the scrotum before birth, passing through the inguinal canal (usually by the 7th month of gestation).

• Contain seminiferous tubules (site of spermatogenesis) and interstitial cells (secrete testosterone).

Scrotum

• Pouch of skin, fascia, and muscle, divided into two compartments by a septum.

• Keeps testes cool (~93°F/34°C) for optimal sperm production.

• Dartos muscle: Causes wrinkling of scrotal skin to reduce heat loss.

• Cremaster muscle: Raises or lowers testes to regulate temperature.

Epididymis

• Stores sperm and is the site of sperm maturation (about 2 weeks).

• Efferent ductules carry sperm from testes to epididymis.

Spermatic Cord

• Contains vas deferens, blood vessels, nerves, lymphatics, and cremaster muscle.

• Connects testes to the abdominal cavity.

Vas (Ductus) Deferens

• Transports sperm from epididymis to ejaculatory duct.

• Passes through inguinal canal and crosses the bladder.

• Joins with duct of seminal vesicle to form ejaculatory duct.

• Vasectomy: Surgical procedure for male sterilization.

Accessory Glands

Gland	Location	Function
Seminal Vesicles	Posterior to bladder	Secrete alkaline, fructose-rich fluid (~60% of semen); nourishes sperm
Prostate Gland	Inferior to bladder, surrounds urethra	Secretes milky, slightly acidic fluid (~25% of semen); contains enzymes and citric acid
Bulbourethral (Cowper's) Glands	Lateral to membranous urethra	Secrete alkaline mucus to lubricate and neutralize urethra

Penis

• Male copulatory organ; introduces sperm into female reproductive tract.

• Composed of three erectile bodies: two corpora cavernosa (dorsal) and one corpus spongiosum (ventral, surrounds urethra).

• Distal end forms glans penis; covered by prepuce (foreskin) unless circumcised.

Spermatogenesis

Spermatogenesis is the process of sperm production, occurring in the seminiferous tubules.

• Spermatogonia divide by mitosis; one cell remains a stem cell, the other becomes a primary spermatocyte.

• Primary spermatocyte undergoes meiosis to produce four sperm cells.

• Fertilization by Y sperm results in a male embryo; X sperm results in a female embryo.

Male Sexual Response

• Erection: Arteries dilate, increasing blood flow; veins constrict, causing erection.

• Ejaculation: Semen is expelled through the urethra by muscular contractions.

Hormonal Control

• Gonadotropic hormones from anterior pituitary:

  • Follicle Stimulating Hormone (FSH): Stimulates spermatogenesis.

  • Luteinizing Hormone (LH/ICSH): Stimulates testosterone secretion.

• Testosterone: Responsible for male secondary sex characteristics and maintenance of reproductive tissues.

Female Reproductive System

Ovary

• Female gonad; site of ova (egg) production.

• Contains ~400,000 follicles at birth; only about 400 mature during reproductive years.

• Supported by ligaments; paired, oval, almond-sized.

Uterine (Fallopian) Tubes

• Site of fertilization; paired tubes (~10 cm long).

• Transport ova via cilia and peristalsis.

• Segments: Interstitial (within uterus), isthmus (narrow), ampulla (wide, common site of ectopic pregnancy), infundibulum (funnel-shaped, with fimbriae).

Uterus

• Unpaired, hollow, muscular, pear-shaped organ.

• Receives uterine tubes, empties into vagina.

• Site of implantation and fetal development.

• Supported by broad and round ligaments.

• Regions: Fundus (top), body (central), isthmus (narrowed), cervix (inferior, extends into vagina).

• Wall layers:

  • Perimetrium (visceral peritoneum)

  • Myometrium (smooth muscle)

  • Endometrium (epithelial, undergoes cyclic changes; subject to endometriosis)

Vagina

• Receives penis during intercourse; passage for menstrual flow; birth canal.

• Located between urethra and rectum.

• Lined with stratified squamous epithelium; acidic environment due to lactobacilli.

• Contains fornix (recess around cervix), hymen (mucous membrane fold), and greater vestibular (Bartholin's) glands (homologous to bulbourethral glands).

Vulva (External Genitalia)

• Mons pubis: Fatty mound over pubic bone.

• Labia majora: Outer folds, homologous to scrotum.

• Labia minora: Inner folds, encircle clitoris, form prepuce.

• Clitoris: Homologous to penis, composed of corpora cavernosa, partially covered by prepuce; function is sexual pleasure.

Breasts

• Structurally part of the integumentary system; functionally reproductive.

• Produce colostrum and breast milk for nourishment of newborn.

Female Reproductive Physiology

Hormonal Control

• Four main hormones: FSH and LH (from pituitary), estrogen and progesterone (from ovaries).

• FSH and LH stimulate follicle growth and maturation.

• Estrogen and progesterone regulate the uterine cycle (endometrial thickening and secretion).

The Ovarian Cycle

• Follicular phase: Follicle development, maturation, and oogenesis.

• Ovulation: Release of mature ovum, typically on day 14 of a 28-day cycle, triggered by LH surge.

• Luteal phase: Formation of corpus luteum from ruptured follicle; corpus luteum secretes estrogen and progesterone.

Follicle Development

• Up to 20 follicles begin maturation each cycle; only one reaches full maturity.

• Others undergo atresia (degeneration).

• Controlled primarily by FSH; FSH and LH stimulate estrogen secretion by follicle cells.

Ovulation

• Caused by LH surge.

• Fimbriae of uterine tube sweep ovum into tube after follicle rupture.

• Ovum is expelled into abdominal cavity and enters uterine tube.

Formation of Corpus Luteum

• Ruptured follicle becomes corpus luteum.

• Corpus luteum secretes estrogen and progesterone, maintaining endometrial lining during pregnancy.

The Uterine Cycle

Phase	Timing	Main Events
Menstrual	Day 1 of 28-day cycle	Shedding of endometrial lining
Proliferative	After menstruation	Estrogen stimulates endometrial proliferation
Secretory	After ovulation	Progesterone stimulates endometrial secretion and thickening

• Ovarian hormones (estrogen and progesterone) control endometrial changes.

Summary Table: Male vs. Female Reproductive Structures

Structure	Male	Female
Gonads	Testes	Ovaries
Gametes	Sperm	Ova (eggs)
Ducts	Vas deferens, epididymis	Uterine (fallopian) tubes
Accessory Glands	Seminal vesicles, prostate, bulbourethral glands	Mammary glands, Bartholin's glands
External Genitalia	Penis, scrotum	Vulva (labia, clitoris, mons pubis)

Additional info: This guide expands on the provided notes with definitions, examples, and structured tables for clarity and exam preparation.