Anatomy & Physiology Study Notes: The Reproductive System

The Male Reproductive System

Spermatogenesis

Spermatogenesis is the process by which sperm cells are produced in the seminiferous tubules of the testes. It involves several stages of cell division and maturation.

• Final Step: Spermiogenesis – Physical maturation of spermatids into spermatozoa.

• Duration: Approximately 24 days for spermiogenesis; occurs in the epididymis.

• Stages: Spermatogonia → Primary spermatocytes → Secondary spermatocytes → Spermatids → Spermatozoa.

• Meiosis: Reduces chromosome number from diploid (46) to haploid (23).

• Example: Spermatogenesis ensures genetic diversity through recombination and independent assortment during meiosis.

Sperm Cell Structure

The sperm cell is specialized for motility and fertilization.

• Size: ~0.06 mm long.

• Head: Flattened oval containing condensed chromatin from 23 chromosomes; lacks most organelles (ER, Golgi, lysosomes, peroxisomes).

• Acrosome: Cap-like structure containing enzymes to penetrate the oocyte.

• Midpiece: Cylindrical, packed with mitochondria for ATP production.

• Tail (Flagellum): Contains microtubules; propels sperm using ATP.

• Example: The acrosome reaction is essential for fertilization, allowing sperm to penetrate the zona pellucida of the egg.

Male Reproductive Tract

The reproductive tract transports sperm from the testes to the outside of the body.

• Epididymis: Twisted tube (~6 m) at the posterior of testes; connects seminiferous tubules to ductus deferens; sperm mature here over ~2 weeks.

• Ductus deferens (Vas deferens): Extends into abdomen, posterior to bladder; transports sperm during ejaculation.

• Seminal glands/vesicles: Sac-like structures producing ~60% of semen; fluid is slightly alkaline, contains fructose, and prostaglandins.

• Ejaculatory duct: Formed by fusion of seminal vesicle duct and ductus deferens; passes through prostate gland into urethra.

Glands

Accessory glands contribute fluids to semen, aiding sperm viability and motility.

• Prostate Gland: Chestnut-shaped, inferior to bladder; secretes enzymes and PSA (prostate-specific antigen) to liquefy semen.

• Bulbourethral Glands: Small glands inferior to prostate; secrete lubricating fluid.

Semen

Semen is the fluid released during ejaculation, containing sperm and glandular secretions.

• Composition: Sperm cells + secretions from seminal vesicles, prostate, and bulbourethral glands.

• pH: Slightly alkaline (~7.5).

• Volume: 2–5 mL per ejaculation; ~120 million sperm cells per mL.

Male External Accessory Reproductive Organs

These structures facilitate sperm delivery and protect reproductive tissues.

• Scrotum: Skin and subcutaneous tissue; regulates temperature for optimal sperm production.

• Penis: Contains erectile tissue (corpora cavernosa and corpus spongiosum); delivers semen during copulation.

Emission and Ejaculation

Emission and ejaculation are coordinated processes for sperm release.

• Emission: Movement of sperm and secretions into urethra; triggered by sympathetic impulses causing peristaltic contractions.

• Ejaculation: Expulsion of semen via rhythmic contractions of skeletal muscles at the base of erectile columns.

• Parasympathetic impulses: Release nitric oxide, dilating arteries and increasing blood flow for erection.

Hormonal Control (Male)

Hormones regulate the development and function of the male reproductive system.

• Gonadotropin-releasing hormone (GnRH): Secreted by hypothalamus; stimulates pituitary to release LH and FSH.

• Luteinizing hormone (LH): Stimulates interstitial cells to produce testosterone.

• Follicle-stimulating hormone (FSH): Stimulates seminiferous tubules for sperm production.

• Testosterone: Main androgen; responsible for development of male reproductive organs and secondary sex characteristics.

The Female Reproductive System

Structures

The female reproductive system includes internal and external organs for gamete production, fertilization, and gestation.

• Ovaries: Female gonads; produce oocytes and sex hormones.

• Accessory structures: Mammary glands, smaller glands secreting into reproductive tract.

• Reproductive tract: Uterine tubes, uterus, vagina.

• External genitalia: Labia and clitoris.

Ovaries

Ovaries are solid, ovoid structures held in place by ligaments and responsible for oocyte production and hormone secretion.

• Size: ~3.5 cm long, 2 cm wide, 1 cm deep.

• Ligaments: Broad, suspensory, ovarian.

• Functions: Produce oocytes, secrete sex hormones (estrogen, progesterone), secrete inhibin.

• Ovarian follicles: Masses of cells where oocytes develop; present from prenatal development.

Oogenesis

Oogenesis is the process of oocyte formation, beginning before birth and continuing through reproductive life.

• Ogonia: Stem cells complete mitosis before birth, forming primary oocytes.

• Meiosis: Primary oocytes begin meiosis during fetal development, but arrest in prophase I until puberty.

• FSH: Triggers resumption of meiosis during ovarian cycle; secondary oocytes released during ovulation.

• Meiosis II: Only completed if fertilization occurs.

• Example: Each menstrual cycle, one oocyte resumes meiosis and is released as a secondary oocyte.

Follicle Maturation

Follicle maturation prepares the oocyte for ovulation and fertilization.

• FSH: Released at puberty, stimulates development of ovarian follicles.

• Stages: Primordial follicle → Primary follicle → Secondary follicle → Mature (Graafian) follicle.

• LH: Triggers ovulation; follicle swells and ruptures, releasing the egg.

• Duration: Entire process takes ~300 days; cycles every ~28 days.

Female Internal Accessory Reproductive Organs

• Uterine tubes (Fallopian tubes): Transport oocyte from ovary to uterus; fertilization typically occurs here.

• Uterus: Hollow, muscular organ; site of implantation and fetal development; wall has three layers: endometrium, myometrium, perimetrium.

• Vagina: Fibromuscular tube (~9 cm); posterior to bladder and urethra; surrounds cervix.

Female External Accessory Reproductive Organs

• Labia majora: Protect other external organs; composed of smooth muscle, adipose, and skin.

• Labia minora: Connective tissue with blood vessels; covered by stratified squamous epithelium.

• Clitoris: Contains corpora cavernosa; many sensory nerve fibers.

• Vestibule: Space between labia minora; contains vaginal and urethral openings; vestibular glands secrete lubrication.

Physiology of Sexual Response (Female)

• Parasympathetic impulses: Release nitric oxide, increasing blood flow and tissue swelling.

• Vestibular glands: Lubricate tissues.

• Orgasm: Sensory nerve stimulation causes rhythmic contractions of uterus and uterine tubes, aiding sperm transport.

Hormonal Regulation (Female)

Hormones regulate development, maintenance, and cyclical changes in the female reproductive system.

• Estrogens: (Estradiol, estrone, estriol) – promote development of secondary sex characteristics and regulate menstrual cycle.

• Progesterone: Prepares endometrium for implantation and maintains pregnancy.

• Sources: Ovaries (primary), adrenal cortex, placenta (during pregnancy).

Menstrual Cycle

The menstrual cycle is a series of hormonal and physiological changes preparing the uterus for pregnancy.

• Menarche: First menstrual cycle; marks reproductive maturity.

• GnRH: Stimulates FSH and LH secretion from pituitary.

• FSH and LH: Stimulate ovarian follicle development and ovulation.

• Estrogen: Rises in first half of cycle, thickening endometrium.

• Progesterone: Rises in second half, stabilizing endometrium.

• If no fertilization: Corpus luteum degenerates, hormone levels fall, endometrial tissue disintegrates, and menstrual flow occurs.

Summary Table: Key Differences Between Spermatogenesis and Oogenesis

Feature	Spermatogenesis	Oogenesis
Location	Seminiferous tubules of testes	Ovarian follicles
Start	Puberty	Before birth
End Product	Four sperm cells per spermatogonium	One ovum, three polar bodies per oogonium
Duration	Continuous after puberty	Monthly cycles from puberty to menopause
Meiosis II Completion	Before fertilization	Only if fertilization occurs

Key Equations

• Chromosome Reduction in Meiosis:

$2n \rightarrow n$

• Semen Concentration:

$\text{Total sperm cells} = \text{Volume} \times \text{Concentration}$ $\text{Total sperm cells} = 2.5\,\text{mL} \times 120,000,000\,\text{cells/mL} = 300,000,000\,\text{cells}$

Additional info: Academic context and terminology have been expanded for clarity and completeness. Figures referenced in the notes illustrate the anatomy and histology of reproductive organs and gametogenesis.