Human Reproduction: Comprehensive Study Guide

1. Historical Figures and Anatomical Eponyms

Franz von Leydig: A German anatomist who discovered Leydig cells, which are named in his honor.
Enricho Sertoli: An Italian histologist who discovered Sertoli cells.
Gabriele Fallopio: A renowned anatomist responsible for naming numerous body parts; the Fallopian tubes are named after him.
Regnier de Graaf: A Dutch physician, anatomist, and physiologist who contributed significantly to reproductive biology; Graafian follicles are his namesake.

2. Introduction to Human Reproduction

Characteristics: Humans are sexually reproducing and viviparous.
Sequence of Reproductive Events:
- Gametogenesis: The formation of gametes (sperms in males and ovum in females).
- Insemination: The transfer of sperms into the female genital tract.
- Fertilization: The fusion of male and female gametes to form a zygote.
- Implantation: The formation and development of a blastocyst and its subsequent attachment to the uterine wall.
- Gestation: The period of embryonic development.
- Parturition: The delivery of the baby.
Timing: These events strictly occur after the onset of puberty.
Sexual Dimorphism in Events: Sperm formation persists even in old age in men, whereas ovum formation in women ceases at approximately $50 ext{years}$ (menopause).
Primary Reproductive Organs (Gonads): Responsible for gamete production and sex hormone secretion. In males: Testis. In females: Ovary.
Secondary (Accessory) Reproductive Organs: Play specific roles in reproduction without producing gametes or hormones. In males: Epididymis, vas deferens, seminal vesicle, prostate, bulbourethral gland, urethra, and penis. In females: Oviduct, uterus, vagina, and Bartholin’s gland.

3. The Male Reproductive System: Anatomy

Location: Situated in the pelvic region.
Testes:
- Site: Located outside the abdominal cavity in a pouch called the scrotum.
- Temperature Regulation: The scrotum maintains temperature $2-2.5^ ext{C}$ lower than the internal body temperature, which is essential for spermatogenesis.
- Connection: Linked to the abdomen via inguinal canals.
- Suspension: Each testis is suspended by a spermatic cord containing the vas deferens, testicular nerve, testicular artery, and testicular veins.
- Muscle Layers: The dartos muscle lies under the skin; the cremaster muscle extends into the spermatic cord. These assist in thermoregulation.
- Dimensions: Oval shape, $4-5 ext{cm}$ length, and $2-3 ext{cm}$ width.
- Internal Structure: Covered by a dense layer; contains approximately $250 ext{testicular lobules}$ . Each lobule contains $1-3$ highly coiled seminiferous tubules.
- Orchidectomy: The surgical removal of one or both testes.
Accessory Ducts:
- Rete Testis: A network of tubules.
- Vasa Efferentia: Ducts leaving the testis to join the epididymis.
- Epididymis: Located on the posterior surface; divided into three parts: Head (upper), Body (middle), and Tail (basal). It is the site for sperm maturation (gain of motility and fertility) and temporary storage.
- Vas Deferens: Ascends from the epididymis into the abdomen, loops over the urinary bladder, and dilates into the ampulla (main sperm reservoir) before joining the seminal vesicle duct.
- Ejaculatory Duct: Formed by the union of the vas deferens and seminal vesicle duct; opens into the prostatic urethra.
Path of Sperm Transport: Seminiferous tubules $ ightarrow$ Straight tubule $ ightarrow$ Rete testis $ ightarrow$ Vasa efferentia $ ightarrow$ Epididymis $ ightarrow$ Vas deferens $ ightarrow$ Ampulla $ ightarrow$ Ejaculatory duct $ ightarrow$ Urethra (Prostatic, Membranous, Penile) $ ightarrow$ Urethral meatus.

4. Male Accessory Glands and Semen

Gland Types:
- Seminal Vesicles: Paired; dorsolateral to the urinary bladder. Secrete alkaline viscous fluid containing fructose (nutrient), fibrinogen, and prostaglandins. Constitutes $2/3$ of seminal plasma volume.
- Prostate Gland: Unpaired; below the bladder. Secrete alkaline milky fluid containing calcium, clotting enzymes, and profibrinolysin. Constitutes $1/3$ of seminal plasma volume.
- Bulbourethral (Cowper’s) Glands: Paired; located on sides of membranous urethra. Secrete alkaline fluid for penis lubrication and neutralization of urinary acids.
Semen Characteristics:
- Composition: Seminal plasma plus sperms.
- pH: Slightly alkaline.
- Ejaculation Volume: $200-300 ext{million}$ sperms per coitus.
- Fertility Requirements: At least 60 ext{ ext{%}} must have normal shape/size; at least 40 ext{ ext{%}} must show vigorous motility.
- Azospermia: Absence or near absence of sperms in semen.
- Asthenospermia: Reduced sperm motility.
External Genitalia:
- Penis: Erectile copulatory organ. Tissue facilitates erection for insemination.
- Glans Penis: Enlarged end covered by a loose fold of skin called the foreskin or prepuce.
- Urethral Meatus: External opening for both urine and semen.
- Impotency: Inability to inseminate a female.

5. Histology of the Testis and Hormonal Control

Seminiferous Tubules:
- Germinal Epithelium: Lined by cuboidal male germ cells (spermatogonia) and columnar Sertoli cells (nurse cells).
- Sertoli Cells: Provide nutrition; secrete Androgen Binding Protein (ABP), inhibin, and factors for spermiogenesis.
- Spermiation: Release of sperm heads from Sertoli cells into the tubule lumen.
- Interstitial (Leydig) Cells: Found in spaces outside tubules; synthesize and secrete androgens (including testosterone).
Hormonal Regulation:
- GnRH: Hypothalamic hormone; stimulates anterior pituitary to release LH and FSH.
- LH (ICSH): Acts on Leydig cells to stimulate androgen production.
- FSH: Acts on Sertoli cells to support spermatogenesis and spermiogenesis.
- Testosterone: Stimulates the spermatogenesis process.
- Inhibin: Suppresses FSH synthesis when sperm production is excessive.
Secondary Sexual Characteristics:
- Males: Puberty at $12-15$ years; facial hair, pubic hair, low-pitched voice.
- Females: Puberty at $11-14$ years; Menarche, breast development, high-pitched voice.

6. The Female Reproductive System: Ovaries and Oviducts

System Components: Pair of ovaries, pair of oviducts, uterus, cervix, vagina, external genitalia, and mammary glands.
Ovaries:
- Function: Primary organs producing ovum and steroid (ovarian) hormones.
- Support: Attached to pelvic wall and uterus by ligaments.
- Size: $2-4 ext{cm}$ length.
- Oophorectomy: Surgical removal of ovaries.
- Stroma: Segmented into peripheral cortex and inner medulla, enclosed by thin epithelium.
Oviducts (Fallopian Tubes):
- Length: $10-12 ext{cm}$ .
- Infundibulum: Funnel-shaped part with fimbriae (finger-like projections) to collect ovum; the opening is called the ostium.
- Ampulla: Wider part; site of fertilization.
- Isthmus: Final narrow part joining the uterus.