Male Reproductive System — Revision Notes

⚡ 30-Second Revision

Primary Organs: — Testes (sperm & testosterone production).
Location: — Scrotum (maintains $2-2.5^circ\text{C}$ lower temp).
Sperm Production: — Spermatogenesis in seminiferous tubules.
Sertoli Cells: — Nourish sperm, form blood-testis barrier, secrete ABP & inhibin.
Leydig Cells: — Produce testosterone (stimulated by LH).
Sperm Maturation & Storage: — Epididymis.
Sperm Transport: — Rete testis $ightarrow$ Vasa efferentia $ightarrow$ Epididymis $ightarrow$ Vas deferens $ightarrow$ Ejaculatory duct $ightarrow$ Urethra.
Accessory Glands:

- Seminal Vesicles: Fructose, prostaglandins, alkaline fluid. - Prostate Gland: Citrate, enzymes (PSA), slightly acidic fluid. - Bulbourethral Glands: Mucus, alkaline fluid.

Hormonal Control (HPG Axis):

- Hypothalamus: GnRH - Anterior Pituitary: LH, FSH - Testes: Testosterone (from Leydig), Inhibin (from Sertoli)

Spermiogenesis: — Spermatid $ightarrow$ Spermatozoon (acrosome from Golgi, tail from centrioles).

2-Minute Revision

The male reproductive system is vital for producing and delivering sperm, and synthesizing male hormones. The testes, located in the scrotum for optimal cooler temperature, are the primary organs.

Within the testes, seminiferous tubules house Sertoli cells (nourish sperm, secrete inhibin) and spermatogonia (undergo spermatogenesis). Between tubules, Leydig cells produce testosterone under LH stimulation.

Sperm mature and gain motility in the epididymis, then travel via the vas deferens to the ejaculatory duct and urethra. Accessory glands – seminal vesicles (fructose, prostaglandins, alkaline fluid), prostate gland (citrate, enzymes, slightly acidic fluid), and bulbourethral glands (mucus, alkaline fluid) – contribute to semen.

The entire system is regulated by the HPG axis: Hypothalamus releases GnRH, stimulating the pituitary to release LH and FSH, which act on testes. Testosterone and inhibin provide negative feedback.

Remember the stages of spermatogenesis and the transformation of spermatids into spermatozoa (spermiogenesis), including acrosome formation from the Golgi apparatus.

5-Minute Revision

Let's quickly review the male reproductive system, focusing on high-yield NEET concepts. The system comprises primary sex organs (testes), accessory ducts, accessory glands, and external genitalia. The testes are housed in the scrotum, which maintains a temperature $2-2.

5^circ ext{C}$ below body temperature, crucial for spermatogenesis. Inside the testes, seminiferous tubules are the sites of sperm production. These tubules contain spermatogonia (germ cells) and Sertoli cells.

Sertoli cells are critical: they nourish developing sperm, form the blood-testis barrier, and secrete inhibin (which suppresses FSH) and androgen-binding protein (ABP). In the interstitial spaces between tubules, Leydig cells produce testosterone under the influence of Luteinizing Hormone (LH) from the anterior pituitary.

Sperm then travel through a series of ducts: from seminiferous tubules to the rete testis, then vasa efferentia to the epididymis. The epididymis is where sperm mature and gain motility, and are stored. From there, the vas deferens transports sperm, joining with the seminal vesicle duct to form the ejaculatory duct, which passes through the prostate and empties into the urethra.

Three accessory glands contribute to semen: seminal vesicles (secrete alkaline fluid with fructose for energy, and prostaglandins), the prostate gland (secretes slightly acidic fluid with citrate and enzymes like PSA), and bulbourethral glands (secrete lubricating, alkaline mucus). These secretions protect sperm, provide nutrients, and aid motility.

Spermatogenesis is the entire process of sperm formation. It involves mitotic division of spermatogonia, meiotic divisions of primary and secondary spermatocytes, leading to haploid spermatids. Spermiogenesis is the final morphological transformation of a spermatid into a mature spermatozoon, involving acrosome formation (from Golgi) and tail development.

Hormonal control is via the HPG axis: Hypothalamus $ightarrow$ GnRH $ightarrow$ Anterior Pituitary $ightarrow$ LH (acts on Leydig cells) and FSH (acts on Sertoli cells). Testosterone and inhibin provide negative feedback.

Remember these key structures, functions, and the hormonal cascade for NEET success.

Prelims Revision Notes

Male Reproductive System: NEET Revision Notes

I. Primary Sex Organs: Testes

Location: — Scrotum, outside abdominal cavity. Essential for maintaining $2-2.5^circ\text{C}$ lower temperature for spermatogenesis.
Structure: — Tunica albuginea (outer capsule), testicular lobules (250 per testis), seminiferous tubules (1-3 per lobule).
Seminiferous Tubules: — Site of spermatogenesis.

* Spermatogonia: Germ cells, undergo mitosis $ightarrow$ primary spermatocytes. * Sertoli cells (Sustentacular cells): Provide nourishment, form blood-testis barrier, phagocytose defective sperm, secrete ABP (Androgen Binding Protein) and Inhibin.

Interstitial Spaces: — Contain Leydig cells (Interstitial cells). Produce androgens (testosterone) under LH stimulation.

II. Accessory Ducts (Sperm Transport Pathway)

1
Seminiferous Tubules — (sperm production)
2
Rete Testis — (network of tubules)
3
Vasa Efferentia (Efferent Ductules) — (10-20 small ducts)
4
Epididymis: — Coiled tube on posterior testis. Site of sperm maturation (acquire motility) and storage.
5
Vas Deferens (Ductus Deferens): — Ascends into pelvic cavity, loops over bladder, forms ampulla.
6
Ejaculatory Duct: — Formed by vas deferens ampulla + seminal vesicle duct. Passes through prostate.
7
Urethra: — Common pathway for urine and semen. (Prostatic, Membranous, Spongy/Penile parts).

III. Accessory Glands (Contribute to Seminal Plasma)

Seminal Vesicles (paired): — Posterior to bladder. Secrete 60-70% of semen volume. Fluid is alkaline, contains fructose (energy), prostaglandins (stimulate uterine contractions), clotting proteins.
Prostate Gland (single): — Inferior to bladder, surrounds urethra. Secretes 20-30% of semen volume. Fluid is milky, slightly acidic, contains citrate (nutrient), enzymes (e.g., PSA for liquefaction), seminalplasmin (antibiotic).
Bulbourethral Glands (Cowper's Glands, paired): — Inferior to prostate. Secrete clear, alkaline mucus (lubricates urethra, neutralizes urine acidity).
Semen: — Sperm + seminal plasma.

IV. External Genitalia: Penis

Copulatory organ. Contains erectile tissue (corpora cavernosa, corpus spongiosum).
Glans Penis: — Enlarged tip, covered by foreskin (prepuce).

V. Spermatogenesis (Sperm Formation)

Occurs in seminiferous tubules, starts at puberty.
Spermatocytogenesis: — Spermatogonia ($2n$) $xrightarrow{\text{mitosis}}$ Primary spermatocytes ($2n$).
Meiosis I: — Primary spermatocyte ($2n$) $xrightarrow{\text{Meiosis I}}$ Two Secondary spermatocytes ($n$).
Meiosis II: — Secondary spermatocyte ($n$) $xrightarrow{\text{Meiosis II}}$ Two Spermatids ($n$). (Total 4 spermatids from 1 primary spermatocyte).
Spermiogenesis: — Transformation of non-motile spermatid ($n$) into motile spermatozoon ($n$).

* Acrosome formed from Golgi apparatus. * Tail (flagellum) formed from centrioles. * Mitochondria form midpiece for energy.

Spermiation: — Release of spermatozoa from Sertoli cells into tubule lumen.

VI. Hormonal Control (HPG Axis)

Hypothalamus: — Secretes GnRH (Gonadotropin-Releasing Hormone).
Anterior Pituitary: — Stimulated by GnRH to release:

* LH (Luteinizing Hormone): Acts on Leydig cells $ightarrow$ Testosterone synthesis. * FSH (Follicle-Stimulating Hormone): Acts on Sertoli cells $ightarrow$ Stimulates spermatogenesis, ABP & inhibin secretion.

Testosterone: — Essential for spermatogenesis, male secondary sexual characteristics, libido.
Inhibin: — Secreted by Sertoli cells. Negative feedback on anterior pituitary (inhibits FSH release).
Negative Feedback: — High testosterone inhibits GnRH and LH. High inhibin inhibits FSH.

Vyyuha Quick Recall

To remember the path of sperm, think: Some Rats Eat Very Expensive Unions.

Seminiferous tubules
Rete testis
Efferentia (Vasa Efferentia)
Epididymis
Vas deferens
Ejaculatory duct
Urethra