Reproductive System Anatomy Study Pack

• •Testes: Gonads Responsible for Spermatogenesis and Steroidogenesis
• •Each testis is enclosed within the tunica albuginea, a dense fibrous capsule that sends internal septa dividing the organ into roughly 250–300 lobules.
• •Each lobule contains one to four coiled seminiferous tubules — the site of sperm production — surrounded by interstitial (Leydig) cells that synthesize testosterone.
• •Sertoli cells line the seminiferous tubules, forming the blood–testis barrier via tight junctions and providing structural and nutritional support to developing sperm cells.
• •The testes are suspended in the scrotum, positioning them 2–3°C below core body temperature; this lower temperature is essential because spermatogenesis fails at normal body temperature.

Thermoregulation Mechanisms of the Testes

• •The cremaster muscle elevates or lowers the testes in response to ambient temperature, pulling them closer to the body when cold and relaxing them away from the body when warm.
• •The pampiniform plexus is a network of veins that surrounds the testicular artery in the spermatic cord; cool venous blood returning from the scrotum absorbs heat from the incoming arterial blood, acting as a countercurrent heat exchanger.

Epididymis: Site of Sperm Maturation and Storage

• •The epididymis is a highly coiled duct, approximately 6 meters long when uncoiled, that caps the posterior surface of each testis.
• •Sperm entering the epididymis are non-motile and incapable of fertilization; during their 2–3 week transit through the epididymis they acquire progressive motility and full fertilizing capacity.
• •The tail (cauda) of the epididymis stores mature sperm until ejaculation.

Duct System: Vas Deferens, Ejaculatory Duct, and Urethra

• •The vas deferens (ductus deferens) is a thick-walled muscular tube that propels sperm from the epididymis toward the urethra via peristaltic contractions during ejaculation.
• •Each vas deferens joins the duct of the seminal vesicle to form the ejaculatory duct, which passes through the prostate gland and empties into the prostatic urethra.
• •The urethra serves a dual role — conducting both urine and semen — and is divided anatomically into prostatic, membranous, and spongy (penile) regions.

Seminal Vesicles

• •The paired seminal vesicles are pouched glands posterior to the bladder that contribute approximately 60% of semen volume.
• •Their secretion is alkaline and rich in fructose (an energy substrate for sperm), prostaglandins (which stimulate uterine contractions to assist sperm transport), and fibrinogen (which causes initial semen coagulation).

Prostate Gland

• •The prostate is a single walnut-sized gland that encircles the prostatic urethra and contributes roughly 25–30% of semen volume.
• •Prostatic secretions are slightly acidic and contain citric acid, proteolytic enzymes such as prostate-specific antigen (PSA) that liquefy the semen clot after ejaculation, and zinc, which stabilizes the sperm chromatin.

Bulbourethral Glands

• •The paired bulbourethral (Cowper's) glands are pea-sized structures located inferior to the prostate that secrete a clear, viscous mucus prior to ejaculation.
• •This pre-ejaculatory secretion neutralizes residual acidic urine in the urethra, reducing the risk of sperm damage before semen is delivered.

Semen as a Composite Fluid

• •A typical ejaculate volume is 2–5 mL and contains 20–150 million sperm per milliliter; the vast majority of semen volume consists of glandular secretions rather than sperm themselves.
• •The combined alkalinity of seminal and prostatic secretions buffers the acidic environment of the vagina, extending sperm survival in the female tract.