Biology · Ch 2 — Human Reproduction
The Male Reproductive System
The Male Reproductive System
The male reproductive system consists of a pair of primary sex organs, the testes, together with a system of accessory ducts and accessory glands, and the external genitalia. The testes are a pair of oval organs that lie outside the abdominal cavity, enclosed within a sac-like pouch of skin called the scrotum. This external position is functionally important: normal spermatogenesis requires a temperature about 2–2.5°C lower than the core body temperature, and the scrotum, whose muscles can draw the testes closer to or further from the body, helps maintain this cooler local temperature. Each testis is oval in shape, about 4–5 cm long, and is enclosed by a tough, whitish fibrous covering called the tunica albuginea, from which thin septa extend inward and divide the interior of the testis into about 250 lobules, each of which packs in one to three highly coiled seminiferous tubules — the site where sperm are actually produced. The seminiferous tubules of each lobule converge and open into a network of tiny channels, the rete testis, which in turn is drained by a set of fine efferent ductules leading into a single, extremely long and tightly coiled tube lying against the back of the testis: the epididymis.
The epididymis is conventionally described in three regions — an upper head (caput), a middle body (corpus) and a lower tail (cauda) — and serves both as the site where sperm, immotile when they leave the testis, complete their maturation and acquire the ability to move, and as a temporary storage site for mature sperm. The tail of the epididymis continues as a much thicker, muscular-walled tube, the vas deferens (ductus deferens), which ascends out of the scrotum, passes through the abdominal wall, loops over the urinary bladder, and widens slightly near its end (the ampulla) before being joined by the duct of the seminal vesicle. The union of these two ducts forms a short ejaculatory duct on each side, which passes through the substance of the prostate gland and opens into the urethra. The vas deferens is muscular enough to actively propel sperm forward by peristaltic contraction at the time of ejaculation, rather than relying only on the movement of fluid. …
What this figure shows. A sagittal (side) view diagram of the human male pelvic region showing a pair of oval testes suspended outside the abdominal cavity within the scrotum, a loose pouch of skin whose position keeps the testes 2–2.5°C below body core temperature, which is necessary for normal spermatogenesis. Each testis is shown enclosed by a tough fibrous capsule (tunica albuginea) and divided internally into lobules packed with coiled seminiferous tubules. On the posterior surface of each testis lies a long, highly coiled tube, the epididymis (with head, body and tail regions), which continues upward as the vas deferens (ductus deferens); the diagram traces the vas deferens looping up out of the scrotum, over the urinary bladder, and joining the duct of the seminal vesicle to form a short ejaculatory duct that opens into the urethra. The prostate gland is shown as a single gland surrounding the urethra just below the bladder, and a pair of small pea-sized bulbourethral (Cowper's) glands are shown opening into the urethra further along its course. The urethra itself is traced the full length of th …