BIOLOGY Volume 3 - A Guide to General Biology - 2004

21. REPRODUCTION

21.7. Human Reproductive Systems

21.7.1. Male Reproductive System

The Structure of the Male Reproductive System is shown in Fig. 21.32, A, and more schematically in Fig. 21.32, B. These figures also depict the excretory system, which is closely linked to the reproductive system. Together, both systems are traditionally referred to as the Urogenital System.

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Fig. 21.32. Schematic diagram of the male reproductive system structure. A. Side view. B. Front view. The Urethra is part of both the reproductive and excretory systems, as it is also connected to the Urinary Bladder. Both systems together are often called the urogenital system. Excretory Organs are colored in gray.

The main parts of this system and their Functions are described below.

1. Testes. The paired testes are the male Gonads, i.e., the organs where male Gametes, or sperm, are produced. They also secrete the male sex hormone, testosterone.

2. Scrotum. The testes are located outside the Abdominal cavity in a Skin pouch called the scrotum, allowing sperm to develop at a Temperature 2–3 °C lower than core body temperature. This is the optimal temperature for their development, whereas higher temperatures significantly reduce sperm lifespan.

3. Seminiferous tubules. Each Testis contains approximately 1,000 coiled seminiferous tubules (Fig. 21.33), about 50 cm long and 200 µm in diameter. The walls of these tubules produce sperm (also known as spermatozoa). The process of sperm production is called Spermatogenesis.

4. Leydig Cells, also known as interstitial cells, are located between the tubules and produce the male sex hormone, testosterone.

5. Efferent ductules. Sperm exit the testes via 10–20 efferent ductules and are transported to the Epididymis (Fig. 21.33).

21.33. Simplified diagram of the human testis structure and the ducts through which sperm pass from the seminiferous tubules into the urethra.

6. Epididymis. The epididymis is a highly coiled tube approximately 6 m long that lies closely pressed against the testis. Sperm take several days to pass through this tube. In the epididymis, sperm concentration reaches up to 500 million per 1 cm³ due to the reabsorption of fluid secreted by the seminiferous tubules. In addition, sperm acquire the capacity for motility, although this ability remains suppressed until ejaculation occurs. Before entering the vas deferens, sperm are stored for a short time at the Base of the epididymis. Chemical substances secreted by the lining of the epididymis are essential for sperm maturation.

7. Vas deferens. This is a straight tube up to 40 cm long through which sperm travel to the urethra. The majority of sperm are stored in the vas deferens.

8. Urethra. Through this tube, urine from the urinary bladder and sperm from the vas deferens exit the body via the Penis.

9. Penis. The penis contains cavernous tissue, also known as erectile tissue. During sexual arousal, this tissue fills with Blood, causing an erection. During intercourse, the erect penis is introduced into the female Vagina, followed by the ejaculation of semen.

10. Seminal Vesicles. The seminal vesicles secrete mucus and a watery alkaline fluid containing nutrients, including the sugar fructose, which serves as an energy source for sperm. Each Seminal Vesicle discharges its contents into the ejaculatory duct during ejaculation, increasing the volume of semen (sperm plus seminal fluid). Other chemicals in this fluid may assist sperm in penetrating the cervical mucus and induce peristaltic contractions of the uterine and Fallopian tube linings, aiding the migration of sperm toward the eggs.

11. Prostate Gland. This gland also secretes mucus and a mildly alkaline fluid that is released during ejaculation and helps neutralize the acidic environment of the vagina, thereby enhancing sperm activity.

12. Bulbourethral (Cowper's) glands. These glands secrete mucus and an alkaline fluid into the urethra. This fluid completely neutralizes any acidity caused by residual urine.