Functional Anatomy of the Male Reproductive System

Leydig Cells: The Hormone Producers

Located in the interstitial spaces between the tubules, Leydig cells are responsible for the secretion of androgens, primarily testosterone and dihydrotestosterone (DHT).

Exam Tip: If a question asks which cell is responsible for the synthesis of testosterone, the answer is the Leydig cell. If it asks which cell supports sperm development or forms the blood-testis barrier, look for Sertoli cells.

The Role of Androgens

Androgens, specifically testosterone and DHT, are vital for both embryonic development and adult male physiology. Their primary roles include:

1. Spermatogenesis: Stimulating sperm production in conjunction with Follicle-Stimulating Hormone (FSH).
2. Secondary Sex Characteristics: Promoting the development and maintenance of male traits during and after puberty.
3. Physical Growth: Stimulating protein synthesis in skeletal muscle and promoting growth hormone secretion for bone growth.
4. Embryonic Development: Promoting the formation of male reproductive structures during the fetal stage.

Sperm Structure and Maturation

A mature spermatozoon is a highly specialized cell designed for motility and fertilization. It consists of three main parts:

• Head: Contains the nucleus (genetic material) and the acrosome, a cap containing enzymes required for the sperm to fuse with the egg.
• Midpiece: Packed with mitochondria to provide the energy required for movement.
• Tail: The flagellum that enables swimming.

The Path of the Sperm

Once released into the lumen of the seminiferous tubules, spermatozoa remain immotile for about 20 days. They are then transported to the epididymis, where they acquire motility. From there, they move through the vas deferens via peristalsis.

Capacitation

Even after reaching the female reproductive tract, sperm are not immediately ready to fertilize an egg. They must undergo capacitation, a process that destabilizes the acrosome membrane, allowing the enzymes to be released for fertilization.

Accessory Glands and Semen Composition

Semen is a complex mixture of sperm and secretions from several accessory glands that provide nourishment and facilitate transport:

• Seminal Vesicles: Secrete an alkaline fluid rich in fructose (energy), enzymes, and prostaglandins.
• Prostate Gland: Contributes citrate and various enzymes.
• Bulbourethral Glands: Produce a viscous, mucus-rich fluid that helps lubricate the urethra.

Physiological Control of the Sexual Response

The male sexual response is regulated by the autonomic nervous system through specific spinal reflexes:

1. Erection: Mediated by the parasympathetic nervous system, leading to increased blood flow to the penis.
2. Emission: Mediated by the sympathetic nervous system. This causes the contractions of the epididymis, vas deferens, and accessory glands, moving semen into the urethra.
3. Ejaculation: Also mediated by the sympathetic nervous system, involving the contraction of smooth muscles in the urethra and skeletal muscles at the base of the penis to expel semen from the body.

Fertilization and the Zygote

The ultimate goal of the male reproductive system is fertilization—the union of a sperm cell with an oocyte. When a sperm successfully penetrates the egg, the resulting single-celled organism is known as a zygote. This marks the beginning of embryonic development, leading to the formation of a blastocyst and eventually implantation in the uterus.