Reproductive System, Male Health Article

Definition

The male reproductive system is composed of organs that work together to produce sperm and deliver them to the female reproductive tract for fertilization of the ovum.

Description

The normal male reproductive system is composed of numerous anatomical structures, including the testis, the excretory ducts, the auxiliary glands, the penis, and the various hormones that control reproductive functions.

Testis

The testis is responsible for the production and maturation of sperm in a process called spermatogenesis. It is also the site of synthesis and secretion of androgens (male sex hormones). The testes (plural) develop in the abdomen and descend into the scrotum in the normal male. The scrotum is a muscular sac in which the testes hang from the spermatic cord.

The testis is subdivided into the tubular compartment and the interstitial compartment. The tubular compartment is composed of up to 900 seminiferous tubules, which are populated by three main types of cells: germ cells, peritubular cells, and Sertoli cells. Germ cells become mature sperm in the spermatogenic process. Peritubular cells produce various factors that aid in the

transportation of mature sperm to the epididymis. Sertoli cells secrete various factors that determine the sperm production and testis size of an adult male.

Androgens are produced in the interstitial compartment of the testis. Leydig cells are responsible for the production and secretion of testosterone. Immune cells such as macrophages and lymphocytes are also found in the interstitial compartment, and aid in the proliferation and hormone production of Leydig cells.

Sperm cells are composed of a head (containing the nucleus and acrosome); the body (containing the mitochondria, or energy-producing organelles); and the tail. The nucleus contains the cell's genetic material (chromatin) while the acrosome contains enzymes that are capable of penetrating the protective layers around the egg. The mitochondria provide energy for tail motility; this is essential for movement of the sperm through the female reproductive tract.

Excretory ducts

The excretory ducts are responsible for the transfer of sperm from the seminiferous tubules of the testis to the urethra, and include the epididymis, the vas deferens, and intratesticular ducts. The epididymis is a tubular structure through which sperm exiting the seminiferous tubules pass. Testicular sperm are not fully mature and would not be able to fertilize an ovum (egg). Complete maturation occurs in the epididymis in the two to twelve days that sperm are typically stored before being passed to the vas deferens. The vas deferens functions to carry mature sperm from the epididymis to the urethra; it is also called the ductus deferens. Secretions from the auxiliary glands are mixed with sperm in the vas deferens to form semen.

Auxiliary glands

The auxiliary glands include two bulbourethral glands, one prostate, and two seminal vesicles. These glands contribute the secretions that compose semen. The bulbourethral glands (also called the glands of Cowper) secrete a fluid that lubricates the urethra prior to ejaculation. The prostate secretes a fluid rich in zinc, citric acid, choline, and various proteins. The secretions of the seminal vesicle are high in fructose (an energy source for sperm) and prostaglandins (fatty acid derivatives).

Penis

The penis is the male organ of sexual reproduction and consists of three elongated bodies that cause erection, the two corpora cavernosa and the corpus spongiosum. These tissues become engorged with blood when stimulated by the nervous system during arousal. Blood is supplied by the superficial and deep arterial systems (which carry blood to the penile skin and erectile tissue, respectively). The urethra runs through the corpus spongiosum to the glans penis (distal end of the penis). The organ is covered with loose skin that forms the prepuce (foreskin) over the glans penis.

Endocrine control

Normal reproductive function is dependent on complex interactions between various hormones. A portion of the brain called the hypothalamus secretes releasing hormones that travel to the pituitary gland, located at the base of the brain. The secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus triggers the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. LH stimulates testosterone production by Leydig cells in the testis, and FSH promotes spermatogenesis.