Testicle


Image Caption : Testicle with Exposed Internal Structure: Medical visualization of a single human testicle with a wedge removed to see the interior; also visible is the epididymis, pampiniform venous plexus, and the testicular artery. The testes are the male gonads, and perform two functions: to manufacture motile sperm and produce male sex hormones, namely testosterone. The center of the testis contains the seminiferous tubules (arranged in lobes that radiate from a central plexus) where sperm production, or spermatogenesis, occurs. Resting directly on top of the testis is a single convoluted tube called the epididymis, where sperm are stored while they mature. Upon ejaculation, sperm enter the vas deferens and leave the penis through the urethra. Leydig cells, which reside in the testis, produce male sex hormones called androgens. The androgen testosterone develops secondary sexual characteristics and maintains sperm development sites. The pampiniform venous plexus and the testicular artery service the testicular area.

TESTES

The male gonads, testes or testicles, begin their development high in the abdominal cavity, near the kidneys. During the last two months before birth, or shortly after birth, they descend through the inguinal canal into the scrotum, a pouch that extends below the abdomen, posterior to the penis. Although this location of the testes, outside the abdominal cavity, may seem to make them vulnerable to injury, it provides a temperature about 3° C below normal body temperature. This lower temperature is necessary for the production of viable sperm.

Illustration of a sagittal section of a testis and epididymis

The scrotum consists of skin and subcutaneous tissue. A vertical septum, or partition, of subcutaneous tissue in the center divides it into two parts, each containing one testis. Smooth muscle fibers, called the dartos muscle, in the subcutaneous tissue contract to give the scrotum its wrinkled appearance. When these fibers are relaxed, the scrotum is smooth. Another muscle, the cremaster muscle, consists of skeletal muscle fibers and controls the position of the scrotum and testes. When it is cold or a man is sexually aroused, this muscle contracts to pull the testes closer to the body for warmth.

Structure

Each testis is an oval structure about 5 cm long and 3 cm in diameter. A tough, white fibrous connective tissue capsule, the tunica albuginea, surrounds each testis and extends inward to form septa that partition the organ into lobules. There are about 250 lobules in each testis. Each lobule contains 1 to 4 highly coiled seminiferous tubules that converge to form a single straight tubule, which leads into the rete testis. Short efferent ducts exit the testes. Interstitial cells (cells of Leydig), which produce male sex hormones, are located between the seminiferous tubules within a lobule.

GONADS

The gonads, the primary reproductive organs, are the testes in the male and the ovaries in the female. These organs are responsible for producing the sperm and ova, but they also secrete hormones and are considered to be endocrine glands.

Testes

Illustration of a testis within the male reproductive system

Male sex hormones, as a group, are called androgens. The principal androgen is testosterone, which is secreted by the testes. A small amount is also produced by the adrenal cortex. Production of testosterone begins during fetal development, continues for a short time after birth, nearly ceases during childhood, and then resumes at puberty. This steroid hormone is responsible for:

  • The growth and development of the male reproductive structures
  • Increased skeletal and muscular growth
  • Enlargement of the larynx accompanied by voice changes
  • Growth and distribution of body hair
  • Increased male sexual drive

Testosterone secretion is regulated by a negative feedback system that involves releasing hormones from the hypothalamus and gonadotropins from the anterior pituitary.

National Cancer Institiute / NIH

The testicle (from Latin testiculus, diminutive of testis, meaning "witness" of virility, plural testes) is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system. The primary functions of the testes are to produce sperm (spermatogenesis) and to produce androgens, primarily testosterone.

Both functions of the testicle are influenced by gonadotropic hormones produced by the anterior pituitary. Luteinizing hormone (LH) results in testosterone release. The presence of both testosterone and follicle-stimulating hormone (FSH) is needed to support spermatogenesis. It has also been shown in animal studies that if testes are exposed to either too high or too low levels of estrogens (such as estradiol; E2) spermatogenesis can be disrupted to such an extent that the animals become infertile.



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