Virtual Medical Centre

Male Reproductive System (Male Urogenital System)

• What is the male urogenital system?
• Testes
  • Formation of sperm
• Epididymis

What is the male urogenital system?

The term urogenital refers to something that has both urinary and genital origins. The word urogenital is used because the urinary and reproductive systems in males merge. The male urogenital system consists of several parts, including the testes, epididymis, vas deferens, ejaculatory ducts, urethra, penis, prostate and accessory glands. 

Testes

The testis is a firm, mobile organ lying within the scrotum; the left testis lies slightly lower than the right. The testes are the primary reproductive organs (gonads) in the male, and are responsible for the production of sperm. The testis is covered by a capsule. The inner surface of the testicular capsule has projections that divide the organ into lobules. Contained within these lobules are the seminiferous tubules, which open into a series of channels called the rete testis. Sperm moves from the rete testis to the upper epididymis via the efferent ductules.

One of the main functional components of the testes are the seminiferous tubules. Other important functional components of the testis are Sertoli cells and Leydig cells.

The Leydig cells in the testis are responsible for the production of testosterone, and are almost nonexistent before puberty. The testosterone secreted by these cells is responsible for the development of secondary sexual characteristics, including:

• Changes to body hair distribution
• Baldness (testosterone decreases hair follicle growth on the top of the head)
• Change in voice
• Increased skin thickness and development of acne
• Increased bone density
• Increased basal metabolic levels
• Increased number of red blood cells
• Increased body water due to increased resorption of water and electrolytes in the kidneys

Formation of sperm

Image courtesy of Blausen Medical Communications. Contact Andrew Walbank.

Sperm production occurs within the seminiferous tubules. The Sertoli cells are the supporting, non-sperm producing cells of the seminiferous tubules, and are abundant in puberty and in the elderly. They provide support for surrounding germ cell growth and maturation. Sertoli cells secrete a protein and a nutritious fluid which sustains the developing sperm and helps transport them to the centre of the seminiferous tube.

The developing sperm undergo a series of divisions during development (meiosis). The first division takes approximately 24 days to complete. The second division occurs within 2–3 days of the first. The end result is four daughter cells, each with half the genetic material that they started off with. The importance of this is that when the sperm unites with the ovum, half the genes in the fertilised egg are from the father and half from the mother.

The development of sperm continues after division. The action of Sertoli cells causes cell remodelling, eventually converting the developing sperm into a spermatozoan.

Points to note:

• The temperature of the testes effects spermatogenesis (sperm formation). The scrotum (the skin covered sac that holds the testicles) functions as a sensitive regulator of temperature; by contracting and relaxing, it modifies testicular temperature. The optimal temperature for the testes is approximately 2 degrees below body temperature (i.e. about 35^oC).
• Sperm count can effect the fertility of males. The normal range for a sperm count is 35–200 million sperm per ejaculate. A male is defined as being infertile if he has a sperm count below 20 million.
• Male fertility is also affected by the morphology (shape and size) of the sperm in the ejaculate. Abnormal morphology can render the sperm ineffective, thus causing infertility even if the sperm count is normal. 

For more information on sperm health, including factors affecting sperm health and investigations of sperm health, see Sperm Health.

Epididymis

The epididymis is a firm structure that consists of three parts: the expanded head, the body, and the tail. The epididymis is a coiled tube covered by connective tissue. Fully expanded, it is approximately 20 m long. At the tail of the epididymis, a tube called the vas deferens emerges.

Sperm pass into the epididymis after they are formed in the seminiferous tubules. The sperm in the seminiferous tubules and early epididymis cannot move. These non-motile sperm gain the potential to move after 18–24 hours in the epididymis, though the production of specific substances within the epididymis prevents actual movement.