The Male Reproductive System - Testes

Testes:

• Testes are the primary male sex organs.
• They are a pair of ovoid bodies lying in the scrotum.
• The testes are situated outside the abdominal cavity within a pouch called the scrotum. 
• Since viable sperms cannot be produced at normal body temperature, the scrotum is placed outside the abdominal cavity to provide a temperature 2-3°C lower than the normal internal body temperature. Thus, the scrotum acts as a thermoregulator for spermatogenesis.
• In adults, each testis is oval in shape, with a length of about 4 to 5 cm and a width of about 2 to 3 cm.
  

  Testis showing inner details

• Testes are enclosed in an outer tough capsule of collagenous connective tissue, the tunica albuginea.
• Each testis is divided by septa into about 200 - 250 lobules called testicular lobules.
• The scrotum is connected to the abdominal cavity through a passage termed inguinal-canal. Through this canal, the testis descends down into the scrotal sacs at the time of birth. The spermatic cord in males passes through the inguinal canal.
• Testes are covered by three coats.

1. Tunica Vaginalis: The outermost covering is called Tunica vaginalis which has a parietal and visceral layer. It covers the whole testis except its posterior border from where the testicular vessels and nerves enter the testis.
2. Tunica albuginea: The middle tough capsule of collagenous connective tissue called tunica albuginea.  The Tunica albuginea is a dense, white fibrous coat covering the testis all around. The posterior border tunica albuginea is thickened to form a vertical septum called the Mediastinum testis.
3. Tunica Vasculosa: Tunica vasculosa is the innermost vascular coat of the testis lining testicular lobules. 

• The failure of one or both testes to descend down into the scrotal sacs is known as cryptorchism (crypto – hidden + orchis – testicle). It occurs in 1 – 3 percent of new born males. A surgical correction at a young age can rectify the defect, else these individuals may become sterile and are unable to produce viable sperms. It can also lead to cancer.
• Internally scrotum is lined by dartos muscle and spermatic fascia. Dartos muscle helps in the regulation of the temperature within the scrotum during the cold season, it becomes contracted in cold & during the warm season, it becomes relaxed. Cremaster muscles line inside the wall of the scrotal & inguinal canal region and help in the elevation of testes.
• Each testis is attached to the walls of the scrotal sac through flexible, elastic fibres. This group of fibres is called Gubernaculum or Mesorchium.
• Each testis is attached to the dorsal body wall of the abdominal cavity through a cord termed the spermatic cord. This cord is made up of elastin fibres & spermatic fascia. The contents of cord are vas deferens, gonadal veins, gonadal arteries, nerves and lymphatics. 

Histology of seminiferous tubules:

• Each lobule contains 1-3 highly coiled testicular tubules or seminiferous tubules. These highly convoluted tubules which form 80 per cent of the testicular substance are the sites for sperm production.
• The stratified epithelium of the seminiferous tubule is made of two types of cells namely sertoli cells or nurse cells and spermatogonic cells or male germ cells.
• Sertoli cells are elongated and pyramidal and provide nourishment to the sperms till maturation. They also secrete inhibin, a hormone which is involved in the negative feedback control of sperm production. Spermatogonic cells divide meiotically and differentiate to produce spermatozoa.
• The regions outside the seminiferous tubules called interstitial spaces contain:
  1) Small blood vessels
  2) Interstitial cells or Leydig cells
  3) Other immunologically competent cells
• Leydig cells synthesise and secrete testicular hormones called androgens, also called male sex hormones.
• Interstitial cells or Leydig cells are embedded in the soft connective tissue surrounding the seminiferous tubules. These cells are endocrine in nature and secrete androgens (also called male sex hormones) namely the testosterone hormone which initiates the process of spermatogenesis. These cells are endocrine in nature and are characteristic features of the testes of mammals. Other immunologically competent cells are also present.
  

  Diagrammatic sectional view of seminiferous tubule