There are two testes (also called testicles) located in the scrotum of males. In addition to producing sperm, the testes produce two major types of hormones: testosterone and inhibin. Testosterone is a steroid hormone and inhibin is a protein hormone.

What is testosterone?

Testosterone is a hormone secreted by the interstitial cells of the testes. Its secretion is stimulated by LH released from the anterior pituitary gland.  Testosterone plays a key role in puberty, stimulating development of the secondary sex characteristics in males.  Testosterone also promotes normal development of sperm in the seminiferous tubules of the testes after puberty.  Perhaps a surprise to some, testosterone is found in both males and females.  The amount of testosterone in females is much lower than that of males and its role in females is not fully understood.  Some functions of estrogen: 

• Growth of the penis and testicles
• Growth of facial and body hair
• Growth of the larynx (causing deepening of the voice)
• Closure of growth plates in bones
• Growth of skeletal muscles

Spermatogenesis

• Promotes maturation of sperm

Others (not fully understood)

•  May play a role in the functioning of the brain, heart, and blood vessels

What is inhibin?

Inhibin is a protein hormone that is secreted by the sustentacular cells of the testes. Inhibin opposes the effects of testosterone.

Some functions of inhibin:

• Signals the anterior pituitary gland to decrease the secretion of FSH
• Signals the hypothalamus to decreased the secretion of gonadotropin releasing hormone (GnRH)
• Helps control the rate of sperm development

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