Describe the role of testosterone in the male reproductive system and explain how it differs from the role of oestrogen in the female reproductive system.

Testosterone is produced by the Leydig cells of the testes and
1. stimulates the production of sperm in the seminiferous tubules.
2. is responsible for the development of male secondary sexual characteristics such as facial hair, a deeper voice and increased muscle mass.

Oestrogen, produced mainly by the ovaries, has
1. a key role in the growth and repair of the uterine lining (the endometrium), a function that testosterone does not perform.
2. drives the development of female secondary sexual characteristics such as breasts and wider hips, whereas testosterone is the hormone that produces the male traits.

Thus testosterone acts mainly on sperm production and male secondary traits, while oestrogen acts on the uterus and female secondary traits.