Gonads and other hormone-producing tissues

The testes, in a pouch outside the body (the scrotal sac), make sperm and are also endocrine glands. Between the sperm-making tubules lie Leydig cells (interstitial cells), which make androgens, mainly testosterone. Testosterone controls the growth of the male accessory sex organs, muscle growth, the growth of facial and armpit hair, a deeper voice, aggressiveness, sperm production and sex drive, and it builds up body tissues (anabolic effects).

The ovaries release one ovum each menstrual cycle and make two steroid hormones:

• Estrogen, made by the growing follicles: it develops the female accessory sex organs and secondary sex characters, the growth of ovarian follicles, the mammary glands, and female sexual behaviour.
• Progesterone: after ovulation, the burst follicle turns into a yellow body, the corpus luteum, which mainly makes progesterone. It supports pregnancy and prepares the mammary glands for milk secretion.

Some organs that are not endocrine glands also make hormones:

• The heart: the wall of the atria makes atrial natriuretic factor (ANF), which widens blood vessels and lowers blood pressure.
• The kidney: its juxtaglomerular cells make erythropoietin, which tells the bone marrow to make more red blood cells.
• The gut makes four hormones: gastrin (makes the stomach glands release HCl and pepsinogen), secretin (makes the pancreas release water and bicarbonate), CCK (cholecystokinin, makes the pancreas release enzymes and the gall bladder release bile) and GIP (gastric inhibitory peptide, slows stomach secretion and movement).

Many other tissues make growth factors, which help in normal growth and in the repair of tissues.