Reproductive System

The reproductive organs are part of the endocrine system in that they involve specific hormones.

The hormone oxytocin, synthesized in the hypothalamus and distributed in the blood by the pituitary, aids in lactation by nursing mothers by causing muscles in the breast to contract. This ejects milk from the saclike milk glands into the nipples. Oxytocin also causes contraction of the muscles of the uterus during childbirth. Oxytocin may also affect male reproductive behavior by causing contraction of the sperm-carrying tubes, as observed in several animal species.

The testes secrete several hormones, collectively called androgens, in response to stimulation from the pituitary gland as noted above. The most important of these is testosterone. The ovaries secrete the steroid hormones estrogen and progesterone.

Reaching a mature state where reproduction is possible is termed puberty, and it is associated with increase in the secretion of releasing hormones by the hypothalamus. This stimulates the pituitary to produce more FSH and LH into the bloodstream, reaching the ovaries or testes and elevating the level of release of the sex hormones. It is generally associated with a growth spurt, and the circulating sex hormones are associated with the development of secondary sex characteristics.