pineal body (epiphysis) In vertebrates other than humans, an outgrowth of the fore brain that secretes hormones affecting reproductive behaviour. In mammals that have a regular oestrus cycle its secretion of melatonin inhibits development of the gonads; the pineal may have a similar function in human children.

pineal body (pineal gland) Small gland attached to the under-surface of the vertebrate brain. In human beings, it has an endocrine function, secreting the hormone melatonin, which is involved in daily rhythms. See also endocrine system