The term epiphysis can refer to two distinct things. It may mean the endocrine gland (called the pineal gland) located in the cerebral region known as the epithalamus in humans and vertebrates. It secretes the hormone melatonin, which regulates the biological rhythms of the organism (seasonal cycles, day/night alternation). The epiphysis can also mean the end of a long bone, composed of spongy tissue. The rest of the bone is composed of diaphysis, between the two epiphyses, and metaphysis in its intermediary section.