In the body, there are organs that produce secretions. These organs are called “glands”. Usually, the word “gland” is applied to endocrine glands or glands of internal secretion. Thay are also called “ductless glands”
These glands produce secretions which do not go into ducts or tubes, but which are absorbed directly into the bloodstream.
The name of these internal secretions is hormones. Hormones are chemical messengers that are carried by the bloodstream and which affect all parts of the body. The body has many glands that produce these internal secretions, and the principal ones are the thyroid, the parathyroids, the thymus, the pineal, the pituitary, the adrenals, the sex glands, and parts of the pancreas.
So we see that the pineal gland is one of the endocrine glands and it is considered part of the endocrine system. Yet we do not know what hormone the pineal gland secrets. In fact, it is rather mysterious little organ.
The pineal gland is about the size of a small pill and is located in the central part of the brain, towards the top of the head. Because of this location, physicians in ancient times thought that the pineal gland was responsible for our thinking. Some writers believed that the pineal gland was the remnant of a “third eye” what man may have once had, similar to that found in reptiles.
Today we believe that this gland either produces some internal secretion or affects other endocrine glands in the work they do. For example, it is quite close to the pituitary gland and possibly has some effect on that gland.