Endocrine glands.

Endocrine glands are ductless glands, that produce hormones. Structurally, the endocrine glands are cells which produce secretions that diffuse directly into the blood stream. Endocrine glands are differentiated from exocrine glands, which consist of a group of cells which pour their secretions into a duct, and from there into another organ such as the intestine.

Endocrine glands produce chemicals called hormones which act on target organs elsewhere in the body. Hormones can be small molecules (eg vasopressin) or large ones (eg insulin). They have varying effects on the body. The major endocrine glands are the pituitary, thyroid, parathyroids, adrenals, pancreas, ovaries and testes. There are several other minor endocrine glands.

Pituitary gland

The pituitary gland is a tiny organ, about a centimeter in size, located at the base of the brain. It lies within a bony cage, the sella turcica. It is considered the master endocrine gland, as its hormonal secretions control several other endocrine glands. The pituitary consists of two parts, an anterior (front) and a posterior (rear). The anterior portion produces the following hormones:

The posterior pituitary produces antidiuretic hormone (ADH) (also called vasopressin) and oxytocin.

The pituitary may produce tumours, called adenomas. These tumours are not cancerous, but can exert pressure on the brain, causing headaches, and on the nearby nerve of the eye, causing changes in vision. Adenomas sometimes produce hormones, depending upon the cells from which they arise (usually ACTH or GH producing cells).

Treatment of pituitary tumours is by surgery or radiotherapy. Surgery, earlier accompanied by marked side effects, is now less traumatic with the development of microsurgical methods and stereotactic surgery.


Adrenal glands

The right and left adrenal glands (also called the suprarenal glands) lie just above the kidneys on either side. The outer layer of the gland is the cortex, and the inner core is the medulla. The cortex produces corticosteroids. The medulla produces adrenaline and noradrenaline (these two hormones are not steroids).