The endocrine system is made up of glands that secrete hormones that perform various functions including regulation of metabolism, blood sugar control, and maintenance of bone calcium levels.
A hormone is a chemical messenger of the body that is secreted by endocrine glands. An endocrine gland secretes hormones that travel through the body to act on target cells. All glands have some features in common. They are ductless organs with a high degree of vascularity, meaning they are rich in blood vessels. This is a critical feature considering that most hormones travel via the bloodstream. Cells in endocrine glands often have a large number of intracellular granules or vacuoles. These membrane-bound intracellular sacs store hormones to be released when triggered by appropriate signals or conditions.
There are several major endocrine glands in the human body, including the pituitary, the thyroid, the parathyroid, the adrenal gland, the pineal gland, and the pancreas. Each of these glands secretes hormones, and those hormones have specific and wide-ranging functions in the body.Previously called the "master gland," the pituitary functions in close association with the hypothalamus. It is made up of an anterior section (also called the adenohypophysis) and a posterior section (also called the neurohypophysis). The hypothalamus is the brain structure responsible for maintaining homeostasis. It connects the endocrine and nervous systems. Homeostasis is a state of equilibrium in a system used to maintain a consistent internal environment in the body. Pituitary hormones target the thyroid, which regulates the body's metabolism. Other glands include the adrenal gland, which responds to stress and low blood sugar; the gonads (testes and ovaries), which produce gametes and sex hormones; the parathyroid, which increases blood calcium levels; the pineal gland, which plays a major role in regulating a person's day-night cycles; and the pancreas, which is vital to maintaining a normal blood glucose level.