The endocrine system is made of many glands—groups of cells that release chemical substances called hormones into the bloodstream. Hormones influence and regulate diverse activities such as metabolism, growth, mental development, and emotional behaviour.
The pituitary gland is a pea-sized gland located in the centre of the skull. The pituitary gland acts as a master controlling gland, releasing a number of hormones that activate other glands.
The parathyroid glands are four small glands located in the neck behind the thyroid gland. These glands secrete a hormone that regulates the body’s use of calcium and phosphorus to maintain healthy bones. Parathyroid hormone also affects muscle contraction and the conduction of nerve impulses.
The thyroid gland, located in the neck, secretes the hormone thyroxine. Thyroxine increases body metabolism, in which food is broken down and converted into heat and energy. Too little thyroxine in the blood produces lethargy and fatigue, while too much thyroxine results in overactivity, nervousness, and weight loss.
The adrenals are two small glands, each located on the top of one kidney. These two glands consist of an inner core, called the adrenal medulla, and an outer area, known as the adrenal cortex. The adrenal medulla releases the hormone epinephrine, which speeds up heart rate and increases blood pressure to help the body cope with emergencies. The adrenal cortex releases hormones that control the level of salts and water in the blood and help regulate the use of sugar. It also secretes small amounts of male sex hormones, or androgens, in both males and females. Of the two parts of the adrenal glands, only the adrenal cortex is under the control of the pituitary gland.
The pancreas is a long, narrow gland located in the abdomen behind the stomach and beneath the liver. The pancreas secretes insulin, a hormone that regulates the body’s use of sugar. When too little insulin is produced, the body tissues cannot use or store sugar, and a disease known as diabetes mellitus develops.
Females have sex glands called ovaries that release hormones called estrogens. These hormones contribute to the development of female sexual characteristics, including skin, hair, and breast development. Estrogens work with certain pituitary hormones to control the menstrual cycle.