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Glands are units of cells that secrete substances used in other parts of the body. There are two types of glands in the body:

• Exocrine. Glands that release their secretions through a duct or directly to epithelial tissue (skin and linings of body cavities and passageways). Examples include the sweat glands, sebaceous glands, salivary glands and prostate gland. Glands in the digestive system that secrete enzymes through ducts also are considered to be exocrine glands.
  
  
• Endocrine. A variety of ductless glands that secrete more than 20 hormones into the bloodstream or lymph nodes. These substances are then transported to other parts of the body and carry messages for how those body parts should act.

Endocrine glands use material in the blood, and synthesize and secrete the chemical or hormone that supports the specified function elsewhere. The major glands in the endocrine system are:

• Pituitary gland. Located at the base of the brain, this “master gland” plays a crucial role in regulating the workings of the endocrine system. Though only the size of a pea, the pituitary gland controls and regulates most of the functions of the other endocrine glands.
  
  The pituitary gland is made up of two parts: the anterior and posterior lobes. Each lobe produces its own hormones. Various factors can influence the production and secretion of pituitary hormones. These range from shifts in emotion to seasonal changes. Pituitary problems include growth disorders such as acromegaly.
  
  
• Hypothalamus. Located in the lower central part of the brain just above the pituitary gland, the hypothalamus regulates homeostasis in the body, including breathing, metabolism, hunger, thirst and temperature. It is considered the “switchboard” of the endocrine system because it is the part of the brain that exerts control over the endocrine system.
  
  The hypothalamus and the pituitary gland are the regulators of the endocrine system. The hypothalamus secretes hormones that direct the pituitary to either stimulate or suppress the secretion of pituitary hormones. Diabetes insipidus (“water diabetes”) usually involves a problem with the hypothalamus or pituitary gland. This condition is unrelated to the far more common diabetes mellitus (“sugar diabetes”).
  
  
• Adrenal glands. Two triangular-shaped glands located above each kidney. There are two distinct parts of the adrenal glands (adrenal cortex and the adrenal medulla) that secrete two distinct sets of hormones. The adrenal glands are responsible for controlling a host of functions, including regulation of salt and water balance, immune system regulation, body reaction to stress, and sexual development. Adrenal gland disorders include hypoadrenal (reduced function) conditions such as Addison disease and hyperadrenal (excessive function) conditions such as Cushing’s syndrome, a disease that may be caused by excessive levels of cortisol (hormone produced by the adrenal glands).
  
  
• Thyroid gland. A small gland located in the lower front part of the throat, the thyroid gland produces thyroid hormones that regulate the body’s metabolism, bone growth and development of the brain and nervous system. Thyroid hormones maintain blood pressure, heart rate, digestion, muscle tone, body temperature, weight and reproductive functions. Thyroid disorders include hypothyroidism and hyperthyroidism.
  
  
• Parathyroid glands. Two pairs of tiny glands located behind the thyroid gland, one set on each side of the gland. They are essential to regulate the balance of calcium in the body. Hyperparathyroidism may cause hypercalcemia, and hypoparathyroidism may cause hypocalcemia.
  
  
• Pancreas. Located behind the stomach, the pancreas serves two functions: digestive (exocrine) and hormonal (endocrine). The portion of the pancreas that secretes digestive enzymes is considered exocrine in its function. The other part consists of cells called islets of Langerhans. They secrete hormones including insulin and glucagon, which work together to regulate glucose (blood sugar).
  
  The various forms of diabetes mellitus, including type 1 diabetes and type 2 diabetes, are pancreatic endocrine diseases. An example of a pancreatic exocrine disease is pancreatitis.
  
  
• Pineal body. Located in the base of the brain, it is involved in regulating the body’s wake-sleep cycle.
  
  
• Thymus. Located in children in the chest above and in front of the heart, this gland is present in infancy and early childhood and provides immune system functioning for the growing child. The gland grows throughout childhood until puberty, when its function begins to decline. Afterward, the tissue is replaced by fat cells and the body’s immune system replaces the immune function formerly provided by the thymus.
  
  
• Gonads. Located in the lower trunk, the reproductive organs produce steroid hormones specific to the sexual characteristics and reproductive functions of males and females beginning at puberty.  The reproductive organs in males are the testes (testicles) and in females are the ovaries.