Endocrinology is a specialty of medicine; some would say a sub-specialty of internal medicine, which deals with the diagnosis and treatment of diseases related to hormones.
Endocrinology covers such human functions as the coordination of metabolism, respiration, reproduction, sensory perception, and movement. Endocrinology also focuses on the endocrine glands and tissues that secrete hormones.
The word "endocrinology" comes from the Greek endon meaning "within", and the Greek krinein meaning "to separate".
What is the endocrine system?
The human endocrine system consists of a number of glands. These glands produce and secrete hormones which control the body's metabolism, growth, sexual development and function. When the hormones leave the glands they enter the bloodstream and are transported to organs and tissues in every part of the body.
Below is a list of glands in the human body and what they do:
Adrenal glands (suprarenal glands)
Located atop the kidneys. Adrenal glands are divided into 2 regions, the right gland is triangular while the left one is semilunar in shape. These glands secrete corticosteroids and catecholamines, such as norepinephrine and adrenaline (epinephrine), which are hormones that are released in response to stress.
The adrenal glands also produce androgens, male sex hormones that promote the development of male characteristics. Testosterone is the major androgen. These glands produce aldosterone which affects kidney function.
Located just above the brain stem, below the thalamus. This gland activates and controls involuntary body functions, appetite, sleep, temperature, as well as the circadian cycles. The hypothalamus links the nervous system to the endocrine system via the hypophysis (pituitary gland).
Ovaries and testicles
The ovaries, located on either side of the uterus in females, secrete the hormones estrogen and progesterone; these hormones ensure sexual development, fertility and healthy menstrual periods. The testicles, located in the scrotum below the penis in males, secrete androgens, mainly testosterone, that control sexual development, puberty, facial hair, sexual behavior, libido, erectile function, and the formation of spermatozoa (spermatogenesis).
Located in the abdomen. The pancreas is both an endocrine gland and a digestive organ. It produces insulin, somatostatin, glucagon, and pancreatic polypeptide. Insulin plays a key role in carbohydrate and fat metabolism in the body. Somatostatin regulates endocrine and nervous system function; it inhibits the secretion of several hormones, such as gastrin, insulin and growth hormone. Glucagon is a peptide hormone which raises blood glucose levels when they fall too low. Pancreatic polypeptide helps control the secretion of substances made by the pancreas. A peptide is a molecule that is made up of at least two amino acids.
Small endocrine glands located in the neck. They produce parathyroid hormone, which regulates calcium and phosphorous in the blood, blood clotting, and neuromuscular excitation.
Pineal body (pineal gland)
A small endocrine gland located in the brain. It secretes melatonin, and is probably involved in controlling the body's sleep patterns.
An endocrine gland located just off the hypothalamus at the base of the brain (a protrusion off the hypothalamus). Known as the main endocrine master gland, because it secretes hormones that regulate the functions of other glands, as well as growth and several body functions.
- The anterior pituitary secretes hormones that affect sexual development, thyroid function, growth, skin pigmentation, and adrenocortical function. If the anterior pituitary is underactive, it can lead to dwarfism in childhood and underactivity in other endocrine glands.
- The posterior pituitary secretes oxytocin, a hormone that raises uterine contractions as well as ADH (antidiuretic hormone) which encourages the reabsorption of water by the kidneys.
An endocrine gland located beneath the breastbone (sternum). T lymphocytes, types of immune cells, mature and multiply in the thymus gland early in life. After puberty the gland shrinks. The thymus gland plays a role in the body's immune system.
An endocrine gland located just below the Adam's apple in the neck; it produces hormones that play a key role in regulatiing blood pressure, body temperature, heart rate, metabolism, and how the body reacts to other hormones. The thyroid gland uses iodine to manufacture hormones. The two main hormones are thyroxine and triiodythyronine. The thyroid gland also produces calcitonin, which stimulates bone cells to add calcium to bone, as well as regulating calcium metabolism.
On the next page we look at diseases of the endocrine system and analyze what happens when each endocrine gland produces too much or too little of its hormones.