Endocrine System

The endocrine system is the collection of glands, each of which secretes different types of hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep and mood, among other things.

Pituitary Gland

The pituitary gland is sometimes referred to as the “master gland” because of its great influence on the other body organs. This gland not only produces hormones that act directly on the body, but also stimulates other endocrine glands to produce their own hormones. Some, but not all, of these hormones include:

  1. Adrenocorticotropin (ACTH) stimulates production of cortisol (the “stress hormone”) by the adrenal glands. This helps maintain blood pressure and blood glucose levels, among other effects.
  2. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to make thyroid hormones, which, in turn, regulate the body’s metabolism, energy, nervous system activity and growth and development.
  3. Luteinizing hormone (LH) regulates testosterone in men and estrogen in women.
  4. Follicle-stimulating hormone (FSH) stimulates the ovaries to release eggs in women. LH and FSH work together to allow normal function of the ovaries or testes, including sperm production.


The hypothalamus controls hormone production in the pituitary gland through several “releasing” hormones, including:

  1. Growth hormone-releasing hormone (GHRH) controls GH release.
  2. Thyrotropin-releasing hormone (TRH) controls TSH release.
  3. Corticoptropin-releasing hormone (CRH) controls ACTH release.

Pineal Gland

The pineal gland makes at least one hormone: melatonin.


The thyroid produces two hormones, T3 (tri-iodothyronine) and T4 (thyroxine), which control the body’s metabolism, stimulate body heat production, and regulate bone growth.

Symptoms of an underactive thyroid include:

  • Feeling tired
  • Feeling cold even when other people are comfortable or even warm
  • Having a slow heart rate and dry skin
  • Being constipated
  • Gaining weight even though you are not eating more or exercising less than usual

Symptoms of an overactive thyroid include:

  • Feeling nervous and irritable
  • Having trouble concentrating
  • Feeling too warm even when other people don’t feel warm
  • Having a fast heart rate and diarrhea
  • Having trouble sleeping
  • Losing weight without trying


These glands (4) make hormones that help control calcium and phosphorous levels in the body and are necessary for proper bone development. These glands also maintain normal blood calcium levels, which is important for normal heart, muscle and nerve function.

Thymus Gland

This gland plays a role in the body’s immune system.

Adrenal Glands

These glands are divided into two regions: the cortex and the medulla. The adrenal gland secretes hormones that influence the body’s metabolism, blood chemicals, and body characteristics, as well as influence the part of the nervous system that is involved in the response and defense against stress.


The pancreas secretes insulin, a hormone that helps glucose move from the blood into the cells where it is used for energy.


The two most important hormones produced by the ovaries are estrogen and progesterone, which are influential in female characteristics.


The testes (testicles) produce the hormone testosterone. Throughout adult life, testosterone helps maintain sex drive, male hair patterns, muscle mass and bone mass