Parts of the Endocrine System

Hormones

Hormones are chemicals that control specific biological functions. They are made in your endocrine glands, secreted in small amounts directly into your bloodstream, and travel to other organs where they induce an action in the organ’s cells.

The Major Glands of the Endocrine System

Hypothalamus 

The hypothalamus, located in your brain, plays a crucial role in your endocrine system by releasing hormones that control hunger, thirst, body temperature and anger. The hypothalamus’ “releasing” hormones regulate the secretion of other hormones in your pituitary gland, which in turn affects other endocrine glands in your body. The hypothalamus’ “inhibiting” hormones, as the name implies, turns off the secretion of some of the hormones released from the pituitary.

Pituitary 

The pituitary gland is located in your brain, directly under your hypothalamus. This gland is tiny, about the size of a pea, but it plays a large role in your endocrine system.  The pituitary gland is composed of two lobes - the anterior (front) and posterior (rear), each of which produces different hormones.            

Anterior Pituitary Gland

Hormones from your anterior pituitary gland are responsible for your growth (growth hormone), reactions to stress (adrenocorticotrophic hormone, abbreviated ACTH), metabolism (thyroid stimulating hormone) and reproductive function (follicle stimulating hormone and luteinizing hormone). Hormones from your anterior pituitary also stimulate the release of hormones from your gonads, thyroid and adrenal glands. Finally, the anterior pituitary secretes a hormone called prolactin, which stimulates milk production in breasts.

Posterior Pituitary Gland

The posterior pituitary gland produces a hormone (anti-diuretic hormone) that regulates how much water is in your body. This gland also secretes a second hormone, called oxytocin, that aids in childbirth (parturition) and stimulates the release of milk from a nursing mother.

Pineal Gland 

Your pineal gland is in your brain. It secretes the hormone melatonin, which plays a role in your sleep-wake cycle. 

Thyroid  

Your thyroid glands, located on either side of your throat, secrete two hormones called thyroxine and triodothyronine. These hormones play a role in metabolism, body temperature, cell growth, and cell differentiation.

Parathyroid 

The parathyroid glands are tiny glands located at the back of your thyroid glands. They secrete parathyroid hormone which regulates your body’s levels of calcium, an important chemical that maintains the proper functioning of cells, and builds muscles and bones.

Adrenals

There are two adrenal glands, one located above each kidney. The adrenal glands are composed of two layers, an outer cortex and an inner medulla. The cortex of the adrenal gland produces the hormones cortisol and aldosterone. Cortisol is released from the adrenal cortex when your body undergoes stress or exercise, and it aids in metabolism. Aldosterone regulates the levels of sodium in the body and this sodium in turn influences the amount of water in the body.

The medulla of the adrenal gland produces epinephrine and norepinephrine, which are also called adrenaline and noradrenaline. The primary hormone released during excitement or stress is epinephrine. This release is commonly known as an “adrenaline rush” and is an important part of your fight-or-flight response.

Pancreas 

Your pancreas is connected to your small intestine where it secretes digestive juices to help break down foods. Its endocrine function is to control blood sugar levels by releasing the hormones insulin and glucagon, which work in opposition to one another. Insulin transports glucose from your bloodstream into your cells to feed them, thereby decreasing blood sugar levels. Glucagon, on the other hand, causes stored glucose from your cells and the liver to be released back into your bloodstream, raising your blood sugar levels.

Gonads

The gonads refer to your reproductive organs. Male gonads are known as testes and female gonads are called ovaries. The testes secrete a hormone called testosterone, which stimulates the production of sperm and secondary male sex characteristics, such as the growth of facial and body hair. Testosterone also helps build muscle.

The ovaries secrete several hormones, namely estrogen and progesterone. Estrogen stimulates the maturation of eggs that reside in the ovaries. Together, estrogen and progesterone regulate breast development during puberty and the menstrual cycle.

Thymus

Your thymus is located just behind your breastbone and secretes thymosins, which help to regulate immune function.

Other Endocrine Tissues

There are other tissues in the body that release hormones, although this is not their primary responsibility in your body.

Adipose (fat)

Adipose tissue is known to produce many different hormones that circulate throughout your body to help maintain homeostasis.  For example, leptin is a hormone that is released from fat tissue after you eat a meal.  It is responsible for telling the brain when you are full.

Kidneys

Your kidneys release erythropoietin, a hormone that tells your body to make more red blood cells. The kidneys also secrete an enzyme called renin, which stimulates the production of a hormone called angiotensin II. This hormone contracts the muscles of your arteries causing blood pressure to increase, and it stimulates the release of another hormone called aldosterone from the adrenal gland (mentioned above).

Heart

Your heart releases a hormone called natriuretic peptide. Breaking down the name, you can see how this hormone causes the body to get rid of sodium (“natri-”) in the urine (“-uretic”). Because water follows salt, when levels of this hormone increase your body responds by getting rid of excess water and your blood pressure decreases.