Endocrine gland

The endocrine system is a network of glands and organs in the body. With the nervous system, it forms the neuroendocrine system. This system helps control many important body functions.

Endocrine glands are special glands that do not have ducts. They release their products, called hormones, right into the blood. These hormones travel to different parts of the body to give instructions.

Some major endocrine glands are the pineal gland, pituitary gland, pancreas, ovaries, testicles, thyroid gland, parathyroid gland, hypothalamus, and adrenal glands. The hypothalamus and pituitary glands are special because they belong to both the endocrine and nervous systems. They help connect the two systems. These glands work together to keep our bodies healthy.

Pituitary gland

Main article: Pituitary gland

The pituitary gland is a small gland at the base of the brain. It helps control many body functions. It has two parts: the front and the back.

The front part makes hormones. These tell other glands in the body what to do. One important hormone is growth hormone. It helps the body grow, especially muscles and bones. Another hormone helps the thyroid gland work. This is important for growth and energy.

The back part stores and releases hormones made by the brain. These help with childbirth, nursing, and keeping the right amount of water in the body.

Thyroid gland

Main article: Thyroid

The thyroid gland is in the front of your neck. It looks like a butterfly with two wings joined by a middle part called the isthmus. It makes important chemicals called thyroid hormones. These help your body use energy faster. The hormones are called thyroxine (T4) and triiodothyronine (T3).

The thyroid also makes a chemical called calcitonin. This helps control the amount of calcium in your blood. When the thyroid is too active, it is called hyperthyroidism. When it is not active enough, it is called hypothyroidism.

Parathyroid glands

Main article: Parathyroid gland

The parathyroid glands are small glands found behind the thyroid glands in the neck. There are usually 4 to 6 of these glands. They release a hormone called parathyroid hormone. This hormone helps control the amount of calcium in the blood. If blood calcium levels drop, these glands release more hormone to raise the levels. If calcium levels are high, the release of this hormone slows down.

Adrenal glands

Main article: Adrenal gland

The adrenal glands sit on top of the kidneys. These glands make important chemicals called hormones. They produce adrenaline, which helps the body react to stress. They also make aldosterone, which helps control salt and water in the body, and cortisol, which helps the body handle stress. They also make Dehydroepiandrosterone sulfate (DHEA). This helps with changes in the body during puberty.

Pancreas

Main article: Pancreas

The pancreas is a special organ found in your belly, just below and behind the stomach. It works as both an exocrine and an endocrine gland. Inside the pancreas, there are groups of cells called pancreatic islets. These islets have alpha cells and beta cells, which are endocrine cells. They release important chemicals called insulin and glucagon into the blood. These chemicals help control the amount of sugar, or glucose, in your blood. When there is not enough sugar in the blood, glucagon tells the liver to release more glucose. Insulin helps cells take in and use the glucose. There are also delta cells that release a chemical called somatostatin, which helps control the release of other chemicals like insulin and glucagon.

Gonads

Main article: Gonad

The ovaries in females release two important hormones when a girl starts puberty. These hormones help a girl's body change and grow.

The testes in males also start making a hormone at puberty. This hormone helps a boy's body change and grow.

Pineal gland

Main article: Pineal gland

The pineal gland is a small part of the brain. It helps control our daily rhythms. It releases a special chemical called melatonin. This chemical helps our bodies know when to sleep or wake up. The pineal gland may also help our skin change color in different light.

Other hormone-producing structures

Many parts of the body that are not usually thought of as hormone glands still make important chemicals. For example, the heart makes a hormone called atrial natriuretic peptide. Parts of the digestive system like the gastrointestinal tract make hormones such as gastrin and secretin. The placenta produces hormones needed during pregnancy, including estrogen and progesterone. The kidneys make erythropoietin and renin. Even the thymus, skin, and adipose tissue can produce hormones like cholecalciferol, leptin, and resistin.

Development

Main article: Development of the endocrine system

Endocrine glands develop from the three basic layers that form early in life. As women age, their ovaries naturally stop working, which is called menopause. With age, all endocrine glands may not work as well. This can sometimes lead to health changes like slower metabolism.

Functions

Hormones

Main article: Hormone

Hormones are special chemicals that travel in the blood to help control many body activities. They work by attaching to special parts called receptors on cells. The body can change how many of these receptors there are, depending on how much hormone is around.

The liver and kidneys help break down hormones, and their levels in the blood change over time. Sometimes, one hormone needs another to work fully. Other times, two hormones work together to make a bigger effect, or one hormone can stop another from working.

Control

Main article: Endocrine system

The endocrine glands are part of the body’s control system. They release hormones that help manage how cells and tissues work. These glands can be triggered to release hormones by signals from the blood, the nervous system, or other hormones. The nervous system can also influence how hormones work.

The nervous system can sometimes change how hormones act.

Clinical significance

Disease

Main article: Endocrine diseases

Diseases that affect endocrine glands are common. Some examples include diabetes, problems with the thyroid gland, and obesity. These diseases happen when hormones are not released correctly or when the body does not respond well to signals.

When endocrine glands do not work well, it can be because they are not making enough hormones or they are making too many. Some diseases affect the thyroid gland, which can make people feel very tired. Other diseases can affect the adrenal glands, which help control how our body manages sugar and blood pressure.