Endocrine gland

The endocrine system is a network of glands and organs located throughout the body. Together with the nervous system, it forms the neuroendocrine system, which helps control and regulate many important body functions.

Endocrine glands are special types of glands in this system that do not have ducts. Instead, they release their products, called hormones, directly into the blood. These hormones act as messages that travel to different parts of the body to tell them what to do.

Some of the major endocrine glands include 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 are part of both the endocrine and nervous systems, acting as important linking organs. These glands work together to keep our bodies healthy and functioning properly.

Pituitary gland

Main article: Pituitary gland

The pituitary gland is a small gland at the base of the brain that helps control many important body functions. It has two parts: the front part and the back part. The front part makes hormones that tell other glands in the body what to do. The back part stores and releases hormones made by the brain.

One important hormone made by the front part is growth hormone, which helps the body grow, especially muscles and bones. Another hormone helps the thyroid gland work, which is important for growth and energy. There are also hormones that help the adrenal glands make substances that control stress and other body processes, and hormones that help with making eggs and sperm. The back part of the pituitary releases hormones that help with childbirth and nursing, and with keeping the right amount of water in the body.

Thyroid gland

Main article: Thyroid

The thyroid gland sits at the front of your neck, shaped like a butterfly with two wings joined by a middle part called the isthmus. It makes important chemicals called thyroid hormones that help your body use energy faster. These hormones include thyroxine (T4) and triiodothyronine (T3).

The thyroid also makes a chemical called calcitonin that helps control the amount of calcium in your blood. When there is too much thyroid activity, it is called hyperthyroidism, and when there is not enough, it is called hypothyroidism.

Parathyroid glands

Main article: Parathyroid gland

The parathyroid glands are small glands located behind the thyroid glands in the neck. There are usually 4 to 6 of these glands. They release a hormone called parathyroid hormone, which helps control the amount of calcium in the blood. When blood calcium levels drop, these glands release more hormone to raise the levels. When 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 in people and in front of the kidneys in other animals. These glands make important chemicals called hormones. They produce adrenaline, which helps the body react to stress by raising blood pressure and heart rate. They also make aldosterone, which helps control the balance of salt and water in the body, and cortisol, which helps the body handle stress. Another hormone they make is Dehydroepiandrosterone sulfate (DHEA). This helps with changes in the body during puberty, like body odor and hair growth.

Pancreas

Main article: Pancreas

The pancreas is a special organ found in the abdomen, just below and behind the stomach. It acts as both an exocrine and an endocrine gland. Inside the pancreas, there are special groups of cells called pancreatic islets. These islets contain 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 the 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 starting at puberty. These hormones help the female reproductive system grow and cause changes in the body.

The testes in males also start making a hormone at puberty that helps the male reproductive system develop and causes changes like more body hair growth.

Pineal gland

Main article: Pineal gland

The pineal gland is a small part of the brain that helps control our daily rhythms. It releases a special chemical called melatonin, which can affect how our bodies know when it's time to sleep or wake up. This gland might also play a role in how our skin changes color in different light conditions.

Other hormone-producing structures

Many parts of the body that aren’t 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 come from the three basic layers that form early in development. As people get older, the ovaries in women naturally stop working, which is called menopause. With age, all endocrine glands tend to work less well. This can lead to more cases of diabetes and a 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. Negative feedback helps keep hormone levels balanced in the blood.

The nervous system can sometimes change how hormones act.

Clinical significance

Disease

Main article: Endocrine diseases

Diseases that affect endocrine glands are quite common. Some examples include diabetes, problems with the thyroid gland, and obesity. These diseases happen when hormones are not released correctly, when the body does not respond properly to signals, when a gland is missing, or when a gland grows too large.

When endocrine glands do not work well, it can be because they are not making enough hormones, they are making too many, or they are not shaped right. Some diseases affect the thyroid gland, which can cause symptoms like feeling very tired or having swelling around the eyes. Other diseases can affect the adrenal glands, which help control how our body manages sugar and blood pressure. These problems can sometimes be very serious.