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Each of the endocrine glands produces certain types of hormones used by the body. The release of these hormones causes specific reactions to occur in the body.

The hypothalamus produces several hormones that regulate the pituitary gland. They include:

• Growth hormone-releasing hormone (GHRH). Sent to the pituitary gland to release growth hormone (GH).
  
  
• Thyrotropin-releasing hormone (TRH). Sent to the pituitary gland to release thyroid-stimulating hormone (TSH).
  
  
• Corticotropin-releasing hormone (CRH). Sent to the pituitary gland to release adrenocorticotropin hormone (ACTH).
  
  
• Somatostatin. Suppresses production of GH and TSH in the pituitary gland.
  
  
• Gonadotropin-releasing hormone (GRH). Stimulates the pituitary gland to produce and release luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which aid puberty and reproductive functions in males and females.

The pituitary gland produces different hormones from its two regions, the anterior and posterior lobes. The hormones produced by the anterior (front) lobe include:

• Growth hormone (GH). Stimulates bone and muscle growth and healthy body composition. In children, too much GH can cause gigantism, a condition in which excessive growth of the long bones results in excessive tallness. Too little GH in children can stunt growth. Deficiencies in adults lead to fat, muscle and bone mass imbalances and deficiencies. Excessive growth hormone in adulthood can lead to acromegaly, a condition in which the bones increase in size.
  
  
• Thyroid-stimulating hormone (also called TSH or thyrotropin). Stimulates the release of thyroid hormones to control metabolism, energy, growth and the nervous system.
  
  
• Adrenocorticotropin hormone (ACTH). Stimulates the adrenal glands to produce aldosterone (which controls sodium and water retention by the kidneys) and cortisol (a steroid hormone that helps maintain blood pressure and glucose levels in times of stress).
  
  
• Luteinizing hormone (LH). Stimulates the cells of the testes to produce and regulate testosterone. Stimulates ovulation (egg release) in women and release of estrogen from a gland known as the corpus luteum. LH also stimulates the secretion of sex hormones in the gonads.
  
  
• Follicle-stimulating hormone (FSH). Stimulates maturation of ovarian follicles (eggs) in females and promotes the process of spermatogenesis (sperm production) in males. FSH also stimulates the secretion of sex hormones in the gonads.
  
  
• Prolactin (PRL). Stimulates milk production in females after childbirth. It plays a role in the metabolism of carbohydrates and fats. PRL also affects the levels of sex hormones in the ovaries and testes.
  
  
• Corticotropin. Stimulates the adrenal glands to produce hormones.
  
  
• Endorphins. Chemical messengers sent to the nervous system to reduce pain sensitivity by deadening pain receptors. Endorphins are chemically related to morphine and are naturally produced by the body in response to pain.
  
  
• Melanocyte-stimulating hormone (MSH). Stimulates the melanocytes in the skin to produce melanin (skin pigment).

The posterior (back) lobe of the pituitary gland stores the following hormones that are secreted by the hypothalamus and transported to the pituitary gland:

• Antidiuretic hormone (ADH or vasopressin). Inhibits the amount of water and sodium excreted from the body. ADH causes the kidneys to produce concentrated urine in lower volumes, and problems with this hormone can cause kidney problems. ADH also stimulates constriction of blood vessels and smooth muscles.
  
  
• Oxytocin. Stimulates milk production and contracts the uterus during childbirth.

The adrenal glands have two distinct parts (adrenal cortex and the adrenal medulla) that secrete two distinct sets of hormones.

The adrenal cortex is the outer portion of the adrenal gland, and it produces corticosteroids such as cortisone. Cortisone is an anti-inflammatory hormone that suppresses immune system response. Corticosteroids raise blood pressure and can produce problems for people with hypertension. The following are corticosteroids secreted by the adrenal cortex:

• Glucocorticoids, such as cortisol. Helps regulate metabolism of carbohydrates (including glucose), fats and proteins. Cortisol also causes the release of glycogen to elevate levels of glucose in the bloodstream and help the body cope with stress.
  
  
• Mineralocorticoids (such as aldosterone). Secreted to stimulate sodium and water retention and the excretion of potassium from the kidneys. These functions help to maintain blood volume and pressure.

The adrenal medulla is the inner portion of the adrenal gland associated with the sympathetic nervous system. It produces the following hormones:

• Epinephrine (also known as adrenaline). Produced in response to fright, stress, caffeine, anger and hypoglycemia (low glucose). Adrenaline increases heart rate, as well as the rate of metabolism and blood flow to muscles. This hormone is secreted as an emergency response to stress. Adrenaline inhibits insulin and raises glucose by stimulating the liver to break down stored glycogen into glucose and release it into the bloodstream.
  
  
• Norepinephrine. Allows the body to maintain normal functioning as opposed to emergency reactions. This hormone stimulates and maintains a normal heart beat.

The thyroid gland produces hormones including thyroxine and triiodothyronine. These help regulate metabolism. Hyperthyroidism occurs when the thyroid gland is too active. Symptoms include unexplained weight loss and restlessness. Hypothyroidism, in which the thyroid gland is underactive, causes symptoms such as unexplained weight gain and fatigue.

The parathyroid glands produce parathyroid hormone (PTH). This hormone increases calcium and reduces phosphorus levels in the body and is produced in response to low levels of dietary calcium in the diet. Proper nerve, muscle and bone structure and functioning are supported by PTH.

The pancreas produces hormones such as:

• Glucagon. Produced by the alpha cells in the islets of Langerhans, glucagon is secreted by the pancreas to stimulate the liver to change stored glycogen to glucose for release into the bloodstream to raise glucose levels. This is an emergency response when the blood sugar levels are too low.
  
  
• Insulin. Produced by the beta cells in the islets of Langerhans, insulin enables sugar in the blood (glucose) to enter cells so they can produce heat and energy. Glucose is the body’s fuel, and insulin is the catalyst that enables the body to use it. If this system works properly, it lowers the blood sugar levels. If not, blood sugar levels may rise out of control, leading to diabetes. Insulin also stimulates glycogen production and storage.
  
  
• Amylin. Produced by the beta cells, it delays emptying of the stomach, promotes feelings of fullness (satiety) and inhibits glucagon. Synthetic amylin is an injected medication recently approved to help treat some cases of type 1 diabetes.
  
  
• Somatostatin. Produced by the islet delta cells, it suppresses insulin and glucagon.

The pineal body produces melatonin. This hormone regulates sleep cycles and is stimulated by the nerves of the eyes. Production increases sharply at night and decreases sharply in the daytime. It also helps the pituitary gland inhibit production of GRH by the hypothalamus.

The thymus releases thymosin. This hormone stimulates the production of T-cells, which attack foreign substances invading the body and are part of the body’s immune system. Thymosin stimulates an immune system response from the lymphoid tissues.

The gonads consist of the ovaries and testes (testicles). The ovaries are the female reproductive organs that produce eggs. They also produce the following female sex hormones:

• Estrogen. Hormones that affect female sexual characteristics such as breast development and widening of the hips that is evident in puberty. Estrogen also affects reproductive functions such as menstruation, pregnancy and egg production.
  
  
• Progesterone. Also crucial in reproductive functions such as menstruation, pregnancy and egg production. Progesterone prepares the uterus for the implantation of the embryo. Also, secretions of progesterone from the placenta help maintain pregnancy. Progesterone also plays a part in regulating menstruation.
  
  
• Inhibin. A protein that inhibits the release of FSH from the pituitary gland to regulate egg development.

Testes are the male reproductive organs that produce sperm and male sex hormones (androgens), including testosterone. These hormones affect the development of male sexual characteristics during puberty, including sexual growth and development, facial hair and voice changes. These hormones continue to affect aspects of an adult male’s sexual life, including sex drive and sperm production, and contribute to male hair patterns, bone mass and muscle mass.