The Endocrine System: Controlling Hormone Production
The endocrine system is made up of glands that produce hormones and release them into the blood. The hormones cause certain reactions to occur in specific tissues. The endocrine system affects a large number of the body’s functions, including temperature, metabolism, sexual function, reproduction, moods, and growth and development. The following list describes the major glands of the endocrine system.
The pituitary: The pituitary gland controls the functions of several other endocrine glands. It’s not very big, though — only about the size of a pea. The pituitary gland is located at the base of the brain, and it secretes several different hormones:
Adrenocorticotropic hormone: Stimulates the suprarenal glands to produce cortisol, which is a stress hormone (meaning production of this hormone is triggered by stressful situations)
Antidiuretic hormone: Regulates fluid balance in the body
Follicle-stimulating hormone: Stimulates the ovaries to produce eggs, or ova, in women and sperm production in men
Growth hormone: Stimulates growth during childhood and helps to maintain bone and muscle mass in adults
Luteinizing hormone: Helps regulate testosterone in males and estrogen in women
Melanocyte-stimulating hormone: Stimulates the production of melanin (skin pigment) by the melanocytes in the skin and hair
Oxytocin: Stimulates lactation (milk production) in the breasts and contraction of the smooth muscles of the uterus during birth
Prolactin: Stimulates milk production after the birth of a baby
Thyroid-stimulating hormone: Stimulates the thyroid gland to produce the thyroid hormones that regulate metabolism and blood calcium levels
The hypothalamus: The hypothalamus is a part of the brain located near the pituitary gland. It assists the pituitary gland in regulating other glands by releasing hormones that communicate with it:
Corticotropin-releasing hormone: Tells the pituitary gland to secrete adrenocorticotropic hormone
Dopamine: Tells the pituitary gland to produce less prolactin
Gonadotropin-releasing hormone: Tells the pituitary to secrete follicle-stimulating hormone and luteinizing hormone
Growth-hormone-releasing hormone: Tells the pituitary gland to secrete growth hormone
Somatostatin: Tells the pituitary gland to release less growth hormone and thyroid-stimulating hormone
Thyrotropin-releasing hormone: Tells the pituitary gland to release thyroid-stimulating hormone and prolactin
The pineal gland: The pineal gland is also located in the brain. It secretes melatonin, which is a hormone that helps regulate sleep cycles and influences sexual development.
The thyroid gland: The thyroid gland is located in the anterior part of the neck, just in front of the trachea below the larynx. It helps regulate the body’s metabolism (how the body gets energy from food) and blood-calcium levels by secreting three hormones:
Calcitonin: Regulates blood calcium levels by slowing down the amount of calcium lost from bones
Thyroxine: Stimulates your body to use more oxygen and increases metabolism
Triiodothyronine: Affects metabolism, growth and development, body temperature, and heart rate
Four small parathyroid glands are located on the thyroid gland. They secrete parathyroid hormone, which raises calcium levels in the blood. They work together with the thyroid gland to keep blood calcium at just the right level.
The thymus: The thymus gland is located in the thoracic cavity, posterior to the sternum. It’s part of the immune system and is made of lymphoid tissue. The function of the thymus gland is to take immature T cells (a type of white blood cells) and develop them into mature T cells that are capable of recognizing foreign substances that may cause damage to the body.
The suprarenals: The suprarenal glands sit atop the kidneys. They respond to stress, affect fluid balance in the body, and make a small amount of sex hormones:
Aldosterone: Decreases sodium loss in the blood to regulate blood volume and blood pressure
Cortisol: Helps regulate the body’s use of proteins, fats, and carbohydrates and helps regulate blood pressure and heart function
Epinephrine (adrenaline): Increases heart rate, increases blood flow to the brain and muscles, and takes glucose out of storage for use as fuel
Norepinephrine (noradrenaline): Constricts blood vessels and increases blood pressure; also takes glucose out of storage to fuel the muscles and brain
Sex hormones: Involved with the development of sex organs at the beginning of puberty
The pancreas: Part of the pancreas makes digestive enzymes, but another part makes insulin, which is a hormone that helps regulate carbohydrate metabolism and fat storage. It’s secreted after a person consumes carbohydrates (starches or sugars).
People who can’t make insulin have a condition called type 1 diabetes mellitus. People with type 2 diabetes mellitus either don’t make enough insulin or can’t use insulin properly. Gestational diabetes occurs during pregnancy. Diabetes results in elevated blood-sugar levels and can cause the person to feel thirsty or hungry more frequently than usual and urinate more frequently. Diabetes is diagnosed by urine tests that detect glucose (blood sugar) in the urine and blood tests that measure levels of blood glucose after a 12-hour fast. Treatment depends on the type and severity of the disease and includes insulin injections, medications that regulate glucose levels, and dietary interventions.