Download GLANDS OF THE ENDOCRINE SYSTEM 1. THE PITUITARY

GLANDS OF THE ENDOCRINE SYSTEM 1. THE PITUITARY GLAND The pituitary gland is a small gland located at the base of the brain and is about the size of a cherry. It produces a large number of hormones, many of which stimulate other endocrine glands. For this reason, the pituitary gland is often referred to as the “master gland”. Some of the hormones secreted by the pituitary gland are: • growth hormone stimulates bone and muscle growth. A deficiency of this hormone during years of skeletal growth will result in dwarfism; pituitary dwarfs are normal in all ways except size. An over-­‐secretion of this hormone during years of skeletal growth will result in a giant-­‐
sized individual. • adrenocorticotrophic hormone (ACTH) stimulates the adrenal cortex to produce glucocorticoids (aldosterone and cortisol). • Antidiuretic hormone (ADH) regulates salt and water balance in the body; reducing water loss through dehydration • thyroid stimulating hormone (TSH) causes the thyroid gland to produce the hormone thyroxin (T4) which is converted into triidothyronine (T3) and controls the body’s metabolic rate. • Prolactin stimulates milk producation in mammals • Luteinizing hormone (LH) controls the release of additional hormones from the ovaries (estrogen and progesterone) and testes (testosterone) • Follicle stimulating hormone (FSH) controls the development of the reproductive organs in men and women by stimulating the ovaries in women and the testes in men to produce hormones. • Oxytocin is involved in contractions of the uterus during childbirth 2. THE THYROID GLAND The thyroid gland is located on the surface of the voice box in the neck region. The thyroid gland produces the hormone thyroxin (T4), which controls the body’s metabolic rate. Iodine is necessary to produce thyroxin. Outside of the thyroid, circulating T4 is converted into the bioavailable form – triiadothyronine (T3). Under normal circumstances, the levels of T3 and T4 should be in sync. Elevated T4 (and therefore T3) can cause an increase in the use of simple sugars and fats, elevated heart rate, and elevated breathing rate. When too much T4 is present, the metabolic rate increases, leading to hyperthyroidism; people with hyperthyroidism consume large amounts of food without gaining weight and may appear nervous and anxious. If too little T4 (and therefore T3) is present, a person is considered to have hypothryoidism, which leads to a low metabolic rate and may reduce normal mental and physical growth in kids. An adult with high T3 may have cold hands and feet and a slow heart beat and respiratory rate. In some cases, the body can’t or has difficulty converting T4 into T3. In these cases, blood tests may reveal high T4 and low T3. This can result from chronic stress, but the exact causes and symptoms are not well-­‐understood. 3. ADRENAL GLANDS The adrenal glands are two small glands which sit like a cap on top of the kidneys. They are divided into two parts: the outer part called the cortex and the inner part called the medulla. The cells of the cortex produce hormones called glucocorticoids. The best known of these is called cortisone. The secretions of the adrenal cortex are involved in the stress reponse and are primarily responsible for the increase the blood sugar level. The cortex also releases aldosterone which controls the salt and water balance in the body and androgens which are involved in reproduction. The inside portion of the adrenal glands, called the medulla, produces epinephrine (adrenaline) plus another closely related hormone called norepinephrine. These are used during the “fight or flight” response of the parasympathetic nervous system. Together, they increase the heart rate and breathing rate (and therefore blood pressure) and cause the release of stored glucose necessary for sudden energy. The secretions of the medulla are not essential to life, whereas those of the cortex are. 4. THE PANCREAS The pancreas is both a ductless and a ducted gland. As a ducted gland, it produces pancreatic juice. Pancreatic juice contains a digestive enzyme which gets into the small intestine through a duct. As a ductless gland, the pancreas produces two hormones. The first, insulin, reduces the amount of glucose in the blood by stimulating and encouraging the uptake of glucose into cells. Without sufficient circulating insulin, the body cannot use glucose as an energy source and it will accumulate in the blood, eventually being excreted through the kidneys into the urine. The second hormone produced by the pancreas is glucagon which has the opposite effect of insulin; it causes the liver to produce and release glucose into the bloodstream, thereby increaing circulating blood sugar.