 This video will cover the first portion of the following objective from the endocrine system, list the major endocrine organs and the hormones they secrete, then for each hormone, discuss its effects on target cells. We've already discussed the role of the hypothalamus, producing the hormones that are secreted from the posterior pituitary gland, antidiuretic hormone and oxytocin, and we've also discussed the role of the hypothalamus producing the releasing hormones that regulate the anterior pituitary gland. Now we're going to focus in more detail on the anterior pituitary gland and how it regulates other endocrine organs. First we'll focus on the thyroid gland that produces the thyroid hormones T3 and T4, stimulating an increase in metabolic rate. The anterior pituitary gland produces tropic hormones, including the thyroid stimulating hormone that targets the thyroid gland and stimulates the thyroid gland to produce the thyroid hormones T3 and T4. T3 and T4 then have the effects of increasing the metabolic rate and stimulating the production of heat warming the body. Adrenal corticotropic hormone, or ACTH, is another tropic hormone which is produced from the anterior pituitary and stimulates the adrenal cortex to release glucocorticoids as a long-term response to stress. One of the functions of glucocorticoids is to increase the blood glucose levels. Another tropic hormone is follicle stimulating hormone. Follicle stimulating hormone will stimulate the reproductive organs and that leads to the stimulation of egg maturation and the production of the sex hormone estrogen in women and in men it stimulates sperm production. Lutinizing hormone is another tropic hormone that regulates the gonads, the endocrine organs that produce the steroid sex hormones. Lutinizing hormone stimulates the production of testosterone in the testes in men and in women, luteinizing hormone stimulates ovulation and also stimulates the production of the steroid sex hormones progesterone and estrogen. Growth hormone is produced by the anterior pituitary and stimulates cell growth and division and stimulates the growth of muscle and bone, stimulates the liver to produce the hormone insulin-like growth factor that also has growth-promoting effects. Prolactin is a hormone produced by the anterior pituitary that stimulates the mammary gland, it stimulates growth of the mammary gland and the production of milk. On the left, we see the chemical structure of the thyroid hormones, T3 on the top, T3 stands for tri-iodothyronine because the chemical structure of T3 contains three iodine atoms and T4, also known as thyroxin, contains four iodine atoms in its chemical structure because the thyroid hormones contain iodine, dietary iodine deficiency impairs the synthesis of thyroid hormones. And this can lead to a goiter, an overgrowth of the thyroid gland which is shown in the picture on the right. The function of the thyroid hormones T3 and T4 is to increase the basal metabolic rate and this stimulates an increase in body temperature. If the metabolic rate and body temperature are too low, the hypothalamus will release TRH, stimulating the anterior pituitary to release TSH, then TSH binds to receptors on the surface of thyroid follicle cells in the thyroid gland and these cells then release T3 and T4 which then bind to receptors within cells all throughout the body leading to increased metabolic rate and the caloricenic effect increasing body temperature. T3 and T4 also bind to receptors within cells in the hypothalamus as a negative feedback mechanism. T3 and T4 inhibit the production of TRH leading to decreased TSH. Iodine deficiency disrupting the production of T3 and T4 removes this negative feedback mechanism leading to excessive TSH production which causes the goiter. Here we see the histology of the thyroid gland that contains follicles filled with coloid which is a storage form of the thyroid hormones. These follicles are lined with a simple cuboidal epithelium of follicular cells. Here we see a higher magnification view of the thyroid gland. The follicular cells are activated by TSH to release the hormones T3 and T4 from storage in the coloid within the follicle. There are also paraphilicular cells or C cells that are found in the thyroid gland. These cells respond to high blood calcium levels also known as hypercalcemia. Hypercalcemia stimulates the C cells to release the hormone calcitonin. In response to hypercalcemia calcitonin released from C cells in the thyroid gland binds to receptors on osteoblasts in bone stimulating osteoblasts to store calcium in the bone. Calcitonin also inhibits osteoclast reducing the rate of calcium reabsorption from the bone. Parathyroid glands are four small glands on the posterior of the thyroid gland that respond to hypercalcemia that is low blood calcium concentration. When blood calcium concentration drops the parathyroid gland releases the parathyroid hormone abbreviated PTH. Then PTH binds to receptors on the surface of cells in the bone and in the kidneys. Parathyroid hormone inhibits osteoblasts and stimulates osteoclasts in bone leading to the release of calcium from the bone. This works to increase blood calcium concentrations. Parathyroid hormone also binds to receptors on the surface of cells in the kidney stimulating the reabsorption of calcium which lowers the loss of calcium in the urine as another mechanism working to increase blood calcium concentrations. Parathyroid hormone also stimulates the production of calcitrile in the kidneys calcitrile is the active form of vitamin D which functions as a hormone produced in the kidneys that travels to the intestine where vitamin D3 or calcitrile binds to receptors in cells lining the intestine and stimulates calcium absorption from the diet.