Thyroid gland and solution

what is the prolactin

Prolactin is another hormone secreted by the anterior pituitary. Prolactin works with estrogen, progesterone, and other hormones to stimulate the mammary glands in the breasts to secrete milk after a woman has given birth to a child. During the menstrual cycle, milk is not produced and secreted because prolactin levels in the bloodstream are very low. Late in the menstrual cycle, however, as the levels of progesterone and estrogen fall, the pituitary is stimulated by the hypothalamus to secrete some prolactin. This rise in prolactin, although not sufficient to cause milk production, does cause the breasts of some women to feel sore before menstruation. After menstruation, estrogen levels begin to rise, and prolactin secretion is once again inhibited. 

Melanocyte-stimulating hormone (MSH)

 acts on cells in the skin called melanocytes, which synthesize a pigment called melanin. This pigment is taken up by epideimal cells in the skin, producing skin colorations from pale yellow(in combination with another pigment called carotene) to black. Variations are caused by the amount of pigment the melanocytes produce; this variation is genetically deter-mined and is an inherited characteristic.

The posterior pituitary 

The posterior lobe of the pituitary stores and releases two hormones that are produced by the hypothalamus: antidiuretic hormone (ADH) and oxytocin. ADH helps control the volume of the blood by regulating the amount of water reabsorbed by the kidneys. For example, receptors in the hypothalamus can detect a low blood volume by detecting when the solute concentration of the blood is high. When the hypothalamus detects such a situation, it triggers its specialized neurosecretory cells to make ADH. This hormone is transported within axons to the posterior pituitary, which releases the hormone into the bloodstreambinds to target cells in the collecting ducts of the nephrons of the kidneys, increasing their permeability. More water then moves out of these ducts and back into the blood, resulting in a more concentrated urine. ADH also acts on the smooth muscle surrounding arterioles. As these muscles tighten, they constrict the arterioles, an action that helps raise the blood pressure. Alcohol supresses ADH release, which is why excessive drinking leads to the production of excessive quantities of urine and eventually to dehydration.

 Oxytocin is another hormone of the posterior pituitary: it is produced in the hypothalamus and transported within axons to the posterior pituitary for secretion. In women, oxytocin is secreted during the birth process, triggered by a stretching of the cervix of the uterus at the beginning of the birth process. Oxytocin binds to target cells of the uterus, enhancing the contractions already taking place. The mechanism of oxytocin secretion is an example of a positive feed-back loop in which the effect produced by the hormone enhances the secretion of the hormone. For this reason, oxytocin is used by physicians to induce uterine contractions when labor must be brought on by external means. Oxytocin also targets muscle cells around the ducts of the mammary glands, allowing a new mother to nurse her child. The suck-ling of the infant triggers the production of more oxytocin, which aids in the nursing process and helps contract the uterus to its normal size.

what is the thyroid gland of human

The thyroid gland

Sitting like a large butterfly just below the level of the voice box, the thyroid gland can be thought of as your "metabolic switch." This gland secretes hormones that determine the rate of the chemical reactions of your body's cells. Put sim-ply, thyroid hormones determine how fast bodily processes take place.

 The thyroid hormones are thyroxine (T4) and triiodothyronine (T3). These hormones are called amines: single, modified amino acids. They are not considered to be "true" peptide hormones, however, because they act on the DNA of target cells as steroid hormones do. They are also unique because an inorganic ion—iodine—is part of their structures.

 Your body uses iodine in the food you eat to help make the thyroid hormones; the 3 or 4 in each hormone name refers to the number of atoms of iodine in each hormone. Foods such as seafood and iodized salt are good sources of dietary iodine. If the diet contains an insufficient amount of iodine, the thyroid gland enlarges. This condition is called a hypothyroid goiter. The hypothalamus and the thyroid gland work together to keep the proper level of thyroid hormone circulating in the bloodstream. This level is detected by the hypothalamus. A low level of thyroid hormones stimulates the hypothalamus to secrete a releasing factor—a chemical message—to the anterior pituitary. This message tells the pituitary torelease more TSH. The thyroid responds, thereby raising the blood level of T3 and T4 back to normal. This mechanism of action is an example of a negative feed-back loop in which the effect produced by stimulation of a gland "shuts down" the stimulus. Shutdown occurs when a sufficient effect has been produced, similar to the mechanism of a thermostat. In your home, your furnace is triggered to go on when the temperature goes below the thermostat setting. The furnace stays on until the house heats up to the desired level. The thermostat then signals the furnace to turn off.

In certain disease conditions the amount of thyroid hormones in the bloodstream cannot be regulated properly. If the thyroid produces too much of the thyroid hormones, a person may feel as though the "engine is racing," with such symptoms as a rapid heartbeat, nervousness, weight loss, and protrusion of the eyes

. This condition is called hyperthyroidism. On the other hand, if the thyroid produces too little of the thyroid hormones, a person may feel "run down," with such symptoms as weight gain and slow growth of the hair and fingernails. This condition is called hypothyroidism. Various factors can be the under-lying cause of such problems; often medication or surgery can correct the situation.

In addition to secreting the thyroid hormones, the thyroid gland secretes a hormone called calcitonin, or CT. This hormone works to balance the effect of another hormone called parathyroid hormone, or PTH. PTH regulates the concentration of calcium in the b

loodstream. Calcium is an important structural component in bones and teeth and aids in the proper functioning of nerves and muscles.

What is  The parathyroid glands

the parathyroid glands 

The parathyroid glands Embedded in the posterior side of the thyroid are the para-thyroid glands. Most people have two parathyroids on each of the two lobes of the thyroid. These are the glands that secrete PTH, which works antagonistically to CT to help maintain the proper blood levels of various ions, primarily calcium. Two of the many problems related to abnormal calcium levels in the blood are kidney stones and osteoporosis. If calcium levels in the blood remain high, tiny masses of calcium may develop in the kidneys. These masses, called kidney stones, can partially block the flow of the urine from a kidney. If calcium levels in the blood remain low, calcium may be removed from the bones, a disorder known as osteoporosis. Osteoporosis is most common in middle-aged and elderly women, who have stopped secreting estrogen at menopause . Estrogen stimulates bone cells to take calcium from the blood to build hone tissue.

PTH and CT work in the following way to keep calcium at an optimum level in the blood: If the calcium level is too low, PTH stimulates the activity of osteoclasts, or bone-destroying cells. These cells liberate calcium from the bones and put it into the bloodstream. PTH also stimulates the kidneys to reabsorb calcium from urine that is being formed and stimulates cells in the intestines to absorb an increased amount of calcium from digested food. CT acts antagonistically to PTH. When the level of calcium in the blood is too high, less PTH is secreted by the parathyroids and more a is secreted by the thyroid. The CT inhibits the release of calcium from bone and speeds up its absorption, decreasing the levels of calcium in the blood. These interactions of PTH and CT are an example of a negative feedback loop that does not involve the hypothalamus or pituitary gland. The level of calcium in the blood directly stimulates the thyroid and parathyroid glands .