Hormonal control of homeostasis From:

The importance of the endocrine system: No cell operates in isolation- body function depends on hormonal chemical control A small amount of hormone can make a big impact Nervous system helps an organism to adjust quickly to changes in environment while endocrine system maintains control over a longer duration (can regulate and sustain development for years)

Hormones (=to excite or set in motion ) Chemicals released by cells that affect cells in other body parts by speeding up or slowing down bodily processes Endocrine hormones: produced in glands and secreted directly into the blood (some glands make multiple hormones, like the thyroid)

Steroid and protein hormones Type and number of hormone receptors varies from cell to cell. (ex: liver and muscle have many insulin receptors…bone and cartilage do not) Two types of hormones: Steroid: made from cholesterol (sex hormones) Diffuse from capillaries (blood) into interstitial fluid then into target cells Combine with receptor molecules located in cytoplasm Hormone-receptor complex moves to nucleus and attaches to DNA where there is a complementary shape A gene is activated that makes a specific protein

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Protein hormones: chain of amino acids of varying length (insulin and GH) Combine with SPECIFIC receptors on the cell membrane This complex (hormone-receptor) activates the production of an enzyme called adenylyl cyclase, which causes the cell to convert ATP into cAMP (cyclic adenosine monophosphate) cAMP functions as a messanger, activating enzymes in the cytoplasm to carry out normal functions

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Pituitary gland: the Master “master” because it controls other endocrine glands a small, sac-like structure, connected by a stalk to the hypothalamus produces AND stores hormones Stimulated through hypothalamus via nerve impulses to release hormones

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Has 2 lobes: –Posterior: Does not make own hormones, stores those made by the hypothalamus such as ADH and oxytocin (labour hormone) –Anterior: produces its own hormones which generally regulate other glands Such as: –thyroid-stimulating hormone (which causes the thyroid to produce thyroxine), – follicle-stimulating hormone (FSH) (development of follicles in ovaries and sperm in males) –(for other examples, see table 1, p377) Release of these hormones is related through nerve impulses from the hypothalamus Hypothalamus also inhibits the secretion of hormones.

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