45 Endocrine system 2009

45 Endocrine system 2009 - Biol 61 The Endocrine System...

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Biol 61 – The Endocrine System (Chapter 45) 4/27/09 We will not be discussing all the hormones mentioned in this Chapter. Focus on the topics and hormones that were discussed in lecture. The endocrine system is the system of organs/tissues in animals that secrete chemical signals called hormones into the blood (Fig. 45.10). Endocrine organs and glands make hormones – chemical signals that are released into the blood, and which act to coordinate the activity of tissues and organs. Endocrine glands are ductless – the cells secrete the hormone directly into the blood. Contrast this with exocrine glands – glands with ducts (that often exit to the outside of the body, such as sweat glands, salivary glands, tear ducts, bile duct, etc.). Many hormones are used for homeostasis – keeping the internal environment of a body as constant as possible (for us this would involve maintaining the right levels of glucose in the blood, the right blood volume, the right blood pressure, etc.). Hormones are important because they are used by a body for global regulation : an organ in one part of the body can secrete a hormone signal that can, in theory, “talk” to any other organ and tissue of the body, giving it new instructions. Of course, not all cells will respond to a particular hormone in the blood, so hormones have specific target tissues that they regulate. Certainly not all hormones are involved in homeostasis. For example, the human sex hormones play a role in regulating the growth, development and maintenance of the male and female reproductive systems, as well as controlling reproductive cycles and sexual behavior. Structure of Hormones What kinds of molecules are hormones? Hormones tend to be fairly large molecules, and types of hormones include: - hydrophilic hormones , which tend to be short polypeptides, just a few amino acids long up to considerably longer (this group includes ADH, insulin and glucagon), or single amino acids and their derivatives (examples include epinephrine & norepinephrine). - hydrophobic hormones , including steroid hormones (compounds derived from cholesterol). The steroid hormone class includes aldosterone (a class of “mineralocorticoid”), estrogen, testosterone and the glucocorticoids (which regulate aspects of metabolism). Thyroxine is also a hydrophobic hormone that is actually a derivative of an amino acid (that is also hydrophobic). Most hormones are hydrophilic, water-soluble compounds that can travel easily in the blood but can’t cross cell membranes. How do these hormones signal their target cells? They bind to receptor proteins on the surface of their target cells (see Fig. 45.5a/45.6). These membrane-bound receptor proteins have an extracellular region that binds to the hormone, but they also contain an intracellular region that can act as an enzyme to affect the activity of other cellular proteins and can activate transcription factors, which can alter gene expression within the target cell. How does a steroid hormone act to stimulate its target cells?
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This note was uploaded on 01/15/2011 for the course BIOL 61 taught by Professor Vierra during the Spring '08 term at Pacific.

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45 Endocrine system 2009 - Biol 61 The Endocrine System...

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