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Unformatted text preview: Chapter 41: Animal Hormones What are hormones and how do they work? • Hormones are chemical messages that allow slow communication between distant cells in the body • They act on a time scale of several seconds to days • can control long-term physiological processes • not useful for controlling rapid actions • Endocrine Cells secrete chemical messages called hormones, which bind to receptors on or in target cells . • In some cases, endocrine cells are aggregated into endocrine glands • They secrete hormones into the interstitial space and/or blood stream • Exocrine Cells secrete substances into ducts that are connected to the outside world • Paracrine hormones diffuse to targets near the site of secretion • Autocrine hormones inFuence the cell that secretes them. Most hormones are delivered to target cells by the circulatory system. • Paracrine hormones are released in tiny amounts, or are inactivated rapidly by enzymes, or are taken up ef¡ciently by local cells. They never get into the circulatory system. • Most hormones diffuse into the blood, which distributes them throughout the body • When the hormone message encounters a cell with the proper receptor, it binds and triggers a response • The same hormone may cause different responses in different types of cells • example: epinephrine (adrenaline) - the nervous system reacts to an emergency very quickly and stimulates adrenal cells to secrete epinephrine - the result is the fght or Fight re- sponse. • Epinephrine acts on different cells in the body: • heart - faster and stronger heartbeat • blood vessels - constrict to send more blood to muscles • liver - glycogen is broken down to glucose to provide quick energy • fat tissue - fats are mobilized as another energy source • Groups o¡ Hormones • Peptides or Proteins • water soluble and transported by vesicles of the the cell that made them • peptide hormone receptors are localized in the surface of target cells • examples: growth hormone and insulin • Steroid Hormones • lipid-soluble and membrane-permeable • can diffuse out of the cell that made them • can diffuse into the target cells • in the blood, they must be bound to carrier proteins • the receptors for lipid-soluble hormones are inside cells, either in the cytoplasm or in the nucleus • example: estrogen • Animal Hormones • derivatives of the amino acid tyrosine • some are water-soluble and some are lipid-soluble • example: epinephrine/adrenaline • Receptors MCDB 1B: Animal Physiology Outline MCDB 1B: Intro to Animal Physiology 1 • Receptors for water-soluble proteins are large glycoproteins on the cell surface with three domains • A binding domain projecting outside the plasma membrane • A transmembrane domain that anchors the receptor in the membrane • A cytoplasmic domain that extends into the cytoplasm of the cell • The cytoplasmic domain initiates the target cell’s response by activating protein kinases or protein phos-...
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- Winter '09
- cells, MCDB 1B