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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 efciently 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 cells response by activating protein kinases or protein phos-...
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- Winter '09