Hormones-four - 41 41 Animal Hormones What are Hormones 41...

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41 Animal Hormones 41 What are Hormones? Hormones are chemical messages that allow slow communication between distant cells in the body. Hormones act on a time scale of several seconds to days. ! can control longer-term physiological processes ! not useful for controlling rapid actions 41 Endocrine cells Hormone-secreting cells are called “endocrine cells” . ! ...they secrete hormones into the interstitial space and/or blood stream In contrast, “exocrine” cells secrete substances into ducts that are connected to the outside world ! ...examples?
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Hydra Epithelial cells face the outside world Epithelial cells face the outside world ~60% of the recognized major human cell types are classified as epithelial cells Figure 42.1 Chemical Signaling Systems
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41 Hormones and Their Actions Some hormones act locally. Autocrine hormones act on the secreting cell itself. Paracrine hormones act on cells near the site of release. Paracrine hormones are released in tiny amounts, or are inactivated rapidly by enzymes, or are taken up efficiently by local cells. They never get into the circulatory system. 41 Hormones and Their Actions 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 can cause different responses in different types of cells. An example is epinephrine (=adrenaline). The nervous system reacts to an emergency very quickly and stimulates adrenal cells to secrete epinephrine. The result is the fight-or-flight response . 41 Hormones and Their Actions Epinephrine acts on different cells in the body: ! In the heart, it stimulates faster and stronger heartbeat. ! Blood vessels in some areas constrict to send more blood to muscles. ! In the liver, glycogen is broken down to glucose to provide quick energy. ! In fat tissue, fats are mobilized as another energy source.
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show movie: effects of epinephrine (1min) Figure 42.14 Some Hormones Can Activate a Variety of Signal Transduction Pathways Epinephrine Norepinephrine G-protein coupled receptors 41 Hormones can be classified into three main groups: ! 1) Peptides or proteins " Are water soluble and transported by vesicles out of the cell that made them. " Peptide hormone receptors are localized in the surface of target cells. " Examples: Growth hormone, insulin Groups of Hormones 41 Hormones can be classified into three main groups: ! 2) Steroid hormones " Are 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.
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