Chapter 47 - Chapter 47: Chemical Signals in Animals Key...

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Chapter 47: Chemical Signals in Animals Key Concepts Animals use at least six major types of chemical signals. Hormones are those chemical signals that are present in tiny concentrations and travel throughout the body to affect target cells. The information in hormonal signals helps animals respond to environmental change, develop as embryos, undergo sexual maturation, and achieve homeostasis. The production of a hormone is tightly regulated—usually by input from the nervous system. Some hormones bind to receptors inside target cells and change gene expression. Other hormones bind to receptors at the cell surface and lead to changes in protein activation. Section 47.1 Outline: Cell-to-Cell Signaling: An Overview Hormone Signaling Pathways What Are the Components of the Endocrine? Chemical Characteristics of Hormones How Do Researchers Identify a Hormone? o There are six major categories of chemical signals in animals (Figure 47.1): 1. Autocrine signals act on the same cell that secretes them. An example is cytokines ; most cytokines amplify the response of a cell to a stimulus. 2. Paracrine signals diffuse locally and act on neighboring cells. When the pancreatic hormones insulin , glucagon , and somatostatin act on nearby pancreatic cells, they ensure a smooth, steady response to changing blood glucose levels. 3. Endocrine signals are hormones produced by cells that may be organized into discrete organs called glands or that may be interspersed among the cells of other organs. 4. Neural signals are the chemical messengers called neurotransmitters . 5. Neuroendocrine signals are released from neurons but act on distant cells instead of acting at the adjacent synapse. 6. Pheromones are released into the environment and act on other individuals. Pheromones help coordinate reproduction in males and females or function in attracting mates.
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These six chemical messenger classes do not coincide with six structurally distinct classes of molecules. A particular family of molecules may function as endocrine, autocrine, and paracrine signals in the same individual. Hormone Signaling Pathways o Hormones act via three pathways (Figure 47.2): – The endocrine pathway can send hormones directly from endocrine cells to effector cells. – The neuroendocrine pathway can release neuroendocrine signals that act on effector cells directly. – In the neuroendocrine–to–endocrine pathway, neuroendocrine signals stimulate cells in the endocrine system, which then respond by producing an endocrine signal that acts on effector cells to trigger a response. o All three pathways are regulated by negative feedback , or feedback inhibition , in which the product of a process inhibits its production. o
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This note was uploaded on 03/14/2010 for the course CHEM 23454 taught by Professor Screwu during the Spring '10 term at Shoreline.

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Chapter 47 - Chapter 47: Chemical Signals in Animals Key...

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