chapter47%20Chemical%20Signals%20in%20Animals-sv[1]

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Chapter 47 Chemical Signals in Animals 1 BLY122 A. Hunter from C. S. Major Chapter 47 Chemical Signals in Animals I. Cataloging Hormone Structure and Function A. There are six major categories of chemical signals: 1. Autocrine signals act on the cells that secrete them. a. Cytokines are released by cells and bind to the cells that release, amplifying their response to stimuli. b. Interleukin 2 is a cytokine that is released by and binds to T cells, helping them to fight infection. 2. Paracrine signals act locally by binding to neighboring cells. 3. Endocrine signals are hormones that travel through the blood to distant locations where they act on target cells in those tissues. 4. Neural signals are chemical messengers called neurotransmitters. 5. Neuroendocrine signals are released from neurons and act on distant cells. 6. Pheromones are signals that are released into the environment and act on cells of a different individual. B. How Do Researchers Identify a Hormone? 1. Research on hormones began with the discovery of secretin. a. Dilute HCl added to dog intestine caused secretion of enzymes from the pancreas, even though all nerves to the pancreas had been cut. b. Hypothesis: A chemical messenger traveled from the small intestine to the pancreas. c. Experiment: Inject an extract of the small intestine into the dog’s neck. d. Result: The dog’s pancreas secreted enzymes. e. The hormone secretin was isolated from the intestinal extract. 2. The first evidence that a tissue produces a hormone often comes from removing the tissue and observing the effects on the animal. a. Removal of dog adrenal gland reduced formation of glycogen in the liver. b. This implied that the adrenal gland produces a hormone that activates glycogen formation. 3. An extract is made from the tissue and injected into animals that lack the tissue. a. If the symptoms are alleviated, the extract contained a hormone. b. Injection experiments provide strong evidence of a chemical messenger. 4. The hormone is purified from the tissue extract. a. The purified molecule is injected into animals to determine if it alleviates the symptoms. b. These types of experiments demonstrated how corticosterone and cortisol (glucocorticoids) work. c. The adrenal medulla produces epinephrine (adrenaline) and norepinephrine. C. Chemical Characteristics of Hormones 1. Three general types of hormones are found in animals. a. Polypeptides b. Amino acid derivatives c. Steroids 2. Despite structural differences, all three types of hormones: a. Are secreted from the cells in which they are synthesized b. Act on target cells remote from their point of origin c. Are present and effective at extremely low concentrations 3. The three types of hormones differ in their interaction with target cells. a.
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