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B6A11Coordinate - Coordination of Body Functions Respond to...

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Coordination of Body Functions Heyer 1 Hormones Respond to Stimuli A key characteristic of Life Respond to Stimuli stimulus sensor Integration & Cognition effector response Respond to Stimuli: Nervous System stimulus sensor effector Sensory Nerves Motor Nerves Central Nervous System = specific muscle or gland response Respond to Stimuli: Endocrine System stimulus sensor Endocrine Gland effector response effector response effector response Nervous System via bloodstream effector = various target tissues throughout the body response Cellular Communication by direct cell-cell contact Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells (a) Communicating cell junctions. Figure 11.3 (b) Cell-cell recognition.
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Coordination of Body Functions Heyer 2 Cellular Communication via chemical messengers 1. Release: initiator cell secretes (exocytosis) a chemical messenger (signal molecules). 2. Reception: messenger molecules bind to receptors (binding proteins) on target cells. 3. Transduction: binding of signal molecule to receptor causes a change in the structure and activity of the receptor protein. 4. Response: the altered receptor protein initiates a change in the enzymatic and/or transcriptional activity of the target cell. EXTRACELLULAR FLUID Receptor Signal molecule Relay molecules in a signal transduction pathway PLASMA MEMBRANE CYTOPLASM Activation of cellular response Figure 11.5 Reception 2 Transduction 3 Response 4 Cellular Communication — Chemical Messengers & Receptors 1. Synapse: the messenger (neurotransmitter) diffuses across a small gap between a neuron and its target cell. 2. Paracrine: the messenger (local regulator, paracrine factor, growth factor, cytokine) diffuses to nearby target cells. 3. Endocrine: the messenger (hormone) diffuses into the bloodstream to travel to target cells all over the body. 4. Exocrine: the messenger (pheromone) diffuses outside of the organism’s body to travel to another organism. One cell releases a molecule (messenger) that initiates a change in another cell by binding to a protein receptor on that target cell. Major Classes of Biochemical Signal Molecules I. Amino acid origin a) Amino acids b) Modified amino acids — bioamines c) Oligopeptides d) Proteins II. Fatty acid origin a) Derived from cholesterol — steroid s b) Derived from arachidonic acid — prostaglandins III. Dissolved gases a) Nitric oxide (NO) b) Carbon monoxide (CO) c) Ethylene (H 2 C=CH 2 ) Mechanisms of Messenger Action • Hydrophilic signal molecules — most amino acid class – Water soluble. – Short half-life: minutes – Do not enter target cells. Act as ligand by binding to protein receptor on cell surface. • Lipophilic signal molecules — steroids & thyroid hormones – Water insoluble. Must be transported in plasma by carrier proteins.
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