Ch. 5 Chemical Messengers, new

Ch. 5 Chemical Messengers, new - Ch. 5 Chemical Messengers...

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Ch. 5 Chemical Messengers 1) Mechanisms of Intercellular Communication a) Gap Junctions: Link adjacent cells and are formed by plasma membrane proteins, called connexins , that form structures called connexons (bridges, I think), that in turn allow ions to pass through with electrical signals b) Chemical Messengers (aka ligands) i) The binding of messengers to receptors produces a response in the target cell through a variety of mechanisms referred to as signal transduction ii) The strength of the target cell response increases as the number of bound receptors increases; the number of bound receptors depends on the concentration of messenger in the interstitial fluid and the concentration of receptors on the target cell (duh) 2) Chemical Messengers a) Functional Classifications i) Paracrines are chemicals that communicate with neighboring cells; it must be able to reach the target cell by simple diffusion (1) Growth factors – proteins that simulate differentiation among cells (2) clotting factors – help form blood clots! (3) Cytokines – peptides released from immune cells that help coordinate the body’s defense (4) Histamine (does this fall under another subcategory?), which is secreted by mast cells, and responsible for inflammation ii) Autocrines are similar to paracrines except they act on the cell that secrets them iii) Neurotransmitters are chemicals released into interstitial fluid from neurons (1) These are released from the axon terminal of the neuron, which is very close to the target cell
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neurotransmitters is called synaptic signaling (3) Upon release from the presynaptic neuron, the neuroT quickly diffuses the short distance from the axon terminal and binds to receptors on the postsynaptic cell, triggering a response (4) E.g. : acetylcholine, which triggers contraction of skeletal muscles iv) Hormones are chemicals released from the endocrine glands which can travel long distances through the bloodstream (1) E.g insulin, which blocks glucose uptake and increases blood glucose v) Neurohormones are released by neurosecretory cells through mechanisms similar to the neurotransmitter release, but then diffuse into the bloodstream (1) E.g. vasopressin, or ADH, which affects the volume of urine excreted in the kidneys b) Chemical Classification of Messengers 1. Lipophilic are lipid-soluble and readily cross the plasma membrane but do not dissolve in water; hydrophilic, or lipiophobic, molecules are water-soluble and do not cross the plasma membrane ii) Amino Acid Messengers (1) Four amino acids are classified as chemical messengers because they function as neurotransmitters in the brain and spinal cord: glutamate, aspartate, glycine, gamma-aminobutryic acis (GABA); the first three are among the 20 that are used in protein synthesis, whereas GABA belongs to a different class of amino acids (2) Lipophobic, dissolve in water but do not cross membranes iii) Amine Messengers
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Ch. 5 Chemical Messengers, new - Ch. 5 Chemical Messengers...

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