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Chapter_5_Chemical_Messengers - Chapter 5 Chemical...

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Chapter 5 Chemical Messengers I. Mechanisms of Intercellular Communication Direct Communication Through Gap Junctions Indirect Communication Through Chemical Messengers CAP JUNCTIONS Channels formed between 2 cells Direct electrical and metabolic coupling THERE IS NO RECEPTOR INVOLVED Common in smooth and cardiac muscle ALSO IN THE BRAIN Indirect Communication Through Chemical Messengers – fig 5.1ab All about the receptor; chemical messenger carries from the secretory cell into the receptor II. Chemical Messengers Functional Classification of Chemical Messengers Chemical Classification of Messengers Synthesis and Release of Chemical Messengers Transport of Messengers Functional Classification of Chemical Messengers Paracrines : released by cell, moves to target cell by diffusion (limited distance) Act on neighboring cells (fig 5.2a) Recpetor on the outside of cell membrane means that the messenger cannot go into the cell; the receptor will trigger the response of the cell Examples: Histamines: release with tissue damage and causes dilation of local blood vessels Clotting factors Testosterones: Moves from the Leydig cells into the seminiferous tubules (sperm is made) Prostaglandins Paracrine substance; ACT LOCALLY; very potent in small amounts Regulate celluar response to hormones Can activate or inhibi adenylate cyclase Controls cAMP production **ALTERS CELL’S RESPONSE TO HORMONES** Wide variety of functions Autocrines Act on cell that release it; the cell releases the messenger and also holds the receptor for reaction to take place (fig 5.2b) Secretory & Target cell
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Neurotransmitters Messengers of nervous system (fig 5.2c) Released from neuron by exocytosis Diffuse to very close target cell across a synapse Hormones Messenger of endocrine system Released from endocrine gland into blood Transported in blood to target Target cell = cells in body with receptors specific to the hormone Neurohormones Hormones released from the axons of neurons in the hypothalamus ADH & Oxytocin in posterior pituitary Inhibiting & releasing hormones into the portal system going to the anterior pituitary CYTOKINES Cytokines = peptides or proteins Can be transported in blood Released by most cell types Involved in cell development, differentiation, and immune response Often act on a wide range of targets CHEMICAL CLASSIFICATION OF MESSENGERS Chemical class determines mechanism of transport and mechanism of action on target cell Lipophilic/ Hydrophobic - can cross plasma membrane; recpetors are going to found inside the cell Lipophobic/ Hydrophilic
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