BIOB30 Ch6 (179-196).docx

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Biological Sciences
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Joanne Nash

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BIOB30Chapter 6 1791961Communication Integration and HomeostasisCellToCell CommunicationHuman body is made of about 75 trillion cellsThere are two basic types of physiological signalsoElectrical signalschanges in a cells membrane potentialoChemical signalsmolecules secreted by cells into the extracellular fluidMost of the bodies communicationTarget cells or targetscells that receive chemical or electrical signals4 basic methods for celltocell communication1Gap functionsallow direct cytoplasmic transfer of electrical and chemical signals between adjacent cells2Contactdependent signalsoccur when the surface molecules on one cell membrane bind to surface molecules on another cells membrane3Local communicationchemicals diffuse through extracellular fluid4Longdistance communicationcombination of electrical signals carried by nerve cells and chemical signals transported in the bloodA single molecule can be used in more than one type eg local and long distance communicationWhen gap junctions are open small molecules can diffuse from one cytoplasm to the otheroEg amino acids ATP and cyclic AMP diffuse from one cytoplasm to the otheroLarger molecules cannot passoMovement of molecules through gap junctions can be modulated or shut offoElectrical signals can pass directly from cell to celloGap functions vary across tissues select different things and are found in almost every mammal cell type2ContactDependent Signals Require CelltoCell ContactContactdependent signaling occurs in the immune system and during growth and developmentDuring development nerve cells send out long extensions that must grow from the central axis of the body to the distal ends of the limbsCAMscell adhesion molecules with a role in celltocell adhesion and celltocell signalingoUses its links to the cytoskeleton and intracellular enzymes to transfer signals in both directions across cell membranesParacrine and Autocrine Signals Carry Out Local CommunicationParacrine signala chemical that acts on cells in the immediate vicinity of the cell that secreted the signalAutocrine signala chemical signal that acts on the cell that secreted itSome molecules act as both paracrine and autocrine signalsParacrine and autocrine reach target cells by diffusing through the interstitial fluidoThis effect is restricted to adjacent cells because distance is a limiting factor for diffusionHistaminea paracrine molecule released from damaged cellsoRaised skin around wound do in part to thisoMakes capillaries around the injury more permeable to white blood cells and antibodiesLongDistance Communication May Be Electrical or ChemicalHormoneschemicals signals that are secreted into the blood and distributed all over the body by the circulationoCommunication used by the endocrine systemoHormones come in contact with most cells but only those with receptors for them are target cells
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