Coordination of Body FunctionsHeyer 1HormonesRespond toStimuliA key characteristic of LifeRespond to StimulistimulussensorIntegration&CognitioneffectorresponseRespond to Stimuli:Nervous SystemstimulussensoreffectorSensoryNervesMotorNervesCentralNervous System= specificmuscleor glandresponseRespond to Stimuli:Endocrine SystemstimulussensorEndocrineGlandeffectorresponseeffectorresponseeffectorresponseNervousSystemvia bloodstreameffector= varioustargettissuesthroughoutthe bodyresponseCellular Communicationby direct cell-cell contactPlasma membranesPlasmodesmatabetween plant cellsGap junctionsbetween animal cells(a) Communicating cell junctions.Figure 11.3(b) Cell-cell recognition.Coordination of Body FunctionsHeyer 2Cellular Communicationvia chemical messengers1. Release: initiator cell secretes (exocytosis) a chemicalmessenger (signal molecules).2. Reception: messenger molecules bind to receptors (bindingproteins) on target cells.3. Transduction: binding of signal molecule to receptor causes achange in the structure and activity of the receptor protein.4. Response: the altered receptor protein initiates a change in theenzymatic and/or transcriptional activity of the target cell.EXTRACELLULARFLUIDReceptorSignal moleculeRelay molecules in a signaltransduction pathwayPLASMA MEMBRANECYTOPLASMActivationof cellularresponseFigure 11.5Reception2Transduction3Response4Cellular Communication —Chemical Messengers & Receptors1. Synapse: the messenger(neurotransmitter) diffusesacross a small gap between aneuron and its target cell.2. Paracrine: the messenger (localregulator, paracrine factor,growth factor, cytokine) diffusesto nearby target cells.3. Endocrine: the messenger(hormone) diffuses into thebloodstream to travel to targetcells all over the body.4. Exocrine: the messenger(pheromone) diffuses outside ofthe organism’s body to travel toanother organism.One cell releases a molecule(messenger) that initiates achange in another cell bybinding to a protein receptoron that target cell.Major Classes ofBiochemical Signal MoleculesI. Amino acid origina) Amino acidsb) Modified amino acids — bioaminesc) Oligopeptidesd) ProteinsII. Fatty acid origina) Derived from cholesterol — steroidsb) Derived from arachidonic acid — prostaglandinsIII. Dissolved gasesa) Nitric oxide (NO)b) Carbon monoxide (CO)c) Ethylene (H2C=CH2)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 proteinreceptor on cell surface.• Lipophilic signal molecules — steroids & thyroid hormones– Water insoluble. Must be transported in plasma by carrier proteins.– Carrier proteins also protect hormone from degradation. Half-lifelonger: 1–2 hours.– Released from carrier protein to diffuse across cell membrane intotarget cells. Act by binding to intracellular protein receptors.Mechanisms of HydrophilicSignal Molecule 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 proteinreceptor on cell surface.1. Since the signal molecule (first messenger) does not enter the cell,the receptor/ligand complex causes a second messenger to beproduced or released within the cell.2. This second messenger acts as a coenzyme/cofactor to regulatecellular enzymes fi change the activity of the cell.Signal transduction pathways viasecond messengersAct as cofactors/coenzymes to modulateintracellular enzyme activitySignal molecule (first messenger)ActiveenzymeInactiveenzymeReceptorActivated relaymolecule (second messenger)Coordination of Body FunctionsHeyer 3Intracellular Receptors for LipophilicSignalMolecules1. Steroid diffuses acrossmembrane into cell2. Intracellularreceptor/steroid complexbinds to DNA3. Transcription factor —turns genes on/off4. Change nature of the cell(Longer-lasting effect)Mechanisms of Messenger Action• Hydrophilic signal molecules — most amino acid class– Bind to membrane receptors on cell surface– Primary effect: turn enzymes on/off Æ D activity of cell.– Secondary effect: enzymes may produce or activate transcriptionfactors Æ turn genes on/off.• Lipophilic signal molecules — steroids & thyroid hormones– Bind to intracellular receptors in cytoplasm or nucleoplasm– Primary effect: turn genes on/off Æ D nature of cell.– Secondary effect: gene expression may produce or activateenzymes Æ turn metabolic pathways on/off.Modulation of signal effect•Priming (upregulation)Signal bindsÆ more receptors synthesizedØmore hormone can bind cell•Desensitization (downregulation)Prolonged exposure to high signal moleculelevels can reduce receptor expression.* Downregulation may be avoided by pulsatilesecretion of the messenger.•Receptor-mediated endocytosisReceptor-ligand complex internalized on vesicleto enhance duration of effect.Compound messenger effects• Antagonistic:– Insulin stimulates lipogenesis; glucagon stimulateslipolysis.• Synergistic:– Both glucagon and epinephrine receptors cause theproduction of cAMP second messenger in the same cell.• Complementary:– FSH and testosterone stimulate different parts ofspermatogenesis.• Permissive:– Glucocorticoids stimulate the synthesis of enzymes thatare regulated by epinephrine.Electrochemical communicationNeurons —1. Membrane potential2. Excitability3. Conduction4. TransmissionNeurons conduct electrochemical impulsesand transmit messages to other cellsCoordination of Body FunctionsHeyer 4Neuron: A Nerve Cell• Dendrites: increase surface area of cellbody to receive signals.• Cell body: location of nucleus and mostorganelles.• Axon: conducts electrochemicalimpulses.• Termini: transmit message to target cell.Membranes of neurons areelectrically charged• Chemical gradients ofions produce electricalgradients• Inside of the cell isnegative relative to theoutside of the cell.• Electrical gradientproduces a membranepotential (voltage)Axons are Polarized:Resting Potential• Na is Not allowed in; K is Kontained.23Resting Membrane Potential• At equilibrium, inside of the cellmembrane would have a higher[negative charges] than the outside.• Potential difference:– Magnitude of difference in charge onthe 2 sides of the membrane..• Depends upon 2 factors:– Ratio of the concentrations of each ionon the 2 sides of the plasma membrane.– Specific permeability of