Chapter 6a Communication Integration and Homeostasis 2013 Pearson Education Inc About This Chapter Cell to cell communication Signal pathways Novel signal molecules Modulation of signal pathways Homeostatic reflex pathways 2013 Pearson Education Inc Cell to Cell Communication Overview Physiological signals Electrical signals Chemical signals Changes in the membrane potential of a cell Secreted by cells into ECF Responsible for most communication within the body Target cells or targets respond to signals 2013 Pearson Education Inc Figure 6 1a ESSENTIALS Communication in the Body Gap junctions form direct cytoplasmic connections between adjacent cells Figure 6 1b ESSENTIALS Communication in the Body Contact dependent signals require interaction between membrane molecules on two cells Figure 6 1c ESSENTIALS Communication in the Body Receptor Autocrine signals act on the same cell that secreted them Paracrine signals are secreted by one cell and diffuse to adjacent cells Figure 6 1d ESSENTIALS Communication in the Body Blood Endocrine cell Cell without receptor No response Cell with receptor Target cell Response Hormones are secreted by endocrine glands or cells into the blood Only target cells with receptors for the hormone respond to the signal Long Distance Communication The nervous system uses a combination of chemical and electrical signals for long distance cell to cell communication Neurocrines are chemical signals secreted by neurons Neurotransmitters Neuromodulators Neurohormones 2013 Pearson Education Inc Figure 6 1e ESSENTIALS Communication in the Body Electrical signal Neuron Target cell Response Neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to the target cell Figure 6 1f ESSENTIALS Communication in the Body Neuron Blood Neurohormones are chemicals released by neurons into the blood for action at distant targets Cell without receptor Cell with receptor No response Response Cytokines Cytokines may act as both local and long distance All nucleated cells synthesize and secrete cytokines in signals response to stimuli In development and differentiation cytokines usually function as autocrine or paracrine signals In stress and inflammation some cytokines may act on relatively distant targets 2013 Pearson Education Inc Figure 6 2 Signal Pathways Most signal pathways consist of the 5 steps shown Use the shapes and colors of the steps shown here to identify the pattern in later illustrations Signal molecule binds to Membrane receptor protein activates Intracellular signal molecules alter Target proteins create Response Figure 6 3a Target cell receptors may be located on the cell surface or inside the cell 1 of 3 Intracellular Signal Receptors Receptor in cytosol Receptor in nucleus Lipophilic signal molecules diffuse through the cell membrane Binding to cytosolic or nuclear receptors triggers Slower responses related to changes in gene activity Figure 6 3b Target cell receptors may be located on the cell surface or inside the cell 2 of 3 Cell Membrane Receptors Extracellular signal molecule binds to a cell membrane receptor Binding triggers Rapid cellular responses Figure 6 3c Target cell receptors may be located on the cell surface or inside the cell 3 of 3 Four Categories of Membrane Receptors Extracellular signal molecules ECF ICF Channel Receptor Receptor Integrin Enzyme G protein Receptor channel Ligand binding opens or closes the channel Receptor enzyme G protein coupled receptor Integrin receptor Ligand binding to a receptor enzyme activates an intracellular enzyme Ligand binding to a G protein coupled receptor opens an ion channel or alters enzyme activity Ligand binding to integrin receptors alters the cytoskeleton Cell membrane Anchor protein Cytoskeleton Figure 6 4 Signal transduction Signal transduction converts one form of signal into a different form External signal Receptor Transducer Amplifier Response Radio waves A radio contains an antenna to receive signals a transducer that converts radio waves into sound waves and an amplifier to increase the strength of the signal Radio Sound waves Figure 6 5a Biological signal transduction 1 of 2 Basic Signal Transduction Signal molecule binds to Membrane receptor protein activates Intracellular signal molecules alter Target proteins create First messenger Transducer Second messenger system Targets Response Response Figure 6 5b Biological signal transduction 2 of 2 Transduction Pathways Extracellular fluid Intracellular fluid Signal molecule binds to Membrane receptor initiates Signal transduction by proteins Ion channel Amplifier enzymes alter Second messenger molecules Protein kinases Increase intracellular Ca2 Phosphorylated Calcium binding proteins proteins Cell response Figure 6 6a ESSENTIALS Signal Transduction Signal transduction pathways form a cascade Signal Inactive A Active A Inactive B Active B Inactive C Active C Substrate Conversion of substrate to product is the final step of the cascade Product Figure 6 6b ESSENTIALS Signal Transduction Signal amplification allows a small amount of signal to have a large effect Receptor ligand complex activates an amplifier enzyme AE Extracellular Fluid Cell membrane Intracellular Fluid L R AE One ligand is amplified into many intracellular molecules Figure 6 6c ESSENTIALS Signal Transduction Second messenger pathways SECOND MESSENGER Nucleotides cAMP ATP cGMP GTP Lipid derived Ions IP3 DAG Ca2 MADE FROM AMPLIFIER ENZYME LINKED TO ACTION EFFECTS Adenylyl cyclase membrane GPCR Activates protein kinases especially PKA Binds to ion channels Phosphorylates proteins Alters channel opening Guanylyl cyclase membrane Guanylyl cyclase cytosol Receptor enzyme Activates protein kinases especially PKG Phosphorylates proteins Nitric oxide NO Binds to ion channels Alters channel opening Membrane phospholipids Phospholipase C membrane GPCR Releases Ca2 from intracellular stores See Ca2 effects below Activates protein kinase C Phosphorylates proteins Binds to calmodulin Binds to other proteins Alters enzyme activity Exocytosis muscle contraction cyto skeleton movement channel opening GPCR G protein coupled receptor IP3 Inositol trisphosphage DAG idacylglycerol Tyrosine Kinase Receptor Tyrosine kinase TK transfers a phosphate group from ATP to a tyrosine an amino acid of a protein Figure 6 7 ECF Signal molecule binds to surface receptor Tyrosine kinase on cytoplasmic side L R TK Cell membrane Active binding site ATP Protein Protein ADP Phosphorylated