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2 types of intracellular communication
- 1. Direct (touching)- through gap junctions connecting adjacent cells
- 2. Indirect- through chemical messengers
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3 functional classes of chemical messengers
- Paracrines
- Neurotransmitters
- Hormones
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Paracrine
- Chemicals that communicate with neighboring cells (tissue level)
- Short distance
- Through diffusion
- Autocrines: chemicals that act on the same cell that secreted them
- (growth factor, clotting factors, cytokines)
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Neurotransmitters
- Chemicals released by neurons -> synapse -> target cell
- Short distance
- Through diffusion
- (acetylcholine)
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Hormones
- Chemicals released by endocrine glands or neurosecretory neuron -> ISF -> blood
- Long distance
- Via blood
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List the 5 chemical classes
- Amino acids
- Amines
- Peptide
- Steroids
- Ecosinoids
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Amino Acids
- Basic monomer for proteins
- Lipophobic
- Functional class: Neurotransmitter
- (aspertate, glycine, GABA)
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Amines
- Derived from amino acids
- Contain NH2 group
- Lipophobic
- Functional Class:paracrine, NT, Hormone
- (Dopamine, serotonin, norepi, epi, histamine)
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Peptide and Proteins
- Chain of amino acids
- Most common
- Lipophobic
- Functional Class: Paracrines, NT, Hormones
- (cytokines)
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Steroids
- Derived from cholesterol
- Lipophillic
- Functional class: HORMONES ONLY
- (testosterone, cortisol, aldosterone, progesterone)
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Eicosanoids
- Derived from fatty acids (arachidonic acid)
- Lipophillic
- Functional Class: Paracrines ONLY
- (prostaglandins, thromboxanes, leukotrienes)
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Signal transduction
- Source releases ligand
- Travels to target cell
- Ligands then bind to receptors either on/in cell -> functional change
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Properties of cell receptors
- Messenger specific
- Multiple receptor types present in/on cell
- The more interactions the greater the effect
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What factors affect interaction with chemical messengers
- Messenger concentration
- Number of receptors
- Affinity (how much the receptor WANTS to bind)
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Intracellular Mediated response
- Receptor is inside cell
- Messenger in lipophillic
- For gene activation or inhibition
- Effects are slow but long lasting
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Membrane Receptor Mediated Response
- Receptors are on membrane
- Messengers are lipophobic
- 3 categories: Channel linked, Enzyme linked, and G protein linked
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Channel- Linked membrane Mediated response
- Receptors act as a channel
- Once activated by messenger, channel opens
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Enzyme Linked membrane mediated response
- Receptor acts as an intracellular enzyme
- Activates enzymes
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G Protein linked membrane mediated response
- Receptor is linked to a group of proteins (G-group) in membrane
- Activates G protein -> activates another membrane bound protein (channels or enzymes)
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Second messengers
- Intracellular molecule produced/ entered as a response to an extracellular messenger
- Amplifies signal
- Most common is Ca2+
- Most important is cAMP.
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Long distance communication
- Required to regulate all body activities
- By: endocrine system to release hormones (Slow) or Nervous system to target cells with NT (fast)
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