APK 2105C Lecture Notes - Lecture 31: Lipophobicity, Somnolence, Cell Membrane
5 Jun 2018
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Chapter 5, Lecture 1
Chemical Messengers
• Mechanisms of intercellular communication
o Only a few mechanisms for all cells to communicate with each other
▪ Direct communication between cells
• Gap junctions = transmembrane proteins that fuse together to
form a tunnel between cells
• Electrical coupling
• Metabolic coupling
• Relatively uncommon
▪ Communication via chemical messengers
• Ligand = chemical messenger molecule which binds proteins
reversibly
• Much more common than direct communication
• Some cell secretes chemical messenger (ex: hormones,
neurotransmitters, etc.)
• Transported to another cell to bind with transmembrane receptor
protein
• Results in signal transduction (something happens in target cell as
result)
• Functional classes of chemical messengers
o Paracrines = reach target cells via simple diffusion
▪ Only have to diffuse a short distance—target cell is
nearby
o Autocrines = act on the cell that secreted them
▪ Subclass of paracrines
o Neurotransmitters = chemical messengers released from
neurotransmitters (axons)
▪ Neurotransmitter is exocytosed and diffuses to
target cell
▪ Synapse = space between neuron and target cell
▪ Synaptic signaling
▪ Synapse-specific = neurotransmitters affect certain
cells
▪ Ach → muscle cells
• Causes contraction of skeletal muscle cells
o Hormones
▪ Typically secreted by endocrine cells (sometimes
neurons)
▪ Flow long distance through blood
▪ Get delivered to all cells, but only cells with
receptors will respond to the hormone
• Clinical correlation = histamine
o Mast cells secrete histamine
▪ Histamine is a paracrine
▪ Secreted right into the cells that are affected
o Histamine is part of the inflammation response
▪ Increases blood flow to the area
▪ Causes capillaries to become more leaky
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