APK 2105C Lecture Notes - Lecture 31: Lipophobicity, Somnolence, Cell Membrane

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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
Much more common than direct communication
Some cell secretes chemical messenger (ex: hormones,
neurotransmitters, etc.)
Transported to another cell to bind with transmembrane receptor
Results in signal transduction (something happens in target cell as
Functional classes of chemical messengers
o Paracrines = reach target cells via simple diffusion
Only have to diffuse a short distancetarget cell is
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
Ach muscle cells
Causes contraction of skeletal muscle cells
o Hormones
Typically secreted by endocrine cells (sometimes
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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