1-Smooth Muscle Physiology Flashcards
development
- mesoderm
- endothelial intermediates
- mesenchymal progenitors
- immature smooth muscle
- mature smooth that aggregate but not fuse
organization
large mononucleated with non-uniform arrangement aka not striated
no z discs instead dense bodies @ cytoplasm for thin filaments or dense plaques @ cell membrane for thick
-linked to each other by intermed filaments
sarcolemma invaginations aka caveolae to inc surface area and lined with receptors instead of t tubules
function in GI
@ upper GI (esophagus and esoph sphincter) important to move food to stomach and regulate entry
@stomach is phasically active/rhythmic to mix food with gastric juices
esoph normally relaxed, sphincter normally contracted
phasically- looks like waves
function in blood vessels and airways
normally partially active to keep open/patent
-if not constantly active then airways/vessels collapse/diff to maintain blood pressure
electrophysiological properties
- action potential sole stimulus for force
- oscillations in membrane potential = gen of action potential = force
- oscillations in membrane potential alter force w/o action potential
- hormones or duge alter force indep of membrane potential
basically diverse- force from membrane pot with or without AP
myogenic response
mechano-dependent response in small A’s and arterioles in cerebral, mesentaric, cardiac, renal beds aka autoregulation blood flow when BP changes
-inc transmural pressure> vessel diameter inc >stretch sensitive ion channels open > inc intracell Ca > vascular smooth contracts to dec blood vessel diameter
myogenic response
mechano-dependent response in small A’s and arterioles in cerebral, mesentaric, cardiac, renal beds aka autoregulation blood flow
-inc transmural pressure> vessel diameter inc >stretch sensitive ion channels open > inc intracell Ca > vascular smooth contracts to dec blood vessel diameter
innervation
general
no motor end plate so instead varicosities release neurotransmitter to diffuse across diffuse junction
varicosities look like beads
methods of contraction
- single unit- contract in unison due to abundance of gap junctions to permit transmission of depolarization/Ca ions
-GI and urogenital tract - multiunit- contraction dependent on local neurotrans release
-airways and vasculature
dual innervation GI
multi converging inputs to control activity
1. intrinsic- enteric system in lining of tract to sense mechanical/chem conditions and control motility via cells of cajal (ICC)
2. autonomic- para/sympathetics to alter motility by regulating ICC
ICC has intrinsic pacemaker activity for rhythmic contractions,
contraction steps
- Ca influx into cytoplasm
- activation of calmodulin (Ca binding protein)
- CaM activates myosin light chain kinase MLCK
- MLCK phosphorylates regulatory light chain on myosin neck (thick fila)
- cross bridge cycle
- free Ca pumped out or sequestered in SR
myosin light chain phosphatase
MLCP reverses MLCK by removing phosphate from myosin
consititutively active but modulated by hormones/neurotrans
cross bridge cycle
- phosphorylation of light chain changes conformation so myosin head bind actin
- ADP and Pi are lost
- power stroke
- new ATP binds myosin head so detach from actin
- ATP hydrolyzed and head cocked position to repeat cycle
excitation stimuli
multi stimuli
1. neurotrans from nerve cells in close proximity (neural)
2. circulating hormones (endocrine)
3. substances from nearby cells (paracrine)
ways to initiate excitation
extracellular
- voltage Ca channels LTCC, need depolarization
- receptor mediated- need ligand
both result in conformational change for extracell Ca to flow in
