smooth muscle Flashcards
where is smooth muscle found
found in vascular systems, airways, GIT, genito-urinary tract
circular muscle in vascular systems important since it controls vasoconstriction/dilation
what are differences between smooth and skeletal muscle
smooth muscle contains contractile proteins actin and myosin, lack troponin found in skeletal muscle
in skeletal muscle actin and myosin are highly organised, in smooth muscle they have a more random appearance
smooth muscle only undergoes slow sustained tonic contractions
how is smooth muscle regulated
autonomic and enteric NS hormones autacoids pacemaker cells vascular endothelium stretch of smooth muscle
what are types of smooth muscle?
single unit: only some cells are innervated, depolarisation spreads from these cells through to other cells through gap junctions, can also be initiated by pacemaker cells
multi unit: these are unusual (found in the eye), each cell is individually innervated, there is little or no communication between cells
what is the mechanism of smooth muscle contraction
increase in free intracellular calcium is trigger for contraction
calcium binds to calmodulin
calcium-calmodulin complex activates myosin light chain kinase (MLCK), an enzyme which phosphorylates myosin light chains in presence of ATP
myosin light chains are 20-kd regulatory subunits found on the myosin heads
phosphorylation of myosin light chains leads to cross bridge formation between myosin heads and actin filaments
what determines calcium concentration in vasculature
intraceullalar concentration of calcium is dependent upon balance between calcium that enters cell from external environment
calcium is released from intracellular storage sites such as sarcoplasmic reticulum
removal is either back into storage sites or out of cell
calcium is retrieved by the sarcoplasmic reticulum via an ATP dependent calcium pump
calcium is either removed from cell via ATP calcium pump or calcium sodium exchanger
what is function of arterioles
contribute major part of vascular resistance, controlling distribution of blood to various organs
how might capillaries cause oedema
increase in capillary hydrostatic pressure or permeability can lead to oedema
how is vascular smooth muscle tone controlled
vascular smooth muscle tone in arterioles is controlled by sympathetic nervous system and local factors such as metabolic need
what effect does stretching have on vascular smooth muscle
stretching can cause contraction from the muscle itself (myogenic response)
how does electrical stimulation effect vascular smooth muscle
causes contraction by opening voltage gated L-type calcium channels
what effect do ergot alkaloids have on smooth muscle
can cause contractions
how do alpha 1 antagonists affect vasculature
such as prazosin, cause vasodilation and fall in blood pressure
how do indirect acting vascoconstrictors work
they are indirect sympathomimetics, cause NA release without exciting nerve, such as amphetamine
cocaine blocks uptake of NA into nerve terminals
what receptors do noradrenaline target in vasculature
alpha 1, coupled via Gq, causes IP3 production via PLC
