smooth muscle Flashcards

1
Q

where is smooth muscle found

A

found in vascular systems, airways, GIT, genito-urinary tract

circular muscle in vascular systems important since it controls vasoconstriction/dilation

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2
Q

what are differences between smooth and skeletal muscle

A

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

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3
Q

how is smooth muscle regulated

A
autonomic and enteric NS
hormones
autacoids 
pacemaker cells
vascular endothelium
stretch of smooth muscle
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4
Q

what are types of smooth muscle?

A

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

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5
Q

what is the mechanism of smooth muscle contraction

A

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

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6
Q

what determines calcium concentration in vasculature

A

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

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7
Q

what is function of arterioles

A

contribute major part of vascular resistance, controlling distribution of blood to various organs

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8
Q

how might capillaries cause oedema

A

increase in capillary hydrostatic pressure or permeability can lead to oedema

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9
Q

how is vascular smooth muscle tone controlled

A

vascular smooth muscle tone in arterioles is controlled by sympathetic nervous system and local factors such as metabolic need

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10
Q

what effect does stretching have on vascular smooth muscle

A

stretching can cause contraction from the muscle itself (myogenic response)

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11
Q

how does electrical stimulation effect vascular smooth muscle

A

causes contraction by opening voltage gated L-type calcium channels

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12
Q

what effect do ergot alkaloids have on smooth muscle

A

can cause contractions

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13
Q

how do alpha 1 antagonists affect vasculature

A

such as prazosin, cause vasodilation and fall in blood pressure

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14
Q

how do indirect acting vascoconstrictors work

A

they are indirect sympathomimetics, cause NA release without exciting nerve, such as amphetamine

cocaine blocks uptake of NA into nerve terminals

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15
Q

what receptors do noradrenaline target in vasculature

A

alpha 1, coupled via Gq, causes IP3 production via PLC

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16
Q

name some vasodilators, what receptors are their targets

A

acetylcholine: M3
histamine: H1
ADP/ATP: P2Y
bradykinin: BK2
substance P: NK1
CGRP: CGRP1

17
Q

what are uses of vasodilators therapeutically

A

Gs agonists:
beta 2 agonists and prostacyclin analogues

beta 2 agonists e.g: salbutamol: asthma and premature labour

prostacyclin analogues: e.g iloprost: pulmonary arterial hypertension

alpha 1 antagonist: e.g prazosin: use: treatment of hypertension and benign prostatic hyperplasia

muscarinic antagonists: e.g atropine: use asthma, urinary incontinence, mydriasis

AT1 antagonists: e.g isoartan, use: hypertension

calcium channel blockers: e.g nifedipine, use: hypertension

potassium channel openers: e.g minoxidil, use: severe hypertension