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31 Cards in this Set
- Front
- Back
What are the sizes of arterioles?
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50 micrometers diameter and below
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What 2 things affect the radius of arterioles?
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Local influences
Reflexes |
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How are arterioles tonically dilated?
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By substances released by the endothelium which act on vascular smooth muscle (NO [nitric oxide] and PG)
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An increase in shear stress leads to an increase in...
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the release of NO and PG
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Some vasolidator substances (e.g. ACh) cause dilation by...
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releasing NO and PGs
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What is myogenic tone?
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Arterioles constrict in response to stretch (intravascular pressure)
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What is the consequence of myogenic tone?
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Maintains a high TPR, therefore high ABP
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Which is greater - myogenic tone or tonic dilator influence of the endothelium?
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Tonic dilator influence of the endothelium
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In which tissues do you find the arterioles with the stronger myogenic responses?
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brain and kidney arterioles
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Why does blood flow remain constant over a wide range of mABP?
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Myogenic responses to change in arterial resistance
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What if functional/active hyperaemia?
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Increase in blood flow to tissues due to increased metabolic activity.
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What is the aim of functional/active hyperaemia?
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To match blood flow to metabolism
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Where is function/active hyperaemia most important?
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Tissues that show large changes in metabolic activity
skeletal muscle, cardiac muscle, brain glandular tissue i.e. sweat glands and salivary glands |
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How much does blood flow increase in:
skeletal muscle during strenuous exercise? cardiac muscle during a large increase increase in cardiac work? brain during increases in neurone activity? |
25
5 3 (regionally) |
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Where do the substances act on arterioles in functional/active hyperaemia?
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From the interstitial fluid
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Which substances are considered to be the most important vasodilators in:
skeletal muscle cardiac muscle brain |
skeletal; high K+ (muscle action potential) and Pi + adenosine (ATP breakdown)
cardiac: high levels adenosine brain: high K+ (AP), CO2, H+ and adenosine, low O2 |
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How is glandular tissue activated?
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Sweat glands: activated by sympathetic cholinergic fibers
Salivary and GIT glands: activated by parasympathetic cholinergic fibres |
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What molecule acts as a vasodilator and where does it come from?
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Bradykinin
Acinar cells secrete secretion + kallikrein Kallikrein cleaves kininogen (plasma globulin) which produces bradykinin |
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What is the innervation of arterioles and where is it most/least dense?
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sympathetic noradnergic fibres
most dense in skin least dense in brain, cardiac muscle and lungs It can be overcome by functional hyperaemia in exercising muscle and cardiac muscle |
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What is the effect of increasing sympathetic activity to arterioles?
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More release of NAdr
Stimulation of alpha adrenoreceptors Vasoconstriction |
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What 2 effects can sympathetic fibers have?
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Increase ABP by acting on all arterioles
redistribute CO by acting on a particular tissue |
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How do you neurologically vasodilate the arterioles?
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tonic effect
remove the sympathetic activity vasodilation |
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What do sympathetic cholinergic fibers supply?
What do they do? |
skeletal muscle
in addition to sympathetic noradnergic fibres existance in humans is doubted vasodilation via mAChR - only active in emotional stress |
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What do parasympathetic cholinergic fibers innervate?
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arterioles in cerebral, coronary circulation
genitalia and reproductive tissues vasodilation via mAChR role in brain + coronary circulation unclear |
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When is parasympathetic cholinergic fiber activity in reproductive tissue important?
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During intercourse, menstrual cycle and pregnancy
Increases blood flow to these tissues |
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What are catecholamines and where do they come from?
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NAdr and Adr
Adrenal medulla |
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What does noradrenaline do?
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weak constriction of all arterioles (alpha receptors)
Increase HR and contractility (beta 1 receptors) |
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What does adrenaline do?
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vasodilation in skeletal muscle (beta 2 receptors)
vasoconstriction everywhere else (alpha receptors) Increase HR and contractility (beta 1 receptors) |
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What do antidiuretic hormone and vasopressin do and where do they come from?
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vasoconstriction
pituitary gland important when ABP is low due to haemorrhage and dehydration |
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What does angiotensin do and where does it come from?
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vasoconstriction
action of renin from kidney important when ABP is low due to haemorrhage and dehydration |
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5-hydroxytryptamine (5-HT) and serotonin
Where do they come from? What do they do? |
release from activated platelets at site of wound
vasoconstrict at site of wound reducing blood loss |