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31 Cards in this Set

  • Front
  • Back
What are the sizes of arterioles?
50 micrometers diameter and below
What 2 things affect the radius of arterioles?
Local influences
Reflexes
How are arterioles tonically dilated?
By substances released by the endothelium which act on vascular smooth muscle (NO [nitric oxide] and PG)
An increase in shear stress leads to an increase in...
the release of NO and PG
Some vasolidator substances (e.g. ACh) cause dilation by...
releasing NO and PGs
What is myogenic tone?
Arterioles constrict in response to stretch (intravascular pressure)
What is the consequence of myogenic tone?
Maintains a high TPR, therefore high ABP
Which is greater - myogenic tone or tonic dilator influence of the endothelium?
Tonic dilator influence of the endothelium
In which tissues do you find the arterioles with the stronger myogenic responses?
brain and kidney arterioles
Why does blood flow remain constant over a wide range of mABP?
Myogenic responses to change in arterial resistance
Myogenic responses to change in arterial resistance
What if functional/active hyperaemia?
Increase in blood flow to tissues due to increased metabolic activity.
What is the aim of functional/active hyperaemia?
To match blood flow to metabolism
Where is function/active hyperaemia most important?
Tissues that show large changes in metabolic activity
skeletal muscle, cardiac muscle, brain
glandular tissue i.e. sweat glands and salivary glands
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)
Where do the substances act on arterioles in functional/active hyperaemia?
From the interstitial fluid
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
How is glandular tissue activated?
Sweat glands: activated by sympathetic cholinergic fibers

Salivary and GIT glands: activated by parasympathetic cholinergic fibres
What molecule acts as a vasodilator and where does it come from?
Bradykinin
Acinar cells secrete secretion + kallikrein
Kallikrein cleaves kininogen (plasma globulin) which produces bradykinin
What is the innervation of arterioles and where is it most/least dense?
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
What is the effect of increasing sympathetic activity to arterioles?
More release of NAdr
Stimulation of alpha adrenoreceptors
Vasoconstriction
What 2 effects can sympathetic fibers have?
Increase ABP by acting on all arterioles
redistribute CO by acting on a particular tissue
How do you neurologically vasodilate the arterioles?
tonic effect
remove the sympathetic activity
vasodilation
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
What do parasympathetic cholinergic fibers innervate?
arterioles in cerebral, coronary circulation
genitalia and reproductive tissues

vasodilation via mAChR

role in brain + coronary circulation unclear
When is parasympathetic cholinergic fiber activity in reproductive tissue important?
During intercourse, menstrual cycle and pregnancy

Increases blood flow to these tissues
What are catecholamines and where do they come from?
NAdr and Adr
Adrenal medulla
What does noradrenaline do?
weak constriction of all arterioles (alpha receptors)
Increase HR and contractility (beta 1 receptors)
What does adrenaline do?
vasodilation in skeletal muscle (beta 2 receptors)
vasoconstriction everywhere else (alpha receptors)
Increase HR and contractility (beta 1 receptors)
What do antidiuretic hormone and vasopressin do and where do they come from?
vasoconstriction
pituitary gland
important when ABP is low due to haemorrhage and dehydration
What does angiotensin do and where does it come from?
vasoconstriction
action of renin from kidney
important when ABP is low due to haemorrhage and dehydration
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