Arterioles: regulate blood flow to Tissues

Question 1

Arterioles: regulate blood flow to Tissues

Answer 1

– Branches of an artery within an organ
– High resistance vessels due to small radius
– Profound fall in mean pressure as blood flows through these small vessels (93>37 mmHg)
– This pressure difference helps to maintain flow of blood downstream

Question 2

Arterioles: regulate blood flow to Tissues

Answer 2

– MAP for all organs is identical, but the amount of blood delivered to each organ varies (& can be temporally adjusted)
– These differences are determined by:
• Organ vascularisation
• Arteriolar resistance

Question 3

R can be changed independently in organs why & how?

Answer 3

1. distribute blood variably according to needs at any point in 4me
2. help regulate arterial blood pressure

Question 4

Vascular tone:

Answer 4

partial constriction for
Sympathetic innervation
baseline resistance due to myogenic activity (intracellular Ca2+) & continuous sympathetic innervation

Question 5

• Vasoconstriction/dilation:

Answer 5

sensitive to various factors & highly innervated by sympathetic nerves

Question 6

Factors that affect arteriolar radius, & therefore R

Answer 6

The vascular smooth muscle can undergo changes in force without ac4on potentials (unlike skeletal & cardiac)

not all or nothing, undergo graded changes

Question 7

Intrinsic factors

– Chemical

Answer 7

regulate distribution of blood, local, right at the site of injury

– Chemical
• Metabolic changes: O2, CO2, lac4c acid, K+, osmolarity,
adenosine, vasoca4ve paracrines from endothelial cells
• Histamine release: not released in response to local changes, important in pathology

Question 8

Intrinsic factors

– Physical

Answer 8

• Vessel stretch/myogenic: opening of mechanically-gated
cation channels causes Ca2+ influx & contraction
• Shear stress: friction of blood on inner surface of vessels
creates a force, releasing NO
• Hot/cold: heat causes localised vasodilation & cold causes vasoconstriction

Question 9

Extrinsic factors

- sympathetic

Answer 9

regulate BP (maintains brain blood flow)
* sympathetic NS, more general to whole body
–  Noradrenaline binds to α1-adrenergic receptors on arteriolar smooth muscle (none on cerebral arterioles)
•  Contributes to ongoing vascular tone & generalised vasoconstriction increases TPR & therefore MAP

Question 10

Extrinsic factors

– Hormonal

Answer 10

• Noradrenaline & adrenalin generally reinforce the
sympathe4c nervous system
• An4-diure4c hormone & angiotensin II also important in fluid balance & blood volume

Question 11

Arterioles

Answer 11

Of all systemic peripheral vessels, arteriolar resistance has the greatest impact on TPR > primary resistance vessels

Question 12

summary

Answer 12

• Arteries: pressure reservoir

- Arterioles: primary resistance vessels