APK 2105C Lecture Notes - Lecture 33: Brachial Artery, Muscle Tone, Arteriole

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Chapter 14, Lecture 4
Vessels & Blood Pressure
o Provide greatest amt of resistance to blood flow (>60% TPR)
Resistance in capillaries vs. arterioles
Capillaries have larger total areaspread out pressure/resistance
o Why they are not more resistant than the arterioles
o Very low resistance in capillaries
o BP drops off in capillaries
o Velocity of blood flow is very low in capillaries
o First part of microcirculation
o Very important for BP regulation and blood distribution to organs/capillary beds
o Through all the arteriesmaintain BP very well/easily
Why can measure BP at brachial artery
When you get to arterioles = drop in pressure (large)
Largest pressure at arterioles because very small radius, lots of
muscle tone
Slows things down, decrease pressure in capillaries
o No pressure in capillaries
o No muscle in wall of capillaries
o Arteriolar tone
Very very small arteries
Small internal radius = some resistance
LOTS of smooth muscle in walls compared to radius
A little constricted at all times
o If fully relaxedcannot vasodilate = cannot increase blood
o Can get 50% more constricted or dilated
o Very common
Regulatory mechanism
Increased or decreased for 2 reasons
o Control of blood flow to capillary beds
Intrinsic control mechanisms (from within organ
Local factors (chemicals)
o Changing MAP
Extrinsic control mechanisms
ANS and hormones
Autonomic NS
o Control of blood flow is more local, change in BP is more
Intrinsic control of BF = distribution of blood to organs
o EXTRINSIC control mechanisms regulate MAP
o INTRINSIC control mechanisms regulate flow of blood
directed to individual capillary beds
Based on metabolic needs of tissues
Decreased demand flow is decreased
Increased demand flow is increased
Locally regulated
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