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Mechanisms of Disease Exam 3


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Poiseuille's Law
Q (flow) = P x Ϭ x r^4/8nL

(P=pressure, n=viscosity, L=length)
In Poiseuille's Law: as radius decreases, what happens to the flow?
-flow exponentially decreases
In Poiseuille's Law: as length increases, what happens to flow?
-flow decreases
In Poiseuille's Law: as viscosity increases, what happens to flow?
-flow decreases
What can change the viscosity of the blood?
-Polycytemia vera (too many RBCs) with hematocrit up in 60s
-severe dehydration
"Resistance" Vessels
Arterioles: because most of the resistance to flow is in the arterioles
Which vessels:
-are very elastic and muscular
Which vessels:
-are relatively compliant and will increase their volume if bp is increased
Which vessels:
-have α1 adrenergic receptors on them
"Capacitance" Vessels
Veins: capacitance of the veins serves a very similar purpose to electric capacitors (storage of charge)
Which vessels:
-contain about 2/3 of all our blood at any moment
Which vessels:
-are very compliant but not very elastic (expand in volume with very small changes in bp but do not spring back well once expanded)
Phenomenon of blood pressure increase as we age is due to:
-the natural change in composition of the blood vessel walls
-ie. less elastic and collagen leads to decreased compliance
The changes in elastic and collagen in arteriolar walls causes what is most strictly called:
-arteriosclerosis (different from atherosclerosis)
The build up of gunk or "gruel in vessel walls is called:
Which is worse: arteriosclerosis or atherosclerosis?
Physiologic determinants of arterial blood pressure
1. Heart Rate
2. Stroke Volume
3. Cardiac Output
4. Total Peripheral Resistance
Physical Determinants of Arterial Blood Pressure
1. Viscosity
2. Circulatory Fluid Volume
3. Arterial Compliance
How to remember which is a physiologic and which is a physical determinant of arterial blood pressure.
-physiologic ones can receive sympathetic tone which can alter them (ie. they can change with changes in neuronal activity)
-physical determinants don't really respond to anything in the short term (they are much more long term)
____ and ____ determine the mean arterial pressure.
-CO and TPR
____ and ____ determine the pulse pressure.
-SV and Arterial Compliance
What is pulse pressure?
-the difference between diastolic and systolic
Mean arterial pressure (Pa) equation
Pa = Pd + (Ps-Pd)/3
= 80 + (120-80)/3 = 99mmHg
Flow (Q) = CO = _____
5-6 L/min
Pressure = _____
Ohm's Law
-V=IR comparable to P=Q x TPR
-solve for resistance: R=V/I
TPR = _____
TPR = (Pa - Pra)/CO
= Pa/CO
= 93mmHg/83ml/sec
= 1.12 mmHg*sec*mL-1
(1 peripheral resistance unit)
What happens to TPR during:
a) goes up
b) goes up as high as 4 PRU
c) goes down because arterioles open up due to CO2 production - CO increases which increases BP
Pulmonary vascular resistance is much _____ than TPR.
Any increase in pulmonary vascular resistance will cause:
-RV failure (Cor pulmonale)
Carotid Sinus Reflex (CSR)
-momentary increase in BP
-detected by stretch receptors of carotid sinus (and aortic arch)
-CSR causes decreased HR and arteriolar dilation
-causes decreased BP
-and vice versa
Area known as the vasomotor center
-the nucleus of the tractus solitarius of the medulla
The carotid sinus nerve becomes ______.
-cranial nerve 9
What kind of receptors are in the vasomotor center?
-alpha 2
83 mL/stroke
5 L/min
EDV (end diastolic volume)
b)normal level
c)during exercise
a)when either ventricle has received all the blood it will receive before it pumps
b)120 mL
a)normal level
b)during exercise
a)37 mL
b)10-20 mL
EJ (ejection fraction)
= 83/120
= 80%
-during exercise: 180/200 = 90%
CI (cardiac index)
= 3
-aortic blood pressure
-the highest BP in the body

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