Cardiac output (HR X SV) x total peripheral resistance
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Poiseuilles Law
describes the factors that determine the flow through a tube in terms of pressure, flow and resistance
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Flow (Q)
Is proportional to the pressure gradient and inversely proportional to the resistance (R)
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flow is directly proportional to Q and r^4 and inversely proportional to
the length of the vessel and the viscosity of the fluid
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flow (Q)
cardiac output (L/ min)
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pressure gradient
blood pressure (mmHg)
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resistance (R)
peripheral resistance
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blood pressure=
cardiac output x peripheral resistance
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blood flow
always from a region of high pressure to a region of low pressure
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flow is independent of
the absolute pressure
this is important as we don't want different flow rates in diff parts of the vessels
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what is needed to allow blood flow?
a pressure difference
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L
longer tube= more resistance= less flow
however length of blood vessels remains constant and therefore does not control blood flow
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viscosity
higher viscosity= more resistance= less flow
related to the hematocrit (RBCs)
- dehydration
- high altitude
- EPO (eryhtropoietin) (RBC production) (more RBCs= higher viscosity)
remains constant under physiological conditions and therefore does not contro
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r
caused by friction of the fluid against the vessel wall
the effect of the changes in radius is raised to the power of 4 (reducing radius by two fold from 2 to 1 reduces the flow by sixteen fold, ie resistance has inc by sixteen fold)
possible to regulate
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total peripheral resistance
the sum of the resistance of all the blood vessels and it determines blood pressure
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thick muscular walls
pressure reservoir
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thin muscular walls
regulate blood pressure and flow to organs
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thin compliant walls with large diameter and valves
large blood volume with low resistance and valves to aid blood return to the heart
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single layer of endothelial cells with small diameter and large SA
sites of gases, nutrient and waste exchange
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arterioles
regulate the flow to diff organs
mostly control peripheral resistance
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why do arteries not have a big effect on resistance?
because they have a large radius
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why do the arterioles create most of the peripheral resistance?
because they have a small radius
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arterioles determine blood flow to
individual organs
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how do they do this?
by opening and closing arterioles is diff areas of the body
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what else determines blood flow to individual organs?
the radius of the arterioles
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systolic
max blood pressure
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diastolic
min blood pressure
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direct measurement of blood pressure
- cannulate artery measure pressure with transducer
- v accurate
- not v convenient
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why is the blood pressure measured in your upper arm?
so that it is level with the blood coming out of your heart
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Korotkoff sounds
measuring when sound comes and goes to determine systolic and diastolic blood pressure
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pulse
vibration of the arteries caused by ejection of the blood from the heart (left ventricle) into the systemic circulation
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typical pulse rates
rest- 70/ min
exercise- 220/ min
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pulse pressure
diff between the systolic and diastolic pressure
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MAP
average pressure over the cycle
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since diastole is around twice as long as the systole
DP + 1/3 PP
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P (pressure, mmHg)=
height x density x gravity
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is the MAP increased or decreased in the legs?
increased
pooling of blood in the feet
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since arterial and venous blood are the same height
blood gradient (change in P)= constant= blood flow cont
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what makes you feel faint?
the initial reduction in blood pressure to the head
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myocardial infarction
rupture of the coronary blood vessels in the heart
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stroke
rupture of the blood vessels in the heart
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what is defined as a high blood pressure (hypertension)?
a blood pressure of about 90 mmHg or higher
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Other cards in this set
Card 2
Front
Poiseuilles Law
Back
describes the factors that determine the flow through a tube in terms of pressure, flow and resistance
Card 3
Front
Flow (Q)
Back
Card 4
Front
flow is directly proportional to Q and r^4 and inversely proportional to
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