Blake_Physio_09_overview of circulation Flashcards
systolic pressure
ventricular contraction ~120mmHg
diastolic pressure
ventricular filling ~80mmHg
What is the arterial pressure when it reaches the vena cava?
0mmHg
Systemic cappilary pressure varies from __ to__mmHg
35-10
Systolic pulmonary artery pressure = ___mmHg
25
diastolic pulmonary artery pressure = __mmHg
8
True or False: Blood pressure cuffs measure the true phasic pressure?
False, Phasic pressure occurs in the aorta
Mean arterial pressure must be time weighted because__________________
more time is spent in a diastole
What are the functional parts of circulation?
Arteries - transport under high pressure
Arterioles - control conduits
Capilaries - Exchange between blood and extracellular fluid
Venules- drain capilaries
Veins - return deoxy blood to heart
What percentage of blood is in systematic circulation? What is the distribution between: veins, arteries, systemic arterioles and capillaries, and heart and lungs
84%
64% veins, 13% arteries, 7% systemic arterioles and capillaries, 16% heart and lungs
Velocity of blood flow is measured by what formula? what are its antecedents?
V=F/A
V= Velocity, F= Volume, A=cross-sectional area
Rank the following in order from smallest to largest cross-sectional area:
Aorta, small arteries, arterioles, capilaries, venules, small veins, vena cavae
(Sum of body vessels)
(smallest) Aorta, Vena Cavae, Small Arteries, Arterioles, Small Veins, Venules, Capillaries (largest)
3 functional principles of the circulatory system
- rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need.
- the cardiac output is controlled mainly by the sum of all the local tissue flows.
- Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control.
In each tissue, _____________ monitor tissue needs. what parameters determine tissue needs?
microvessels
O2, nutrients, CO2 accumulation, tissue waste accumulation
How does the heart respond to the demands of tissues?
in addition to the decrease in pressure from expanding vessels, nerve signals may signal the heart to pump the required amount of blood.
If arterial pressure falls below 100mmHg, nervous reflexes do the following 4 things:
- increase force of heart pumping
- constrict large venous reservoirs
- Generally constrict most of the arterioles
- kidneys may later play an important role in pressure control.
Pressure gradient
pressure difference between two ends of a vessel
resistance
impediment of blood flow through vessel
Blood flow formula and antecedents:
F=deltaP/R
deltaP = P1-P2
F= flow in mL/min
P1 = upstream pressure
P2=pressure at end of segment
R=resistance between P1 and P2
Flow is ____ proportional to pressure difference, but _____ proportional to resistance
directly
inversely
Laminar blood flow (4)
streamline flow
steady rate
long and smooth vessel
streamlines (layers)
Blood flows in streamlines (layers) (4)
- each layer maintains same distance from vessel wall
- central-most portion of teh blood stays in the center
- each layer slips easily past surrounding layers
- velocity of fluid flowing in center is greater than that of fluid flowing towards the outer edges.
Tubulent Flow: (4 outcomes)
- Nonlayered
- creates murmurs
- more resistance than laminar
- eddy currents creat even more resistance
Turbulent flow (4 causes)
- flow is too great
- obstruction w/in vessel
- sharp turns
- rough surfaces
Tendency for turbulent flow changes with 4 variables
- directly to velocity
- directly to diameter of vessel
- directly to density of blood
- inversely to viscosity
Laminar flow is determined by what formula? Give the formula and its antecedents.
Reynolds formula for Laminar Flow
Re=(v*d*rho)/eta
Re= Reynolds number=measure of teh tendency for turbulence to occur
v=mean velocity(cm/sec); d= diameter (cm); rho= density; eta=viscocity (poise) (normal~1/30poise)
When Re rises above _____, turbulent flow will occur in some reagions of a vessel.
200-400
When Re rises above ____, turbulence will occur even in a straight vessel
2000
Blood pressure means_____________
Presure can be measured with _________
force exerted by blood against any unit area of the vessel wall
a mercurey manometer or with electronic transducers
Resistance is__________
How is resistance measured?
the impediment to blood flow in a vessel
It must be indirectly calculated from blood flow and pressure (pressure/volume/time)
3 Major variables that determine resistance:
vessel radius
blood viscosity
vessel length
What is the formula for resistance? what are the antecedants?
R=(8*eta*l)/πr4)
R=resistance
eta = viscosity
l = lenght of vessel
r = radius of blood vessel
cardiac output
the rate of blood flow through the entire circulatory system
What is the unit of resistance for entire systemic circulation
PRU = peripheral resistance unit
In conditions where vessels are strongly constricted, total peripheral resistance may rise to ____ PRU
4
When vessels are greatly dilated, the resistance can fall to as little as ___ PRU
0.2
Mean pulmonary arterial pressure averages ___ mmHg
Mean left atrial pressure averages _____ mmHg
=> cardiac output is normal (100mL/sec), the total pulmonary vascular resistance is _________PRU
16
2
= (16-2)/100 = 0.14 PRU
Conductance
The measure of blood flow through a vessel for a given pressure difference.
Conductance is usually expressed in ______
Conductance is:
ml/sec per mmHg
the exact reciprocal of resistance (1/R)
=> directly proportional to diameter
a 4x increase in vessel diameter can increase the flow by as much as _______. Therefore________
256x
minor changes in diameter can cause a vast increase in flow.
Poiseuille’s Law
A determinant of conductance which is the reciprocal of resistance.
F=(π*DeltaP*r4)/(8*eta*l)
for blood vessels arranged in paralel, the total resistance to blood flow is expressed as________
THerefore, total resistance _________________
1/Rtot
Is far less than the resistance of any single blood vessel
Total conductance for vessels arranged in parallel is ___________________________
the sum of the conductance of each parallel pathway
Circulations arranged in parallel: (6)
brain
kidney
muscle
gastrointestinal
skin
coronary circulation
Amputation of a limb or removal of a kidney removes a parallel circuit: therefore: (3)
reduces total vascular conductance
reduces total blood flow
increases total peripheral vascular resistance
Viscosity
a measure of internal resistance
the greater the viscosity, the greater the resistance
the prime determnant of blood viscosity is the _____
hematocrit
The viscosity of normal blood is about ____ times as great as the viscosity of water because____
3x
the large numbers of suspended red cells
Hematocrit of men and women
men~42
women~38
Viscosity of whole blood at normal hematocrit
~3
When hematocrit rises to 60-70
polycythemia
viscosity~10
The viscosity of blood plasma alone
~1.5
