Overview of the Circulation; Biophysics of Pressure, Flow, and Resistance Flashcards
percentage of blood in systemic circulation and heart and lungs?
84% in sys circu
and 16% in hurt and lungs
he mean pressure in the aorta
100 mm hg
blood pressure falls to 0 mm hg when?
in systemic circulation when the blood is at termination of inf and sup vena cavea
“functional” pressure in most vascular beds is
17 mm hg
35 near arterioles
10 mm hg in venous ends
a mean
pulmonary arterial pressure
16 mm hg
systolic 25
diastolic 8
The mean
pulmonary capillary pressure averages
7 mm hg
BASIC PRINCIPLES OF
CIRCULATORY FUNCTION
- Blood flow to most tissues is controlled according to
the tissue need. - Cardiac output is the sum of all the local tissue
flows
3.Arterial pressure regulation is generally independent
of either local blood flow control or cardiac output
control
- Blood flow to most tissues is controlled according to
the tissue need.explain
microvessels in each tissue monitor the need tissue needs, such as
the availability of oxygen and other nutrients and
the accumulation of carbon dioxide and other tissue
waste products, and these microvessels in turn act
directly on the local blood vessels, dilating or constricting them, to control local blood flow precisely
to that level required for the tissue activity.
Cardiac output is the sum of all the local tissue
flows. explain
When blood flows through a tissue, it immediately returns by way of the veins to the heart. The heart responds automatically to this increased inflow of blood by pumping it immediately back into the arteries. Thus, the heart acts as an automaton, responding to the demands of the tissues
Arterial pressure regulation is generally independent
of either local blood flow control or cardiac output
control
For instance, if at any time the
pressure falls significantly below the normal level of about 100 mm Hg, within seconds a barrage of nervous reflexes elicits a series of circulatory changes to raise the pressure back toward normal.
The nervous signals especially (a) increase the force of heart pumping, (b) cause contraction of the large venous reservoirs to provide more blood to the heart, and (c) cause generalized constriction of the
For instance, if at any time the
pressure falls significantly below the normal level of about 100 mm Hg, within seconds a barrage of nervous reflexes elicits a series of circulatory changes to raise the pressure back toward normal. The nervous signals especially (a) increase the force of heart pumping, (b) cause contraction of the large venous reservoirs to provide more blood to the heart, and (c) cause generalized constriction of the
Blood flow through a blood vessel is determined by
two factors:
pressure gradient which is the difference between the pressure at the 2 ends of the arterioles
and vascular resistance which is then impediment in the blood flow
blood flow means
Blood flow means the quantity of blood that passes a
given point in the circulation in a given period of time.
Ordinarily, blood flow is expressed in milliliters per minue or liters per minute
cardiac output
5000 ml/min.
laminar flow
When blood flows
at a steady rate through a long, smooth blood vessel, it flows in streamlines, with each layer of blood remaining
the same distance from the vessel wall. Also, the centralmost portion of the blood stays in the center of the vessel.
This type of flow is called laminar flow or streamline flow,
turbulent flow
which is blood
flowing in all directions in the vessel and continually
mixing within the vessel, as discussed subsequently.
“parabolic profile for velocity of blood flow.”
The fluid molecules touching the wall move slowly because of adherence to the vessel wall. The next layer of molecules slips over these, the third layer over the second, the fourth layer over the third, and so forth. Therefore, the fluid in the middle of the vessel can move rapidly because many layers of slipping molecules exist between the middle of the vessel and the vessel wall; thus, each layer toward the center flows progressively more rapidly than the outer layers.
when blood goes into turbulent flow
when it turns suddenly oy goes over an obstruction
eddy currents
when blood flow is turbulent it moves crosswise which forms whorlpools called as eddy currents
the currents add to the friction to the flow of the blood so acts as a resistance to the vascular flow
Reynolds’ number and the measure of the
tendency for turbulence to occur is measured by
ν is the mean velocity
of blood flow (in centimeters/second), d is the vessel
diameter (in centimeters), ρ is density, and η is the viscosity (in poise)
blood pressure means
blood pressure means
the force exerted by the blood against any unit area of the
vessel wall
resistance must be calculated
pressure difference between 2 points and blood flow
PRU
Total Peripheral Vascular Resistance
is equal to the cardiac output that is 100ml/sec so the PRU is 1 that means the different in pressure between the arteriole end and vein is of 100mmhg.
Total
Pulmonary Vascular Resistance
mean pulmonary arterial
pressure averages 16 mm Hg and the mean left atrial pressure averages 2 mm Hg, giving a net pressure difference of 14 mm. Therefore, when the cardiac output is
normal at about 100 ml/sec, the total pulmonary vascular resistance calculates to be about 0.14 PRU
conductance of blood vessel
is the measure of blood flow through a vessel for a given pressure difference
its the reciprocal of resistance
