Overview of the Circulation; Biophysics of Pressure, Flow, and Resistance

Question 1

percentage of blood in systemic circulation and heart and lungs?

Answer 1

84% in sys circu

and 16% in hurt and lungs

Question 2

he mean pressure in the aorta

Answer 2

100 mm hg

Question 3

blood pressure falls to 0 mm hg when?

Answer 3

in systemic circulation when the blood is at termination of inf and sup vena cavea

Question 4

“functional” pressure in most vascular beds is

Answer 4

17 mm hg
35 near arterioles
10 mm hg in venous ends

Question 5

a mean

pulmonary arterial pressure

Answer 5

16 mm hg
systolic 25
diastolic 8

Question 6

The mean

pulmonary capillary pressure averages

Answer 6

7 mm hg

Question 7

BASIC PRINCIPLES OF

CIRCULATORY FUNCTION

Answer 7

1. Blood flow to most tissues is controlled according to
   the tissue need.
2. 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

Question 8

1. Blood flow to most tissues is controlled according to

the tissue need.explain

Answer 8

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.

Question 9

Cardiac output is the sum of all the local tissue

flows. explain

Answer 9

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

Question 10

Arterial pressure regulation is generally independent
of either local blood flow control or cardiac output
control

Answer 10

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

Question 11

Blood flow through a blood vessel is determined by

two factors:

Answer 11

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

Question 12

blood flow means

Answer 12

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

Question 13

cardiac output

Answer 13

5000 ml/min.

Question 14

laminar flow

Answer 14

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,

Question 15

turbulent flow

Answer 15

which is blood
flowing in all directions in the vessel and continually
mixing within the vessel, as discussed subsequently.

Question 16

“parabolic profile for velocity of blood flow.”

Answer 16

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.

Question 17

when blood goes into turbulent flow

Answer 17

when it turns suddenly oy goes over an obstruction

Question 18

eddy currents

Answer 18

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

Question 19

Reynolds’ number and the measure of the

tendency for turbulence to occur is measured by

Answer 19

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)

Question 20

blood pressure means

Answer 20

blood pressure means
the force exerted by the blood against any unit area of the
vessel wall

Question 21

resistance must be calculated

Answer 21

pressure difference between 2 points and blood flow

PRU

Question 22

Total Peripheral Vascular Resistance

Answer 22

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.

Question 23

Total

Pulmonary Vascular Resistance

Answer 23

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

Question 24

conductance of blood vessel

Answer 24

is the measure of blood flow through a vessel for a given pressure difference
its the reciprocal of resistance

Question 25

resistance of blood flow when vessels are arranged In series

Answer 25

th total resistance to blood flow is equal to the sum of resistance of each blood vessel cause the blood flow is same in each vessel
Rtotal: R1+R2+R3

Question 26

resistance of blood flow when vessels are arranged In paralle

Answer 26

the total resistance will be much less than the resistance of the blood flowing through each vessel

Question 27

relate the conductance and parralel flow

Answer 27

parallels flowing of blood increases the conductance
as it adds a ‘another’ pathway for the flow for example the kidney git etc are all arranged parallels and adds to the conductance of blood flow and increases the cardiac output. if anyone one of them is removed the total vascular resistance will be increased and the cardiac output will be decreased

Question 28

viscoity and blood flow relation

Answer 28

the greater the viscouscity the slower will be the blood flow

Question 29

hematocrit

Answer 29

the amount of blood cells present in your blood
if your hematocrit level is 40 means 40 percent of your blood volume is blood cells
42 is men hematocrit and 38 is female

Question 30

polycythemia and blood flow

Answer 30

the hematocrit level increases to 60-70 in people with polycythemia so the visocusicty of blood increases and the blood flow decreases

Question 31

hormonal vasoconstrictors

Answer 31

epinipherine, angitensin II, vasopressin, endothelin

all reduces blood flow.

Question 32

inhibition of symoathteic stimulation

Answer 32

dilates the blood vessels and vice versa