Chapter 14 Overview Of The Circulation: Pressure, Flow And Resistance

Question 1

What is the function of arterioles?

Answer 1

They act as control conduits of the tissue blood flow. They have strong muscular walls which can contract to completely obliterate the tissue perfusion or dilate to increase blood flow.

Question 2

Distribution of blood in the heart?

Answer 2

7%

Question 3

Distribution of blood volume in arteries?

Answer 3

13%

Question 4

Distribution of blood in arterioles and capillaries?

Answer 4

7%

Question 5

Distribution of blood in veins, venules, and venous sinuses?

Answer 5

64%

Question 6

Distribution of blood in pulmonary circulation?

Answer 6

9%

Question 7

What is the velocity of blood flow in the aorta?

Answer 7

33cm/ sec

Question 8

What is the velocity of blood flow in the capillary beds?

Answer 8

0.3mm/ second

Question 9

What is the normal BP in aorta?

Answer 9

100mmHg

Question 10

Blood pressure in the large arteries?

Answer 10

120 mmHg

Question 11

Blood pressure in vena cave?

Answer 11

0 mmHg

Question 12

Pressure at the arterioler end ?

Answer 12

35 mmHg

Question 13

Blood pressure at the venous end ?

Answer 13

10 mmHg

Question 14

Average functional blood pressure of vascular beds ? 17 mmHg

Question 15

Blood pressure at the glomerular capillary bed ?

Answer 15

60 mm hg

Question 16

Systolic and diastolic pressure of the pulmonary arteries?

Answer 16

25 mmHg and 8 mmHg

Question 17

Mean pulmonary artery pressure?

Answer 17

16 mmHg

Question 18

Blood pressure in pulmonary capillary bed?

Answer 18

7 mmHg

Question 19

What are the basic principles of circulatory function?

Answer 19

1) Local blood flow to most tissues are controlled according to the tissue need. It is orchestrated by the local arterioles along with nervous and hormonal control of tissue perfusion.
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: whenever the arterial pressure falls below 100 mmHg, a barrage of nervous reflexes will increase the force of heart pumping, cause contraction of the large venous blood reservoir by increasing diastolic volume, cause generalized constriction of arterioles to increase intra- arterial blood pressure.

Question 20

Ohm’s law of blood flow:

Answer 20

F= delta P/ vascular resistance.
Delta P= ( P1-P2)
The blood flow is directly proportional to delta P and inversely proportional to vascular resistance.

Question 21

What is the blood flow in total circulation in a min ( cardiac output) at rest?

Answer 21

5000 ml/ min.

Question 22

What is the difference between laminar flow and turbulent flow of blood in the blood vessels?

Answer 22

In laminar blood flow: the center most layer of blood column flows faster than the progressively outermost layers with highest velocity.
Turbulent flow occurs when laminar flow is obscureed by intra vessel obstructions, which will cause the blood flow to develop whirlpools called Eddy currents increasing the resistance to blood flow.

Question 23

What are the causes of turbulent flow?

Answer 23

Too great flow rate, obstruction in a vessel, when the flow takes a sharp turn, when it passes over a rough surface.

Question 24

The whirlpools occurs during turbulent flow of blood are called?

Answer 24

Eddy currents

Question 25

What is the measure of the tendency for turbulent blood flow?

Answer 25

Reynold's number abbreviated as Re. Re= v.d.p/ n V= velocity of blood flow in CM per second d= Vessel diameter in CM. P= density of the blood in Grams/mL n= viscosity of the blood in poise

Question 26

Normal viscosity of the blood?

Answer 26

1/30 poise

Question 27

Normal density of the blood?

Answer 27

1060 kg/ M^3

Question 28

What is the Raynold's number threshold for turbulent flow to occur?

Answer 28

200 to 400 in large arteries and it will die away

Question 29

The rate of blood flow through the entire circulatory system is equal to ____ and what is it in normal human being?

Answer 29

Cardiac output and is 100 ml/ seconds in normal human.

Question 30

What is the pressure difference between the systemic arteries to the systemic veins?

Answer 30

100 mmHg

Question 31

What is the total peripheral resistance of the entire systemic circulation?

Answer 31

The rate of blood flow of the entire circulatory system= 100 ml/sec The pressure difference of systemic arteries and veins= 100 mmHg Therefore, the total peripheral resistance of the entire circulation= 100/100 or 1 PRU.

Question 32

What is the maximum peripheral resistance increase of the systemic circulation in generalized vasoconstriction?

Answer 32

4 PRU.

Question 33

What is the peripheral resistance decrease of the systemic circulation in generalized vasodilation?

Answer 33

0.2 PRU

Question 34

What is the normal pulmonary vascular resistance?

Answer 34

0.14 PRU Because the average pulmonary arterial pressure= 16 mmHg The left atrial pressure during normal cardiac output= 2 mmHg Therefore the net pressure gradient of the pulmonary circulation= 14 mmHg. Hence, pulmonary vascular resistance= 14 mmHg/ 100 mL/ second or 0.14 PRU.

Question 35

Conductance of blood flow in a vessel is equal to ____?

Answer 35

It is the reciprocal of the vascular resistance or 1/ resistance

Question 36

The conductance of blood flow through a vessel increase in proportion to _____?

Answer 36

Fourth power of the diameter of the vessel. For example at a pressure gradient of 100 mmHg the blood conductance through a vessel with a diameter of 2 mm increase to 16 ML/ min. While though a vessel with a diameter of 4 mm increases to 256 ML/ min.

Question 37

What is the significance of the vessel diameter fourth power law?

Answer 37

In muscular arterioles a small change in arterioler diameter ( normal range 4 micrometers to 25 micrometers) can increase or decrease the blood flow to the fourth power of it's diameter.

Question 38

What is the normal hematocrit level?

Answer 38

Males = 42 or 42% of the blood volume In females= 38% A significant reduction in hematocrit concentration is called anemia. A significant increase is called polycythemia

Question 39

Poiseuille equation of blood flow ?

Answer 39

F= pi. Pressure gradient. r^4/ 8nl Pi.r^4= diameter of the vessel Pressure gradient= pressure at one end of the vessel - the other end pressure. n = viscosity of the blood l = length of the vessel

Question 40

What is blood flow autoregulation?

Answer 40

The ability of each tissue to adjust it's arterioler vascular resistance in response to changes in arterial blood pressure between 70 and 175 mmHg is called blood flow autoregulation.

Question 41

Explain pressure flow relationship in passive elastic vascular beds?

Answer 41

When the arterial pressure increases it not only increases the force that push the blood through the artery but also decreases vascular resistance by stretching the elastic walls of the artery. Conversely, a fall in BP will lead to reduction in blood flow and increase in vascular resistance due to collapse of the elastic arterial wall. When the pressure falls below the critical closing pressure the flow through the vessel completely ceases due to the collapse of the vessel wall.

Question 42

Explain the Law of Laplace for vascular wall tension?

Answer 42

Wall pressure (T) for a thin walled tube is proportional to the transmural pressure gradient ( ∆P) times the radius of the blood vessel (r) divided by its wall thickness (h). T = ∆P. (r/). ∆P = intravascular pressure Pi- extravascular pressure Pt.

Question 43

What enables large elastic blood Vessel Wall to withstand high transmural pressure gradient?

Answer 43

The support of collagen fibrous bands.

Question 44

What is vascular sheer stress?

Answer 44

It is the frictional force or drag exerted by the blood flow on the endothelial cells. It is directly proportional to the flow velocity and viscosity of the blood and inversely proportional to the radius cubed.