Principles of Blood Flow

Question 1

T/F: the velocity of blood flow in the large arteries is from 100 to 500 times faster than in the capillaries

Answer 1

True

Question 2

T/F: the blood volume in the arteries is approximately equal to that in the veins

Answer 2

False, venous vessels contain >50% of total blood

Question 3

T/F: the total cross-sectional area of the capillaries is about 10-fold that of the arteries

Answer 3

Total cross sectional area of capillaries (4500 cm^2) is about 225X that of arteries (20 cm^2)

Question 4

T/F: the velocity of blood flow in the veins is greater than in the arteries

Answer 4

False, blood flow velocity is much higher in arteries than in veins

Question 5

Compared to rest conditions exercise causes the biggest increase in blood flow in which organ systems?

Answer 5

Muscle and skin
Rest: 1.25 L/min
Exercise: 21.0 L/min

Question 6

The total circulation time for one pass through the entire systemic and pulmonary circulation is about how long?

Answer 6

1 minute

Question 7

What two factors is directly proportional to the flow rate as expressed in the Poiseulle equation?

Answer 7

The flow rate is directly proportional to the radius to the 4th power and also to perfusion rate (P1-P2)

Flow rate= (P1-P2) X (πr4)/8(L)(η)

Question 8

What is the equation that describes the relationship between blood flow (Q), pressure difference (P1-P2), and resistance (R)?

Answer 8

Q= (P1-P2)/R
Blood will move if the forces (pressures) at the ends of a region are different from a region of higher pressure to one of lower pressure. Resistance to flow comes from the walls of the vessel (which are not moving) and also from viscosity of the blood. Balancing all forces leads to the basic equation of blood flow.

Question 9

T/F: The amount of fluid flowing between two points depend on the diameter and velocity of the vessels

Answer 9

False, flow it constant…the velocity of fluid and resistance of fluid will change with changing diameter but the amount of fluid is constant

Question 10

The flow of oxygen in arteries (mL O2/min) = ______X_______

Answer 10

Flow of O2 in arteries = Cardiac output (L blood/min) X arterial oxygen content (mL O2/L blood)

Question 11

What does the continuity equation tell us about the relationship between the rate of blood flow, cross-sectional area of vessels, and the velocity of fluid?

Answer 11

Rate of blood flow (Q) = cross-sectional area (A) x velocity (v)

A larger cross-sectional area and/or higher velocity will increase the rate of flow

Question 12

T/F: the linear velocity if blood flow varies inversely with the cross-sectional area?

Answer 12

True, Q=A x V

Rearranging the continuity eq: v= Q/A

Question 13

What is the relationship between blood flow (Q), pressure (P) and resistance (R)?

Answer 13

Q= (deltaP)/R

Question 14

Since the length of blood vessels and the viscosity of blood do not normally change, the major physiological variable that determines the resistance to the flow of blood is what?

Answer 14

The radius of vessels, primarily arterioles.

Given by Pouseuille’s law that shows that blood flow (Q) is directly proportional to radius to the 4th power…rearranging this shows that Resistance is inversely related to the radius to the 4th power

Question 15

Pressure drops more quickly over the length of small or large vessels?

Answer 15

blood pressure drops more gradually along the length of large arteries, more rapidly along the length of small arterioles and capillaries and more gradually along the length of veins

Question 16

Why is systemic arterial pressure in the adult approximately 6-fold that of pulmonary arterial pressure?

Answer 16

Systemic resistance exceeds pulmonary resistance.
Pressure = resistance X flow. Because the flow from the left ventricle approximately equals the flow from the right ventricle, resistance becomes the determining factor. Right and left ventricular stroke volumes are approximately equal.