Overview of Circulation

Question 1

Blood flow resistance is indirectly proportional to what?

Answer 1

vessel diameter

Question 2

Reynolds number is a measure of what parameters?

Answer 2

tendency for turbulence

Question 3

What is the viscosity of blood with a hematocrit of 38-42?

Answer 3

3.0

Question 4

Velocity of Blood Flow equation

Answer 4

velocity of blood flow (v) = Volume of blood flow (F)/vascular cross-sectional area (A)

V = F/A

Question 5

What are the functional principles of the circulatory system?

Answer 5

1. Rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need (demand style system)
2. the cardiac output is controlled mainly by 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 6

What are the factors determining blood flow?

Answer 6

• pressure difference between the two ends of a vessel (pressure gradient)
• impediment to blood flow through the vessel (resistance)

Question 7

Blood flow equation

Answer 7

Flow in mL/min (F)= pressure difference (P1-P2)/ resistance between P1 and P2

F= (P1-P2)/R

Question 8

What is laminar blood flow?

Answer 8

1. blood flows at a steady rate
2. blood vessel is long and smooth
3. blood flows in streamlines (layers)

Question 9

What is turbulent flow?

Answer 9

• nonlayered flow that creates murmurs and produces more resistance than laminar flow

Question 10

When does Turbulent flow occur? (4 listed)

Answer 10

1. when flow is too great
2. when blood passes an obstruction within the vessel
3. when blood has to make a sharp turn
4. when blood passes over a rough surface

Question 11

Tendency for turbulence equation

Answer 11

Reynolds number (Re) = (mean velocity of blood flow in cm/sec (v) * vessel diameter in cm (d) * density (p))/ viscosity in poise (n)

Re= (Vdp)/ n

Question 12

What does Reynolds number have to be above for turbulence to occur in a straight vessel?

Answer 12

2000

Question 13

What does reynolds number have to be above for turbulent flow to occur in some regions of a vessel?

Answer 13

200-400

Question 14

What are the three major variables that determine resistance?

Answer 14

1. vessel radius
2. Blood viscosity
3. vessel length

Question 15

Resistance equation

Answer 15

Resistance (R) = (8* viscosity of blood (n) * length of vessel (l))/ (pi * radius of the blood vessel to the 4th power (r^4))

R = 8nl/ pi*r^4

Question 16

What is pulse pressure?

Answer 16

the difference between systolic and diastolic pressures

Question 17

What is conductance?

Answer 17

the measure of blood flow through a vessel for a given pressure difference

Question 18

How does conductance compare to resistance?

Answer 18

conductance = 1/resistance

Question 19

What is conductance directly proportional to?

Answer 19

the diameter of the vessel to the 4th power

Question 20

Poiseuille’s Law: equation for conductance

Answer 20

Rate of blood blow (F) = (pressure difference between ends of the vessel (delta P) * pi * radius of vessel to the forth power ( r^4))/ (8 * blood viscosity (n) * vessel length (l))

F = (pi * delta P * r^4)/(8 * n * l)

Question 21

What does anemia do to viscosity and what does polycythemia do to viscosity?

Answer 21

anemia = decreases
polycythemia = increases

Question 22

84% of the blood volume is in the systemic circulation. Of this 64% is found where?

Answer 22

veins

Question 23

Why does blood continue to move through the arterial system during relaxation?

Answer 23

It is due to the elasticity of the arterial system

Question 24

Why is pulmonary artery pressure so much lower than systemic artery pressure?

Answer 24

It doesn’t take much pressure to send blood from the heart to the lungs and back to the heart because of the short distances needed to travel

Question 25

Why would the velocity of blood flow be slower in capillaries at rest comparded to the aorta at rest?

Answer 25

Because in the capillaries in order to get the maximum exchange in the tissues the blood needs to move slower

Question 26

What are the functional principles of the circulatory system?

Answer 26

- 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

Question 27

What happens if arterial pressure falls below 100 mm Hg, the nervous reflexes?

Answer 27

- Increase force of heart pumping - constrict large venous reservoirs - generally constrict most of the arterioles throughout the body (increases arterial pressure) - kidneys may later play important role in pressure control

Question 28

What are eddy currents?

Answer 28

occur when blood flows crosswise in the vessel and along the vessel, usually forming whorls in the blood. simillar to whirlpools

Question 29

How does eddy currents effect the resistance of blood flows?

Answer 29

Blood will flow with greater resistance

Question 30

What is blood pressure physiologically?

Answer 30

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

Question 31

If resistance is increased what doest that mean for the blood flow, upstream pressure, and downstream pressure?

Answer 31

Blood flow: decreases Upstream pressure: increases downstream pressure: decreases

Question 32

Why is there a low pressure drop across major arteries?

Answer 32

Because they have low resistance

Question 33

Where is the largest pressure drop and why?

Answer 33

in the arterioles because they have the highest resistance

Question 34

What is resistances relationship to blood pressure?

Answer 34

they are inversely proportional to each other

Question 35

What is pulse pressure?

Answer 35

the difference between systolic and diastolic pressure

Question 36

How will the amputation of a limb or removal of a kidney which removes a parallel circuit affect circulation?

Answer 36

- reduces total vascular conductance - reduces total blood flow - increases total peripheral vascular resistance

Question 37

What is the prime determinant of blood viscosity?

Answer 37

the hematocrit of blood

Question 38

What is blood flow autoregulation?

Answer 38

the ability of each tissue to adjust its vascular resistance and to maintain normal blood flow through changes in arterial pressure between approximately 70 and 175 mm Hg

Question 39

What happens if you get beyond 70 and 175 mm Hg for arterial pressure?

Answer 39

autoregulation will fail