Unit 1: CV System Part B

Question 1

List the 4 factors that determine the rate of blood flow (F) to tissues and organs

Answer 1

a. Pressure gradients (ΔP)

b. Resistance to blood flow caused by friction

c. Poseuille’s Law

d. Velocity of Flow

Question 2

Pressure gradients (ΔP) definition

Answer 2

differences in pressure b/t 2 locations in the CV system

Question 3

Blood flows from areas of _____ pressure to areas of _____ pressure, (_____ the pressure gradient)

Answer 3

HIGH

LOW

DOWN

Question 4

Over the entire CV system, pressure is HIGHEST closest to the _______, & ________ as you move further away from this pump

Answer 4

VENTRICLES

DECREASES

Question 5

Where is pressure the highest?

Answer 5

highest in ventricles and aorta

Question 6

Where is pressure the lowest?

Answer 6

lowest pressure in the vena cava and atria

Question 7

Pressure ____ continuously as blood moves FARTHER from the heart

Answer 7

FALLS

Question 8

What is blood flow directly proportional to?

Answer 8

Blood flow is directly proportional to the size of the pressure gradient

Question 9

Blood flow is DIRECTLY proportional to the size of the pressure gradient (F ∝ Δ P), therefore

Answer 9

the GREATER the pressure difference b/t the 2 locations, the HIGHER the flow

• the SMALLER the pressure difference, the LOWER the flow
• WITHOUT a pressure gradient (ΔP = 0), there is NO flow

Question 10

The GREATER the pressure difference b/t the 2 locations, the _______ the flow

Answer 10

HIGHER

Question 11

The SMALLER the pressure difference, the _____ the flow

Answer 11

LOWER

Question 12

WITHOUT a pressure gradient (ΔP = 0), there is _____ flow

Answer 12

NO

Question 13

What causes vascular resistance?

Answer 13

Resistance to blood flow (vascular resistance) is caused by friction (of blood cells in contact with vessel walls and
with each other).

Question 14

List the 4 factors that determine vascular resistance:

Answer 14

i. Vessel length (L)

ii. Internal vessel radius (r)

iii. Blood viscosity (η)

iV. equation R= 8Ln/ pier^4

Question 15

Vessel length (L)

Answer 15

longer blood vessels increase resistance

Question 16

Internal vessel radius (r)

Answer 16

Ø decreasing radius (vasoconstriction), increases resistance
Ø increasing radius (vasodilation), decreases resistance

Question 17

Blood viscosity (η)

Answer 17

Ø friction between molecules in a flowing fluid

Question 18

Blood viscosity (ŋ) is proportional to ______

Answer 18

proportional to hematocrit (the proportion of of the
blood volume that is red blood cells)

Question 19

INCREASING hematocrit, _______ viscosity, which _______ resistance to blood flow

Answer 19

Increasing hematocrit,increases viscosity, which increases resistance to blood flow.
Ø analogy: water (low viscosity) vs honey (high viscosity) moving through a tube

Question 20

What do L & r determine?

Answer 20

determine the surface area of the vessel in
contact with the blood

The more surface area in
contact with the blood, the higher the resistance

When vessels constrict, more of the blood is in direct
contact with the vessel wall, so resistance increases.

Question 21

Explain F = ΔP/R

Question 22

Describe the equation: R = 8Lŋ/πr^4

Answer 22

Ø where 8 and π are constants.

Ø however, in humans, L (vessel length) does not change
(an exception is the lengthening of blood vessels that
occurs in obesity), and η (viscosity) is relatively constant.
So R (resistance) is mainly determined by changes to
vessel radius (R μ 1/r 4 )

Question 23

A SMALL change in the RADIUS, produces a _____ change in _______. For example, ______

Answer 23

: a small change in the radius, produces a large
change in resistance. For example, increasing the
radius of a vessel by a factor of two (e.g. from 2mm to
4mm) decreases the resistance by a factor of 16X

Question 24

Poseuille’s Law:

Answer 24

Equation that combines the effects that pressure gradients and the factors determining resistance have on blood flow

Question 25

Velocity of Flow

Answer 25

The distance a fixed volume of blood travels in a given period of time.

Formula: v = Q/A

Question 26

Formula for Velocity of Flow explained

Answer 26

Formula: v = Q/A
Ø Q = Flow rate (the volume of blood that passes a given point in the system per unit time)
Ø A = cross-sectional area of the tube

Question 27

Velocity ______ when cross sectional area DECREASES

Answer 27

increases

Question 28

Velocity ______ when cross sectional area INCREASES

Answer 28

decreases