Unit 1: CV System Part B Flashcards
List the 4 factors that determine the rate of blood flow (F) to tissues and organs
a. Pressure gradients (ΔP)
b. Resistance to blood flow caused by friction
c. Poseuille’s Law
d. Velocity of Flow
Pressure gradients (ΔP) definition
differences in pressure b/t 2 locations in the CV system
Blood flows from areas of _____ pressure to areas of _____ pressure, (_____ the pressure gradient)
HIGH
LOW
DOWN
Over the entire CV system, pressure is HIGHEST closest to the _______, & ________ as you move further away from this pump
VENTRICLES
DECREASES
Where is pressure the highest?
highest in ventricles and aorta
Where is pressure the lowest?
lowest pressure in the vena cava and atria
Pressure ____ continuously as blood moves FARTHER from the heart
FALLS
What is blood flow directly proportional to?
Blood flow is directly proportional to the size of the pressure gradient
Blood flow is DIRECTLY proportional to the size of the pressure gradient (F ∝ Δ P), therefore
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
The GREATER the pressure difference b/t the 2 locations, the _______ the flow
HIGHER
The SMALLER the pressure difference, the _____ the flow
LOWER
WITHOUT a pressure gradient (ΔP = 0), there is _____ flow
NO
What causes vascular resistance?
Resistance to blood flow (vascular resistance) is caused by friction (of blood cells in contact with vessel walls and
with each other).
List the 4 factors that determine vascular resistance:
i. Vessel length (L)
ii. Internal vessel radius (r)
iii. Blood viscosity (η)
iV. equation R= 8Ln/ pier^4
Vessel length (L)
longer blood vessels increase resistance
Internal vessel radius (r)
Ø decreasing radius (vasoconstriction), increases resistance
Ø increasing radius (vasodilation), decreases resistance
Blood viscosity (η)
Ø friction between molecules in a flowing fluid
Blood viscosity (ŋ) is proportional to ______
proportional to hematocrit (the proportion of of the
blood volume that is red blood cells)
INCREASING hematocrit, _______ viscosity, which _______ resistance to blood flow
Increasing hematocrit,increases viscosity, which increases resistance to blood flow.
Ø analogy: water (low viscosity) vs honey (high viscosity) moving through a tube
What do L & r determine?
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.
Explain F = ΔP/R
Describe the equation: R = 8Lŋ/πr^4
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 )
A SMALL change in the RADIUS, produces a _____ change in _______. For example, ______
: 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
Poseuille’s Law:
Equation that combines the effects that pressure gradients and the factors determining resistance have on blood flow
Velocity of Flow
The distance a fixed volume of blood travels in a given period of time.
Formula: v = Q/A
Formula for Velocity of Flow explained
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
Velocity ______ when cross sectional area DECREASES
increases
Velocity ______ when cross sectional area INCREASES
decreases
