Unit 1 - CV System The Heart PART B Flashcards
The rate of blood flow (F) to tissues & organs is determined by (4 things):
a. Pressure gradients (ΔP)
b. Resistance to blood flow caused by friction
c. Poseuille’s Law
d. Velocity of Flow
Pressure definition
in a fluid is the force exerted by the fluid on its container
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
Pressure is highest in ________
ventricles & aorta
Lowest pressure in the __________
vena cava & atria
If fluid is NOT moving, the pressure it exerts is called ________, & force is exerted _____ __ ___ ______
HYDROSTATIC PRESSURE
EQUALLY IN ALL DIRECTIONS
The pressure created in the ventricles is called the _____ _______, b/c __________
DRIVING FORCE
it is the force that drives blood through the blood vessels
think: squeezing water balloon
Pressure ____ continuously as blood moves FARTHER from the heart
FALLS
In a system in which fluid is flowing, pressure FALLS over distance as __________
energy is lost b/c of friction
Blood flow is _______ proportional to the size of the pressure gradient (F ∝ Δ P)
DIRECTLY
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
When fluid-filled container EXPANDS, pressure exerted on the fluid ______,
therefore, when heart RELAXES & EXPANDS, pressure in the fluid-filled chambers _______
DECREASES
FALLS
The MEAN BLOOD PRESSURE of the systemic circulation ranges from a high of 93 mm Hg in the _____ to a low of a few mm Hg in the ______ ______
AORTA
VENAE CAVAE
Fluid flows only if there is a ________ pressure gradient (ΔP)
POSITIVE
If the tube has NO pressure gradient, then ____ flow
NO
Flow depends on the ______ ______, not on the _______ _______.
PRESSURE GRADIENT (ΔP)
ABSOLUTE PRESSURE (P)
Blood flow takes the path of _____ resistance
LEAST
Resistance definition
tendency of the CV system to oppose blood flow
Resistance to blood flow (vascular resistance) caused by ______
friction (of blood cells in contact with vessel walls & with each other)
What 4 things is vascular resistance determined by?
- Vessel length (L)
- Internal vessel radius (r)
- Blood viscosity (ŋ)
- The equation: R = 8Lŋ/πr^4
Vessel length (L)
LONGER blood vessels INCREASE resistance
analogy: don’t need to suck as hard on a short straw as on a long one
Internal vessel radius (r)
- DECREASING radius (vasoCONTRICTION), INCREASES resistance
- INCREASING radius (vasoDILATION), DECREASES resistance
analogy: drinking milkshake through a fat straw is much easier than through a skinny cocktail straw
Vasoconstriction
DECREASES blood flow through a vessel
Vasodilation
INCREASES blood flow through a vessel
Blood viscosity (ŋ)
- friction b/t molecules in a flowing fluid
Blood viscosity (ŋ) is proportional to ______
HEMATOCRIT (the proportion of the blood volume that is RBC’s)
INCREASING hematocrit, _______ viscosity, which _______ resistance to blood flow
INCREASES
INCREASES
analogy: water (low viscosity) vs honey (high viscosity) moving through a tube
- drinking water through a straw is easier than drinking a thick milkshake
What do L & r determine?
the SA of the vessel in contact with the blood
The MORE SA in contact with the blood, the ______ the resistance
HIGHER
Explain F = ΔP/R
an INCREASE in R, causes a DECREASE in blood flow (F) (& vice versa)
Describe the equation: R = 8Lŋ/πr^4
- where 8 & π are CONSTANTS
- however, in humans, L (vessel length) does NOT change (an exception is the lengthening of blood vessels that occurs in obesity), & ŋ (viscosity) is RELATIVELY constant
- So R (resistance) is MAINLY determined by changes to vessel radius (R ∝ 1/r^4)
What is the exception to L (vessel length) not changing in humans?
an exception is the lengthening of blood vessels that occurs in obesity
A SMALL change in the RADIUS, produces a _____ change in _______. For example, ______
LARGE
RESISTANCE
For example, INCREASING the radius of a vessel by a factor of 2 (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 & the factors determining resistance have on blood flow
F = ΔP/R = ΔPπr^4/8Lη
Velocity of Flow
the distance a fixed volume of blood travels in a given period of time
Velocity (AKA velocity of flow)
measure of HOW FAST blood flows past a part
Formula for Velocity of Flow explained
v = Q/A
- Q = Flow rate (the volume (HOW MUCH) of blood that passes a given point in the system per unit time)
- A = cross-sectional area of the tube
Velocity ______ when cross sectional area DECREASES
INCREASES
Velocity ______ when cross sectional area INCREASES
DECREASES
Velocity is ______ in NARROW sections
FASTER
Velocity is ______ in WIDER sections
SLOWER
If flow rate (Q) = 12 cm^3/min, that is identical along the length of the vessel that means…
that in 1 min, 12cm^2 of fluid flow past point X in the narrow section, & 12cm^3 of fluid flow past point Y in the wide section
