Lecture 23-24 Flashcards by Jennifer Becker

Flow

movement of a fluid (fluids assume shape of container, continuous and amorphous, gas and liquid)

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Hemodynamics

blood flow under the action of external forces (volume, pressure, and resistance) within the circulatory system

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Driving force of flow

difference in total fluid energy

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Driving force of blood flow

directly proportional to energy

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Blood flow (F) is proportional to

difference in pressures P1-P2 F=P (pressure gradient)

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Blood flow (F) is INVERSELY proportional to

resistance F = 1/R

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Resistance is proportional to

Blood vessel length (increased L) (longer vessel more resistance)

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Resistance is inversely proportional to

blood vessel radius (larger vessel less resistance)

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Ohm’s Law for Flow

F = (P1-P2)/R

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Definition of Pressure

force (f) applied to a surface area

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Units of Pressure

Pascal (N/m2) = (kg x m/s2)

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1 mmHg = ____Pa

133.3 Pa

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cm H2O = ____Pa

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Definition of gravitational pressure

form of potential energy due to gravity

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Definition of Hydrostatic pressure

the pressure that fluid exerts on the walls of its containers due to gravity (fluid is static)

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Hydrostatic Pressure is dependent on

density, height, and the gravitational acceleration (9.8m/s2)

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Ps =

ρ x g x h

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Hydrostatic pressure is usually described as the change in P

between two heights

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Definition of Hydrodynamic Pressure

pressure generated by blood movement

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Kinetic pressure within the cardiovascular system is generated by

the heart and the elastic recoil of large arteries

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Driving pressure within vessels

sum of dynamic and hydrostatic pressures

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Transmural pressure

pressure difference inside the vessels vs outside the vessels

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Hydrodynamic Pressure Pk =

(ρ x v2)/2

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Series vs Parallel circuit of resistors

Series: arranged in a chain (head to tail); Parallel (resistors are connected with heads at one end and tails at the other

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Series circuits correspond to what in the body

progressive circulation through vessels in the circulatory tree (LV > Aorta > artery > arteriole > etc

Parallel circuits correspond to what in the body

Circulation through different organs/regions of the body

Total resistance of series circuits Rt =

R1 + R2 + R3

Total conductance of parallel circuits g =

1/Rt = 1/R1 + 1/R2 + 1/R3

Flow is proportional to

conductance

In a series, total resistance is ______ than individual resistances.

greater than

In a parallel circuit, total resistance is ______ than individual resistances.

less than

Blood flow is _____ proportional to the axial pressure gradient.

DIRECTLY

Blood flow is _____ proportional to the vessel radius raised to the 4th power.

DIRECTLY

Blood flow is _____ proportional to the vessel resistance.

INDIRECTLY

Blood flow is _____ proportional to the vessel length and blood viscosity.

INDIRECTLY

Capillaries have a _____ diameter than arterioles

SMALLER

Capillaries have a _____ resistance than arterioles

LOWER; b/c the number of capillaries is MUCH GREATER than the number of arterioles

Resistance is greatest in which region of the circulatory tree

ARTERIOLE

Poiseuille's Law F =

ΔP x Π x r4 / 8 x L x viscosity

Viscosity is described as

the shear stress required to produce a particular shear rate; shear stress: f applied to a sheet to make is move faster; shear rate:velocity gradient between two moving sheets

Viscosity is measured as η =

shear stress / shear rate = (f/A) / (v/distance) = P/V

Units of viscosity

Poise (dyne s/cm2)

Laminar flow

the shearing laminae of blood in the concentric cylinders of the vessels

Describe the velocity of the inner most cylinder of laminar flow and the outermost

Inner most cylinder moves with the highest velocity | Outer most cylinder moves with the slowest velocity

Effects of hematocrit on viscosity

higher hematocrit the greater the viscosity

Axial Streaming

RBCs accumulate in the center of the lumen of small vessels (<300um)

Axial streaming doesn't apply to

Large vessels or small vessels (like capillaries)

Blood viscosity is ________ in relation to velocity

independent

Laminar flow

fluid moves in parallel concentric layers

Turbulent flow

disorderly pattern of fluid movement

When does turbulent flow occur

when the driving pressure increases and flow reaches a critical velocity

Turbulent flow dissipates energy and causes

resistance to flow

In what pathological conditions does turbulent flow occur

heart murmurs and bruits, korotkoff sounds (BP), damage to endothelial lining, thrombi

Reynold's Number

>3000, indicates the propensity for turbulent flow

Determinants of laminar vs turbulent flow and REYNOLD'S NUMBER Rn =

tube diameter (D), velocity (v), density (ρ), and viscosity (η) (ρ x D x v) / η

Bernoulli Principle

PE and KE are interconvertible and in a constant flow system the total remains constant

PE is equivalent to

HYDROSTATIC pressure/TRANSMURAL P

KE is equivalent to

velocity of flow

Et =

PE + ((ρ x v2) / 2)

As the cross-section of a rigid tube varies, flow will remain the same, but ________________ changes

velocity will change with varying cross-sections

In an abrupt decreases in vessel cross-section

PE is converted to KE (flow), PE (transmural P) decreases and velocity of flow increases

Laplace's Law

relates transmural pressure and tension, radius, and thickness of vessel walls

Laplace's Law

in a perfused vessel the wall is stretched bc of the difference between the pressures outside and inside the walls

Laplace's Law Equation T =

(Transmural P (Pt) x r ) / wall thickness

Capillary wall tension T (LaPlaces law)

low wall tension due to a very SMALL radius, which prevents capillaries in the feet from bursting under high pressure

arteriole vasoconstriction wall tension

greater wall thickness/lumen diameter ratio = low wall tension

Large radius vessels wall tension

LARGE radius = high wall tension

Large wall tension can result in

aneurysm, tearing of the vessel wall under tension

Dilated Hearts wall tension

LARGE radius = high wall tension, more work, higher O2 consumption, to overcome high wall tension

What accounts for the non-Newtonian system of vessels?

Elasticity of blood vessels causes a nonlinear pressure-flow relationship

What 4 tissue types make up vascular walls of blood vessels

Endothelial cells, elastic tissue, vascular smooth muscle cells, and fibrous tissue

Endothelial cells

single, continuous layer lining vessels

Elastic tissue

elastin and microfibrils account for the stretch

Vascular smooth muscle

not found in capillaries, surround vessel and exerts tension by contracting,

As contraction occurs and tension increases, elasticity ______

decreases

Fibrous tissue

outer layer of collagen for tensile strength, less extensible

Higher wall thickness/lumen ratio gives greater control to vessel diameter and blood flow, this is highest when? Lowest when?

Precapillary sphincters greatest ratio and greatest control to diameter and flow Veins have a very small wall thickness/diameter ratio and regulate volume, not flow and pressure

Poiseeuille's law predicts a linear pressure-flow relationship for a rigid tube, however vessels are elastic

resulting in a NON-LINEAR PRESSURE-FLOW relationship

Blood flow _____ under higher pressure

increases (resistance decreases)

Blood flow _____ under low pressure

decreases (resistance increases)

resistance is greatest in which vessels

arterioles

Resistance vessels

permit regulation of tissue blood flow and aids in control of arterial blood pressure

Pressure _____ along arterioles

drops

Steady blood flow reaches the capillaries, it has been converted from pulsatile blood flow of the arteries due to

distensibility of the large arteries and frictional resistance in the smaller arteries

Compliance

distensibility; change in volume caused by a change in pressure

Greater compliance means

more easily the vessel can be stretched

Compliance is first achieved by...

elastin and smooth muscle and LASTLY by collagen

Compliance will peak at a certain pressure, after that peak

compliance will decrease

Arteries behave as

RESISTORS

Veins behave as

CAPACITATORS

Large veins have ______ compliance compared to large arteries

MUCH HIGHER COMPLIANCE

Aortic compliance with age

distensibility decreases with age (less elastin, more collagen)

Low aortic compliance

wider pulse pressure and more cardiac work