CVS - Flow Through Tubes Flashcards Preview

Semester 2 > CVS - Flow Through Tubes > Flashcards

Flashcards in CVS - Flow Through Tubes Deck (44):

What must happen to blood pressure to allow it to keep flowing?

The pressure must fall all the way from the aorta to vena Cavae


What is blood flow driven by?

What is flow proportional to?

Gradient of pressure

Proportional to the pressure difference between the ends of the vessel

Higher the pressure going to low pressure = increased flow


What is flow resistance?

What is it determined by?

Flow for a given pressure is determined by the resistance of the vessel

Nature of fluid and the vessel


Define flow

Define velocity

The volume of fluid passing a given point per unit time

The rate of movement of fluid particles along the tube


At given flow rate, In vessels with small cross sectional area e.g. Aorta what would the velocity of blood flow be?

High velocity


What is meant by laminar?

There is a gradient of velocity from middle to the edge of the vessel

Velocity is highest in the centre and fluid is stationary at the edges.


What is meant by turbulent?

What happens to flow resistance?

As mean velocity increases, flow eventually becomes turbulent.

Velocity gradient breaks down as layers of fluid try to move over each other faster than physics will allow

Fluid tumbles over --> greatly increasing flow resistance


What type of flow occurs in most blood vessels?

Laminar flow


In a vessel with constant pressure driving flow, how is flow determined?

What does that depend upon?

Mean velocity

Dependent upon - viscosity of the fluid, radius of the tube


What is viscosity?

What would happen to the flow in high viscosity?

What would the average velocity be?

The extent to which fluid layers resist sliding over one another

Central layers flow slower, lower average velocity


What does viscosity determine?

What is the effect of the radius of the tube on flow rate?

What is mean velocity proportional to?

Slope of the gradient of velocity

Wider the tube, the faster the middle laters will move

Cross sectional area of the tube.


What may cause hyperviscosity?

Abnormally high plasma proteins

Abnormally high RBC or WBC count

Underlying condition must be treated otherwise it re-occurs


What may cause cardiac murmurs in a severely anaemic patient?

High blood flow velocities

Decreased viscosity of the blood caused by low RBC


What is the relationship between pressure, resistance and flow?

What factors affect flow resistance?

Pressure = flow X resistance

Resistance increases as viscosity increase

Resistance decreases to the fourth power of an increase in radius


If pressure is fixed, what will happen to resistance and flow?

If flow is fixed, what is the effect of high resistance?

Higher resistance, lower the flow

Higher resistance, the greater the pressure change from one end of the vessel to the other


What happens to flow at all points in circulation?

What resistance are arteries?



Flow is the same

Low resistance

High resistance

Low resistance


Why is the pressure within the arteries high?

Due to the arterioles high resistance.

It is difficult to push blood into them, therefore pressure increases


When does flow become turbulent?

Flow velocity is high
Low viscosity
Lumen of vessel is irregular

If vessel irregularly narrowed ee.g atherosclerosis


Given each capillary is very small and has high resistance why is their collective resistance low?

Many capillaries are connected together in parallel which gives them low resistance


What is the transmural pressure?

What happens when pressure increases?

The pressure difference between the inside and outside of the tube

Pressure increase --> walls stretch --> resistance falls


What is capacitance?

Distensible vessels being able to store blood


What is the function of the:

Heart - cyclic muscular pump, enable circulation
Arteries - gross conduction and distribution of blood supply
Arterioles - local distribution of fine control to defined tissue volume
Capillaries - micro diffusion and filtration
Veins - collection, return and capacitance


Define compliance

Define capacitance

Ability to distend and increase volume due to pressure increase

Effectively same as compliance - measure of relative volume increase per unit increase in pressure. (reservoir)


Define pressure

Measure of mechanical energy gradient in blood that drives its flow around different parts of the system


How do you measure cardiac output?

What is it about?

Stroke volume X heart rate
5l.min to the -1


Define the total peripheral resistance

The sum of all Arteriolar resistance

The sum of the resistance of all the peripheral vasculature in the systemic circulation


Describe the arterial pressure in systole

And diastole

Maximum arterial pressure

Minimum arterial pressure


What drives flow at all times in the cardiac cycle?

Blood pressure gradient


What is the typical systolic and diastolic pressure?

120 mmHg

80 mmHg


What factors affect systolic and diastolic pressure

How hard the heart pumps

Arterial compliance 'stretchiness' of elastic arteries

Total peripheral resistance


What happens to the pulse pressure down the arterial tree?

Variation in pulse pressure decreases

Approaches smoothed mean prior to flowing capillary circulation


What happens to the pressure gradient by the time it gets to the capillaries?

Decreases substantially by the time it gets to capillaries - but there is enough pressure to drive it through otherwise you would get Ischaemia


Name two resistance vessels

What is the resistance in these vessels?

Arterioles and pre capillary sphincters

High resistance - narrow lumen due to proportionately large amount of smooth muscle


Why do Arterioles have high resistance?

Narrow lumen due to the large amount of smooth muscle in tunica intima


What is vasomotor tone?

What is one of the main influences?

Continuous contraction of the muscle.

As muscles do not actively relax, expect under maximum flow there must always be some vasoconstriction.

Vasodilation is reduced vasoconstriction

Sympathetic branch of the autonomic nerves system


What happens to vasomotor tone at rest?


High vasomotor tone - tonic contraction of smooth muscle

Modest resource demand, no need to employ large functional reserve, increase SNS activity driving alpha 1 GPCRs - contraction leads to further vasoconstriction


What type of metabolites do metabollically active tissues produce?

Name four.

What effect do they have on blood flow?

Vasodilation metabolites

H+, K+, Adenosine, Lactate, CO2

Relax vascular smooth muscle, lowering resistance and increasing blood blow


What would decrease vasomotor tone?

How are metabolic factors removed?

Metabolic activity and release of vasodilation factors (usually acute)

Increased blood supply removes metabolic factors with gradual return to vasomotor tone dominated by SNS


In reactive hyperthermia when blood flow is restored why are the local arterioles dilated maximally and blood flow very high?

As blood to an organ has been cut off and then restored.

Organ/limb has continued metabolising and producing vasodilators during the period of no circulation.

When circulation is restored, arterioles dilate maximally and blood flow very high


What is compliance?

The ability of a blood vessel wall to expand and contract passively with changes in pressure

E.g. Veins - high compliance - accommodate change rapidly


What is the pressure in veins determined by?

Volume of blood they contain

Which is determined by:
Cardiac output
Body metabolic demand
Back pressure from pressure waves


What is central venous pressure?

What is it usually?

What does it depend on?

Pressure measured in the great veins supplying the heart

Required for filling RA in diastole

2-6 mmHg

Return of blood from body, pumping of the heart, gravity and muscle pumping


How do arterioles control variable blood flow to tissues?

Walls contain much smooth muscle whose state of contraction determines lumen diameter and therefore flow resistance


What are the two major subdivisions of the vascular system?

How are they arranged?

What is each subdivision composed of?

How are most vessels of a given type arranged?

Systemic and pulmonary circulations

In series with one another

Number of types of vessels (arteries, arterioles, capillaries, venules and veins)

In parallel