5 Flow through tubes

Question 1

What is the relationship between pressure and flow?

Answer 1

The higher the pressure difference, the higher the flow

Question 2

What is the definition of ‘flow’?

Answer 2

The volume of fluid passing a given point per unit time (L per min)

Question 3

What is the definition of ‘velocity’?

Answer 3

The rate of movement of fluid particles along the tube (meters per second)

Question 4

How does velocity vary if the flow remains constant?

Answer 4

Varies with cross-sectional area

Question 5

What is the relationship between velocity and cross-sectional area?

Answer 5

Inversely proportional
Small cross-sectional area, high velocity eg. aorta
Large cross-sectional area, low velocity eg. capillaries

Question 6

What is ‘laminar flow’?

Answer 6

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

Question 7

What is ‘turbulent flow’?

Answer 7

There is no velocity gradient. Fluid moves in various directions at various speeds.

Question 8

What is ‘viscosity’?

Answer 8

The extent to which fluid layers resist sliding over each other.

Question 9

What is the relationship between viscosity and velocity?

Answer 9

Inversely proportional

The higher the viscosity, the lower the velocity

Question 10

At a constant velocity, what is the relationship between viscosity and cross-sectional area?

Answer 10

Proportional

The larger the cross-sectional area, the

Question 11

What causes flow of blood around the vessels?

Answer 11

The gradient of pressure

Question 12

How does the resistance of vessels combine when those vessels are:

i. ) In series
ii. ) In parallel

Answer 12

i.) Add together
ii.) R1 x R2
———-
R1 + R2

Question 13

Where does the main pressure drop occur in the CVS?

Answer 13

The arterioles

Question 14

Why is pressure in the arteries high?

Answer 14

The arterioles are high resistance vessels

Question 15

What happens to the resistance inside a vessel when the wall distends?

Answer 15

The pressure increases so the resistance falls

Question 16

The blood flow will stop before the pressure reaches zero. At what point will it stop?

Answer 16

At the critical closing pressure

Question 17

What is ‘capacitance’ in a vein?

Answer 17

The ability to store blood

Question 18

What is the consequence of blood cells congregating in the middle of the vessel?

Answer 18

Blood cells travel quicker than the plasma

Question 19

What is ‘cardiac output’?

Answer 19

The product of stroke volume and heart rate

Question 20

The heart ejects blood intermittently but blood flow is continuous. Why is this?

Answer 20

In systole, arteries stretch so more blood flows IN than OUT. This means the pressure does not rise significantly. As the arteries recoil in diastole the flow can continue as normal.

Question 21

What is the arterial pressure in:

i. ) Systole?
ii. ) Diastole?

Answer 21

i. ) 120mmHg

ii. ) 80mmHg

Question 22

What is the ‘pulse pressure’?

Answer 22

The difference between the systolic and diastolic pressures (40mmHg)

Question 23

What is the ‘average blood pressure’?

Answer 23

The diastolic pressure plus 1/3 of the pulse pressure

Question 24

What is ‘vasomotor tone’?

Answer 24

Tonic contraction of smooth muscle

Question 25

What happens when the circulation to an extremity is cut off for a short period of time?

Answer 25

When there is no blood flow, metabolites accumulate so the arterioles dilate fully. When flow returns, the resistance is low and so the flow is very high. The high flow removes the metabolites and the smooth muscle constricts.

Question 26

What is ‘central venous pressure’?

Answer 26

The pressure in the great veins which fills the heart in diastole.