Factors affecting flow through tube

Question 1

Define pressure

Answer 1

Force exerted per unit area

Question 2

Define resistance

Answer 2

A force that tends to oppose the flow of a substance

[Nb. resistance is determined by radius of vessel/ airway]

Question 3

Define pressure gradient

Answer 3

The difference in forces exerted (per unit area) at either end/ side of an object (e.g. a tube or membrane)

Pressure gradient = flow x resistance

Question 4

Define flow

Answer 4

The volume of fluid passing a given level of the circulation/ airways per unit time.

Usually measured in ml.s-1 or l.min-1

Flow = pressure gradient / resistance

Question 5

Define velocity

Answer 5

The rate of movement of fluid particles along a vessel/ airway.

Measured in cm.s-1

Question 6

Define laminar flow

Answer 6

Fluid does not move at the same velocity across the width of the tube - layers of fluid essentially move one over the top of another.

Velocity will be lowest at the edges.

Question 7

Define turbulent flow

Answer 7

Layers of fluid move in a disordered fashion.

Results in damage to endothelium.

Question 8

Define viscosity

Answer 8

Properties of fluid (e.g. thickness or stickiness) that affect ability to flow through tubes (resistance)

Question 9

Define capacitance

Answer 9

The distensibility of blood vessels allowing them to readily accommodate changes in blood volume

Question 10

When may turbulent flow occur?

Answer 10

1. When velocity is high
2. When viscosity of blood is low
3. When blood vessel diameter is high

Question 11

What is the relationship between flow, pressure gradient and resistance?

Answer 11

Flow is proportional to the pressure difference between the ends of vessels and airways (so the larger the pressure difference, the larger the flow)

For any given pressure gradient, flow is determined by resistance (the higher the resistance, the lower the flow)

Question 12

What is the relationship between flow, velocity and cross-sectional areas in tubes?

Answer 12

Flow will remain constant through an airway/ vessel but the velocity may vary if the cross-sectional area of the tube varies.

At any given flow, velocity is inversely proportional cross sectional area (meaning that velocity will decrease as the cross-section gets larger in order to even out flow rate)

Question 13

What is the difference between resistance in series and resistance in parallels?

Answer 13

Resistance in series = resistance is a sum of resistance in each vessel (so resistance accumulates but flow remains the same)

Resistance in parallels = drop in resistance and flow through each vessel is inversely proportional to its resistance

Question 14

What factors determine levels of resistance in a tube?

Answer 14

Length of tube
Radius of tube
Viscosity of fluid