Factors Affecting Flow Through Tubes -- 5.1

Question 1

Define flow

Answer 1

The volume of fluid passing a given point per unit time

Question 2

Define velocity

Answer 2

Rate of movement of fluid particles along the tube

Question 3

Describe laminar flow

Answer 3

there is a gradient of velocity from the middle to the edge of the vessel. Velocity is highest in the centre, and fluid is stationary at the edge. The flow in most blood vessels is laminar.

Question 4

Describe turbulent flow

Answer 4

As mean velocity increases, flow eventually becomes turbulent.
Velocity gradient breaks down – layers of fluid try to move over each other faster than physics will allow.
This greatly increases flow resistance.

Question 5

Define viscosity

Answer 5

The extent to which fluid layers resist sliding over one another.

Question 6

Describe the effects of viscosity on rate of low

Answer 6

Higher viscosity leads to slower flow of central layers, so the average velocity will be slower.
Low viscosity – difference between the centre and the edge is greater. There is a smaller difference with high viscosity liquids.

Question 7

What are the factors that occur in turbulent flow?

Answer 7

• • flow resistance is increased greatly so is harder to pump blood around.
• • noise is generated which can be heard with a stethoscope

Question 8

What is flow determined by?

Answer 8

Mean velocity

– the higher the mean velocity, the more flow there is

Question 9

What occurs when there is more viscosity?

Answer 9

Lower average velocity

Question 10

What effects does the tube diameter have on flow rate?

Answer 10

At a constant velocity, the wider the tube the faster the middle layers flow.

Question 11

What is velocity proportional to?

Answer 11

Mean velocity is proportional to the cross sectional area of the tube.

Question 12

What determine the slope of the gradient of velocity?

Answer 12

The viscosity of the fluid

Question 13

What are the relationships between mean velocity, viscosity and cross sectional area?

Answer 13

Mean velocity is inversely proportional to viscosity

Mean velocity is directly proportional to cross sectional area

Question 14

At fixed pressure, what changes are seen in velocity and the tube diameter?

Answer 14

Increased velocity occurs when the diameter increases

Question 15

At fixed flow, what changes are seen in velocity and the tube diameter?

Answer 15

Increasing the diameter of the tube will decrease the velocity of blood flow

Question 16

What is Poiseulles Law?

Answer 16

Pressure = Flow x Resistance

Question 17

What happens to resistance when velocity increases?

Answer 17

Resistance increases as velocity increases

– harder to push “thicker blood” around the vessels

Question 18

Why does the resistance decrease with he fourth power of the radius?

What is the application of this?

Answer 18

The flow increases by SA x SA which is equivalent to the radius^4

Small radius changes produce large resistance changes – it is more difficult to push blood through smaller vessels

Question 19

When flow is fixed, what is the relationship between pressure and resistance?

Answer 19

The higher the resistance, the greater the pressure change from one end of the tube to the other

Question 20

If the pressure is fixed, what is the relationship between the resistance and the flow?

Answer 20

The higher the resistance, the lower the flow

Question 21

What occurs when you have two vessels connected in series?

Answer 21

For vessels in series, resistances add together

Question 22

What occurs when you have vessels in parallel?

Answer 22

For vessels in parallel, the effective resistance is lower, as there is more than one path for the current to flow down.

Question 23

How does the flow change throughout the whole circulation?

Answer 23

It doesnt – the flow is constant throughout the whole circulation.

Question 24

What kind of resistance to arteries have?

Answer 24

Low resistance, so they have a low pressure drop

Question 25

What kind of resistance to arterioles have?

Answer 25

High resistance, so have a larger pressure drop

Question 26

What kind of resistance to vein and venules have?

Answer 26

Low resistance, so have a low pressure drop

Question 27

Why is arterial pressure high?

Answer 27

High pressure is needed in the arteries in order to drive the blood through the arterioles
– For a given total flow, the higher the arterioles resistance the higher the arterial pressure.

Question 28

What happens when the heart pumps more blood but the resistance of the arterioles remains the same?

Answer 28

The arterial pressure will rise

Question 29

Why do capillaries only need a small pressure to maintain blood flow?

Answer 29

They have a parallel conformation and low resistance

Question 30

What do narrower vessels lead to?

Answer 30

Turbulent flow –> atherosclerosis

Question 31

Define transmural pressure

Answer 31

The difference in pressure between teh outside of the blood vessel and the inside of the blood vessel

Question 32

What is a special characteristic of blood vessel walls?

Answer 32

They are distensible

– increased pressure stretches the wall which increases the radius and therefore decreases the resistance

Question 33

Why is flow easier when the pressure is higher in veins?

Answer 33

Higher pressure causes the diameter of the vessel to increase which lowers the resistance and increase the flow.

Question 34

What happens when the pressure falls too low in veins?

Answer 34

The walls will eventually collapse and blood flow will cease before the driving pressure falls to zero.

Question 35

How does distensibility of blood vessel produce capacitance?

Answer 35

As vessels widen, more blood flows in than out, so distensible vessels are able to “store” blood.
– veins are the most distensible

Question 36

What occurs when blood pressure is low?

Answer 36

There is low pressure, so vessels will collapse and the surrounding tissues will die as they are not receiving oxygen and nutrients.

Question 37

What is a specific characteristic of blood?

Answer 37

RBCs will congregate in the middle of flow, amking it appear more viscous. The plasma remains at the edges of vessels.
This causes RBCs to move around faster than plasma will.