Session 5

Question 0

Define velocity

Answer 0

Rate of movement of fluid particles alone the tube. Relationship between velocity and flow determines blood pressure.

Question 1

Define flow

Answer 1

Volume of fluid passing a given point per unit time (e.g. ml/min)

Question 2

Describe the relationship between velocity and cross sectional area for a given flow

Answer 2

Velocity is inversely proportional to cross sectional area.
Therefore vessels such as aorta have a high velocity whereas capillaries have a low velocity (capillaries have a large csa)

Question 3

What is laminar flow?

Answer 3

When there is a uniform gradient of velocity from the middle to the edge of the vessel

Question 4

What is turbulent flow?

Answer 4

Break down of velocity gradient. Fluid tumbles over, flow resistance increases greatly.

Question 5

What does the mean velocity depend on?

Answer 5

Viscosity of fluid

Radius of tube

Question 6

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

Answer 6

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

Question 7

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

Answer 7

The higher the resistance, the lower the flow.

Question 8

Which of the two have a higher resistance; arteries or arterioles?

Answer 8

Arteries because the pressure drop in the arteries is small whereas the pressure drop in the arterioles is larger.

Question 9

Why is the resistance in capillaries low?

Answer 9

Although they have high resistance individually there are multiple capillaries connected in parallel therefore overall their resistance is low.

Question 10

Is the resistance in veins and venules high or low?

Answer 10

Low because the pressure drop is low.

Question 11

Is pressure within arteries high or low?

Answer 11

High resistance of arterioles means that there is a greater total peripheral resistance and therefore the pressure in the arteries is high.

Question 12

Define transmural pressure

Answer 12

Transmural pressure is the difference in pressure between two sides of a wall.

Question 13

What does the distensibility of blood vessels allow?

Answer 13

Allows changes in blood pressure to not disrupt the flow dramatically however if the pressure falls too much then the walls will eventually collapse.

Question 14

How is capacitance possible?

Answer 14

As vessels widen with increased pressure, more blood flows transiently in than out and vice versa. Distensible vessels therefore store blood.

Question 15

Which of the vessels are most distensible?

Answer 15

Veins

Question 16

What is the composition of blood in the vessels?

Answer 16

Two main components - cells and plasma. Blood cells congregate in the middle of the flow, so apparent viscosity increases and cells go round faster than the plasma.

Question 17

What are the resistance vessels?

Answer 17

The blood vessels, including small arteries, arterioles, and metarterioles that form the major part of the total peripheral resistance to blood flow.

Question 18

Describe the flow of the blood by the heart

Answer 18

Pulsatile flow i.e. the heart ejects blood intermittently

Question 19

Describe the pressure changes in the arteries in systole and diastole

Answer 19

In systole - arterial pressure rises to a max
In diastole - arterial pressure falls to a minimum
The pressure goes up faster than it goes down (systole occupies 2/3 of the time)

Question 20

What are the values of arterial pressure during systole and diastole?

Answer 20

Systole - 120mmHg

Diastole - 80mmHg

Question 21

What are the factors affecting systolic pressure?

Answer 21

Contraction force of the heart
Total peripheral resistance
Stretchiness (compliance) of the arteries

Question 22

What are the factors affecting diastolic pressure?

Answer 22

Systolic pressure

Total peripheral resistance

Question 23

Define pulse pressure and give a value for it

Answer 23

Difference between systolic and diastolic pressure (approx. 40 mmHg)

Question 24

Define vasomotor tone

Answer 24

Tonic contraction of smooth muscle. Constant contraction –> tonic contraction.
Vasoconstriction/vasodilatation

Question 25

What are the factors affecting smooth muscle contraction?

Answer 25

Vasomotor tone mostly produced by sympathetic brach of NS
Tone is antagonised by vasodilator factors.
Actual resistance is determined by a balance between the two

Question 26

What is reactive hyperaemia?

Answer 26

Circulation to an area (e.g. arm) is cut off for a minute or two. When blood flow is restored there’s an enormous increase for a short while.

Question 27

Give examples of vasodilator metabolites

Answer 27

H+, K+, adenosine.
H+ produced due to a decrease in oxygen
K+ and adenosine leak from cells due to compromised metabolic activity

Question 28

What happens to metabolites when there is no blood flow?

What happens when the flow is returned?

Answer 28

They accumulate, causing the arterioles to dilate maximally. Thus when flow is returned, resistance is very low and therefore the flow is high. The high flow washes the metabolites away therefore causing constriction of the arterioles.

Question 29

Which organ is good particularly good at autoregulation?

Answer 29

Kidney

Question 30

What is the relationship between total peripheral resistance (TPR) and the body’s need for blood?

Answer 30

TPR is inversely proportional 1/body’s need for blood

Question 31

What is the central venous pressure?

Answer 31

Pressure in RA (or great veins). Fills the heart during diastole.

Question 32

What does the central venous pressure depend on?

Answer 32

Return of blood from the body
Pumping of the heart
Gravity and ‘muscle pumping’

Question 33

What is autoregulation?

Answer 33

If supply pressure changes, blood flow will decrease therefore metabolite concentration increases. This alters the resistance of arterioles so blood flow returns to an appropriate level for metabolism.

Question 34

Define venous pressure

Answer 34

The pressure exerted on the walls of the veins by the circulating blood