Continuous and intermittent flow

Question 1

What do elastic arteries do?

Answer 1

Convert the intermittent pumping of the heart into continuous blood flow

Question 2

What are the elastic arteries?

Answer 2

The aorta, and main arteries supplying the heart and the legs

Question 3

What is the composition of the elastic arteries?

Answer 3

Endothelium
Elastin
Smooth muscle
Collagen

Question 4

What is the function of the elastic arteries?

Answer 4

Distribution of blood
dampening of pressure changes
conversion of intermittent pumping of the heart to continuous blood flow

Question 5

What happens to energy during the cardiac cycle of the elastic arteries?

Answer 5

Mid systole - Energy used to stretch elastin
End systole - elastic energy stored in elastin
Mid diastole - elastin recoils and energy transferred to blood
End diastole - elastin returns to original shape

Question 6

What happens to the pressure in the elastic arteries during the cardiac cycle?

Answer 6

Aortic pressure (systole) = 120mmHg
(diastole) = 80mmHg

Left ventricular pressure (systole) = 120mmHg
(diastole) = 5mmHg

Question 7

what determines the arterial blood pressure?

Answer 7

Elastic arteries which is also the driving force for flow

Question 8

How do you calculate the mean arterial blood pressure (MAP)

Answer 8

MAP = DP + (SP-DP)

SP - systolic pressure
DP - diastolic pressure
pressure that determines the flow

Question 9

what is the systolic pressure determined by?

Answer 9

Stroke volume
Aortic/arterial distensibility
ejection velocity
DP of previous beat

Question 10

What leads to an increase in SP?

Answer 10

EDV increase leading to SV increase (more venous return)

Increased contractility leading to increased SV (exercise, circulating catecholamines)

Question 11

What determines MAP?

Answer 11

Arteriolar resistance
aortic/arterial distensibility
Heart Rate

Question 12

What is the effect of ageing on the elastin in elastic fibres?

Answer 12

Cannot stretch the aorta as much and therefore there is an increase in systolic pressure but also since the aorta is not stretched, the pressure falls further during diastole.
Increased pulse pressure

Question 13

What is the effect of exercise on systolic pressure and total peripheral resistance?

Answer 13

Increased SV
Decreased TPR
Increased systolic pressure and decreased diastolic pressure (therefore increased pulse pressure)

Question 14

How does breathing maintain constant gases in the alveolar space?

Answer 14

Breathing is an intermittent pump but results in constant gases in the alveolar space since a relatively small volume is added to a larger constant volume.
As long as the CO2 out is matched to the CO2 in, then there will be a constant blood gas

Question 15

What is the function of the capillaries?

Answer 15

the circulations exchange vessels which are involved in diffusion and filtration

Question 16

What are the composition of capillaries?

Answer 16

Endothelium (mostly)
Elastin
Smooth muscle
Collagen

Question 17

how do we set up conditions for good diffusion in the capillaries?

Answer 17

Flow = velocity x cross sectional area

Blood velocity in capillaries is very slow - good conditions for exchange by diffusion and filtration.
This is due to having a large number of capillaries in parallel and therefore an increased cross sectional area which leads to a decreased flow velocity.

Question 18

how is filtration brought about?

Answer 18

Forces favouring filtration,
Forces favouring reabsorption

Hydrostatic pressure and oncotic pressure

Question 19

How do you calculate net filtration?

Answer 19

Kf x [(Pc + πi) – (Pi + πp)]
Net filtration = Kf x (forces favour filtration) – (forces favouring reabsorption)

Kf reflection coefficient (leakiness of capillary)0]0

Question 20

What are the forces favouring filtration in capillaries?

Answer 20

Capillary hydrostatic pressure

interstitial oncotic pressure

Question 21

What are the forces favouring reabsorption in the capillaries?

Answer 21

Interstitial hydrostatic pressure

Plasma oncotic pressure

Question 22

What are starlings forces on peripheral capillaries?

Answer 22

Blood enters capillary with a hydrostatic pressure of 35mmHg
Blood leaves capillary with a hydrostatic pressure of 15mmHg

Plasma oncotic pressure of 25mmHg stays constant.

Question 23

What happens at the arterial end of the capillaries in terms of filtration?

Answer 23

at the arteriolar end of the capillary: Net filtration 𝜶 Pc - p
35 – 25 mmHg = 10mmHg favouring filtration of fluid out of capillary

Question 24

What happens at the venous end of the capillaries in terms of filtration?

Answer 24

at the venous end of the capillary: Net filtration 𝜶 Pc - p

15 – 25 mmHg = – 10mmHg favouring reabsorption of fluid into capillary

Question 25

What is the effect of pre-capillary vasoconstriction on net filtration?

Answer 25

downstream capillary hydrostatic pressure decreases as blood moves through the capillaries. Overall net reabsorption of fluid due to filtration < reabsorption at a the venular end of the capillary.

Question 26

What is the effect of pre-capillary vasodilation on net filtration?

Answer 26

Overall net filtration of fluid due to increased filtration and decreased reabsorption as there is an increase in Pressure within the capillaries.

Question 27

What happens to the excess net fluid taken up

Answer 27

Taken up by the lymphatic vessels which then take the fluid back to the heart via the subclavian veins in the chest.