CVS Session 8- Special Circulations

Question 0

What is ventricular fibrillation?

Answer 0

Uncoordinated contraction of the ventricles. They contract very fast and therefore CO plummets.

Question 1

What does a longer P-R interval indicate?

Answer 1

A problem at the AV node causing delayed spread of electrical activity to the ventricles.

Question 2

What are the two lung circulations and what do they do?

Answer 2

• bronchial- part of the systemic circulation and meets the metabolic requirements of the lungs
• pulmonary- provides blood supply to alveoli and is required for gas exchange.

Question 3

What is the cardiac output at rest for a typical 70kg man?

Answer 3

5L/min

Question 4

What is the max cardiac output?

Answer 4

20-25L/min

Question 5

What has the pulmonary circulation got to be able to do?

Answer 5

Accommodate the entire cardiac output determined by the systemic circulation.

Question 6

What is the main difference between the pulmonary and systemic circulation?

Answer 6

Pulmonary is supply driven where as systemic is demand led.

Question 7

What is the mean arterial pressure in the pulmonary circulation?

Answer 7

12-15mmHg

Question 8

What is the mean capillary pressure in the pulmonary circulation?

Answer 8

9-12mmHg

Question 9

What is mean venous pressure in the pulmonary circulation?

Answer 9

5mmHg

Question 10

What adaptations mean that resistance is low in the pulmonary circulation?

Answer 10

• short wide vessels,
• lots of capillaries,
• arterioles have little smooth muscle

Question 11

What two adaptations means that the pulmonary circulation has efficient gas exchange?

Answer 11

• large surface area due to a high density of capillaries in alveolar walls
• short diffusion distance due to a thin tissue separating plasma and gas.

Question 12

What is the optimum ventilation perfusion ratio?

Answer 12

0.8

Question 13

How does hypoxia pulmonary vasoconstriction ensure that this ratio is maintained?

Answer 13

It causes vasoconstriction of poorly ventilated vessels, therefore they are less perfused and this blood is shunted to well ventilated alveoli.

Question 14

What is the effect of gravity on lung vessels?

Answer 14

Apex vessels collapse during diastole
Middle vessels at heart level are patent
Base vessels are distended.

Question 15

What 2 conditions cause pulmonary oedema due to high LA pressure?

Answer 15

Mitral valve stenosis

Let ventricular heart failure.

Question 16

What is used to relieve symptoms of pulmonary oedema?

Answer 16

Diuretics

Question 17

What is the result of lack of blood flow to the brain after:

• seconds
• minutes

Answer 17

• syncope

- death

Question 18

How does the brain meet its high oxygen demand?(3)

Answer 18

• has a high capillary density and therefore a large surface area and short diffusion distance
• has a high basal flow rate
• high oxygen extraction

Question 19

What 3 factors ensure a secure cerebral blood supply?

Answer 19

• anastomoses between basilar and internal carotid arteries
• Myogenic autoregulation
• metabolic regulation

Question 20

What is the benefit of Myogenic autoregulation when blood pressure falls?

Answer 20

It causes vasodilation to increase blood flow to the brain despite this drop in blood pressure.

Question 21

What is hypercapnia and what benefit does it have on cerebral blood flow?

Answer 21

It is a high partial pressure of carbon dioxide.

It causes vasodilation and therefore increases blood flow to the brain.

Question 22

What happens due to Cushing’s reflex when intracranial pressure increases?

Answer 22

Cerebral blood flow decreases

Question 23

What 2 factors increase intracranial pressure?

Answer 23

-cerebral tumour or haemorrhage

Question 24

What pathway does decreased cerebral blood flow increase?

Answer 24

Sympathetic

Question 25

Which molecules can diffuse freely across the blood brain barrier?

Answer 25

Lipid soluble ones e.g oxygen and carbon dioxide.

Question 26

Where do the left and right coronary arteries arise from respectively?

Answer 26

The left and right aortic sinuses

Question 27

When does blood flow in the coronary arteries mainly occur?

Answer 27

During diastole.

Question 28

Why does coronary blood flow mainly occur during diastole?

Answer 28

Because during systole, the ventricular walls compress against the coronary vessels and therefore reduce their blood flow.

Question 29

How is the oxygen demand met in the coronary circulation?(3)

Answer 29

• small fibre diameter therefore short diffusion distance
• high capillary density therefore efficient oxygen exchange
• nitric oxide production by coronary endothelium causes vasodilation and therefore an increased basal flow rate.

Question 30

What is the normal state of capillaries and arterioles in skeletal muscle and why?

Answer 30

-arterioles have high vasomotor tone and are therefore constricted
-a lot of capillaries are shut off by pre-capillary sphincters
This allows recruitment of extra capillaries and dilatation of arterioles during exercise, in order to increase blood flow.

Question 31

What are 5 vasodilators?

Answer 31

Increased potassium conc. 
increased osmolarity 
Inorganic phosphates 
Adenosine 
High H+ conc.

Question 32

What does blood flow through in the cutaneous circulation?

Answer 32

Arterio-venous anastomoses

Question 33

What do these anastomoses do when body temperature increases and why?

Answer 33

They dilate in order to increase heat dissipation .

Question 34

Where are these anastomoses found?

Answer 34

In the peripheries- e.g fingers, toes, ears, nose etc.

Question 35

What influences AVAs?

Answer 35

The sympathetic nervous system.