CVS Session 8- Special Circulations Flashcards

0
Q

What is ventricular fibrillation?

A

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

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1
Q

What does a longer P-R interval indicate?

A

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

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2
Q

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

A
  • 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.
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3
Q

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

A

5L/min

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4
Q

What is the max cardiac output?

A

20-25L/min

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5
Q

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

A

Accommodate the entire cardiac output determined by the systemic circulation.

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6
Q

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

A

Pulmonary is supply driven where as systemic is demand led.

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7
Q

What is the mean arterial pressure in the pulmonary circulation?

A

12-15mmHg

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8
Q

What is the mean capillary pressure in the pulmonary circulation?

A

9-12mmHg

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9
Q

What is mean venous pressure in the pulmonary circulation?

A

5mmHg

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10
Q

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

A
  • short wide vessels,
  • lots of capillaries,
  • arterioles have little smooth muscle
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11
Q

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

A
  • 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.
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12
Q

What is the optimum ventilation perfusion ratio?

A

0.8

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13
Q

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

A

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

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14
Q

What is the effect of gravity on lung vessels?

A

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

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15
Q

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

A

Mitral valve stenosis

Let ventricular heart failure.

16
Q

What is used to relieve symptoms of pulmonary oedema?

A

Diuretics

17
Q

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

  • seconds
  • minutes
A
  • syncope

- death

18
Q

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

A
  • has a high capillary density and therefore a large surface area and short diffusion distance
  • has a high basal flow rate
  • high oxygen extraction
19
Q

What 3 factors ensure a secure cerebral blood supply?

A
  • anastomoses between basilar and internal carotid arteries
  • Myogenic autoregulation
  • metabolic regulation
20
Q

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

A

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

21
Q

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

A

It is a high partial pressure of carbon dioxide.

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

22
Q

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

A

Cerebral blood flow decreases

23
Q

What 2 factors increase intracranial pressure?

A

-cerebral tumour or haemorrhage

24
Q

What pathway does decreased cerebral blood flow increase?

A

Sympathetic

25
Q

Which molecules can diffuse freely across the blood brain barrier?

A

Lipid soluble ones e.g oxygen and carbon dioxide.

26
Q

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

A

The left and right aortic sinuses

27
Q

When does blood flow in the coronary arteries mainly occur?

A

During diastole.

28
Q

Why does coronary blood flow mainly occur during diastole?

A

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

29
Q

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

A
  • 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.
30
Q

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

A

-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.

31
Q

What are 5 vasodilators?

A
Increased potassium conc. 
increased osmolarity 
Inorganic phosphates 
Adenosine 
High H+ conc.
32
Q

What does blood flow through in the cutaneous circulation?

A

Arterio-venous anastomoses

33
Q

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

A

They dilate in order to increase heat dissipation .

34
Q

Where are these anastomoses found?

A

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

35
Q

What influences AVAs?

A

The sympathetic nervous system.