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CVS > Special Circulations > Flashcards

Special Circulations Flashcards

0
Q

Features of the pulmonary circulation in the lungs? How?

A

Low pressure and low resistance in order to accept the whole cardiac output.
Low resistance due to short, wide vessels and lots of capillaries connected in parallel

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1
Q

What are the two circulations of the lungs?

A

Pulmonary and bronchial

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2
Q

Normal pulmonary artery pressure?

A

12-15 mmHg

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3
Q

Normal pulmonary capillary pressure?

A

9/12 mmHg

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4
Q

Normal pulmonary vein pressure?

A

5mmHg

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5
Q

What adaptations does the pulmonary circulation have to promote efficient gas exchange?

A

High density of capillaries ➡️ large surface area

Short diffusion distance

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6
Q

How is the optimal ventilation-perfusion ratio maintained?

A

Diverting blood away from alveoli which are not well ventilated by hypoxic pulmonary constriction
Increased resistance means less flow to these alveoli.

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7
Q

What can chronic hypoxic vasoconstriction cause?

A

Right ventricular failure caused by a high afterload

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8
Q

What effect does being in the upright position have on pressure in the lungs?

A

Greater hydrostatic pressure on vessels in the lower part of the lung leading to fluid formation at the base of the lungs.

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9
Q

What is oncotic pressure?

A

Pressure exerted by large molecules such as plasma proteins which draws fluid into the capillary

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10
Q

What has the greatest effect in capillary hydrostatic pressure?

A

Venous pressure

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11
Q

If there is low pressure in the pulmonary system, how much fluid will leave the capillaries

A

A relatively small amount

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12
Q

What happens if pulmonary capillary pressure increases too far?

A

Pulmonary oedema can occur

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13
Q

What effect does pulmonary oedema have?

A

Impairs gas exchange

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14
Q

What percentage of the cardiac output does the brain receive?

A

15%

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15
Q

How does the cerebral circulation meet the high demand for oxygen?

A

High capillary density - large SA for gas exchange and reduced diffusion distance
High basal flow rate - (10x average of whole body)
High oxygen extraction - (35% above average)

16
Q

How long does it take for irreversible damage to occur to neurones in ischaemia?

A

4 mins

17
Q

What is a secure blood supply ensured by in the brain?

A

Structure - anastomoses between basilar and internal carotid arteries
Function - brain stem regulates other circulations; myogenic auto regulation; metabolic factors

18
Q

What does myogenic autoregulation allow?

A

Maintains perfusion during hypotension by vasodilatation

19
Q

What is hypercapnia? What does it lead to?

A

High pO2

Vasodilatation

20
Q

What can panic hyperventilation cause?

A

Cerebral vasoconstriction leading to dizziness and fainting

21
Q

What can and can’t pass through the blood-brain barrier?

A

Can: lipid soluble molecules such as O2 and CO2

Can’t: lipid insoluble solutes such as K+ and catecholamines

22
Q

What is Cushing’s reflex?

A

An increase in intracranial pressure leads to impaired blood flow to vasomotor control regions. This increases sympathetic vasomotor activity which increases arterial blood pressure to help maintain cerebral bloodflow.

23
Q

Where do the right and left coronary arteries arise from?

A

The right and left aortic sinuses

24
Q

Why do the coronary arteries only fill during diastole?

A

In systole, contraction of the muscle makes the pressure in the arteries too high for filling

25
Q

How is cardiac muscle adapted for high blood flow?

A

High capillary density to efficiently deliver oxygen

Continuous production of NO by coronary endothelium maintains a high basal flow

26
Q

Why do you get angina on exercise if you have atheroma?

A

Coronary arteries fill mostly during diastole. Diastole is shortened during exercise and cannot meet high oxygen demand.

27
Q

Other than exercise, what can also cause angina?

A

Stress and cold. Causes sympathetic coronary vasoconstriction.

28
Q

What does the skeletal muscle circulation need to be adapted to do?

A

Increase oxygen nutrient delivery during exercise.
Remove metabolites during exercise.
Regulate arterial blood pressure.

29
Q

How is blood flow increased during exercise to skeletal muscle?

A

Opening more capillaries under influence of vasodilators. Nervous activity and metabolites reduce vasoconstrictor tone.

30
Q

About what percentage of capillaries in skeletal muscle are open at rest?

A

50%

31
Q

What regulates AVAs?

A

Sympathetic nervous system

CVS (19 decks)

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