Properties of special circulations

Question 1

What can cause the bohr shift
(decreased affinity for oxygen, curve shifts to the right)

Answer 1

Increase in CO2
Increase in H+
Increase in 2-3 bisphosphoglycerate
Increase in temperature

Question 2

What percentage of oxygen is the myocardium able to extract?

Answer 2

75%

compared to 25% in other tissues

Question 3

The heart is susceptible to both sudden and slow obstruction. Outline both

Answer 3

Sudden = acute thrombosis = myocardial infarction

Slow = atheroma = angina

Question 4

Where are occlusions most common

Answer 4

left anterior descending artery

Question 5

How can an occlusion be viewed?

Answer 5

Angiography

Question 6

Mechanical factors reducing coronary flow:

Answer 6

1. Shortening diastole, eg. high heart rate.
2. Increased ventricular end-diastolic pressure, eg. Heart failure (aortic stenosis, stiffening of ventricle).
3. Reduced diastolic arterial pressure, eg. hypotension, aortic regurgitation

Question 7

What are Arterio-venous anastomoses (AVAs)

Answer 7

Direct connections of arterioles and venules expose blood to regions of high surface area.

Closed at low temps
Open at high temps to lose heat

Question 8

Cold-induced vasoconstriction conserves heat

Answer 8

• Sympathetic nerves react to local cold by releasing noradrenaline which binds to a2 receptors on vascular smooth muscle in skin.
• a2 receptors bind NA at lower temperatures than a1 receptors.

Question 9

what is postural hypotension

Answer 9

fainting
heat causes increased blood flow to extremities so heat can be lost
less flow to brain

Question 10

what dies prolonged obstruction of flow by compression cause

Answer 10

Severe tissue necrosis
BEd sores
on weight bearing areas
Avoided by shifting