Physiology - Special Circulation

Question 1

What are the special adaptations of coronary circulation?

Answer 1

There is high capillary density
High basal blood flow
High O2 extraction even under resting conditions. Slide 8

Question 2

How can more O2 be extracted by the heart from the coronary blood flow?

Answer 2

By increasing coronary blood flow, not by increasing extra O2. Slide 8

Question 3

What are the intrinsic mechanisms to control coronary blood flow?

Answer 3

Decrease in pO2 (vasodilation)
Metabolic hyperaemia matching flow to demand
ADP (vasodilation)
Slide 9

Question 4

What are the extrinsic mechanisms to control coronary blood flow?

Answer 4

Sympathetic vasocontrictor nerves**
Circulating adrenaline (vasodilation)
Slide 10

Question 5

Why does sympathetic vasocontrictor nerves to coronary arterioles not have a major impact?

Answer 5

Cause it is overridden by metabolix hyperaemia as a result of increased heart rate and SV. Slide 10

Question 6

In the cardiac cycle, when is there coronary blood flow and why?

Answer 6

Left coronary blood flow:
During diastole as in systole the left ventricular pressure is high constricting the coronary vessels.
Right coronary blood flow:
During systole and diastole
the right ventricular pressure is much lower. so the vessels aren’t that constricted.
Slide 12

Question 7

What happens if a patient had tachycardia in relation to coronary blood flow?

Answer 7

There would be a shorted diastole which results in reduced coronary flow. Slide 12

Question 8

What is the blood supply to the brain and why is it important for their to be special adaptations for cerebral circulation?

Answer 8

It is supplied by internal carotids and vertebral arteries.
Grey matter is very sensitive to hypoxia and results in loss of consciousness.
Permanent damage can occur within 3 minutes if not fixed. Slide 15

Question 9

What are the special adaptations of the cerebral circulation?

Answer 9

The circle of Willis formed by Basliar and carotid arteries anastomosing.
Allows cerebral perfusion to be maintained veni f a carotid artery is obstructed.
Autoregulation fo cerebral blood flow Slide 16+18

Question 10

What are the main two types of strokes?

Answer 10

Haemorrhage
Ischaemic stroke (block)
Slide 17

Question 11

What is meant by autoregulation of cerebral blood flow?

Answer 11

Guards the brain against changes in cerebral blood flow if MAP changes within a range.
If MAP increases the cerebral vessels constrict to limit blood flow. Slide 20
Slide 18

Question 12

What is the MAP when people start beign confused, faint or get brain damage?

Answer 12

Roughly 50mmHg. Slide 20

Question 13

What are other regulations of cerebral blood flow?

Answer 13

Decrease in pCO2 causes cerebral vasocontriction, e.g. hyperventilation.
Increased blood flow to active parts of the brain. Slide 21

Question 14

How can cerebral perfusion pressure be calculated and what is the normal intracranial pressure?

Answer 14

CPP = MAP - ICP

Normal ICP = 8-13mmHg. Slide 24

Question 15

What is the Blood brain barrier and why does it have such high selectivity?

Answer 15

Cerebral capillaries which have very tight intracellular junctions.
Highly permeable to O2 and CO2.
Needs hgih selectivity to protect brain neurones form fluctuating ion levesl in blood.
Slide 25 +26

Question 16

What is the normal pulmonary artery BP?

Answer 16

(20-25)/ (6-12)

Slide 28

Question 17

What are special adaptations of the pulmoanry circulation?

Answer 17

Hypoxia causes vasocontriction, directing blood to more ventilated areas.
Absorptive forces exceed filtration forces (protects against pulmonary oedema). Slide 29

Question 18

What innervation does blood flow to skeletal muscle have?

Answer 18

Sympathetic vasocontrictor tone. Slide 31

Question 19

When is the sympathetic vasocontrictor tone overcome?

Answer 19

During exercise as metabolic hyperaemia overcomes it. Slide 32

Question 20

What are varicose veins adn why do they not cause a reduction of cardiac output?

Answer 20

When venous valves become incompetent and cause pooling of blood in the lower limbs.
As it is a gradual chronic condition, the blood volume increases to compensate. Slide 34