Special Circulations

Question 1

where does the coronary circulation arise from?

Answer 1

base of the aorta

Question 2

where does the venous blood from the coronary circulation drain into?

Answer 2

drains via the coronary sinus which then drains into the right atrium

Question 3

what is the percentage of oxygen extraction by the heart?

Answer 3

75%

Question 4

what does adenosine do in the coronary arteries?

Answer 4

it is a potent vasodilator and causes vasodilatation

Question 5

what does a decrease in PO2 in coronary arteries cause?

Answer 5

vasodilatation (as the heart requires a lot of oxygen)

Question 6

what can cause intrinsic mechanisms to override extrinsic mechanisms of heart physiology?

Answer 6

metabolic hyperaemia (as a result of increased CO, so sympathetic stimulation has to cause coronary vasodilation to meet oxygen demand)

Question 7

when does most left coronary artery blood flow occur?

Answer 7

during diastole (as during systole the ventricles contract and so compress the left coronary arteries)

Question 8

what effect does shortening diastole have on coronary blood flow?

Answer 8

it decreases the amount of blood flow can take place in the left coronary artery

Question 9

what arteries is the brain supplied by?

Answer 9

both internal carotids and both vertebral arteries

Question 10

where do the vertebral arteries arise from?

Answer 10

subclavian arteries

Question 11

what are the 2 types of strokes?

Answer 11

haemorrhagic (blood leaks out damaged arterial wall) and Ischaemic (obstructive)

Question 12

what is the most common type of stroke?

Answer 12

Ischaemic

Question 13

what happens when there is an increase in PCO2 in the cerebral arteries?

Answer 13

cerebral vasodilation

Question 14

what is the reason why hyperventilating can lead to fainting?

Answer 14

elimination of CO2, decreased PCO2, therefore cerebral vasoconstriction so lack of blood flow to the brain

Question 15

what happens in cerebral arteries when MAP drops?

Answer 15

they vasodilate (so that the blood flow can remain constant)

Question 16

what happens in cerebral arteries when MAP rise?

Answer 16

they vasoconstrict in order to limit the blood flow)

Question 17

what is the normal intracranial pressure (ICP)?

Answer 17

8-13mmHg

Question 18

what is the formula for Cerebral Perfusion Pressure?

Answer 18

CPP= MAP- ICP

Question 19

what is the blood brain barrier impermeable to?

Answer 19

hydrophilic substances eg ions and proteins

Question 20

where does the pulmonary circulation originate from?

Answer 20

right ventricle

Question 21

what happens to the pulmonary circulation during hypoxia?

Answer 21

pulmonary vessels vasoconstrict (maintains the PO2)

Question 22

what is the difference between the pressure in the pulmonary circulation and the systemic circulation?

Answer 22

pulmonary circulation pressure is much lower (right ventricle is pumping against low pressure so is smaller than left)

Question 23

in skeletal muscle what condition overcomes sympathetic constrictor activity?

Answer 23

metabolic hyperaemia

Question 24

What does the contraction of muscles do to Venous Return?

Answer 24

Increases it

Question 25

what is the pathophysiology of varicose veins?

Answer 25

the valves are incompetent and so there is backflow which builds up and the pressure in the superficial veins and then they become dilated and tortuous

Question 26

what effect do varicose veins have on cardiac output?

Answer 26

none