1: Special circulations

Question 1

Where do the right and left coronary arteries arise from?

Answer 1

Base of the aorta

Question 2

Where does coronary venous blood drain into?

Answer 2

Coronary sinus

Question 3

The coronary circulation has a ___ capillary density.

Answer 3

high

Question 4

What occurs in the capillaries?

Answer 4

Gas exchange (oxygen and carbon dioxide)

Question 5

What is the oxygen extraction rate in the coronary circulation compared to the normal rate in the body?

Answer 5

75% compared to 25%

Question 6

The only means of increasing coronary oxygen supply is increasing blood flow -why?

Answer 6

Oxygen extraction is already greater compared to normal circulation - cannot be increased any more

Question 7

Reduced partial pressure of oxygen in the coronary arteries causes ___.

Answer 7

vasodilation

Question 8

Which chemical, found in ATP, is a potent vasodilator?

Answer 8

Adenosine

Question 9

The net effect of sympathetic stimulation in the coronary arteries is ___.

Answer 9

vasodilation.

Question 10

The net effect of sympathetic stimulation in the coronary arteries is ___.

Answer 10

vasodilation.

Question 11

Most left coronary blood flow occurs during diastole - why?

Answer 11

During systole, subendothelial coronary arteries are squeezed by ventricular contraction

Question 12

Keeping in mind the point during the cardiac cycle at which left coronary blood flow is greatest, what could cause reduced coronary blood flow?

Answer 12

Reduced length of diastole (e.g tachycardia)

Question 13

Why is there no difference in right coronary blood flow during systole compared to diastole?

Answer 13

Pressure in right ventricle isn’t high enough to squeeze coronary arteries

Question 14

Which blood vessels supply the brain with oxygen?

Answer 14

Internal carotid arteries

Vertebral arteries

Question 15

Grey matter is (sensitive/insensitive) to hypoxia.

Answer 15

sensitive

Question 16

Arteries supplying the brain anastomose to form what?

Answer 16

Circle of Willis

Question 17

What is the benefit of having a Circle of Willis?

Answer 17

Cerebral perfusion maintained even if one carotid artery is blocked

Question 18

What causes stroke?

Answer 18

Blocked blood supply to a region of the brain

Question 19

What are the two main types of stroke?

Answer 19

Haemorrhagic (bleeding) stroke, caused by blood leaking out of arterial wall

Ischaemic stroke - atheroma

Question 20

Within which range of MAP can autoregulation of cerebral blood flow work?

Answer 20

60 - 160 mmHg

Question 21

Sympathetic stimulation has a (significant / insignificant) effect on cerebral blood flow

Answer 21

insignificant

Question 22

If MAP increases, cerebral blood vessels automatically __ to limit blood flow.

Answer 22

constrict

Question 23

If MAP decreases, cerebral blood vessels automatically __ to increase blood flow.

Answer 23

dilate

Question 24

What occurs in the brain if MAP < 50mmHg?

Answer 24

Confusion, fainting, brain damage

Question 25

Why can hyperventilation lead to fainting?

Answer 25

Decreased partial pressure of CO2 (blown off) causes vasoconstriction (cerebral blood flow decreases)

Question 26

Increased partial pressure of CO2 causes ___.

Answer 26

vasodilation

Question 27

What is intracranial pressure?

Answer 27

Pressure within the skull

Question 28

What is the normal range for intracranial pressure?

Answer 28

8 - 13 mmHg

Question 29

How can cerebral perfusion pressure be calculated?

Answer 29

CPP = MAP - ICP

Question 30

Why may intracranial blood pressure increase?

Answer 30

Head injury, brain tumour (same volume of gas, less space in the skull)

Question 31

What effect does increasing ICP have of cerebral perfusion pressure and therefore cerebral blood flow?

Answer 31

ICP increases CPP decreases Cerebral blood flow decreases (Less perfusion, dizziness>fainting>brain damage)

Question 32

Cerebral capillaries have very tight intercellular junctions - what name is given to this obstruction?

Answer 32

Blood brain barrier

Question 33

What easily passes through the blood brain barrier?

Answer 33

Oxygen, carbon dioxide, glucose

Question 34

What is the blood brain barrier impermeable to?

Answer 34

Hydrophilic substances: | ions, catecholamines (adrenaline), protein

Question 35

The pulmonary circulation takes the __ cardiac output.

Answer 35

entire

Question 36

The airways themselves (are / aren't) supplied by the pulmonary circulation.

Answer 36

aren't

Question 37

Which circulation supplies airway tissue?

Answer 37

Systemic (bronchial) circulation

Question 38

How high is pulmonary resistance compared to systemic resistance?

Answer 38

Only around 10% of systemic resistance

Question 39

What are the typical values for systolic and diastolic pulmonary artery BP?

Answer 39

20-25 mm Hg (systolic) | 6 - 12 mm Hg (diastolic)

Question 40

The pulmonary circulation is a __ resistance, __ pressure system.

Answer 40

low , low

Question 41

The capillary pressure in the pulmonary circulation is lower than that of the systemic capillaries - why?

Answer 41

Absorptive forces > filtration forces Protects against pulmonary oedema

Question 42

What does the low pressure of pulmonary capillaries protect against?

Answer 42

Pulmonary oedema

Question 43

Hypoxia causes __ in the SYSTEMIC circulation.

Answer 43

vasoconstriction

Question 44

Hypoxia causes __ in the pulmonary circulation. Why?

Answer 44

vasoconstriction V/Q mismatch - aim to divert blood from poorly ventilated lung and match again

Question 45

During exercise, skeletal muscle blood flow ___.

Answer 45

increases

Question 46

Why does skeletal muscle blood flow increase during exercise?

Answer 46

1. Metabolic hyperaemia overcomes sympathetic tone 2. Adrenaline causes vasodilation 3. Cardiac output increases

Question 47

What component of veins prevents backflow of blood?

Answer 47

Valves

Question 48

Contraction of muscles aids __ __.

Answer 48

venous return

Question 49

Contraction of muscles helps blood to move through the veins (towards / away from) the heart.

Answer 49

towards

Question 50

What happens if valves in the veins become incompetent?

Answer 50

Blood pools in lower limb veins

Question 51

What is the name given to veins with incompetent valves which have acquired a pooling of blood?

Answer 51

Varicose veins

Question 52

Why don't varciose veins reduce the cardiac output in the long term?

Answer 52

Blood volume increases to compensate

Question 53

What is metabolic hyperaemia?

Answer 53

The matching of blood flow to metabolically active tissue

Question 54

Why can metabolic hyperaemia match greater blood flow to more active tissue?

Answer 54

Metabolites (e.g CO2, adenosine, H+ and K+, etc) are all vasodilators