1: Special circulations Flashcards
Where do the right and left coronary arteries arise from?
Base of the aorta
Where does coronary venous blood drain into?
Coronary sinus
The coronary circulation has a ___ capillary density.
high
What occurs in the capillaries?
Gas exchange (oxygen and carbon dioxide)
What is the oxygen extraction rate in the coronary circulation compared to the normal rate in the body?
75% compared to 25%
The only means of increasing coronary oxygen supply is increasing blood flow -why?
Oxygen extraction is already greater compared to normal circulation - cannot be increased any more
Reduced partial pressure of oxygen in the coronary arteries causes ___.
vasodilation
Which chemical, found in ATP, is a potent vasodilator?
Adenosine
The net effect of sympathetic stimulation in the coronary arteries is ___.
vasodilation.
The net effect of sympathetic stimulation in the coronary arteries is ___.
vasodilation.
Most left coronary blood flow occurs during diastole - why?
During systole, subendothelial coronary arteries are squeezed by ventricular contraction
Keeping in mind the point during the cardiac cycle at which left coronary blood flow is greatest, what could cause reduced coronary blood flow?
Reduced length of diastole (e.g tachycardia)
Why is there no difference in right coronary blood flow during systole compared to diastole?
Pressure in right ventricle isn’t high enough to squeeze coronary arteries
Which blood vessels supply the brain with oxygen?
Internal carotid arteries
Vertebral arteries
Grey matter is (sensitive/insensitive) to hypoxia.
sensitive
Arteries supplying the brain anastomose to form what?
Circle of Willis
What is the benefit of having a Circle of Willis?
Cerebral perfusion maintained even if one carotid artery is blocked
What causes stroke?
Blocked blood supply to a region of the brain
What are the two main types of stroke?
Haemorrhagic (bleeding) stroke, caused by blood leaking out of arterial wall
Ischaemic stroke - atheroma
Within which range of MAP can autoregulation of cerebral blood flow work?
60 - 160 mmHg
Sympathetic stimulation has a (significant / insignificant) effect on cerebral blood flow
insignificant
If MAP increases, cerebral blood vessels automatically __ to limit blood flow.
constrict
If MAP decreases, cerebral blood vessels automatically __ to increase blood flow.
dilate
What occurs in the brain if MAP < 50mmHg?
Confusion, fainting, brain damage
Why can hyperventilation lead to fainting?
Decreased partial pressure of CO2 (blown off) causes vasoconstriction (cerebral blood flow decreases)
Increased partial pressure of CO2 causes ___.
vasodilation
What is intracranial pressure?
Pressure within the skull
What is the normal range for intracranial pressure?
8 - 13 mmHg
How can cerebral perfusion pressure be calculated?
CPP = MAP - ICP
Why may intracranial blood pressure increase?
Head injury, brain tumour (same volume of gas, less space in the skull)
What effect does increasing ICP have of cerebral perfusion pressure and therefore cerebral blood flow?
ICP increases
CPP decreases
Cerebral blood flow decreases
(Less perfusion, dizziness>fainting>brain damage)
Cerebral capillaries have very tight intercellular junctions - what name is given to this obstruction?
Blood brain barrier
What easily passes through the blood brain barrier?
Oxygen, carbon dioxide, glucose
What is the blood brain barrier impermeable to?
Hydrophilic substances:
ions, catecholamines (adrenaline), protein
The pulmonary circulation takes the __ cardiac output.
entire
The airways themselves (are / aren’t) supplied by the pulmonary circulation.
aren’t
Which circulation supplies airway tissue?
Systemic (bronchial) circulation
How high is pulmonary resistance compared to systemic resistance?
Only around 10% of systemic resistance
What are the typical values for systolic and diastolic pulmonary artery BP?
20-25 mm Hg (systolic)
6 - 12 mm Hg (diastolic)
The pulmonary circulation is a __ resistance, __ pressure system.
low , low
The capillary pressure in the pulmonary circulation is lower than that of the systemic capillaries - why?
Absorptive forces > filtration forces
Protects against pulmonary oedema
What does the low pressure of pulmonary capillaries protect against?
Pulmonary oedema
Hypoxia causes __ in the SYSTEMIC circulation.
vasoconstriction
Hypoxia causes __ in the pulmonary circulation. Why?
vasoconstriction
V/Q mismatch - aim to divert blood from poorly ventilated lung and match again
During exercise, skeletal muscle blood flow ___.
increases
Why does skeletal muscle blood flow increase during exercise?
- Metabolic hyperaemia overcomes sympathetic tone
- Adrenaline causes vasodilation
- Cardiac output increases
What component of veins prevents backflow of blood?
Valves
Contraction of muscles aids __ __.
venous return
Contraction of muscles helps blood to move through the veins (towards / away from) the heart.
towards
What happens if valves in the veins become incompetent?
Blood pools in lower limb veins
What is the name given to veins with incompetent valves which have acquired a pooling of blood?
Varicose veins
Why don’t varciose veins reduce the cardiac output in the long term?
Blood volume increases to compensate
What is metabolic hyperaemia?
The matching of blood flow to metabolically active tissue
Why can metabolic hyperaemia match greater blood flow to more active tissue?
Metabolites (e.g CO2, adenosine, H+ and K+, etc) are all vasodilators
