Cardiology: Special Circulations Flashcards
Where do the coronary arteries arise from?
Base of the aorta
Where does the coronary sinus drain to?
Right atrium
What are the special adaptations of the coronary circulation?
High capillary density
High basal blood flow
High oxygen extraction
What is the consequence of the coronary ciculation having a high oxygen extraction?
Extra oxygen (when required) cannot be supplied by increasing extraction- it must be supplied by increased blood flow.
What are the intrinsic mechanisms that control coronary flow?
Decreased PO2 results in vasodilation
Metabolic hyperaemia matches flow demand
Adensoine release from ATP when the heart muscle is working hard is a potent vasodilator
What are the extrinsic mechanisms which control coronary flow?
Sympathetic stimulation- results in increased HR and SV- increased ATP break down and casodilation
Adrenaline activates B2 adrenoceptors causing vasodilation
When is coronary blood flow at its peak in the cardiac cycle?
Diastole
What supplies the brain?
Internal carotids
Vertebral Arteries
What forms the circle of willis?
BASILAR (two vertebral arteries) and the carotid arteries anastomoses
What is the purpose of the circle of willis?
Ensures that brain is perfused if major artery becomes blocked
What happens if there is an obstruction in a smaller branch?
That area of the brain is deprived of blood
Name the two types of stroke?
Haemorrhagic
Ischaemic
In what MAP range can the autoregulation of the brain control blood flow?
60-160mmHG
What happens to cerebral flow is MAP rises?
Vasoconstriction- limits blood flow
What happens is MAP decreases?
Vasodilation - decreased blood flow
What MAP can result in brain damage
50 mmHg or less
What effect does and increased of CO2 have on the cerebral circulation?
Vasodilation
What effect does a decrease of Co2 have on the cerebral circulation?
Vasoconstriction
What is normal intracranial pressure?
8-13mmHg
How do you calculate cerebral perfusion pressure?
MAP-ICP
What happens if you increase ICP?
Decreased CPP- decreased cerebral flow
What can be a consequence of raised ICP?
Failure of autoregulation
What is the BBB permeable to?
Oxygen
CO2
Glucose
What is the BBB impermeable to?
Hypdrophillic substances eg ions, catecholamines and proteins
What is the pulmonary BP compared to the systemic BP?
Much lower pressure
What is the advantage of the pulmonary circulation being so low?
Protects against oedema because absorptive forces exceed filtration forces
What does hypoxia cause in the pulmonary circulation?
VASOCONSTRICTION- this is the opposite to the systemic circulation
Why does hypoxia cause vasconstriction in the pulmonary circulation it do this?
Diverts blood away from poorly ventilated areas
Why is resting blood flow in the systemic circulation low?
Sympathetic vasocontrictor tone
What happens to the muscles in exercise?
Metabolic hyperaemia overcomes sympathetic vasoconstrictor activity
Adrenaline causes vasodilation
What is the skeletal muscle pump?
COntraction of muscles in lower limbs aids venous return to the heart
What condition arises due to incompetent venous valves?
Varicose veins
Why does this condition not lead to a chronic decrease in CO?
Compensatory mechanism chronically increased BLOOD VOLUME
