cardiovascular- Special circulations Flashcards
What 2 arteries arise from the base of the aorta?
Right and left coronary arteries
Where does most coronary venous blood drain?
Via Coronary sinus into the right atrium
What are special adaptations of coronary circulation?
- High Capillary Density
- High Basal Blood Flow
- High Oxygen Extraction (~75% compared to 25% whole body average) under resting conditions
- This means extra O2 (when required) cannot be supplied by increasing O2 extraction
How can extra O2 (when required) be supplied?
Can only be supplied by increasing coronary blood flow
How is coronary blood flow controlled by intrinsic mechanisms?
- decreased PO2 causes vasodilatation of coronary arterioles
- metabolic hyperaemia matches flow to demand
- adenosine (from ATP) is a potent vasodilator
How is cononary blood flow controlled by extrinsic mechanisms?
-coronary arterioles supplied by sympathetic vasoconstrictor nerves BUT over-ridden by metabolic hyperaemia
Why does sympathetic stimulation of the heart result in coronary vasodilation despite direct vasoconstriction effect
Sympathetic vasoconstrictor nerves are over-ridden by metabolic hyperaemia as a result of increased HR and SV
When does peak left coronary flow occur and what does this mean?
diastole
- shortening diastole due to fast heart rate results in decreased coronary flow
When does most of coronary blood flow and myocardial perfusion occurs in diastole?
when the subendocardial vessels from the left coronary artery are not compressed
What arteries supply the brain?
-internal carotid arteries and vertebral arteries
What happens during hypoxia to the brain?
- Grey matter is very sensitive to hypoxia
- after few seconds of ischaemia consciousness is lost
- after 3 minutes-irreversible cell damage
What forms the circle of willis?
The basilar (formed by two vertebral arteries) and the carotid arteries
What arises from the circle of willis?
major cerebral arteries
What causes a stroke?
interruption/ cut off of blood supply to a region of the brain
What does autoregulation of cerebral blood flow guard against?
Changes in cerebral blood flow if mean arterial blood pressure changes within a range of (60-160mmHg)
What has little effect in the overall cerebral blood flow?
direct sympathetic stimulation
Using autoregulation , what happens if MABP rises or falls?
rises- resistance automatically conctrict to limit blood flow
falls- resistance vessels automatically dilate to maintain blood flow
When does auto regulation fail?
MABP- falls below 60mmHg or rises above 160mmHg
When MABP drops below 50mmHg , what happens?
confusion
fainting
brain damage- if not quickly corrected
What does an increase of PCO2 cause?
cerebral vasodilatation
what does a decrease of PCO2 cause?
cerebral vasoconstriction
What is normal intracranial pressure within the skull?
8-13 mmHg
What is cerebral perfusion pressure(CPP)?
MAP- normal intracranial pressure (ICP)
What causes an increase of ICP and what are the consequences?
- head injury or brain tumour
- decreases CPP and cerebral blood flow
What is the blood brain barrier?
cerebral capillaries have very tight intercellular junctions
How does glucose cross the BBB?
facilitated diffusion using the specific carrier molecules
What is the BBB impermeable to?
hydrophilic substances - ions, proteins
Whats meets the metabolic needs of airways?
systemic bronchial circulation
Why do absorptive forces exceed filtration forces?
protects against pulmonary oedema
In pulmonary circulation, what affect does hypoxia have on pulmonary arterioles
vasoconstriction - help divert blood from poorly ventilated area in lungs
What percentage of body mass does skeletal muscle make up?
40%
why is resting blood flow low?
sympathetic vasoconstrictor tone
what happens during exercise to overcome vasoconstrictor activity?
metabolic hyperaemia
What does circulating adrenaline cause?
vasodilatation (B2 receptors)
What does skeletal muscle pump reduced the chance of?
hypotension and fainting
What is it called when blood pools in lower limb veins are caused by venous valves become incompetent?
Varicose veins
why doesn’t varicose veins lead to reduction of cardiac output?
chronic compensatory increase in blood volume
