Special Circulations Flashcards
where do the right and left coronary arteries arise from?
arise from base of the aorta
where does most of the coronary venous blood drain via and into what?
Drains via = coronary sinus
Drains into = right atrium
what are 3 special adaptations does the coronary circulation have to deliver maximal O2 to myocardium?
1) high capillary density
2) high basal blood flow
3) high oxygen extraction (75% compared to 25% whole body average) under resting conditions
what does the higher oxygen extraction, in the special adaptation of coronary circulation mean?
means extra O2 (when required) CANNOT be supplied by increasing O2 extraction
how can extra O2 only be supplied to the myocardium ?
by increasing coronary blood flow
BECAUSE;
- the O2 extraction at the capillaries cannot be increased any further
how is coronary blood flow controlled?
1) intrinsic mechanisms
2) extrinsic mechanisms
in the intrinsic control of coronary blood flow, what happens to PO2 levels and what does this cause?
= Decreased PO2
= causing vasodilation of coronary arterioles
what matches coronary bloods flow to demand in the intrinsic control?
metabolic hyperaemia
what is hyperaemia?
increased blood flow to an organ
what is an example of a potent vasodilator involved in the intrinsic mechanism of coronary blood flow?
Adenosine (from ATP).
what are the coronary arterioles supplied by?
supplied by sympathetic vasoconstrictor nerves
However, why is there no vasoconstriction in the coronary arterioles then?
1) as the sympathetic system is over-ridden by metabolic hyperaemia
(- due to increased HR & SV)
2) causes vasodilation so heart gets increased flow
what is released from the adrenal gland that activates B2 adrenergic receptors causing vasodilation?
adrenaline
when does peak left coronary flow happen and why?
= during diastole
- as its when the left ventricle contracts during systole the left coronary artery is also affected
when does most of the coronary blood flow and myocardial perfusion occur?
occurs in diastole when the sub-endocardial vessels from the left coronary artery are not compressed
which 2 main arteries supply the brain?
1) internal carotids
2) vertebral arteries
what is grey matter?
darker tissue in CNS that consists of nerve cells bodies.
- consciousness is lost after a few seconds of ischaemia, irreversible cells damage within 3minutes
what is grey matter very sensitive to?
sensitive to hypoxia
when is consciousness of grey matter lost?
when is irreversible cell damage done?
Consciousness lost
= after few seconds of ischaemia
Irreversible cell damage
= within 3 minutes
what forms the circle of willis?
= BASILAR (formed by 2 vertebral arteries) & CAROTID arteries anastomoses
what arises from the circle of willis?
major cerebral arteries
how does circle of willis maintain cerebral perfusion?
- even is one carotid artery gets obstructed, the others can redistribute their blood at the anastomosis
what causes a stroke?
interruption/cut-off blood supply to a region of the brain
what does auto regulation of cerebral blood flow do?
= gourds against changes in cerebral blood flow if MABP changes within a range (60-160mmHg)
i.e. stops flow changing even if there are changes in pressure;
what happens to the resistance of the vessels if MABP rises?
vessels automatically constrict to limit blood flow.
what happens to the resistance of the vessels if MABP falls?
vessels automatically dilate to maintain blood flow
what happens if MABP falls below 50mmHg?
- confusion
- fainting
- brain damage if not quickly corrected
what does an increase and decrease in PCO2 do to cerebral flow?
Increase = causes vasodilation
Decrease = causes vasoconstriction
what is normal intra-cranial pressure within the skull?
about 8-13mmHg
what is the relationship between cerebral percussion pressure (CPP), MAP and ICP?
CPP = MAP - ICP
what does increasing inter-cranial pressure, i.e. due to head injury or brain tumour, do to cerebral perfusion pressure and blood flow?
= decreases cerebral perfusion pressure and blood flow
what is the blood brain barrier?
= very tight inter-cellular junctions at the cerebral capillaries
what are the cerebral capillaries highly permeable to?
O2 and CO2
how does glucose cross the BBB?
by facilitated diffusion using specific carrier molecules.
what is the BBB impermeable to and why is this useful?
hydrophilic substances;
e.g. ions, catecholamines, proteins
- useful as it protects the brain neurones from fluctuating levels of ions in the blood
where does the entire cardiac output flow from and into?
flows from right ventricle into pulmonary circulation
is the pulmonary system a high or low pressure system?
low
what type of force exceeds filtration forces and what does this protect from?
absorptive forces
= protecting against pulmonary oedema
does hypoxia constrict or dilate PULMONARY arterioles and why?
constricts them
= diverts blood away from poorly ventilated areas of lung
True or false.
Resting blood low is low because of parasympathetic vasoconstrictor tone.
False.
- it is low due to SYMPATHETIC vasoconstrictor tone
what happens during exercise in terms of vasoconstriction/dilation in skeletal muscles?
- local metabolic hyperaemia overcomes sympathetic activity causing vasodilation
- adrenaline causes vasodilation (B2 adrenergic receptors)
- increased CO increasing skeletal muscle blood flow
where does the skeletal muscle pump originate from? and what does contraction of these muscles aid?
large veins in limbs lie between skeletal muscles
= aids venous return
what does the skeletal muscle pump reduce the chances for?
= postural hypotension & fainting
what are varicose veins?
when valves in veins of lower limbs become incompetent and so blood pools form in them
how does varicose veins not reduce cardiac output?
because there is a chronic compensatory increase in blood volume
