special circulations Flashcards
name some special adaption of coronary circulation
high capillary density
high basal blood flow
high oxygen extraction
how can extra O2 be supplied
not be inc O2 extraction (at max) - only be inc coronary blood flow
what does dec O2 cause
vasodilatation of coronary arterioles
wha is adenosine
vasodilator
what does inc HR and SV do to coronary arterioles
controlled by sympathetic vasoCONSTRICTOR nerves but these are overridden by metabolic hyperaemia = VASODILATATION despite vasoconstrictor effect
what is this called
functional sympatholysis
when does peak coronary flow occur
diastole
what does shortening diastole do
eg in fast HR - dec coronary flow
what is grey matter sensitive to
hypoxia
where is gray matter found in the brain
outer - cell bodies
where is white matter found in the brain
inner - myelinated axons
what does auto regulation of MABP fail below
60mmHg
what does MABP below 50mmHg cause
confusion, fainting, brain damage
why does hyperventilation lead to fainting
dec PCO2 causes vasoconstriction
why does hypercapnia cause morning headache
inc CO2 causes cerebral vasodilation
what is the normal ICP in the skull
8-13 mmHg
what does CPP =
MAP-ICP
what does inc ICP do
dec CPP and cerebral blood flow
what inc ICP
head injury or brain tumour
wht can the BBB let across
glucose
how does glucose cross teh BBB
facilitated diffusion
what does the BBB do
protect the brain from fluctuating levels of ion int he blood - doesn’t let ions through
why does hypoxia cause vasoconstriction of pulmonary arterioles
to divert the blood from poorly ventilated areas of the lung
why do varicose veins form
blood pools in lower limbs if venous valves become incompetent
