special circulations Flashcards
what 4 special systemic circulations?
- cerebral
- coronary
- skeletal
- cutaneous
why is cerebral circulation important?
what % of total CO does it recieve?
why does grey matter consume so much O2?
how does cerebral circulation meet the high demand ?
when does irreversible hypoxic damage to neurone occur?
the brain has a high O2 demand, neurones are sensitive to hypoxia
15%
active neurones require lots of O2
high capillary density (large SA and erduced diffusion distance), high basal flow rate, high O2 extraction
after 4 minutes
how is the cerebral blood supply secured?
structurally?
functionally?
many anastomoses between basilar and internal carotid artieries = alternate blood supply
myogenic autoregulation to maintain perfusion during hypotension, metabolic factors, brain stem regulates other circulations
what is myogenic autoregulation?
what happens when blood pressure drops?
what happens when blood pressure rises?
at what point does this regulation fail?
a method to allow perfusion to the brain even when there is hypotension
cerebral vessels are well developed myogenically
vasodilation - allows blood to flow and perfuse still
vasoconstriction - so flow doesn not increase toooo much
when bp drops below 50mmHg
how is blood supply to the brain maintained metabolically?
in an area of increased blood flow what metabolites would there be?
what is a powerful vasodilator of cerebral arterioles?
why can panic lead to fainting?
hypercapnia (high CO2) = vasodilation = more blood flow to active neurones - vice versa
high CO2, high K+(dur to many APs), Adenosine (from ATP breakdown), low O2 (as its used up)
adenosine
panic = hyperventiation = hypocapnia = cerebral vasoconstriction = less blood flow = dizzy/faint
what is the cushings reflex ?
what triggers it?
what happens when is it activated?
what sympathetic activity helps the brain get O2?
what is a classic sign of a space occupying lesion?
a system that controls blood flow to the brain via the sympathetic nervous system
can be triggered by cerebral tumor or haemmorhage = cranium doesnt allow expansion
increase in intercranial pressure impairs cerebral blood flow = impaired blood flow to vasmotor contol region in brain = increase sympathetic activity
inc BP
bradycardia (baroreceptors lower HR due to high BP) with hypertension
when does flow mainly occur in the coronary arteries?
what faetures of coronary circulation allow it to meet the hearts needs?
how does the coronary circulation meet increased demand ?
diastole - in sytole the ventricles contract and compress the arteries and stop flow
high basal rate, can increase work five fold, small fibres and high capillary density (short diffusion distance), NO production by coronary endothelium keeps vessels always patent
increases blood flow - vasodilation from metabolic hyperaemia (adenosine, K+, H+)
why are coronary arteries likely have pathologies?
what does a narrowed artery lead to?
what else can cause angina?
what causes an MI?
functional end arteries
few anastomoses - no alternate blood flow
prone to atheroma
angina - diastole is reduced in exercise so the coronary arteries cannot have as much flow = pain
stress and cold = sympathetic vasoconstriction = less blood flow
sudden obstruction by thrombus
when is skeletal muscle circulation most important?
what do skeletal arterioles have an important role in?
exercise - delivery and removal of metabolites
regulate arterial BP - lots of sympathetic vasoconstrictior fibres
what are features of skeletal muscle circulation
capillary density ?
what muscles have more capillary density?
vascular tone?
what does this allow?
precapillary sphincters?
at rest what % of capillaries are opn/perfused?
capillary density depends on muscle type
postural muscles - continuously active
high vascular tone
lots of vasodilation - flow can increase 20X in active muscle
opening of these sphincters allow more capillaries to be perfused - increases flow and reduced diffusion distance
50%
what are the vasodilators in skeletal blood vessels?
what problems can arise in skeletal muscle circulation?
- K+
- osmolarity
- adenosine
- H+
- adrenaline on B2 receptors
atheroma formation, intermittent claudication
what is the main role of cutanous circulation ?
what does it also control?
how to arterovenous anatsomoses regulate temperature in apical skin?
how do sweat glads in non aical skin control temp?
temperature regulation
BP
AVAs are connections between the arteries and veins in the skin. they move blood from arteries to veins - bypass caps In low core temperature - sympathetic innervation is increased, increases vasomotor tone in the AVAs - less blood flows to the apical skin - reduces heat loss
cholingeric fibres activate sweat galds = inc heat loss
sweat glands also produce vasodilators to further help this (bradykinin)
problems with cutanous circulation
how are pressure sores caused?
what is raynauds?
what can cause postural hypotension?
pressure sores/ulcers - causes by decreased blood flow to area from increased pressure pushing on that area
excessive vasoconstriction in response to cold on hands and feet = white skin
excessive vasodilation in respinse to heat (kina opposite to raynauds)
