Circulation Flashcards
resistance vessels
- are arterioles (have ability to dilate and contract)
- thick SM (tunica media) of A → due to A subjected to high pressure
capacitance vessels
- veins, acts as collectors and reservoirs
- have valves and prevent backflow
exchange vessels
capillaries
- carries blood from arterioles to venules
- allows delivery and exchange of substance
- thin SM (tunica media)
principles of circulation
1) fluid does not flow when pressure is the same in all parts
2) fluid flows from high→low pressure
3) BF b/w 2 points can be predicted by pressure gradient
what is the chief determinant of blood flow
vol of blood in arteries
factors affecting SV
- length of myocardial fibres before contraction
- determined by starling’s law (increase preload stretch → increases contraction)
factors affecting HR
- ANS
- baroreflex - via CN9
(aortic, carotid baroR)
factors affecting CO
preload - vol of blood in vent at the end of diastole
- affected by BV and posture
afterload - res vent contracts against
- affected by A elasticity, blood viscosity
contractility
- affected by SNS, amount of viable muscles
peripheral resistance
- A resistance (accounts for half of TPR in systemic circulation)
- characterised by viscosity or diameter of arterioles
vasomotor pressoreflex (baroreflex)
inc BP → inc baroR firing → inhibit vasomotor centres in medulla → dec SNS + inc PNS
chemoR and chemoreflexes
sensitive to changes in pH
- excess CO2 → stimulates inc ventilation
- acidosis
- dec blood O2 (less sensitive)
all stimulates vasomotor centres → inc HR and SV
medullary ischaemic response
a last ditch effect
- BF to brain severely compromise (i.e. from trauma)
- dec O2 deficiency, inc CO2
- stimulates vasoconstrictor centres
venous return to heart
from vein constrictions
- skeletal muscle pumps → force blood flow through veins
- resp pump → create pressure gradient b/w ab and thorax
