Lecture 5 - Blood Flow Flashcards
what is flow?
volume of fluid passing a given point per unit timevolume/time
what is velocity?
rate of movement of fluid particles along the tubedistance/time
what is laminar flow?
gradient of velocity from middle to edge of vesselhighest in centre, stationary at edge
what is turbulent flow?
when the mean velocity increases, the velocity gradient breaks down as layers of fluid try to move over each other so the fluid tumbles
what is viscosity?
the extent to which layers resist sliding over each otherthe difference between central and edge velocity is higher with lower viscosity
how does tube diameter affect flow rate?
at a constant gradient, the wider the tube the faster the middle layers movemean velocity is proportional to the cross sectional area of the tube
what is the relationship between pressure, flow and resistance?
pressure = flow x resistanceresistance = pressure/flow
how are flows combined?
for vessels in series, resistances add togetherfor vessels in parallel, the effective resistance is lower
how does flow change through the circulation?
it doesnt
how does pressure change through the circulation?
arteries: pressure drop is smallarterioles: pressure drop is largeveins: pressure drop is small
how do vessels achieve capacitance?
vessels widen with increasing pressure so more blood transiently flows in than out
what is total peripheral resistance?
sum of the resistance of all peripheral vasculature in the systemic circulation
what are produced by metabolically active tissues?
vasodilator metabolites egHKadenosine
what is reactive hyperaemia?
when circulation has been cut off for a short period of time and is restored so a large amount of blood enterslocal arterioles dilate maximally
what is autoregulation?
most organs can automatically take the blood flow they need given the arterial pressure is appropriateq
