Revision 5: Blood Flow

Question 1

define flow and velocity and state the relationship

Answer 1

flow=vol. of liquid passing a point per unit time

velocity= rate of movement of fluid particles along tube

Flow is the same all along the vessel, velocity can inc/dec with dec/inc. vessels diameter

At a given flow therefore, velocity is inversely proportional to the cross-sectional area

Question 2

define laminar and turbulent flow

Answer 2

laminar: grad. of velocity from middle (highest) to edge (stationary)
turbulent: vel. grad. breaks down as the layers try to move too fast over each other causing the particles to tumble over each other, flow resistance is greatly inc.

Question 3

define resistance, relationship with pressure and flow and factors affecting it

Answer 3

any factor that impedes the flow of fluid eg roughness, contraction, bends

resistance=pressure/flow

factors: inc. w/ viscosity inc., also dec. with an inc. in the 4th power of the radius

Question 4

flow resistance calculations in series and parallel

Answer 4

series: resistances add
parallel: (R₁xR₂)/(R₁+R₂)

Question 5

pattern of pressure and flow resistance in systemic circulation

Answer 5

flow is the same everywhere

arteries, venules and veins have low resistance therefore the press. drop is small

arterioles have high resistance so a) pressure drop is high and b) arteries have a high pressure to pump blood in

Question 6

desc. how distensibility of vessels affects relationship between flow and resistance, as well as capacitance

Answer 6

inc. pressure -> generates transmural pressure -> vessel stretches -> inc. diameter of lumen -> resistance dec. -> flow inc.

as vessels widen w/ inc. press., more blood flows in than out -> allows distended vessels to store blood - capacitance

Question 7

define systolic, diastolic, pulse and average pressure

Answer 7

max./min. arterial press, 120/80mmHg normally

pulse = systolic-diastolic ~ 40mmHg

avg. press. = diastolic press. + 1/3 of pulse pressure as systole lasts a shorter time than diastole

Question 8

define Total peripheral resistance

Answer 8

sum of resistance of all peripheral vasculature in systemic circulation

Question 9

describe reactive hyperaemia

Answer 9

if circulation is cut off for a minute or two then restored, the build up of metabolites causes local arterioles to dilate -> large amount of blood enters and supplies the cut off tiss.

Question 10

describe autoregulation

Answer 10

at most levels of metab. activity, organs can automatically take the blood flow they need with the metabolites, so long as pressure remains in certain boundaries

Question 11

define central venous pressure and venous return

Answer 11

press. in great veins supplying the heart

rate of blood flow back to heart (the limiting factor for CO)

Question 12

how do vessel walls affect syst. and diast. pressure?

Answer 12

if they were rigid, they would have two outputs: max. in syst then immediately drop afterwards to 0 in diast.

however, as they are distensible, in systol ethey stretch so press. does not rise so much, recoil in diastole and flow continues through arterioles, giving an arterial pressure wave form