In humans, blood flows from the heart into the aorta, from which it passes into
ID: 2005845 • Letter: I
Question
In humans, blood flows from the heart into the aorta, from which it passes into the major arteries. These branch into the major arteries. These branch into the small arteries, which in turn branch into myriads of tiny capillaries. The blood returns to the heart via the veins. The radius of the aorta is about 1.0 cm and the blood passing through it has a speed of about 30 cm/s. A typical capillary has a radius of about 4x10-4 cm. and blood flows through it at a speed of about 5x1O-4 ms. Estimate how many capillaries there are in the body.Explanation / Answer
A1V1=nA2V2 n= number of capillaries r1= radius of aorta r2=radius of capillary pi(r1^2)(v1)=n(pi)(r2^2)(v2) pi's cancel so... (r1^2)(v1)=(n)(r2^2)(v2) n=(r1^2)(v1)/(r2^2)(v2) n=(.01)^2(.30m/s)/(4*10^-6m)^2(5*10^-4m/s) n=3.75*10^9 capillaries in the body