question about capillary

It's to increase the total surface area of blood vessel.

In terms of so much branches,capillary which can totally carry a larger amount of blood to cells. And the main reason is for faster material exchange.For example,so much branches of capillary around the air sac, gas exchange will occur at a faster rate, as the surface are for gas exchange is large,hence it can maintain a steeper concentration gradient.

Also.it can ensure enough oxygen and food is provided to cells such as the cells formed muscle.They can therefore carry out respiratoin to release energy at a higher rate.Energy is continuously produced for muscle contraction.

These are why capillary have so much branches.

2006-11-20 21:32:18 補充：
GOOD