2
They are so thin that only one blood cell can pass through at a time
3
Capillaries are so small that they are called ______.
5
____ are exchanged in the capillaries
6
Nutrients are exchanged here
7
They (plural) carry oxygen rich blood
9
Veins have these to aid blood on its way back to the heart
10
Arteries have a thick layer of smooth_______, therefore it can withstand high pressures.
12
They(plural) carry blood going from the body to the heart
13
Veins have a _____ layer of smooth muscle
