Remember how small you learned that cells were? How large could the blood vessels that carry blood to each cell be?

What do you think? Make a prediction.

Look at the picture your teacher will show you. This is a river delta with many branches.

We might think of this as an analogy for blood vessels. Large vessels (arteries) come from the heart. As they move out to all parts of the body the arteries branch off into smaller and smaller blood vessels to get blood to every area of the body.

Remember the animation of the circulatory system. You learned that it was a closed system that took blood out to all the cells of the body and then returned to the heart.

What do you think happens when the branches get small enough to reach the cells?

What do you think the arrangement of the three types of vessels is?