5. Flow versus velocity and total cross-sectional area

What does this mean? “As a vascular tree branches, the total cross-sectional area changes. The total cross-sectional area is small in the aorta and vena cava, much larger across all capillaries combined, and then becomes smaller again as vessels merge on the venous side.”

The area of the aorta and vena cava are small compared to the area of combined capillaries, this forces the blood to slow, and nutrients can be absorbed. It begins to shrink again as vessels come together in veins going back up to the heart.

The slow velocity in capillaries is a consequence of the _.

large total area of many capillaries, not the small diameter of one capillary considered in isolation

Slow capillary velocity provides _.

time for exchange and helps protect fragile capillary walls

Flow rate through the overall circulation is continuous. What does that mean? Except?

The same volume unit must pass every area in the same unit of time, this is possible because even though capillaries are moving slower, there is more of them; except fro temporary storage.

How does this relate to capillaries/arteries? “When the same volume of fluid spreads across a larger area, the fluid can move more slowly while maintaining the same flow rate. When the total area narrows, velocity increase”

the larger area = the total area capillaries make up (meaning they move slower)