Cross-sectional area of arteries and capillaries?

Hi there,

I'd be grateful if anyone might help me to understand something I'm confused about regarding the cross-sectional area of blood vessels. I've read three facts about this topic in three different books.
First I read that the total cross-sectional area of the vessels increases between the aorta and the capillaries and that this causes an increased frictional resistance between the blood and the vessel wall, decreasing the rate of blood flow. However, in one of the other books, I read that capillaries are very narrow so that they can permeate tissues and so that red blood cells are squeezed flat against their sides to reduce the diffusion path for the exchange of materials. Finally, I read, in the third book, that hydrostatic pressure occurs at the arterial end of the capillaries due to blood that is pumped from the heart having passed through "arteries, even narrower arterioles, and even narrower capillaries" (I've written this in quote marks as it is exactly what the book says).
What I can't understand is how the total cross-sectional area can increase between the arteries and the capillaries (as stated in book 1) and yet arterioles and capillaries are said to be increasingly narrower than arteries, in order to create hydrostatic pressure of blood that passes through them, and so that the capillaries can permeate tissue and also be narrow enough for red blood cells to be squeezed flat against their sides?
How does this work? When book 1 describes the total cross-sectional area of vessels as increasing, does it perhaps not refer to the lumens of these vessels, which in fact actually get narrower?
I'm really confused!

If anyone could clear this up for me and explain I'd be so appreciative!

Thank you!

x

Think about it in terms of the numbers of each blood vessel:

Artery --> Arteriole --> Capillary

Few --> More --> Most

Therefore, even though the cross sectional area decreases, the total surface area increases dramatically as the number of each blood vessel increases.

Thank you very much for your reply!
So, do you mean that the diameter of the lumens decrease but the surface area of the vessels increase, and that it is this increase in surface area that accounts for the increased frictional resistance (stated by the first book) and hence a reduced rate of blood flow?