AP BARRONS BIO. pg 255.

[Imazergling]

The following answer was deemed TRUE for a true/false question:

"Blood flow is slowest in capillaries to maximize the diffusion of nutrients and wastes."

what? slowest? I thought it was the FASTEST there. is this a mistake?

 

[xoltarin]

The following answer was deemed TRUE for a true/false question:

"Blood flow is slowest in capillaries to maximize the diffusion of nutrients and wastes."

what? slowest? I thought it was the FASTEST there. is this a mistake?

Sounds true aren't capillaries under the least pressure therefore less speed?

 

[IsaacYankem]

That's definitely true. Capillary walls is where a majority of nutrient exchange takes place. As such, they are thin (single cell layer usually) and have the slowest blood movement to give more time for exchange. O2 goes to tissues needing it, and CO2 goes from tissues back to blood to heart.

Blood flows fastest through the aorta as it's being ejected, and the largest resistance to flow occurs across the arterioles.

Hope that helps.

 

[Imazergling]

thanks. it makes sense. it's just that i remember someone telling me that because capillaries have such a short diameter, blood is supposed to move really fast through it..guess she was wrong lol.

SOMETHING about the capillaries was relatively large though compared to other parts of the circulatory system. I just can't put my finger on what that characteristic about the capillaries is...hmm...

 

[Glimmer1991]

They have large surface area.

 

[acoburn73]

The total surface area of the capillaries is larger than the total surface area of the arterioles, hence the slower flow. This is especially true in the lung tissue where oxygen exchange is the most important. There's a gradient calculation for this transfer that can actually tell you just how slow the flow must be for exchange to be the most efficient (derived from surface area of the capillaries), but I don't recall the formula. However, this isn't necessary for the DAT, just fun knowledge while you're tinkering around and studying!

 

[FeralisExtremum]

Blood velocity is inversely proportional to the cross-sectional area. A single artery, for example, is much bigger than a capillary - but there are far more capillaries than arteries, hence it has the total highest cross-sectional area. Capillaries have the highest cross-sectional area, so capillaries have the slowest blood velocity.