Function: Facilitates the exchange of substances between blood and tissue cells in the body
-
smallest blood blood vessels
-
connect arteriole and venules
-
walls are one cell thick.
- partially permeable for efficient diffusion of nutrients and waste products.
- short diffusion distance
-
increase total cross sectional surface area as they are highly branched
-
narrow lumen - RBC flows in a single file
capillaries unite to form venules before leaving organ or tissue. venules form larger veins. carry blood back to the heart.
- lower blood pressure so that blood flows slower and smother, walls of the vessels are no longer so thick.
| To increase rate of exchange of substances, capillaries need: | How it is achieved |
|---|---|
| large surface area | numerous branches of capillaries |
| short diffusion distance | walls of the capillaries are 1 cell thick. {walls of the capillaries made up of a single layer of flattened cells} |
| steep concentration gradient | continuous flow of blood through the capillaries. |
How are substances transferred between capillaries and tissue fluid