Capillaries
Capillaries connect the smallest branches of arteries and veins
The walls of capillaries are just one cell thick. Capillaries therefore allow the exchange of molecules between the blood and the body's cells - molecules can When particles spread out from a region of higher concentration to a region of lower concentration. across their walls. This exchange of molecules is not possible across the walls of other types of blood vessel.
Exchange of molecules
- Gaseous element making up about 20% of the air, which is needed by living organisms for respiration. diffuses through the capillary wall, into the Fluid which is derived from blood plasma that passes through the walls of capillaries., and the cells.
- A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis. diffuses from the cells into the tissue fluid, then across the capillary walls into the The liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea..
- A simple sugar used by cells for respiration. diffuses from the blood plasma, across the capillary walls to the tissue fluid, and then to the cells.
- The waste product A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine. diffuses from the cells of the The large organ, beside the stomach, which has many functions, including processing substances absorbed by the digestive system and a role in the storage of the body's carbohydrate., to the tissue fluid, and then across the capillary walls into the blood plasma.