Blood vessels
Blood is transported in Blood vessels that carry blood away from the heart., A blood vessel with valves that transports blood to the heart. and Tiny blood vessels with walls one-cell thick where exchange of materials occurs..
Blood is pumped from the heart in the arteries. It is returned to the heart in the veins.
The capillaries connect the two types of blood vessel, and molecules are exchanged between the blood and the cells across their walls.
Arteries carry blood away from the heart
| Arteries | Veins |
| Always carry blood away from the heart | Always carry blood to the heart |
| Carry oxygenated blood, except for the pulmonary artery | Always carry deoxygenated blood, except for the pulmonary vein |
| Carry blood under high pressure | Carry blood under low or negative pressure |
| Have thick muscular and elastic walls to pump and accommodate blood | Have thin walls - have less muscular tissue than arteries |
| A type of supporting tissue called connective tissue provides strength | Have less connective tissue than arteries |
| The channel in the blood vessel that carries blood - the lumen - is narrow | Have a wide lumen |
| Arteries | Always carry blood away from the heart |
|---|---|
| Veins | Always carry blood to the heart |
| Arteries | Carry oxygenated blood, except for the pulmonary artery |
|---|---|
| Veins | Always carry deoxygenated blood, except for the pulmonary vein |
| Arteries | Carry blood under high pressure |
|---|---|
| Veins | Carry blood under low or negative pressure |
| Arteries | Have thick muscular and elastic walls to pump and accommodate blood |
|---|---|
| Veins | Have thin walls - have less muscular tissue than arteries |
| Arteries | A type of supporting tissue called connective tissue provides strength |
|---|---|
| Veins | Have less connective tissue than arteries |
| Arteries | The channel in the blood vessel that carries blood - the lumen - is narrow |
|---|---|
| Veins | Have a wide lumen |
Capillaries
Capillaries connect the smallest branches of arteries and veins.
The capillaries are where molecules are exchanged between the blood and the body's cells.
The walls of capillaries are just one cell thick. Capillaries therefore allow molecules to When particles spread out from a region of higher concentration to a region of lower concentration. across the capillary walls. This exchange of molecules is not possible across the walls of other types of blood vessel because the walls are too thick.
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.
