Blood Vessels

• The circulatory system is made up of the heart, blood, and blood vessels.
• Blood vessels are the network of tubes that carry the blood, pumped by the heart, around the body.
• Blood vessels' length is 100,000 km.
• There are three types of blood vessels. Artery, capillary, and vein.
• Artery - carries blood away from the heart.
• Capillary - carries blood to and from the body's cells.
• Vein - carries blood back into the heart.
• Blood that is pumped from the heart to the body' cells along the arteries is oxygen-rich blood or blood at high pressure.
• Artery is suitable for carrying blood at high pressure because arteries have thick outer wall, thick inner layer, and narrow central tube.
• Arteries expand to cope with the increased blood flow when a surge of blood enters the arteries. To cope, the elastic fibers of an artery stretches under the pressure. The muscle fibers contract to push the blood along and keep it flowing.
• To feel how your artery stretches, you can feel your pulse *wrist. Because the stretching of an artery passes between bone and the surface of the skin.
• Veins are the blood vessels that carry blood back into the heart.
• Blood that travels back to the heart from the body' cells along the veins is oxygen-poor blood or blood at low pressure.
• Veins are suited for carrying blood at low pressure because veins have thin outer layer, thick inner layer, and wide central tube.
• If the blood pressure is too low and has to move against gravity, the blood in the leg veins might slow down and flow in the wrong direction.
• Veins have valves that have thin walls and relies on nearby muscles to prevent backflow.
• Capillaries are tiny blood vessels that carry a blood supply to/from the body's cells. Capillaries link arteries to veins.
• Capillaries are the only blood vessels where substances can be exchanged between the blood and body cells.
• Capillaries are suited for the exchange of substances between the blood and body cells because capillaries have very thin wall made of a single layer of cells and have a narrow central tube.
• In capillaries, substances are exchanged by diffusion. Useful substances in the blood diffuse across the capillary wall into body cells. Waste products from the body cells diffuse across the capillary wall into the blood.
• A network of capillaries is called a capillary bed.