Blood Vessels
- Created by: Nicola Carter
- Created on: 30-12-12 16:36
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- Blood Vessels
- Open circulatory systems
- The blood isn't always in the vessels.
- The blood fluid circulates through the body cavity, so the tissue and cells of the animal are bathed directly in blood
- EG insects
- In insects there is a muscular pumping organ much like a heart. Blood from the body enters the heart through pores called ostia
- Why don't all animals have an open system?
- An open system works for insects because they are small. The blood doesn't have to travel far.
- Also, they don't have to rely on blood to transport oxygen and carbon dioxide, have a separate system for this.
- In a open circulatory system, the blood remains at a low pressure, and the flow is slow
- Wouldn't be a sufficient supply of nutrients
- An open system works for insects because they are small. The blood doesn't have to travel far.
- Closed circulatory system
- Blood always remains in blood vessels
- Tissue fluid bathes the tissues and cells. This enables the heart to pump the blood at a higher pressure, so it flows more quickly - can deliver oxygen and nutrients more quickly and remove carbon dioxide and other wastes more quickly
- EG Fish
- There must be exchange surfaces at the gills and at the body tissues, to allow materials to be exchanged between blood and tissue fluid
- Blood flows through a series of vessels. Each is adapted to its particular role in relation to its distance from the heart.
- All types of blood vessels have an inner layer or lining, made of a single layer of cells called the endothelium. This is a thin layer that is particularly smooth to reduce friction with the flowing blood
- Arteries
- Carry blood away from the heart. The blood is at a high pressure, so the artery wall must be able to withstand that pressure
- Lumen - small to maintain pressure
- Wall - thick to give strength to withstand pressure.
- Elastic tissue in wall - allows wall to stretch and recoil
- Smooth muscle in wall - can constrict the artery, narrows the lumen
- Endothelium - folded and can unfold when the artery stretches
- Veins
- Carry blood back to the heart. Has a low pressure and the walls don't need to be thick
- Lumen - large, to ease the flow of blood.
- Walls - thinner layers of collagen, smooth muscle and elastic tissue.
- They don't need to stretch and recoil, not actively constricted to reduce blood flow
- Contain valves - to help blood flow back to the heart and to prevent it flowing in the opposite direction.
- Capillaries
- Very thin walls, allow exchange of materials between the blood and cells of tissue via the tissue fluid
- Lumen -very narrow (diameter same as a RBC) ensures the RBC are squeezed as they pass along the capillary wall reducing the diffusion path
- Open circulatory systems
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