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What are the different types of blood vessels? And what do they do

Arteries - carry blood away from from the heart and into arterioles

Arterioles- are smaller arteries that control blood flow from arteries to capillaries

Capillaries - Tiny vessels that link arterioles to veins

Veins - carry blood from capillaries back to the heart


What’s the basic layered structure of the arteries arterioles and veins

Tough fibrous outer layer - resists pressure changes from both within and outside

Muscle layer - can contract and so control the flow of blood

Elastic layer - helps maintain blood pressure by stretching and springing back

Endothelium - smooth to reduce friction and thin to allow diffusion

Lumen - not actually a last but the central cavity of the blood vessel through which blood flows


What is the job of the arteries

Transport blood rapidly under high pressure from heart to the tissues


How is the arteries structure adapted to its function

Muscle layer is thick - means smaller arteries can be constricted and dilated in order to control the volume of blood passing through them

Elastic layer is relatively thick - important for blood pressure to be high for it to reach all over the body. Helps maintain high pressure

Overall thickness of wall is great - also resists the vessel bursting under pressure

No valves - as blood is under constant high pressure so it tends not to flow back


What do the arterioles do

Carry blood, under low pressure then arteries, from arteries to capillaries


How is the arterioles structure adapted to its function

Muscle layer is relatively thicker than in arteries - contraction of this muscle layer allows constriction of the lumen of the arteriole. This restricts the flow of blood and so controls its movement into the capillaries that supply the tissues with blood


What do veins do

Transport blood slowly, under low pressure, from the capillaries in tissues to the heart.


How is their structure related to their function (veins)

Muscle layer is relatively thin - veins carry blood away from tissues and therefore their constriction and dilation cannot control the flow of blood to the tissues

Elastic layer is thin - low pressure of blood within the veins will not cause then to burst and pressure is too low to create a recoil action

Overall thickness of the wall is small - there is no need for a thick wall as the pressure within the veins is too low to create any risk of bursting. Allows them to be flattened easily, siding the flow of blood within them

Valves at intervals throughout - to ensure that blood does not flow backwards, which it might otherwise do because the pressure is so low. When body muscles contract, veins are compressed, pressurising the blood within them. The valves ensure that this pressure directs the blood in one direction only:toward the heart


What do the capillaries do

Is to exchange metabolic materials such as oxygen, carbon dioxide and glucose between the blood and the cells of the body


How does the capillaries relate to their function

Their walls consist mostly of the lining layer - making them extremely thin, so distance of diffusion is short - rapid diffusion

Numerous and highly branched- providing a large SA for exchange

Narrow diameter - and so spread throughout the tissues, meaning no cell far from a capillary and there is a short diffusion pathway

Narrow lumen - red blood cells are squeezed flat against the side of a capillary, bringing them closer to the cells which they supply oxygen. Reducing distance distance

Spaces between the lining cells - that allows white blood cells to escape in order to deal with infections within tissues


What does tissue fluid do

It’s a water liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen. They supply all of these substances to the tissues


What does tissue fluid get in return

Carbon dioxide and other waste materials from the tissues


Where is tissue fluid formed

From blood plasma


What’s hydrostatic pressure

Pumping by the heart creates pressure


The hydrostatic pressure causes tissue fluid to move out of the blood plasma. What forces is the outward pressure opposed by?

Hydrostatic pressure of the tissue fluid outside the capillaries, which resists outward movement of liquid

The lower water potential of the blood, due to the plasma proteins that cause water to move back into blood within the capillaries


What’s ultrafiltration

Filtration assisted by blood pressure


Describe the return of tissue fluid to the circulatory system

Loss of tissue fluid from capillaries reduces the hydrostatic pressure inside them

As a result, by the time the blood has reached the venous end of the capillary network its hydrostatic pressure is usually lower than that of the tissue fluid outside it

Therefore tissue fluid is forced back into capillaries by the higher hydrostatic pressure outside them

The plasma has lost water and still contains proteins. In therefore has a lower water potential than the tissue fluid

As a result water leaves the tissue by osmosis down a water potential gradient


What are the contents of the lymphatic system moved by

Hydrostatic pressure of the tissue fluid that has left the capillaries

Contraction of body muscles that squeeze the Lymph vessels - valves in the lymph vessels ensure that the fluid inside them moves away from the tissues in the direction of the heart