Arteries, Capillaries, Veins and Arterioles

Artery

• Every cell in the body needs oxygen in order to respire.
• Oxygenated blood is carried within the arteries this is generally the flow of blood going away from the heart, the exception being the Pulmonary Artery.
• When the blood leaves the heart it is under very high pressure and arteries need to be string enough to contain the high pressure blood.
• In order to do this the Arteries have thick muscular walls with elastic fibres to withstand the pressure which recalls as the heart beats.

Stucture

• The Arteries have a small lumen compared to that of a vein, maintaining a high blood pressure.
• The walls surrounding the lumen are made up of layers of muscle and elastic fibre.
• The total diameter of the artery is large comapared to a vein.

Arterioles

• Arterioles are able to control blood flow by restricting and opening the lumen.
• The muscle layer is thicker than in the Arteries:
  • when the muscle contracts in the Arterioles, the lumen constricts and blood flow becomes restricted.
• The elastic layer is thinnner than in the Arteries:
  • there is lower blood pressure in Arterioles so does not need to expand as much.

Veins

• Veins carry deoxygenated blood, generally back towards the heart with exception to the pulmonary vein.
• Veins have thinner walls that are flexible and can expand holding large volumes of blood.
• The blood contained within the veins is at a much lower pressure than in the Arteries.
• Veins that run within or close to skeletal muscles have blood squezed as the muscles contract.
• Movement of the blood is assited by valves which prevent backflow of blood.

Stucture

• Veins have a very large lumen and thin walls surrounding the lumen.
• there are valves within the veins preventing back flow.

Capillaries

• Arteries and veins are linked by a series of capillaries.
• These are tiny blood vessels with walls one cell thick, to allow exchange of oxygen, carbon dioxide, nutrients and waste between the blood and tissue.
• The capillary walls have small pores in the wall through which tissue fluid and White blood cells can pass.

Substance movement

• Diffusion of lipid soluble subtances passes through the plasma membrane.
• Diffusion of lipid Insoluble substances passes though pores in capillary wall.
• Bulk flow of water with dissolved substances also passes though pores in capillary walls.
• Osmosis of water passes out of the capilary.