Blood Vessel

• • have thick muscular walls containing elastic fibre to maintain high pressure of blood from the heart.
  • have a narrow lumen to maintain high pressure.


  Arteries carry oxygenated blood from the heart to every tisuues in the body.

  • except pulmonary artery.
• FUNCTION OF ARTERIES:

  • diameter of arteries and thickness of their wall steadily decrease their distance from their heart increases
  • Aorta is the largest artery and pressure is highest in it.
  • tunica media contains a large amount of elastic fibres to prevent bursting.
  • pulse is the stretching outwards of the artery.


  -when blood at high pressure enters artery the artery becomes wider reducing pressure..

  -when blood at low pressure enters artery it recoils inward giving a little push to raise the pressure.
• Veins carry deoxygenated blood from every tissue in the body to the heart at low pressure. -except pulmonary vein


  -they have thin wall and large lumen (to reduce resistence to flow).

  -they have semi-lunar valves to prevent backflow of the blood. - movement of blood in vein is due to the contraction of skeletal muscles
• it is difficult for the blood to flow upwards through the legs to the heart; the flow is helped by contraction of the leg and abdominal muscles.
• capillaries are very small vessels that connect arterioles with venules, they are only one cell wide so that all cells can be supplied with nutrients easily
• capillaries carry both oxygenated and deoxygenated blood at low pressure within tissues.


  -they have narrow and one cell thick walls which are leaky .
• • Have a wall that is one cell thick for substances to diffuse easily in and out of them
  • Have a small lumen so that red blood cells have to touch both sides to pass through
  • Have tiny gaps between the individual cells that form the endothelium, this allows plasma to leak out and form tissue fluid -they are microscopic which allows blood to come in close contact with body cells
• • Capillaries are arranged in a network called a capillary bed
  • Capillaries form a network throughout every tissue in the body except cornea and cartilage


  -thus, Have a large surface area helping rapid diffusion between blood and cell

  -No cells in the body are more than 2 cells away from a capillary
• ARTERIOLES

  • arteries divde more as they get get further away from the heart, they get narrower
  • the narrow vessels that connect arteries to capillaries are called arterioles 


  they have a greater proportion of smooth muscle to regulate blood pressure by contracting.
• VENULES

  • the narrow vessel that capillaries to vein are called venules.
  • vein get narrower the further they are away from the heart.
• blood vessel network diagram;

  
• TISSUE FLUID

  • As blood passes through capillaries, some plasma is forced out through gaps in the walls of the capillary to surround the cells of the body
  • The exchange of substances between cells and the blood occurs via the tissue fluid
• tissue fluid diagram;