Blood vessels

• Systemic system

  • high pressure from the left ventricle to the capillary bed due to contraction
  • Pressure drop at capillary bed
  • low pressure from the capillary bed to right atrium
  • high pressure = High velocity of flow
  • Low pressure = low velocity of flow
  • From the ventricle to the capillary bed the total cross sectional area is increasing
  • Low pressure at the capillary bed due to a huge total cross sectional area
  • From the capillary bed to the right atrium there is a decrease in total cross sectional area
• Capillaries

  • Exchange surface between blood and body cells

  1. Large surface area - lots of them, large total cross sectional are
  2. Thin for short diffusion pathway - endothelial cells = 1 cell thick
  3. Moist - capillaries are surrounded by tissue fluid and can exchange materials with it
  4. Permeable - the walls have gaps/fenestrations which allows exchange of fluid
  5. Maintain a concentration gradient - good blood supply
• Oxygen, glucose and amino acids diffuse into tissue fluid then into the body cell down a diffusion/concentration gradient.

  Maintaining a concentration gradient - oxygen and glucose are used in aerobic respiration - amino acids are used in protein synthesis

  Heat may leave body fluid
• Reducing velocity of flow

  = more time for the exchange of molecules

  • red blood cells have a larger diameter than the lumen of the capillary = increased friction = increased resistance to blood flow
  • decreased pressure due to increased total cross sectional area
• Blood

  Plasma:

  • water
  • oxygen
  • glucose
  • amino acids
  • hormones
  • mineral salts (ions)
  • heat
  • carbon dioxide
  • urea
  • large plasma protein

  Cells:

  • Erythrocytes - red blood cells
  • White blood cells
  • Platelets
• Large plasma proteins are too large to leave fit out of fenestrations in the capillary wall - they are retained in the capillary - and maintain the low water potential of the blood
• At the arteriole end of the capillaries the hydrostatic pressure is high.

  At the venule end of the capillaries the hydrostatic pressure is low
• Fluid exits the capillaries due to the high hydrostatic pressure.

  Fluid goes in due to low hydrostatic pressure and higher osmotic pressure
• pressure is maintained in the aorta by elastic recoil of the elastic fibres
• Artery structure:

  Out to in

  A) Tunica externa (collagen fibres)

  B) Tunica Media (smooth muscle and elastic fibres)

  C) Tunica Interna (smooth endothelium)

  D) basement membrane

  
• Artery structure and function:

  • Thick wall to resist and sustain high pressure
  • Smooth endothelium - one cell thick - smooth lining to reduce friction and minimise resistance to flow
  • Thick layer of elastic fibres and smooth muscle to accommodate changes in blood flow and pressure as the blood is pumped out of the heart - stretch and recoil
  • Outer layer of connective tissue (collagen fibres) resist over-stretching
  • Narrow lumen to maintain high pressure
  • Arterioles use smooth muscle to adjust diameter - vasoconstriction/vasodilation
  • contains high pressure blood flowing away from the heart
• Capillary structure and function:

  • Connects small arteries with small veins and allows exchange of materials with tissues across the capillary wall which is:
  • thin for a short diffusion pathway - 1 cell thick
  • narrow diameter = slow moving blood which allows time for exchange
  • pores/fenestrations leak to allow exchange pf materials e.g. small solute materials and ions through the endothelial cells
• Vein structure and function:

  • thinner wall (especially muscle layer) as the pressure in the blood is now reduced
  • smooth endothelium - 1 cell thick - smooth lining to reduce friction and minimise resistance to flow
  • Outer layer of collagen to resist stretching
  • Has a wider lumen than arteries
  • Valves along their length to ensure flow of blood in one direction under low pressure - called pocket valves
  • Low pressure blood flowing towards the heart
• Vein structure:

  out to in

  A) Tunica externa (collagen fibres)

  B) Tunica Media (smooth muscle and elastic fibres)

  C) Tunica Interna (smooth endothelium)

  D) basement membrane