ch5.1 blood as a transport medium

• blood is composed of:

  • plasma (55%)
  • formed elements (45%)
• plasma = liquid part of blood, contains dissolved substances

  • function = transport components of blood throughout the body
• erythrocytes (red blood cells)

  • biconcave shape = increase SA:Vol for oxygen diffusion
  • haematocrit = ratio of erythrocytes to the total volume of blood
  • function = contains haemoglobin to transport oxygen from lungs to cells throughout the body
• leucocytes (white blood cells)

  • many different types
  • function = protect the body from infection by removing dead or injured cells and invading micro-organisms
• thrombocytes (platelets)

  • small fragments of cells
  • function = when a blood vessel is inured, the platelets adhere to the lining and form a scaffold to clot the blood
• transport of oxygen:

  • 3% carried in plasma, 97% carried in combination with haemoglobin molecules (oxyhaemoglobin)
  • Hb + O2 -> HbO2
  • high oxygen concentration = oxygen combines with haemoglobin
  • low oxygen concentration = oxyhaemoglobin breaks down to Hb + O2
• erythrocytes are well suited to their function of carrying oxygen:

  • contain haemoglobin
  • don't have a nucleus
  • biconcave shape
• transport of carbon dioxide:

  • 8% dissolved in plasma, 22% combines with haemoglobin (carbaminohaemoglobin), 70% carried in plasma as bicarbonated ions (HCO3-)
  • most reacts with water to form H2CO3-
  • CO2 + H2O <-> H2CO3 <_> H+ + HCO3-
• transport of nutrients + waste:

  • dissolved + transported in blood plasma
  • inorganic nutrients transported as ions (eg. sodium ions, calcium ions, chloride ions)
  • organic wastes (eg. urea, creatine, uric acid)