Constituents of blood...
- Red blood cells (erythrocytes)
- White blood cells (leukocytes)
- Platelets (thrombocytes)
Red blood cells contain haemoglobin, an iron-containing protein, which
facilitates transportation of oxygen by reversibly binding to this respiratory
gas, and greatly increasing it's solubility in blood. In contrast, carbon
dioxide is almost entirely transported extracellularly, dissolved in plasma as
Red cells live for 120 days, and have a density of 5
million/mm³. White cell density is 5,000 - 10,000/mm³.
Adult (70 kg)...
- 5 litres of circulating blood
- 1 litre in heart, artery and capillary circulations
- 1 litre in pulmonary circulation
- 3 litres in venous circulation.
Platelets aggregate at site of injury, causing
a plug, and preventing capillary bleeding, and local vasoconstriction. To arrest
haemorrhage, Fresh Frozen Plasma (contains clotting factors) and platelets needed.
Normally, body has balance of coagulation and clot breakdown (fibrinolysis)
- Heparin has immediate effect, but only lasts 4-6 hours.
- Warfarin takes 24-48 hours to take effect.
- Group A people have Agglutinogen A on the surface of their red cells.
- Those with Agglutinogen A and B on their cells belong to group AB.
- AB people are universal recipients.
- Group AB people do not have anti-A or anti-B agglutins in their plasma
- Those with neither A or B, are type O.
people do not possess any factor likely to cause blood group
incompatibility due to agglutination.
people have anti-A and anti-B agglutins but, by the time these
agglutins are diluted into the recipient, the amounts in the plasma will be
insufficient to cause agglutination. Group O
people are universal donors, but
must be Rhesus Negative.
Only when transfusion of blood is completed, is
it necessary to cross match and group blood, because agglutinogens A and B are
only present on the surface of red cells. Plasma and other products can be given
without cross matching procedures.
Blood test bottle top colour codes
|Colour ||Test |
|Pink ||Blood group, Transfusion cross match|
|Lavender ||FBC, Viscocity, Sickle cell, HIV|
|Grey ||Glucose, Lactate (blood , CSF)|
|Gold ||Biochemistry, Thyroid|
|Light blue ||Clotting (coag), Thrombophilia, Lupus|
|Yellow ||Transplant immunology|