haemolysis

The breakdown of red blood cells. A normal occurrence, chiefly in the blood sinuses of the spleen, when the cells are ageing after 3-4 months in circulation, but it can happen abnormally in the circulating blood, causing haemolytic anaemia. In either case, the cells become more fragile than normal, disintegrate, and shed their contents. Normally the haemoglobin is broken down and recycled, so its iron is not lost. When free haemoglobin is released in the plasma, some products are retained, but excessive amounts are excreted from the kidneys (haemoglobinuria). Fragility of cells in a blood sample can be assessed by placing them in a series of salt solutions of progressively lower osmolality than the blood itself, which causes them to swell, and finding the osmolality at which they burst.

— Stuart Judge

See blood; haemoglobin.

Disintegration of red blood cells. The cell membrane ruptures, releasing the contents, including haemoglobin. Premature haemolysis can lead to anaemia. Haemolysis can result from physical trauma to capillaries, for example, when the foot repeatedly strikes the ground during long-distance running (a condition known as exertional haemolysis or foot-strike haemolysis). See also march haemoglobinuria.