Cancer and other problems of cell growth

Cells reproduce in order to replace other cells which are continually being lost, e.g. on the surface of the skin by wear and tear or by damage such as that caused in a woimd. 

Sometimes, cells do not develop as nature intended and a variety of abnormal cells may be formed, some of which may endanger life. Some examples of maldevelopment are given below  

Aplasia The tissues may fail to develop. This happened in the unfortunate cliildren whose mothers had taken the drug thalidomide during their pregnancies, hi some of these babies, the limbs were only partly developed (hypoplasia). 

Hyperplasia The organ or tissue has an increased number of cells. When the cells increase in size this is termed hypertrophy. The latter condition may occur in the muscles of a leg when the other has been amputated and the remaining limb has to work harder. 

Metaplasia This process involves changes in the types of cell present in a tissue often from a complicated cell to a more simple one. Long lashng irritation from chemicals may bring about this change which is often seen in the lining of the air passages of smokers. 

---