Erythrocytes are sensitive to the osmotic pressure of the blood plasma. An increase in osmotic pressure shrivels them by withdrawing water, while they swell up and burst in a weaker solution, their pigment is released, and the blood is said to be hemolysed.
Before birth, red blood cells are formed in the bone marrow, liver, spleen, and lymph glands. After birth, the marrow is their only source; in early life the bones are full of red marrow, but later this retreats to the bone ends, leaving the shaft occupied by yellow fatty marrow. In humans, the number of erythrocytes in the blood varies between 4.5 and 5.5 million per cubic millimeter. They survive for about 120 days and are then destroyed in the spleen and liver.
Related category• CELL BIOLOGY
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