Pyknosis, or
karyopyknosis, is the irreversible condensation of
chromatin in the
nucleus of a
cell undergoing
necrosis or
apoptosis. It is followed by
karyorrhexis, or fragmentation of the nucleus. Pyknosis (from Greek
pyknono meaning "to thicken up, to close or to condense") is also observed in the maturation of erythrocytes (a
red blood cell) and the
neutrophil (a type of white blood cell). The maturing metarubricyte (a stage in RBC maturation) will condense its nucleus before expelling it to become a
reticulocyte. The maturing neutrophil will condense its nucleus into several connected lobes that stay in the cell until the end of its cell life.
