Pyknosis, or karyopyknosis, is the irreversible condensation of

chromatin Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in r ...

in the

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

of a

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...

undergoing

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

. It is followed by

karyorrhexis Karyorrhexis (from Greek κάρυον ''karyon'', "kernel, seed or nucleus", and ῥῆξις ''rhexis'', "bursting") is the destructive fragmentation of the nucleus of a dying cell whereby its chromatin is distributed irregularly throughout the c ...

, or fragmentation of the nucleus. Pyknosis (from Ancient Greek meaning "thick, closed or condensed") is also observed in the maturation of

erythrocyte Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

s (a red blood cell) and the

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...

(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 Reticulocytes are immature red blood cells (RBCs). In the process of erythropoiesis (red blood cell formation), reticulocytes develop and mature in the bone marrow and then circulatory system, circulate for about a day in the blood stream before ...

. The maturing neutrophil will condense its nucleus into several connected lobes that stay in the cell until the end of its cell life. File:4_Bd_obs_4_680x512px.tif,

Micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a mic ...

of an infarct in the

biliary tract The biliary tract, (biliary tree or biliary system) refers to the liver, gallbladder and bile ducts, and how they work together to make, store and secrete bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and co ...

, with pyknotic nuclei (arrows) (400x). Pyknotic nuclei are often found in the

zona reticularis The zona reticularis (sometimes, reticulate zone) is the innermost layer of the adrenal cortex, lying deep to the zona fasciculata and superficial to the adrenal medulla. The cells are arranged cords that project in different directions giving a n ...

of the adrenal gland. They are also found in the keratinocytes of the outermost layer in parakeratinised epithelium. Another use of the word pyknotic, introduced in mathematics in 2019, is for pyknotic objects, which are hypersheaves on the site of compacta; this use is unrelated to cell biology or nuclei.

References

Cellular processes Programmed cell death Cellular senescence {{Cell-biology-stub

See also

References