Cell pathology

Pathology is the study of abnormalities in living systems.  These abnormalities are recognized as diseases.  Cellular pathology on the other hand is the study of the abnormalities of the cell as occurs in disease conditions.

            Disorders of  the cell can be divided into two major categories.

  •  1.    Disorder that finally leads to death of the cell which is called necrosis.

  • 2.       Disorders of varying magnitude which do not lead to necrosis or cell death.

Abnormalities of the cell can be caused by the following.

  • 1.                  Genetic aberration

  • 2.                  Lack of nutrient essential for growth, as a result of poor diet.

  • 3.                  Disorders of absorption which also lead to low nutrients in tissue

  • 4.                  Disorders of the circulatory system which may lead to low  perfusion by oxygen.

  • 5.                  Harmful physical agents e.g. ionizing radiation or radiomimetic agents

  • 6.                  Harmful chemical agents

  • 7.                  Disorders caused by living agents like microbes.

Genetic aberration

            Chromosomal changes as a result of mitotic pathology can lead to abnormalities in the behavior of the cell.  In a condition called Mongolian idiocy or Down’s syndrome there is a chromosomal aberration and a cellular genetic pathology which then leads to considerable changes in morphology and physiology of the individual e.g. low intelligence.  A much more simple example of cellular affectation due to genetic abnormality is sickle cell disease.  In this condition, the patient has an abnormal hemoglobin which then  causes the red blood cells to become sickled.

Lack of nutrients

            There are two important nutrients for tissue perfusion

  1. Oxygen

  2. Glucose

 A reduction in any of the two or both of them will lead to some disorders of the cell.  For example in starvation, the liver will not be able to produce enough albumen due to shortage of oxygen perfusing it and so osmotic pressure of the blood falls due to lack of protein and a condition called hunger edema then ensues.

Disorders of circulation

            In disorders of circulation there is a reduction in oxygen perfusion of cells.  This is known as ischemia.  Ischemia can be general and is therefore called general ischemia as often occurs in reduction of oxygen to tissues as in heart failure.  Ischemia can also be local ischemia when there is a reduction of oxygen and blood flow to particular regions of the body.

Ionizing radiation

            This is one of the physical agents that can affect the cell.  It usually affects the dividing cell leading to all forms of mitotic aberrations and sometimes death. 

 

Chemical agents

            Chemical agents that can affect the cell include toxins like carbon tetracholoride (CCL.). 

Effects by living agents

            Cells that have phagocytic abilities engulf other invading cells and these invading agents may cause abnormalities in the phagocytic cells.  Microbes generally have the ability to invade living cells and cause abnormalities in them.

MECHANISMS OF CELL INJURY (DISORDERS)

The following mechanisms of cell injuries are known to occur

  1. 1        Disarray of the macromolecular fabric of the cell.  When a cell is injured, the macromolecules like DNA or RNA are affected in such a way that their constituent molecules are disrupted.  The molecules of proteinaceous compounds are also similarly disarrayed.

  2. Chemical fission  In chemical fission, catabolism is accelerated over anabolism in the living cell so that chemical substances within the cells are broken down into smaller molecules and no one is rebuilt

  3. 3        Protoplasmic disintegration. In the mechanism of protoplasmic disintegration two main modes of affectation are recognized

  • a.       Cytoplasmic disintegration

  • b.      Nuclear disintegration

In cytoplasmic disintegration, cytoplasmic organelles are affected.  The cell membrane becomes permeable to fluid and so a lot of fluid enters the cell.  There is also the arrest of the sodium pump mechanism of the cell.  Active transport breaks down because of the unavailability of adenosine triphosphate (ATP).  The cytoplasm therefore swells and becomes vacuolated.  The mitochondria swell and loose the power of oxidative phosphorylation.  They then break up into fragments in a process known as chronolysis. Fragmentation of the endoplasmic reticulum also occurs.

In rough endoplasmic reticulum, injury to the cell leads to loss of ribosomes from the surface of the endoplasmic reticulum.  The ribosomal particles then enter right into the cytoplasmic matrix.  As the injury becomes advanced ribosomes disappear in a process known as chromatolysis which leads to loss of basophilia of the cytoplasm.  Basophilia is the affinity of the cell for basic dyes like hematoxylin (eosin is an acidophilic dye).  Lysosomes play very little role in the early stages of cell injury.  Their role is mainly terminal.

 

Nuclear disintegration occurs in three main processes

1.                  Karyolysis, which is the disappearance of the nucleus.

2.                  Karyorrhexia which is the dispersal of nuclear material into fine granules which become highly basophilic and stain deeply with Feulgen reaction.

3.                  Pyknosis in which the nucleus becomes clumped into a single darkly stained entity.

 

 


    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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