1.] All forms of organ injury starts with molecular or structural alteration in cell.
2.] Normal cells have fairly normal narrow range of functions or steady state known as homeostasis.
3.] Excess physiologic or pathologic stress may force the cell to a new steady state :-
- Adaptation : Change in cell morphology and function in response to a stimulus. It is reversible.
- Injury : Too much stress exceeds the cell adaptive capacity. Stress may be physiologic or pathologic stimulus.
4.] Cell injury is defined as a variety of stresses a cell encounters as a result of its internal and external environment.
CAUSES ( ETIOLOGY ) OF CELL INJURY :-
Cell injury is caused by :-
A.] Genetic causes.
B.] Acquired causes : examples of acquired causes are :-
- Physical agent : road accidents, extreme heat and cold, electricity and radiation.
- Chemical agent : poison like cyanide, mercury and arsenic, strong acid, insecticide, pesticides, narcotic drugs, alcohol etc.
- Microbial agent : bacteria, fungi, viruses etc.
- Hypoxia and ischemia: die to decreased blood supply, heart and lung diseases.
- Immunological disorders
- Nutritional derangement
- Psychogenic diseases.
CELLULAR ADAPTATION :-
It is the modification of cell morphology and function in relation to stress it is reversible and preserves the viability of cell. It includes :-
- Hypertrophy : It is an increase in size of individual cells, in response to a stimulus or injury. Example muscle hypertrophy after regular exercise.
- Atrophy : It is decrease size and weight of an organ due to decreased size and number of its component cells.
- Hyperplasia : It is an increase in absolute number of cells, in response to stimulus or persistent to cell injury. It may be physiological or pathological.
- Metaplasia : A reversible change in which one mature / adult cell type (epithelial or mesenchymal) is replaced by another mature cell type of the same category.
PHYSIOLOGIC ADAPTATIONS : Responses of cell to normal stimulation by hormone. Example hormone induced enlargement of breast and uterus during pregnancy.
PATHOLOGIC ADAPTATIONS : Responses to stress that allow cells to modulate their structure and function and thus escape injury.
TYPES OF CELL INJURY :-
There are two types of cell injury :-
1.] Reversible cell injury : a.) cellular swelling b.) fatty change
2.] Irreversible cell injury : a.) autolysis and heterolysis b.) necrosis c.) apoptosis
A.] MORPHOLOGY OF REVERSIBLE CELL INJURY :- cellular swelling is the result of failure of energy dependent ion pump in the plasma membrane, leading to an inability to maintain ionic and fluid homeostasis cellular swelling the first manifestation of almost all types of cell injury. It is a reversible alteration that may be difficult to locate with light microscope but it may be apparent at the level of whole organ. It causes increase in weight of organ.
B.] MORPHOLOGY OF IRREVERSIBLE CELL INJURY :-
- Autolysis (self digestion) : Disintegration of cell by its own hydrolytic enzyme liberated from lysosomes. Autolysis in some tissues such as pancreas and gastric mucosa; intermediate in tissues like heart, liver and kidney ; slow in fibrous tissues.
- Heterolysis : Disintegration of cell by hydrolytic enzymes liberated from inflammatory mediators like neutrophils etc.
- Necrosis : Necrosis is a series of morphological changes that occurs in lethally injured cells. It is a type of cell death associated with loss of membrane integrity and leakage in cellular contents resulting in dissolution of cells due to degradative action of enzymes on lethally injured cells.
- Apoptosis : It is also known as programmed cell death. Apoptosis is a pathway off cell death which cells activate enzymes that degrade cells own nuclear DNA, Nuclear and Cytoplasmic proteins.
MULTIPLE CHOICE QUESTIONS [MCQs] :-
1.] Caspases are involved in ?
2.] True about apoptosis are all except ?
a. Inflammation in present
b. Chromosomal breakage
c. Clumping of chromatin
d. Cell shrinkage
3.] Most pathognomic sign of irreversible cell injury ?
a. Amporphous densities in mitochondria
b. Swelling of the cell membrane
c. Ribosome detached from endoplasmic reticulum
d. Clumping of nuclear chromatin
4.] Programmed cell death is known as ?
5.] Irreversible cell injury in cell is ?
a. Deposition of Ca++ in mitochondria
c. Mitotic figure
d. Ribosomal detachment
6.] Apoptosis is ?
a. Cell degradation
b. Type of cell injury
c. Cell regeneration
d. Cell activation
7.] Apoptosis is alternatively called as ?
a. Ischemic cell death
b. Programmed cell death
c. Post traumatic cell death
d. All of the above
8.] Liquefactive necrosis is seen in ?
9.] Coagulative necrosis is founded in which infection ?
d. Fungal infection
10.] Caspases are seen in which of the following ?
a. Cell division
1.] (b) apoptosis
2.] (a) inflammation
3.] (a) amporphous densities in mitochondria
4.] (b) apoptosis
5.] (a) deposition of Ca++ in mitochondria
6.] (b) type of cell injury
7.] (b) programmed cell death
8.] (b) brain
9.] (a) TB
10.] (b) apoptosis
1.] Textbook Of Pathology By Harsh Mohan; 7th edition; Page no. 09 – 41
2.] Robbin’s Basic Pathology; 5th edition; Page no. 02 – 27