cellinjury

Irreversible cell injury(necrosis)
Necrosis refers to a sequence of morphologic changes that follow cell death in living tissue or organ .
The morphologic appearance of necrosis is the result of enzymatic digestion of the cell and denaturation of proteins.
In necrosis there are cytoplasmic and nuclear changes Cytoplasmic changes:-
1-Necrotic cell is more eosinophilic than viable cells attributable in part to loss of the normal basophilia imparted by the RNA in the cytoplasm and in part to the increased binding of eosin to denatured intracytoplasmic proteins
2-The cell may have more glassy homogenous appearance than normal cells mainly as a result of the loss of glycogen particles
Nuclear changes:- the nuclear changes assume one of three patterns:
1- pyknosis: characterized by nucleus shrinkage and increased basophilia so transformed into small round mass
2-karyorrhexis: the pyknotic nucleus become fragmented into several particles
3- karyolysis with time there is progressive disintegration of chromatin with subsequent disappearance of nucleus
Types of cell necrosis
A- coagulative necrosis 1-preservation of the basic outline of the coagulated cells for at least some days. 2-the most common cause is ischemia except the brain which undergo liquefactive necrosis 3- The affected tissues exhibit a firm texture.
B- Liquefactive necrosis 1- complete digestion of dead cells by enzymes and thus the necrotic area is eventually liquefied 2- microscopically diagnosed as cyst filled with WBCs ,debris and fluid 3- the most common cause is bacterial and some time fungal infection
C- Fat necrosis This is a specific pattern of cell death in adipose tissue due to action of lipase, most commonly seen in acute pancreatitis, but its could be seen after trauma
D- Caseous necrosis 1-It is a distinctive form of necrosis encountered most often in the center of granuloma of tuberculosis(T.B.) 2- the term caseous is derived from the cheesy, white gross appearance of the central necrotic area 3-microscopically, the necrotic focus is composed of structure less, amorphous granular debris enclosed with in a distinctive ring of granulomatous inflammation E-Fibrinoid necrosis Occur in arterial wall, the cause is hypertension Characterized by intense eosinophilic material deposit within the arterial wall
F- Gangrenous necrosis It is not a distinctive pattern of cell death, the term is still commonly used in surgical clinical practice. It is usually applied to a limb, generally the lower leg, that has lost its blood supply and has undergone coagulation necrosis. When bacterial infection is superimposed, coagulative necrosis is modified by the liquefactive action of the bacteria and the attracted leukocytes (so-called wet gangrene).
Examples
Fatty necrosis of breast
It is an uncommon and innocuous lesion that is significant only because it produce a mass Causes
1-trauma to the breast
2-FNAB(fine needle aspiration biopsy)
3- core biopsy
Macroscopically Mass, tender, small in size, rarely more than 2 cm in diameter sharply localized Microscopically
1-fat necrosis consists of irregular steatocytes with no peripheral nuclei
2-there is intervening pink amorphous necrotic material and chronic inflammatory cells, in which lipophages(macrophages containing lipid giving their cytoplasm a foamy appearance) and plasma cells may be present in large number.
3-interstitial fibrosis

Tuberculosis(TB)
It is a communicable chronic granulomatous disease caused by mycobacterium tuberculosis. Its usually involve the lungs but may affect any organ or tissue in the body. Typically the center of tubercular granuloma undergo caseous necrosis
Risk factors for developing TB
1-poverty 2- crowding 3-malnutrition 4- alcoholism 5-chronic debilitating illness like DM ,chronic renal failure and etc.
Grossly 1-Granulomatous disease grossly appears as irregularly sized rounded nodules that are firm and tan. Larger nodules may have central necrosis known as caseation- 2-The caseous material is soft, friable, whitish, cheesy material
Microscopically 1-the TB characterized by granuloma formation which is 0.5-2mm in diameter and its formed by collection epithelioid cells(transformed macrophage) usually surrounded by a rim of lymphocytes and some time fibroblast 2-the caseous necrosis occupy the center of granuloma, it has distinctive amorphous granular pinkish debris. 3-Langhans giant cell is seen with in the granuloma, this cell is formed by fusion of several epithelioid cells , so it appear as large cell with one cytoplasm and several nuclei which arranged at periphery as horseshow
Clinical feature
Anorexia, weight loss, lassitude sleep sweating, evening pyrexia
Myocardial infarction
This is an example of coagulative necrosis, this disease occure following occlusion of a coronary artery , its presented with sever chest pain radiated to the left arm associated with sweating and vomiting
Risk factors: 1- hyperlipidemia 2-hypertention 3-DM 4-smoker 5-obesity 6-male sex 7-stressfull condition 8-family history of disease
Macroscopically The infracted area appear geographic(map-like) , and appear pallor than normal, the margins of the infarct become better defined by the development of a narrow rim of hyperemia Microscopically
1- the infracted cardiac muscle fibers exhibit patchy loss of striation 2-and become more intensely stained by eosin 3-and most of cardiac muscle fibers have lost their nuclei 4-there is marked infiltration by netrophils into the oedematous interstitium