(A) the concept of necrosis

The death of local tissue cells in vivo characterized by the change of enzyme solubility is called necrosis.

(2) types of lesions and necrosis

The basic pathological changes of necrosis: the change of nucleus is the main morphological sign of cell necrosis, which is characterized by nuclear concentration, nuclear fragmentation and nuclear dissolution; The cytoplasm is eosinophilic.

Pathological changes of 1. necrosis

(1) nuclear changes: This is the main morphological sign of cell necrosis, which is manifested by nuclear concentration, nuclear fragmentation and nuclear dissolution.

(2) Cytoplasmic changes: Due to the solidification or dissolution of cytoplasm, he staining showed crimson granules, such as eosinophils with necrotic hepatocytes.

(3) Interstitial changes: Due to the action of various lytic enzymes, the matrix disintegrates, collagen fibers swell, break or liquefy, and fuse with necrotic cells to form red-dyed granular unstructured substances.

2. Types of necrosis

(1) Coagulation necrosis:

Necrotic tissue changes from dehydration to protein coagulation, and becomes a grayish yellow, relatively dry and solid solidified body, so it is called coagulative necrosis. Coagulation necrosis is common in ischemic necrosis (infarction) of heart, kidney, spleen and other organs.

Macro-morphology: The necrotic tissue in the early stage is obviously swollen, dark in color and fuzzy in texture. After that, the necrotic focus gradually becomes hard and yellow, and there is often a bleeding area around the necrotic focus, which is clearly demarcated from healthy tissue. Light microscope: the nuclei of necrotic tissues were concentrated, fragmented, dissolved and eosinophilic stained, but the outline of tissue structure still existed.

(2) liquefactive necrosis:

In necrotic tissue, there is less protein that can be coagulated, or necrotic cells and infiltrated neutrophils release a large amount of hydrolase, or the tissue is rich in water and phospholipids, and the cell tissue is easy to dissolve and liquefy, which is called liquefaction necrosis. Liquefactive necrosis mainly occurs in tissues with low protein content and high lipid content (such as brain) or tissues with high protease production (such as pancreas).

When coagulated necrotic tissue is infected by bacteria, it contains a large number of neutrophils. Because of its destruction, a large number of hydrolases are released, which can dissolve tissues and cause liquefactive necrosis.

Special type of coagulative necrosis

① Caseous necrosis: necrosis mainly caused by mycobacterium tuberculosis. Because it contains more lipid components, it is softer and looks like cheese. The caseous necrosis; Such as caseous tuberculosis.

(2) Gangrene: After tissue necrosis, there are different degrees of putrefying bacteria infection, which makes the necrotic tissue show a special morphological change of dark brown.

Dry gangrene: due to arterial occlusion, the vein is still unobstructed, the water content of necrotic tissue is low, and the air evaporates, which makes the diseased tissue dry, bacteria are not easy to reproduce, and the lesion develops slowly, which is more common at the ends of limbs. The causes are lower extremity atherosclerosis and thromboangiitis obliterans.

Wet gangrene: often occurs in limbs or organs (intestine, uterus, lungs) that communicate with the outside world. Due to arterial occlusion, venous reflux is blocked, and necrotic tissue is rich in water, which is suitable for the growth of spoilage bacteria, local swelling and black pollution. Causing stench.

Gas gangrene: Due to the open wound of deep muscle complicated with anaerobic infection, cells decompose necrotic tissue to produce a large amount of gas, which makes necrotic tissue honeycomb due to bubbles and distort according to it.