Necrosis

types of cell death

Necrosis

Apoptosis

Nuclear changes

Pyknosis, hyperchormatosis, karyorrhexis, karyolysis

Pyknosis

Nucleus is decreased in size, but round more perfectly that it was during life

Nucleus is black and homogenous

Lack nucleolus, chromatin granules, and internal structure characteristic of most living nuclei

Hyper-chromatosis

Concentration of chromatin on the nuclear membrane

The centre of nucleus paler, crossing of cell membrane, binding of chromatin

Karyorrhexis

The nuclear membrane ruptures and the chromatic fragments are concentrated into small, darkly stained aggregates

Karyolysis

Dissolution of the nuclear material

Nucleus appears as a hollow sphere with only the nuclear membrane remaining

Cytoplasmic changes

Acidophilia of the cytoplasm

Cytoplasmolysis

Acidophilia of cytoplasm

It's reaction is more basic than during life, stain is usually red

Cytoplasmic structure is obscured

Cytoplasmolysis

Cytoplasm tends to become less and less, ultimately disappears completely

Changes in the cell

Loss of cell outline

Loss of differential staining

The absence of the cell

Loss of cell outline

Loss of the form and outline of cell

Cell material of which they are made of is still present

Seen in caseous necrosis of a tubercle or in an inflammatory exudate

Loss of differential staining

Colour of nuclei and cytoplasm cannot be distinguished

Absence of the cell

If the cell cannot be found, it must be assumed to have died

Types of necrosis

Coagulative necrosis

Liquefactive (colliquative) necrosis

Coagulative necrosis

desaturation of cellular proteins → firm mass of necrotic cells whose outlines may persist for days or even weeks before dissolved and removed by enzymatic lysis

Occurrence: infarct (local ischaemia), toxic products of certain bacteria, locally acting poisons, milder burns

Types of Coagulative necrosis

Caseous necrosis

Zenker's necrosis

Caseous necrosis

Tuberculotic lesion

Friable, cheesy, amorphous material

Mixture of degenerative tissue protein and fat which is derived from the lipid capsule of the organism

Zenker's necrosis

Coagulation of proteins of the sarcoplasm

Occurs in striated muscle

Toxins of pathogenic microorganisms

Grossly: muscle is white or pale, rather shiny, and somewhat swollen

Micro: fibres are swollen, homogenous and hyaline, the sarcoplasm is acidophilic, the myofibrils presented lack cross striation, the nuclei are small and dark

Liquefactive (colliquative) necrosis

Rapid liquefaction of dead cells

Types of Liquefactive necrosis

Abscesses

Malacia

Haemorrhagic necrosis

Abscess

Liquid is represented by pus (Ne, tissue fluid, tissue debris)

Malacia

Breakdown of myelin, result in cerebral softening

Encephalo-malacia - brain

Myelo-malacia - spinal cord

Haemorrhagic necrosis

Variant of necrosis when the necrotic tissue is congested with blood

Due to blockage of venous drainage of an organ or tissue

Commonly observed in malposition of intestine (volvulus, intussusception)

Fat necrosis

Occurs in the abdominal cavity or under the skin

Types of fat necrosis

Traumatic

Enzymatic

Abdominal

Traumatic fat necrosis

Traumatic rupture of fat cells

Free fat evokes a tissue reaction resulting in reparative changes -> fibroblastic area of scar tissue and firm nodules

Enzymatic fat necrosis

Also known as pancreatic necrosis

Occurs when neutral fats are split by lipases into fatty acids and glycerol

FAs saponify with alkalis to form chalky white precipitates

Abdominal fat necrosis

Large masses of necrosis fat in mesentery, omentum, and retroperitoneum

The outcome of necrosis

1. Liquefaction and removal of the fluid via the blood and lymph system

2. Liquefaction and formation of a cyst-like accumulation of fluid

3. Liquefaction with abscess formation

4. Encapsulation without liquefaction

5. Desquamation or sloughing

6. Replacement by scar tissue

7. Sequestration

8. Calcification

9. Gangrene

10. Atrophy of the organ, tissue, or part there of is followed by necrosis

11. Regeneration

Gangrene

Necrotic tissue which has undergone secondary influences

Types of gangrene

Dry

Wet

Gas

Dry gangrene

gradually + slow reduction of the blood flow in the arteries

There is no subsequent bacterial decomposition

Tissues are dry and shrivelled, cold, lacking in pulse, first brown then black colour

Moist (wet) gangrene

Tissues are well filled with blood at the time the necrosis begins

Sudden stoppage of blood - burning by heat or acid, freezing

Tissue is swollen, pulpy, dark, or black in colour

Gas gangrene

Occurs in dirty lacerated wound infected by anaerobic bacteria (clostridium)

Acute, severe, painful condition

Grossly: dark red-black with gas bubbles and fluid exudates that may contain blood

Apoptosis

Programmed cell death

Different characteristics between apoptosis and necrosis