5

NECROSIS

“Necrosis is the morphological changes that follow cell death in a living tissue or organ,

Resulting from the progressive degenerative action of enzymes on the lethally injured cell.”
So,
Necrosis begins with an impairment of the cell’s ability to maintain homeostasis, leading
to an influx of water and extracellular ions

Apoptosis vs Necrosis

The word apoptosis mean falling off.

“Apoptosis is a process of programmed and targeted

cause of cellular death”

Necrosis is differ from apoptosis:

Apoptosis
Necrosis
Physiological or pathological
Always pathological
Cell shrinkage
Cell swelling
Apoptotic bodies form

Do not form

Dna cleavage
No DNA cleavage
Beneficial
Detrimental
Characteristic nuclear changes
Nuclei lost
No leak of lysosomal enzymes
Leak of lysosomal enzymes

Causes of necrosis

Anoxia
Ischemia
Physical agents
Chemical agents
Biological agents
Immunological


Pathogenesis
Necrotic changes in tissues are caused By
Digestion of cell by enzymes
Denaturation of proteins

Digestion of cell by enzymes

This digestion is of two types
Autolysis: Digestion of cell by enzymes derived from their own lyosomes
Heterolysis: Digestion of cell by enzymes derived from lysosmes of leukocytes.

By Denaturation of proteins

Denaturation of proteins caused by intracellular acidosis
and due to this result is that:

Injury to the cell membrane

Severe impairment of phosphorylation of cell
Increase permeability of the cell
Influx of Na+ and Ca+ in the cell
Decreased intracellular activity of the cell


Changes in Necrosis

Changes inside the cell

Changes in mitochondria

Changes in Nucleus

Changes in cytoplasm

Changes inside the cell

Endoplasmic reticulum is disorganized
There is rupture of membrane
Ribosomes are shed off
Disorganization of polysomes & their structures

Changes in mitochondria

Mitochondria become swallon
Loss of interamitochondrial granules
Loss of cristae & change their shape
Rupture of outer membrane of Mitochondria


Changes in Nucleus
Nucleus becomes smaller
Chromatin loses & become clumped

Nucleus shows following changes

Pyknosis
Karyorrhexis
Karyolysis

PYKNOSIS

“When the DNA is broken down by endonucleases
fragments are formed & the nucleus becomes acid
and stains basophillic”

KARYORRHEXIS

“The pyknotic nucleus may break up into fragments
and disappear. This process is called karyorrhexis”
KARYOLYSIS
“The pyknotic nucleus may undergo lysis by the
enzyme DNAse”


Changes in cytoplasm
Cytoplasm becomes more eosinophilic:

Due to loss of RNA & denaturation of cytoplasmic proteins

Cytoplasm becomes opaque.

TYPES OF NECROSIS

Basic types
Coagulative necrosis
Liquefactive necrosis
Caseous necrosis
In special sites
Fat necrosis
Fibrinoid necrosis
Gangrenous necrosis

COAGULATIVE NECROSIS

“In this type of necrosis, the necrotic cell retains its
cellular outline for several days”


Coagulative necrosis typically occurs in solid organs such as kidney, heart and adrenal gland usually as a result of deficient blood supply and anoxia.
Examples
Myocardial infarction

Mechanism

Denaturation of protein is the basic mechanism of coagulative necrosis

The injury and the subsequent increasing acidosis

denatures not only the structural proteins but also the enzymic proteins, thus blocking the cellular proteolysis.
Morphology
Preservation of basic structural outline of the coagulated cells
Appears as a mass of coagulated, pink staining homogenous cytoplasm










LIQUEFACTIVE NECROSIS
It is the type of necrosis that occurs due to autolytic and
heterolytic actions of enzymes that convert the proteins
of cells into liquid.

It is characterized by softening and liquifaction of tissue.

Examples
Ischemic necrosis of brain
Suppurative inflammation.

Mechanism

Enzymatic degradation of proteins is the basic mechanism of liquefactive necrosis

Morphology

Complete loss of cellular detail
Cellular outline is also destroyed

CASEOUS NECROSIS

Combination of coagulative and liquefactive necrosis
Characterized by the presence of soft, dry, cheesy homogenous necrotic material.
It is not liquefied

Examples

Principaly in the center of tuberculous granuloma
Morphology
Microscopically the necrotic focus is composed of structureless amorphous granular debris enclosed within a ring of granulomatous inflammation.






Necrosis in special sites Fat necrosis

It occurs in two forms:

Enzymatic fat necrosis

Traumatic fat necrosis

Enzymatic fat necrosis

Most commenly seen in acute pancreatitis.
“Refers to the necrosis in adipose tissue, induced by the
action of pancreatic enzymes which are lead due to
trauma to the pancreas”

Morphology

Chalky white opaque spots surrounded by inflammatory margins are seen
Necrotic area shows acute inflammatory changes with dissolved fat cells

Traumatic fat necrosis

It occur following severe injury to the tissues with high fat content such as the breast, subcutaneous tissue and abdomen.


Morphology
Foam cells and gaint cells are seen.
necrotic foci contain a lot of phagocytes containing fat known as foam cells

FIBRINOID NECROSIS

Type of connective tissue necrosis especially affecting arterial walls.

Mostly seen in two conditions

Auto immune diseases e.g
Rheumatic fever
SLE
Malignant hypertension

GANGRENOUS NECROSIS

Gangrene is the necrosis of tissue with superadded putrefaction (enzymatic decomposition).

It is the clinical condition in which extensive tissue necrosis is complicated to a variable degree by secondary bacterial infection.

Gangree= Necrosis + infection + putrefaction

Causes of gangrene

Arterial obstructon due to:
Thrombosis of atherosclerotic artery
Embolus
Diabetes:- atherosclerotic artery , loss of sensation
results reapeted trauma & increase chances of infection
Infection
Gas gangrene
Gangrene of scrotum
Trauma
Crush injuries
Physical agents
Burns
Chemicals


Types of gangrene

Dry gangrene

Wet gangrene

Gas gangrene

Dry gangrene of foot

Wet gangrene of intestine

Wet gangrene of appendix