Etiology of cell death :
Major Factors
Accidental Genetic
Necrosis Apoptosis
Necrosis:
The sum of the morphologic changes that follow cell death in a living tissue or organ
Apoptosis:
a physiological process that includes specific suicide signals leading to cell death Etiology of cell death
Necrosis: consequences of cell injury :
Necrosis: consequences of cell injury
Types of necrosis :
Types of necrosis Coagulation necrosis (ischemia)
Liquefaction necrosis (escape of hydrolases)
Enzymatic fat necrosis (escape of lipases)
Caseous necrosis (e.g., bacterial liquefaction)
Gangrenous necrosis (ischemic + bacterial liquefaction)
Slide 5:
Necrosis: a pathological response
to cellular injury Chromatin clumps Mitochondria swell and rupture Plasma membrane lyses Cell contents spill out General inflammatory response is triggered Apoptosis: a physiological
response to specific suicide signals,
or lack of survival signals Chromatin condenses and migrates to nuclear
membrane. Internucleosomal cleavage leads
to laddering of DNA at the nucleosomal
repeat length, ca. 200 bp. Cytoplasm shrinks without membrane rupture Blebbing of plasma and nuclear membranes Cell contents are packaged in membrane
bounded bodies, internal organelles still
functioning, to be engulfed by neighbours. Epitopes appear on plasma membrane
marking cell as a phagocytic target.
No spillage, no inflammation
APOPTOSIS AS A PHYSIOLOGICALLYIMPORTANT PROCESS :
APOPTOSIS AS A PHYSIOLOGICALLYIMPORTANT PROCESS In embryonic and
fetal development: Tissue developmental programs which control
sculpting of embryonic form
• Developmental organization of the nervous system
• Elimination of self-reactive components of the immune system In the adult: On stimulation by T-lymphocytes
• In response to DNA damage or abnormality, e.g. by
radiation, viral infection or transformation
• In certain organs and tissues, on withdrawal of
supporting hormones In addition, there are often apoptotic centers in tumors, accounting for the paradox of slow gross enlargement in the face of rapid cell proliferation, and the rare spontaneous remission.