1. Cell Injury & Cell Death
Grace Denton & Stephanie Tristram

2. What are some of the causes of cell injury and cell death?
Loads of stuff can cause ‘cell injury’ – from a car crash to minute internal abnormalities such as a genetic mutation.
Chemical and drugs
E.g. Glucose + salt at high levels / poisons / pollutants / booze
Oxygen deprivation (hypoxia)
E.g. reduced blood flow (ischaemia) / cardiorespiratory failure / severe blood loss
Infectious agents
E.g. Bacteria / viruses / tape worms
Physical agents
Stuff that makes you say ouch – car crash / stab wound / burn
Immune reactions
Immune reactions can cause cell injury. Fact.
Genetic derangements
E.g. Sickle-cell anaemia (one amino acid substitution = red blood cell dies early)
Nutritional imbalances
Starvation / excess cholesterol = atherosclerosis / obesity = diabetes + cancer…
Causes of cell injury  CHIPING: Chemical, Hypoxia, Infections, Physical, Immune, Nutrition, Genetic
Sometimes the cell will be able to repair itself. If it can’t, it is lethally injured, and will die – via apoptosis or necrosis.

3. What are the different mechanisms of cell injury (cellular level)?
Reduced ATP
Mitochondrial damage leads to the leakage of pro-apoptotic proteins
Entry of Ca2+ leads to increased mitochondrial permeability and activation of multiple cellular enzymes
↑ reactive oxygen species (ROS) damages lipids, proteins and DNA
Membrane damage
Protein misfolding, DNA damage leads to the activation of pro-apoptotic proteins

4. What are the different types of Cell Death?
Necrosis
Result of irreversible cell injury.
Necrosis is the principal outcome in many commonly encountered injuries, such as those following:
Ischemia
Exposure to toxins
Various infections
Trauma
Apoptosis
Result of irreversible cell injury.
In situations when the cell’s DNA or proteins are damaged beyond repair, the cell kills itself by apoptosis, a form of cell death that is characterized by:
Nuclear dissolution
Fragmentation of the cell without complete loss of membrane integrity
Rapid removal of the cellular debris
No inflammation

6. What are the comparisons of Necrosis and Apoptosis?
What are the comparisons of Necrosis and Apoptosis?
Feature
Necrosis
Apoptosis
Cell Size
Enlarged (swelling)
Reduced (shrinkage)
Nucleus
Digested
Fragments
Plasma membrane integrity
Disrupted
Intact
Fate of cell contents
Digested, leak out of cell
Intact, packaged into apoptotic bodies
Local inflammation
Frequently  leaked enzymes cause local destruction
No  apoptotoic bodies are neatly phagocytosed
Physiological or pathological
Always pathological
culmination of irreversible cell injury
Sometimes pathological
after some forms of cell injury – e.g. DNA damage
Sometimes physiological
a way of eliminating unwanted cells
Necrosis or
Apoptosis?
Physiologic or Pathologic: Either? Always pathological?
Cell size: Reduced? Enlarged?
Nucleus: Fragments? Digested?
Plasma membrane integrity: Disrupted? Intact?
Cell contents: Digested, leaked? Intact, packaged?
Associated inflammation: Often? None?

7. Describe the process of apoptosis
The nucleus and cytoplasm condense down (reduction in cell size)
Plasma membrane fragments (apoptotic bodies) are phagocytosed by normal tissue phagocytes
No inflammation
More:
Apoptosis … AKA ‘programmed cell death’
Apoptosis does not trigger an inflammatory reaction - intracellular enzymes degrade the cells’ DNA and proteins but there is no disruption to the cell membrane
So, because the cell membrane is intact, there is no leakage of intracellular contents (e.g. destructive enzymes), and there is no inflammation

8. Give some examples of physiological and pathological apoptosis.
Embryogenesis (e.g. developmental involution)
Involution of hormone dependent tissue (endometrial breakdown during menstrual cycle)
Cell loss in proliferating cell populations (epithelial cells in intestinal crypts)
Elimination potentially harmful lymphocytes (so as to prevent autoimmune reactions)
Cells no longer required
Cells with DNA damage
Cells with Endoplasmic Reticulum Stress (i.e. mis-folded proteins accumulation in the ER)
Some infections e.g. Viruses
Pathological atrophy if a duct is obstructed

9. The form and structure of necrosis is the result of:
This is a little bit of background info on necrosis, in case you don’t want to just rote-learn the types:
NECROSIS
The form and structure of necrosis is the result of:
denaturation of intracellular proteins
enzymatic digestion of the lethally injured cell 
Necrotic cells are unable to maintain membrane integrity and their contents often leak out, a process that often elicits inflammation in the surrounding tissue
The enzymes that digest the necrotic cell come from within the dying cells themselves, and from the lysosomes* of leukocytes (white blood cells) that are called in as part of the inflammatory reaction
When large numbers of cells die the tissue or organ is said to be necrotic
So, a myocardial infarct is necrosis of a portion of the heart caused by death of many myocardial cells
Necrosis of tissues has several morphologically distinct patterns, which are important to recognise because they may provide clues about the underlying cause…
*Lysosome = a cell organelle (part) which has its own membrane, and contains enzymes …enlarge this pic to see one 

10. What are the 6 different patterns of tissue necrosis?
You just need to know the names, and where you’d find them, but understanding might be good too…
What are the 6 different patterns of tissue necrosis?
Coagulative
A form of necrosis in which the architecture of dead tissues is preserved for a span of at least some days, so the affected tissue has a firm texture
The cell injury denatures both the proteins but also enzymes within the cell, so stops the enzymes digesting the dead cells … ultimately the necrotic cells are removed by phagocytosis
Ischemia caused by obstruction in a vessel may lead to coagulative necrosis of the supplied tissue in all organs except the brain. A localised area of coagulative necrosis is called an infarct
Liquefactive
Characterized by digestion of the dead cells, resulting the tissue becoming a liquid viscous mass
The necrotic material is often creamy yellow because of the presence of dead leukocytes and is called pus
For unknown reasons, hypoxic death of cells (i.e. due to lack of oxygen) within the central nervous system (i.e. the brain) often manifests as liquefactive necrosis
Caseous
Encountered most often in foci of tuberculous infection … i.e. you’ll hear about it in TB
The term “caseous” (cheese-like) is derived from the crumbly white appearance of the area of necrosis
4. Fibrinoid
Necrosis usually seen in immune reactions involving blood vessels

11. The last two aren’t ‘real’ necrosis, but the terms are used in clinical practice…
5. Fatty
Refers to areas of fat destruction seen in acute pancreatitis typically resulting from release of activated pancreatic lipases into the substance of the pancreas and the peritoneal cavity
These escaped pancreatic enzymes liquefy the membranes of fat cells in the peritoneum
6. Gangrenous
It is usually applied to a limb, generally the lower leg, that has lost its blood supply and has undergone necrosis (typically coagulative necrosis)

12. Where would you see liquefactive necrosis?
The brain (first answer I would give to this question)
Name 3 organs where you would expect to see coagulative necrosis.
Kidney, heart, adrenal glands (may occur in all organs - except the brain…!)
What is the key difference between coagulative and liquefactive necrosis?
Coagulative – tissue architecture is maintained (for a few days, at least)
Liquefactive – tissue architecture is not maintained … it is a liquid viscous mass
When do you see fatty necrosis?
Fatty necrosis is really just fat destruction.
Acute pancreatitis. Damaged pancreatic cells release lipases which degrade fat cells in the peritoneum
When would you expect to see caseous necrosis?
Tuberculosis (first answer I would give to this question)

13. What causes white infarction?
Define infarction
What causes white infarction?
Infarction = an area of ischaemic necrosis in a tissue or organ
Arterial occlusion in most solid tissues e.g. heart, spleen, kidney
I.e. blood can’t get in…
What are the two types of infarction?
White
Red/haemorrhagic
What causes red/haemorrhagic infarction?
Venous occlusion
Infarction in loose tissues (e.g. lung) where blood can collect in the infarcted zone
Tissues with dual blood supply (e.g. lung + small intestine)
Tissues that have been previously congested by sluggish venous outflow
I.e. blood can’t get out…

14. How are free radicals generated in cell injury?
What is a free radical?
A free radical is defined as “any species capable of independent existence that contains one or more unpaired electrons”
(It’s a highly reactive molecule that reacts with things that it shouldn’t in order to stabilise itself)
How are free radicals generated in cell injury?
Chemicals/drugs
reperfusion injury
Inflammation
Irradiation
oxygen toxicity
carcinogenesis
How are free radicals removed?
Spontaneous decay
Anti-oxidants: Vit E, Vit A, Ascorbic acid (Vit C), glutathione
Storage proteins: Transferrrin, ferritin
Enzymes: Glutathione peroxidase
What 3 things do free radicals damage?
Nucleic acids
Cellular proteins
Cellular lipids

15. APPENDIX.
(Some of the notes we wrote on this stuff last year…)

16. Cell injury / death - BACKGROUND:
Once cells are stressed beyond their adaptive capacity, are exposed to inherently harmful stimuli or have an intrinsic abnormality they become damaged. This damage may lead to:
Cell injury
Reversible (if stimulus is removed can return to normal)
Irreversible (culminating in cell death)
Hallmarks - inability to reverse mitochondrial dysfunction and profound disturbance in membrane function.
Cell death
Apoptosis
Necrosis

17. Mechanisms of Cell Injury
Biochemical mechanisms link the injury with resultant cellular and tissue changes and associated changes in function. Principles of cell injury:
The cellular response to injury depends on
The type of injury
The duration of injury
The severity of the injurious stimulus.
The consequences of the injurious stimulus depend on the following cellular characteristics:
The cell type and status
Adaptability of the cell
Genetic make-up of the cell
The injury and its associated derangements usually reflect damage to one of 5 key cellular components.
Mitochondria and reduced ATP production
Cell membrane
Protein synthesis
Cytoskeleton
Genetic apparatus of the cell