Injuries To Cells & Tissue Injury And Repair Flashcards
What are the 4 types of cell adaptation?
Hyperplasia, Hypertrophy, Atrophy & Metaplasia
What is Hypertrophy?
The increase in cell size resulting in the increase in size of the organ.
- Physiological example - body builders muscles
- Pathological example - heart from hypertension (common cause of heart failure)
Which 2 types of cell adaptation can occur together?
Hypertrophy & Hyperplasia
What is Hyperplasia?
The increase in number of cells resulting in a larger (hypertrophied) organ.
- Physiological example - menstrual cycle
- Pathological example - endometrial hyperplasia (if hormonal stimuli persists) > can progress to cancers and other diseases
What is Atrophy?
Shrinkage in size of the cell > due to loss of cell substance.
Could be due to; decrease in workload, reduced blood supply, inadequate nutrition, loss of hormonal stimulation and ageing.
EXAMPLE - body builders stopping lifting weights.
What is Metaplasia?
When one cell type is replaced by another cell type.
This adaptation is in order to cope with stimulus. It is a reversible process and the new type of cell can withstand stress of environment.
EXAMPLE - Barrett’s Oesophagus - stratified squamous changes to simple columnar with goblet cells to cope with acid reflux.
Name 8 causes of cell injury.
Hypoxia - low oxygen supply
Ischaemia - loss of blood supply > oxygen and nutrients
Chemical exposure - cigarette smoke, alcohol, paracetamol ( and other drugs)
Infection
Radiation
Lack of nutrients
Ageing
Immunologic reactions (cells attack themselves e.g. HIV)
What are the 2 reversible forms of cell injury?
Cellular swelling & fatty change
What are the 2 types of cell death?
Necrosis & Apoptosis
What is Necrosis?
Damage to cell membranes, allow enzymes to digest the cell > this causes local inflammation.
Necrosis is always pathological.
What is ischaemic necrosis?
Lack of blood supply to cells > leading to cell death.
What is Apoptosis?
“Programmed cell death” - cells killing themselves.
Irreparable damage to cells protein/DNA OR cell deprivation of growth factors.
Can be pathological or physiological.
Describe the method of necrosis.
Normal cell > cellular swelling > break down of cell membrane + leakage of cell contents into surrounding tissues causing inflammatory response to prevent further damage > cell death.
Describe the method of apoptosis.
Normal cell > proteins break down and cell begins to digest itself (no inflammatory response occurs as no leakage of cell contents) > bits of cell fall off and phagocytosis occurs (macrophages engulf dead bits of cell) > cell death.
Describe physiological apoptosis.
Embryogenesis > shrinkage of hormone dependent tissues (e.g. Womb) as a result of hormone deprivation > elimination of cells which have served their purpose > elimination of potentially harmful self-reactive lymphocytes.
(This process does not cause any further damage and helps in the prevention of auto immune diseases).
What are the 2 mechanisms of apoptosis?
Mitochondrial pathway (intrinsic pathway)
Fans (death) receptor pathway (extrinsic pathway)
Both these pathways result in cell death and occur from the activation of enzymes called caspases.
Name the 4 types of necrosis.
- Coagulative - most common & occurs after loss of blood supply and after infections
- Liquefactive
- Caseous
- Fat
The names of the types of necrosis are due to their appearance.
Coagulative necrosis…
- lack of blood supply
- lack of oxygen
Also called ischaemic necrosis.
Caseous necrosis…
It can be caused by fungal infections- it should be assumed that caseous necrosis is a sign of TB unless proven otherwise.
Lump - looks like cheese.
Liquefactive necrosis…
Typically occurs in the brain - effect of stroke.
Causes a hole in the brain - the brain doesn’t heal by scarring, holes occur which are areas of necrosis.
Areas of liquefactive necrosis can have abscesses growing within them - this usually comes secondary to infection.
Fat necrosis…
Occurs due to activation of lipase’s.
Result of fat cell death, commonly occur in breast diseases as lumps.
Can mimic tumours secondary to breast trauma.
Name the 6 mechanisms of cell injury.
- Depletion of ATP
- Mitochondrial damage
- Increased intracellular calcium
- Oxidative stress
- Damage to the cell membrane
- DNA damage
Depletion of ATP…
Energy store of cells - decrease in cellular energy if process is effected.
Reduced supply of oxygen and nutrients, mitochondrial damage and poisons.
Effects; ATP dependant sodium pumps - electrolyte inbalance
Increased intercellular lactic acid (noxious stimuli), failure of calcium pumps and damage to protein structures.
Mitochondrial damage…
Causes proton leakage, depletion of ATP and leakage of cytochrome C which triggers apoptosis.
A decreased level in ATP, radiation can affect mitochondria directly > leads to decreased production of energy.
Increased intracellular calcium…
Activates enzymes which further deplete ATP.
Effects; increased intracellular calcium > activation of enzymes > damage to cellular components.
Can be a trigger of apoptosis.
Oxidative stress…
Accumulation of reactive oxygen species (free radicals).
Produced by normal cellular function - excess can lead to cell damage.
Some insults increase their production e.g. Paracetamol overdose - increase in production of free radicals + cell death in the liver.
Removed by antioxidants. React with and damage proteins, fat, DNA and reproduce causing further damage.
Damage to the cell membrane…
Results in necrosis and damages various sites such as; damage of the mitochondrial membrane, lysosomal membrane and plasma membrane > proteins in wrong place = cell death.
Mechanisms of damage - decrease in phospholipid synthesis = decreased levels of ATP, oxygen free radicals and lipid breakdown.
What may occur post radiation/oxidative stress?
Damage to DNA and proteins
What is NEOPLASIA?
Gene mutation due to mild DNA damage.
Mutations gather and eventually lead to abnormal cells > cancers.
What is DYSPLASIA?
Disordered abnormal growths secondary to Metaplasia.
DNA and protein damage…
If beyond repair, can directly trigger apoptosis.
What is tissue regeneration?
Complete reconstitution.
E.g. The epithelium of the GI tract can continuously renew itself after injury.
What is tissue repair?
A combination of regeneration and scar formation - depends on capacity to regenerate, extent of injury and extent of scarring.
What are parenchymal cells?
Cells that make up the bulk of an organ and performs the specific functions of that organ.
How to cells respond to noxious stimuli?
Normal cells - narrow range of functions and structure.
Stressors or noxious stimuli cause cell adaptation > is cell in unable to recover, then cell injury occurs. (Response depends on type of injury, duration and severity).
