Cell Injury and Cell Death Flashcards
What is atrophy vs hypertrophy?
Muscle atrophy is a decrease in muscle mass; muscle hypertrophy is an increase in muscle mass due to an increase in muscle cell size
What is oncosis?
Pre lethal changes preceding cell death (generally regarded as a severe injury to cell membrane integrity or other vital functions)
What is ‘reversible cellular injury’?
This occurs if extreme stress persists and the cell is unable to adapt to overcome the stress. This type of injury results in cellular and morphological changes, that can still be reversed if the stress is eventually removed.
What are the hallmarks of reversibly injured cells?
- ATP depletions (due to decreased levels of oxidative phosphorylation) 2. Oxygen and oxygen derived free radicals 3. Loss of intercellular calcium hemostasis 4. Defects in membrane permeability 5. Cell swelling
What is cellular swelling?
An enlargement of an acutely injured cell, caused by changes in ion concentration and water influx
Describe the steps leading to cellular swelling in reversible cellular injury.
- Decreased ATP due to decreased levels of oxidative phosphorylation
- Decreased Na+/K+ pump as this is ATP dependent
- Increased Na in the cell
- Increased water in the cell (osmosis)
- Cellular swelling
It is the first change to occur during cell injury.
What are the components of Na+ regulation?
- Plasma Membrane 2. Plasma Membrane Na+ pump. 3. ATP concentration.
The plasma membrane is slightly ‘leaky’ to Na+. What does this allow?
This allows minimal amounts of Na+ to gradually move into the cell
How is this gradual influx of Na+ compensated for? What does this ensure?
There is a perpetually active Na+/K+-/ATPase pump, that pumps Na+ out of the cell constantly, in exchange for pumping K+ into the cell. This K+ is able to leave the cell freely. This ensures that Na+ does not buildup within the cell
In cellular injury, what 3 things may interrupt the Na+ movement in and out of a cell? What is the end result of all 3 of these processes?
- The plasma membrane may be damaged, increasing its leakiness to Na+, and thus overriding the capacity of the Na+/K+-ATPase pump to keep Na+ at low levels.
- The Na+K+-ATPase pump may be directly damaged, and thus Na+ is able to slowly build up within the cell without being removed.
- Interfering with the synthesis of ATP, the fuel source for the Na+/K+-ATPase pump.
End result –> osmotic pressure builds within the cell due to increased ions, and water and fluids move into the cell, resulting in the cell becoming swelled.
How does ATP depletion lead to cellular swelling?
- Decreased ATP
- Decreased activity of Na/K pump
- Increased Na in cell
- Increased water in cell (osmosis)
- Cell swelling
Characteristics seen in reversible cell injury?
- Pallor (paleness)
- Appears enlarged
- Hydropic change
- Cell swelling
- Vacuolar degeneration
What is vacuolar degeneration? How does fluid building up in the cell lead to this?
- Cell becomes distended and cellular organelles appear to become more spaced out within the cell.
- Most of the extra fluid actually builds within the ER, causing the ER to appear much more distended.
- As time goes on, regions of the ER burst and become encapsulated in clear vacuoles containing chunks of the ER –> This is known as vacuolar degeneration.
Characteristics of irreversible cell injury?
Mitochondrial swelling, lysosomes swells, damage to membrane, leakages of enzymes
Diagram of irreversible cell injury
Which 3 types of membrane damage can lead to irreversible cell injury?
- Lysosome membrane damage
- Cell membrane damage
- Mitochondria membrane damage
What is a lysosome?
- A membrane-bound cell organelle that contains digestive enzymes
- They break down excess or worn-out cell parts. They may be used to destroy invading viruses and bacteria.
How can membrane damage to the lysosome lead to irreversible cell injury?
Leakage of lysosomal enzymes into the cytosol –> this leads to enzyme degradation of the cell
How does damage to the cell membrane affect Ca? How does this lead to irreversible cell injury?
Increased Ca into the cell:
- Ca activates proteases and other enzymes –> enzymatic degradation of cell
- Ca activates caspaces –> triggers apoptosis
What are 2 features that characterise irreversibility from reversible injury?
- Irreversible mitochondrial damage
* results in ATP depletion and lack of oxidative phosphorylation - Profound disturbances in membrane function,
* especially those that affect internal ionic concentrations, and lysosomal enzyme activity
Examples of causes of cell injury?
Hypoxia/Ischemia
Excess Heat or Cold
Radiation
Chemicals. drugs and toxins
Infectious Agents
Immunologic/Autoimmune
Inflammation
Nutrition
Genetics
These causes of cell injury may be caused by one of more of the following mechanisms of cell injury:
- Depletion of ATP
- Mitochondrial Damage
- Influx of Ca2+ and loss of Calcium Homeostasis
- Accumulation of Oxygen Derived Free Radicals (Oxidative Stress)
- Defects in Membrane Permeability
- Damage to DNA and Proteins
How can membrane damage to mitochondria lead to irreversible cell injury?
Cyt C leakage –> activates caspaces –> triggers apoptosis
Cyt C:
- Location?
- Role in apoptosis?
- The cytochrome complex is a small hemeprotein found loosely associated with the inner membrane of mitochondria.
- Plays a major role in cell apoptosis by activating caspaces
What is apoptosis?
Programmed individual cell death seen in physiological growth control and in disease
What is necrosis?
- Death of tissue
- Includes inflammation and repair
Difference between necrosis and apoptosis?
Necrosis - uncontrolled cell death
Apoptosis - programmed cell suicide
Difference in size of between necrosis and apoptosis. How many cells are affected?
Necrosis:
- Cellular swelling
- Many cells affected
Apoptosis:
- Cellular shrinking
- One cell affected
What are the cell contents ingestd by in necrosis vs apoptosis? What inlammatory response does this result in?
Necrosis:
- Cell contents ingested by macrophages
- Significant inflammation
Apoptosis:
- Cell contents ingested by neighbouring cells
- No inflammatory response
What happens to membrane of cell in necrosis vs apoptosis? What does this lead to?
Necrosis:
- Loss of membrane integrity
- Cell lysis occurs
Apoptosis:
- Membrane blebbing but integrity maintained
- Apoptotic bodies form –> these are small membrane-surrounded fragments are cleared by phagocytosis without triggering an inflammatory response
What is autophagy?
consumption of the body’s own tissue as a metabolic process occurring in starvation and certain diseases.
Does necrosis lead to an inflammatory response?
Yes
Does apoptosis lead to an inflammatory response?
No
Does autophagy lead to an inflammatory response?
No
Does necrosis lead to cell swelling?
Yes - and intracellular membrane dilatation
Process of apoptosis?
- Cell shrinkage
- DNA fragmentation
- Caspases activation
- Apoptotic bodies formation
What happens in autophagy?
- Increased quantity of autophagosomes formation
- Atg proteins participation
Necrosis vs apoptosis diagram
What is apoptosis? Is it natural?
Apoptosis, or programmed cell death, is a form of cell death that is generally triggered by normal, healthy processes in the body
Yes, is natural
What is necrosis? Is it natural?
Necrosis is the premature death of cells and living tissue.
Caused by factors external to the cell or tissue, such as infection, toxins, or trauma.
Is apoptosis always detrimental? Is necrosis?
Apoptosis: Usually beneficial. Only abnormal when cellular processes that keep the body in balance cause too many cell deaths or too few.
Necrosis: Always detrimental
Process of apoptosis?
- Membrane blebbing (bubble like spots on membrane)
- Shrinkage of cell
- Nuclear collapse (i.e. degradation of genetic and protein)
- Apoptopic body formation
- Attracts macrophages to find and engulf the dead cells and their fractions
- Macrophages release cytokines that inhibit inflammatory responses
Process of necrosis?
- Membrane disruption
- Respiratory poisons and hypoxia which cause ATP depletion
- Metabolic collapse
- Cell swelling and rupture leading to inflammation.
- Necrotic cells are not targeted by macrophages for cleaning of their cellular debris, so the effects of the cell rupture can spread quickly and throughout the body for long periods of time.
How is an inflammatory response inhibited in apoptosis?
Macrophages release cytokines that inhibit inflammatory responses
Does necrosis require energy input? Does apoptosis?
Apoptosis is energy-dependent, meaning it requires input from a cell for cell death to occur.
Necrosis does not require any energy input from a cell, as external factors or localised infections are what trigger necrosis.
What are caspases?
A family of protease enzymes that trigger apoptosis
Do cells and organelles swell in necrosis? In apoptosis?
Cells and organelles swell in necrosis
Cells shrink in apoptosis