Degeneration and necrosis Flashcards
What are the major components of a cell?
Cilia
Cytoskeleton
RER
Mitochondria
Nucleus
Microvilli
Desmosome
Lysosome
Golgi apparatus
SER
Nucleolus
Chromatin
Name the mechanisms of cell injury
Ischaemic (lack of blood flow to a tissue)
Hypoxic (Lack of oxygen) injury
Free radical injury
Chemical injury (toxins, lysins, etc)
Direct injury by infectious agents
How does hypoxia/ischaemia cause cell injury?
inhibit aerobic respiration in the cell: ATP depletion
What causes membrane damage?
Defects in membrane permeability
Which parts of the cell are most vulnerable to injuries that induce degeneration and necrosis?
Cell membranes
Aerobic respiration (mitochondria)
Synthetic apparatus (proteins, enzymes)
Genetic apparatus (DNA)
What changes can be observed in a cell?
Cell membrane: folds, blebs, holes
ER: loss of ribosomes, dilation
Mitochondria: changes in shape, swelling
If extensive enough can be viewed under the light microscope
The changes are known as cell degenerations and imply that the cell is “unwell”.
What does the suffix -osis mean?
Degenerative lesions
Describe cell swelling
damage to the cell membrane causes the cell to swell as fluid is drawn into the cell due to osmosis.
There is often disruption to the Na+ pump, allowing Na+ to move into the cell (taking water along with it).
It is the most common response to cell damage, irrespective of the causal agent.
Under the light microscope the cytoplasm of cells appears paler, and the nucleus may also appear swollen.
If the injury progresses and the cell cannot recover vacuoles appear in the cytoplasm.
Define calcification
Deposition of calcium salts into soft tissue
What are the two types of calcification?
Dystrophic
Metastatic
Describe dystrophic calcification
Dystrophic follows damage or death of cells, this allows calcium salts to enter the cell.
In some cell types there is a large uptake of calcium, which leads onto calcification (muscle; skeletal and cardiac; tendons)
or there is calcification around specific chronic tissue-destroying lesions (T.B., Liver Fluke and other parasites).
Describe metastatic calcification
Metastatic calcification occurs as calcium deposition on basement membranes and elastic fibres (gut, kidney, blood vessels etc.) due to high circulating levels of calcium
e.g Tumours of the parathyroid gland (↑parathyroid hormone (PTH))
Define necrosis
Necrosis is the final stage of an irreversible degeneration at a cell level.
It is the death of the cell and a limited portion of tissue.
It occurs prior to the death of an animal in a fatal disease.
Under light microscope changes can be identified in the nucleus, cytoplasm and the cell as a whole.
What are the 4 nucleus changes that occur during necrosis?
Pyknosis – the darkening and shrinkage of the nucleus.
Karyorrhexis – the shattering of the nucleus
Karyolysis – dissolution of the nucleus leaving a ghost outline.
Absence
What are other signs of necrosis of the cell?
In the cytoplasm the changes are an increased acidophilic colouring (pink),
or a pale vacuolated appearance (lysis of the cytoplasm)
Define coagulation necrosis
Coagulation necrosis refers to an area of necrosis where it is still possible to make out the structure of the tissue and some of the cells.
This is a frequent finding in skeletal muscle damage.
Define caseous necrosis
Caseous necrosis refers to an area of necrosis where it is no longer possible to make out the normal tissue structure
Grossly this necrosis appears cheesy.
Define liquefactive necrosis
semi-solid or fluid mass that has undergone self-digestion. Pus is the presence of necrotic neutrophils.
How does necrosis affect surrounding tissue?
Necrosis initiates a reaction in the surrounding tissue caused by chemical mediators released from the necrotic tissue
an inflammatory reaction to wall off or liquefy the necrotic area and contain or remove the infection
fibrous tissue is eventually laid down around or in the area to produce scar tissue
If necrosis affects large amount of tissue internally then it is walled off, and a sequestrum is formed (bone).
Describe gangrene
Gangrene occurs where bacteria grow in necrotic tissue and produce putrefaction.
It is classified into wet and dry gangrene, depending on the availability of fluid for rapidly growing bacteria.
Describe dry gangrene
Dry gangrene occurs in ischaemic conditions or in freezing of tissues (frostbite).
It has a dry appearance on the cut surface. These lesions tend to wall off.
Describe wet gangrene
contains bubbles of gas and is very blackened.
It is rapidly fatal due the release of toxins.
Define apoptosis
normal programmed death of cells - goes on continuously throughout an animal’s life.
New cells normally replace the removed cells
different from necrosis - it does not provoke a reaction from the surrounding healthy cells
