Degeneration and necrosis

Question 1

What are the major components of a cell?

Answer 1

Cilia

Cytoskeleton

RER

Mitochondria

Nucleus

Microvilli

Desmosome

Lysosome

Golgi apparatus

SER

Nucleolus

Chromatin

Question 2

Name the mechanisms of cell injury

Answer 2

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

Question 3

How does hypoxia/ischaemia cause cell injury?

Answer 3

inhibit aerobic respiration in the cell: ATP depletion

Question 4

What causes membrane damage?

Answer 4

Defects in membrane permeability

Question 5

Which parts of the cell are most vulnerable to injuries that induce degeneration and necrosis?

Answer 5

Cell membranes

Aerobic respiration (mitochondria)

Synthetic apparatus (proteins, enzymes)

Genetic apparatus (DNA)

Question 6

What changes can be observed in a cell?

Answer 6

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”.

Question 7

What does the suffix -osis mean?

Answer 7

Degenerative lesions

Question 8

Describe cell swelling

Answer 8

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.

Question 9

Define calcification

Answer 9

Deposition of calcium salts into soft tissue

Question 10

What are the two types of calcification?

Answer 10

Dystrophic

Metastatic

Question 11

Describe dystrophic calcification

Answer 11

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).

Question 12

Describe metastatic calcification

Answer 12

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))

Question 13

Define necrosis

Answer 13

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.

Question 14

What are the 4 nucleus changes that occur during necrosis?

Answer 14

Pyknosis – the darkening and shrinkage of the nucleus.

Karyorrhexis – the shattering of the nucleus

Karyolysis – dissolution of the nucleus leaving a ghost outline.

Absence

Question 15

What are other signs of necrosis of the cell?

Answer 15

In the cytoplasm the changes are an increased acidophilic colouring (pink),

or a pale vacuolated appearance (lysis of the cytoplasm)

Question 16

Define coagulation necrosis

Answer 16

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.

Question 17

Define caseous necrosis

Answer 17

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.

Question 18

Define liquefactive necrosis

Answer 18

semi-solid or fluid mass that has undergone self-digestion. Pus is the presence of necrotic neutrophils.

Question 19

How does necrosis affect surrounding tissue?

Answer 19

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).

Question 20

Describe gangrene

Answer 20

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.

Question 21

Describe dry gangrene

Answer 21

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.

Question 22

Describe wet gangrene

Answer 22

contains bubbles of gas and is very blackened.

It is rapidly fatal due the release of toxins.

Question 23

Define apoptosis

Answer 23

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