Infarction and Necrosis Revision

Question 1

What is necrosis?

Answer 1

Cell death due to disease, injury of loss of blood supply

Question 2

What is infarction?

Answer 2

Cell death caused by obstruction of blood supply

Question 3

What is the initial cell response to injury?

Answer 3

Cell swelling (reversible cell injury)

Question 4

What happens during myocardial infarction?

Answer 4

Following occlusion of a coronary artery, a zone of myocardium becomes severely hypoxic and the cells die

Question 5

What are early cytoplasmic changes during reversible cell injury?

Answer 5

1. Cell swells

2. Blebbing of plasma membrane

Question 6

With a continued injury, such as a reduced oxygen supply (hypoxia), the changes become irreversible. What happens?

Answer 6

1. Rupture of plasma membrane
2. Calcium matrix density formation in mitochondria
3. Lysosomal breakdown producing autodigestion
4. Cellular degradation.

Question 7

What causes the cell to swell during loss of blood supplu?

Answer 7

Damages the sodium-potassium membrane pump

Question 8

What happens when cell ruptures?

Answer 8

Cytosolic contents leak out from necrotic cells –> causing injury and inflammation to surrounding tissue

Question 9

What are the 3 central mechanisms leading to cell rupture in necrosis?

Answer 9

1. Loss of selective plasma membrane permeability
2. Loss of calcium homeostasis
3. Failure of membrane ion pumps

Question 10

How is calcium homeostasis lost during hypoxia?

Answer 10

Necrotic cells accumulate calcium (cytoplasmic increase), leading to calcium matrix density formation in the mitochondria.

Question 11

What else can calcium ions activate?

Answer 11

Enzymes:

1. Proteases, which can break down membrane protein pumps.
2. Phospholipases, which can attack lipids in the plasma membrane.

Question 12

What is the relationship between ATP and membrane permeability?

How is this shown in necrosis?

Answer 12

ATP depletion leads to increased permeability

Injured cells often become ATP depleted, such as in hypoxia with lack of oxygen.

Question 13

How can ATP depletion below critical levels lead to defective membrane pumps?

Answer 13

These pumps use ATP to maintain the normal ionic gradients across the cell membrane.

This leads to osmotic influx of water (and eventually rupture)

Question 14

What are the 3 major mechanisms behind necrosis?

Answer 14

1. membrane permeabilisation
2. ATP depletion
3. Reactive oxygen intermediates generation

Question 15

What are the 2 types of necrosis seen in ischaemia?

Answer 15

1. Coagulative

2. Liquefactive / colliquative

Question 16

What is coagulative necrosis?

Answer 16

• Cell death mainly caused by ischaemia
• Proteins denature so unable to break down cell structure

Result:

• ‘Ghost’ outlines of cells left behind for a few days –> ‘eosinophilic ghost cells’
• Tissue remains firm

Question 17

Where does coagulative necrosis occur?

Answer 17

Coagulative necrosis occurs primarily in tissues such as the kidney, heart and adrenal glands

Question 18

What is liquefactive necrosis?

Answer 18

• Infiltration of dead tissue by large numbers of neutrophils leads to digestion of cell proteins
• Loss of normal tissue architecture
• Creates cavity or cyst when it heals (not dense scar tissue)

Question 19

Where does liquefactive necrosis occur?

Answer 19

Mainly in brain