Lecture 16 How Cells Respond to Injury

Question 1

What are the three types of ways in which tissue grows?

Answer 1

Multiplicative - Increase in cell numbers by mitotic division

Auxetic - Increase in cell size

Accretionary - Increase in extracellular tissue

Question 2

What are the three types of cell abilities we get for proliferation

Answer 2

Labile Cells - Cells that continuously proliferate, have a short lifespan and rapid turnover time (white blood cells, many epithelial cells)

Stable cells - Cells that have a good regenerative ability but would normally have low cell turnover (quiescent tissue eg hepatocytes)

Permanent Cells - Cells that have little or no regenerative ability (terminal differentiation eg keratinocytes, neurons, cardiac and skeletal muscle, red blood cells)

Question 3

What is hypertrophy?

Answer 3

• Increase in cell size due to increase in structural components (enlarged cell, tissue and organ)
• Increased workload activates PI3K/AKT and G-Coupled Pathways

Question 4

What is hyperplasia and its mechanism?

Answer 4

• Increase in cell number
• Requires cells to be able to divide
• Often happens in conjunction with hypotrophy

Mechanism: Growth Factor Activation and Stem Cell Activation

Examples include hormonal hyperplasia that increases functional capacity (eg breast development) and compensatory hyperplasia (eg when tissue was lost)

Question 5

What is atrophy and its mechanism?

Answer 5

• Reduction of size of cells and organelles
• Reduction of cell numbers (apoptosis)

Mechanism: Degradation of cellular organelles by ubiquitin-proteosome pathways

Question 6

What is metaplasia?

Answer 6

• Reversible change where one differentiated cell type/tissue is replaced with another differentiated cell type/tissue
• Usually seen in the epithelium but possible in mesenchymal tissue

Mechanism: Stem cells differentiate along a different pathway owing to a change in the local microenvironment and/or colonisation of by differentiated cells from nearby tissues

Question 7

Give an example of pathological metaplasia

Answer 7

Metaplasia from bronchial ciliated columnar to stratified squamous epithelium

Question 8

What is necroptosis

Answer 8

Cell death featuring apoptosis and necrosis

Question 9

What is Pyroptosis?

Answer 9

Apoptosis with fever and IL-1 signalling

Question 10

What is the main differences between apoptosis and necrosis?

Answer 10

• Apoptosis is local whereas necrosis is regional
• In apoptosis, cells shrink whereas in necrosis, cells swell
• In apoptosis, nuclei fragment whereas in necrosis, nuclei shrink
• In apoptosis, membranes are intact but altered and in necrosis, the membranes rupture
• In apoptosis, apoptic bodies form whereas in necrosis, cell content leaks
• In apoptosis, there is no inflammation but it attracts phagocytes whereas in necrosis there is inflammation,
• Only necrosis is always pathological

Question 11

What is the difference between coagulative necrosis and liquefactive necrosis?

Answer 11

• In coagulative necrosis, the shape is preserved for some time
• in liquefactive necrosis, the shape liquefies anf soft lesions form, typical in bacterial infections

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Question 12

What is ischaemia reperfusion injury?

Answer 12

Restoration of blood flow exacerbates tissue damage

Question 13

What is autophagy?

Answer 13

Survival mechanism in nutrient deprivation in which cells canabile themselves by lysosomal degradation