Cellular response to injury

Question 1

Identify the many types of cellular injuries using examples (5)

Answer 1

• Physical: heat, cold, irradiation, trauma
• Chemical: chemical burns, toxins, pH changes, osmotic pressure
• Infective: pathogens, toxins from pathogens, direct interactions with the host
• Immunological: host response to its own cells
• Nutritional/ metabolic: abnormal nutrition, heritable disorders which alters protein shape and function

Question 2

Identify morphological changes associated with cellular injury (6)

Answer 2

• Hyrdopic change: Cellular swelling due to increased amount of water
• Fatty change: Accumulation of lipids
• Hypertrophy: Increase in size of cells
• Atrophy: Decrease in either the number of cells (apoptosis) or the size of a cell (autophagy, destroying intracellular components)
• Hyperplasia: Increased number/ proliferation of cells
• Metaplasia: Transformation from one differentiated cell type to another

Question 3

List the different types of cell death (3)

Answer 3

1. Apoptosis
2. Necrosis
3. Autophagy

Question 4

Describe apoptosis, using an example, while also mentioning the pathway’s of cell death in apoptosis.

Answer 4

• This cell death is programmed
• The cell begins to break apart into smaller segments
• These smaller fragments are eaten by phagocytes before they begin to leak out to the external environment
• Intrinsic pathway: cell kills itself because it can sense something isn’t right
Extrinsic pathway: cell kills itself because it receives signals from other cells to do so

EXAMPLE: cells need to die for fusion of the palate in the embryo OR if it succumbs to a radiation injury, it will respond via apoptosis

Question 5

Describe necrosis, and mentioning the types of necrosis as your examples (4)

Answer 5

• This cell death is not programmed
• Caused by external factors such as infection, toxins or trauma
• Should not normally occur otherwise
• Cellular leakage occurs

EXAMPLES:
• Liquefactive necrosis: lysosomes digest microbes, resulting in liquification of cell

• Coagulative necrosis: Formation of a gelatinous (gel-like) substance in dead tissues in which the architecture of the tissue is maintained. Coagulation occurs as a result of proteindenaturation, causingalbumin
to transform into a firm and opaque state

• Caseous necrosis: This type is specifically seen during tuberculosis infections, although some other fungi can also cause it. In this type, the dead tissue has a whitish, cottage cheese-like appearance. The structure has a large number of activated macrophages and lymphocytes. The entire structure is called a granuloma

Fat necrosis: Adipocytes are specialized cells that store energy in the form of fat. If necrosis occurs in a place that is rich in these cells, the enzymes break down the adipocytes to release free fatty acids. These then appear as white blotches on the skin.

Question 6

Describe autophagy

Answer 6

• The cell begins to ‘eat’ its own organelles and proteins to survive
• Occurs when the cell is starved of nutrients
* It is also a normal process that enables cells to recycle unnecessary and dysfunctional components

Question 7

What are causes of cell death/ necrosis? (5)

Answer 7

• Inadequate oxygen supply: cannot make enough O2 affects the ability make proteins, maintain membrane pumps and replicate/ repair DNA
• Inadequate nutrient supply: not being able to produce energy means proteins cannot be produced
• Inadequate removal of wastes: lysosomes may rupture, causing unnecessary consumption of cellular components
• Ca Enzyme activation: when there is too much Ca in the cell, either by a compromise in the membrane or by the rupturing of mitochondria/ ER, the Ca enzymes will activate; ATP-ases which will deplete any remaining ATP, proteinases which will destroy remaining proteins, endonucleases which will destroy DNA etc
* Radical generation: protein and DNA damage, increase peroxide levels

Question 8

Differentiate histologically the features of skin and buccal epithelia

Answer 8

Skin epithelia:

• Contains an extra stratum lucidum: a thin, clear layer of dead skin cells in the epidermis, and makes skin a little stretch
• Stratum granulosum

There are also 3 main groups of cells in the epidermis:
1. Keratinocytes (skin cells): Keratinocytes develop from the basal layer and then migrates upwards to the outer surface
(stratum corneum) where it is shed

2. Melanocytes (pigment cells): The melanocytes produce pigment = differences in skin colour
3. Langerhans cells (immune cells): Langerhans cells are specialised immune cells

Buccal epithelia:
* Buccal epithelia is para/ non- keratinised
• Granules layer contains a lipid rich secretion and acts as a water sealant
• Both para- and non-Keratinized surfaces have no granules layer and are therefore pervious to water, unlike the epidermis of the skin
* The Stratum Spinosum/ Prickely layer, contains a large amount of intermediate filaments (keratin) and desmosomes and during fixation the cells shrink and take on the prickly appearance

Question 9

What are the similar characterists between skin and buccal epithelia?

Answer 9

• Stratum Corneum
• Stratum Spinosum
• Stratum Basalis