Responses To Cell And Tissue Injury

Question 1

What is necrosis?

Answer 1

Necrosis is the death of tissues following bioenergetic failure and loss of plasma membrane integrity

Question 2

What does necrosis do?

Answer 2

+ Pathological process

+ Often invokes an inflammatory response and repair

+ Often affects solid mass of tissue

Question 3

What types of necrosis are there?

Answer 3

\+ Coagulative  
\+ Colliquative  
\+ Caseous
\+ Gangrene
\+ Fibrinoid
\+ Fat

Question 4

What are features of coagulative necrosis?

Answer 4

+ The most common type

+ Involves coagulation of cellular proteins

+ Initially firm but later soft

+ Microscopically

• appearances develop over time
• ghost outlines of cells
• inflammatory response

Question 5

What are features of colliquative necrosis?

Answer 5

+ In the brain

+ Liquefaction with formation of cystic spaces occurs

+ Proteolysis dominates over coagulation

Question 6

What is caseous necrosis?

Answer 6

+ Characteristic of tuberculosis

+ There is pale yellow semi-solid material

Question 7

What are features of gangrenous necrosis?

Answer 7

+ Necrosis with putrefaction

• wet and dry forms
• gas gangrene due to C perfringens

+ Follows vascular occlusion or certain infections

+ Black

Question 8

What are features of fibrinoid necrosis?

Answer 8

+ Microscopic feature in arterioles

+ Most commonly associated with ‘malignant’ hypertension

+ Histological phenomenon

Question 9

What are features of fat necrosis?

Answer 9

+ May occur following direct trauma and cause a mass,

+ May follow pancreatitis visible as multiple white spots (enzymatic lysis)

+ Related to death of fat cells

Question 10

When does necrosis occur?

Answer 10

Necrosis occurs when a cell is damaged by an external force such e.g toxins, trauma, infection or ischaemia

Question 11

What is apoptosis/PCD

Answer 11

The death of cells which occurs as a normal and controlled part of an organism’s growth or development.

Question 12

How does apoptosis differ from necrosis?

Answer 12

Necrosis is the premature death of living cells and tissues caused by factors external to the cell/tissue.

Apoptosis is programmed and a healthy, natural process:
+ removes a cell discreetly
+ takes our individual cells rather that groups of tissue
+ minimal fuss
+ preserves function as best as possible

Question 13

What’s the difference between apoptosis and Programmed Cell Death (PCD)?

Answer 13

Apoptosis is morphological; PCD is intent

Question 14

Name some examples of apoptosis/PCD

Answer 14

+ Embryology: lumen of tubes
+ Growth signal response: menstrual cycle
+ Inflammation: resolution, death of neutrophils
+ Immune defence: T and Killer cell responses
+ Tumour prevention: prevent mutation
+ Autoimmune disease: self destruct
+ HIV/AIDS - HIV and activated T cell death

Question 15

What are the types of abnormal apoptosis?

Answer 15

+ Reduced apoptosis

+ Increased apoptosis

Question 16

Give examples of reduced apoptosis

Answer 16

+ Neoplasia

+ Autoimmune disease

+ Viral infection

Question 17

Give examples of increased apoptosis

Answer 17

+ Neurodegenerative disorders

+ HIV infection of T lymphocytes

Question 18

Apoptosis vs Necrosis: Induction

Answer 18

Apoptosis: physiological or pathological

Necrosis: pathological

Question 19

Apoptosis vs Necrosis: Extent

Answer 19

Apoptosis: single cells

Necrosis: cell groups

Question 20

Apoptosis vs Necrosis: Biochemical Events

Answer 20

Apoptosis: energy-dependent fragmentation of DNA

Necrosis: abnormal ion homeostasis

Question 21

Apoptosis vs Necrosis: Cell Membrane Integrity

Answer 21

Apoptosis: maintained

Necrosis: lost

Question 22

Apoptosis vs Necrosis: Morphology

Answer 22

Apoptosis: cell shrinkage and fragmentation

Necrosis: cell swelling and lysis

Question 23

Apoptosis vs Necrosis: Inflammatory Response

Answer 23

Apoptosis: none

Necrosis: usual

Question 24

Apoptosis vs Necrosis: Fate of dead cells

Answer 24

Apoptosis: phagocytosed by neighbouring cells

Necrosis: phagocytosed by inflammatory cells

Question 25

What is pyroptosis?

Answer 25

+ Highly inflammatory form of programmed cell death + Occurs most frequently upon infection with intercellular pathogens + Likely to form part of the antimicrobial response + Part apoptosis but then necrosis + Associated with Salmonella infection

Question 26

What happens to cells after injury?

Answer 26

+ Death + Healing + Repair

Question 27

What is healing?

Answer 27

The restitution with no/minimal residual defect E.g superficial skin abrasion, incised wound healing by first intention

Question 28

What is the difference between hearing and repair?

Answer 28

+ Healing is complete resolution + Repair is necessary when there is tissue loss: healing by second intention (second best option)

Question 29

What three types of cell populations are there?

Answer 29

+ Labile + Stable + Permanent

Question 30

What are features and examples of labile cells?

Answer 30

+ continuous regeneration + short lifespan + Skin, blood, gut

Question 31

What are features and examples of stable cells?

Answer 31

+ Few divisions + Spend most of the time in the quiescent G0 phase of the cell cycle + Only multiply/repair when needed/ injured + Liver, Kidney, endocrine glands

Question 32

What are features and examples of permanent cells?

Answer 32

+ Cannot regenerate once injured + Brain/neurones, skeletal muscle

Question 33

What is organisation?

Answer 33

+ Repair of specialised tissue by formation of a scar

Question 34

What does organisation involve?

Answer 34

+ Formation of granulation tissue + Removal of dead tissues by phagocytosis + Wound contraction and scarring

Question 35

Describe the process of healing by first intention (wound with opposed edges)

Answer 35

1. Limited cell death 2. Basement membrane disrupted 3. Incisional space fills with blood 4. Scab forms 5. Neutrophils move towards the clot 6. Epidermis thinkers at its cut edges 7. Epidermal cells migrate among cut margins if the dermis 8. Epithelial cells fuse in midline beneath surface scan 9. Day 3 neutrophils largely replaced by macrophages 10. Day 5 granulation tissue invades incision space 11. Collagen fibres bridge the incision 12. Epidermis recovers to normal thickness

Question 35

What happens during the second week of healing by first intention? (Wound with opposed edges)

Answer 35

+ Proliferation of fibroblasts + Collage accumulation + Leucocytes infiltrate, oedema reduced + Vascularity virtually disappeared

Question 35

What happens by the end of the first month of healing by first intention? (Wound with opposed edges)

Answer 35

+ Scar consists of cellular connective tissue + Tensile strength now increases

Question 36

Describe healing by second intention (wounds with separated edges) compared to first intention

Answer 36

+ Extensive cell loss + Common denominator is large tissue defect that must be filled + Large defects - more fibrin - more necrotic tissue - inflammatory reaction more intense + Much larger amounts of granulation tissue + Wound contraction plays an important role in reducing size of defect

Question 37

What most clearly differentiated healing by first intention and healing by second intention?

Answer 37

Wound contraction

Question 38

What are the stages of bone healing?

Answer 38

+ Repair + Remodelling + Resolution

Question 39

What are the steps involved in liver healing/repair?

Answer 39

+ Necrosis + Regeneration + Fibrous scarring + Architectural disruption

Question 40

What is the wound strength process?

Answer 40

``` + Sutures removed end of week 1 + Strength 10% of unwounded skin + Strength increases rapidly over the following 4 weeks + Rate of increase slows + By third month strength at 70-80% + Full strength may not be recovered ```

Question 41

What are the systemic factors that influence wound healing?

Answer 41

AGE: delayed healing in old and very young NUTRITION: affects proteins and collagen synthesis METABOLIC STATUS: healing delayed in diabetics CIRCULATORY STATUS: adequate blood supply essential HORMONES: glucocorticoids are anti-inflammatory but impair collagen synthesis

Question 42

What are the local factors that influence wound healing?

Answer 42

INFECTION: most important cause of healing delay MECHANICAL FACTORS: early movement of wounds delays healing FOREIGN BODIES: e.g sutures or glass SIZE/LOCATION/TYPE OF WOUND: wounds heal better in richly vascularised areas

Question 43

What are some types of abnormal wound repair?

Answer 43

+ Deficient scar formation - dehiscence - ulceration + Excessive formation of repair components - keloid scar + Formation of contractures - exaggerated contraction - deformity if the wound and surrounding tissues

Question 44

What are the effects of scarring?

Answer 44

+ Functionally imperfect + Provides permanent patch + Allows surrounding tissue to continue to function

Question 45

What sort of problems might scarring cause?

Answer 45

+ Cosmetic + Functional - site e.g stricture - size e.g healed myocardial infarct

Question 46

Define keloid scars.

Answer 46

Excessive fibroblast proliferation and collagen production.

Question 47

What processes are involved in sublethal injury?

Answer 47

+ Hydropic change/ oncosis + Fatty change/ steatosis + Reversible Over longer time: + Autophagy + Atrophy