Flashcards in Responses To Cell And Tissue Injury Deck (49):
What is necrosis?
Necrosis is the death of tissues following bioenergetic failure and loss of plasma membrane integrity
What does necrosis do?
+ Pathological process
+ Often invokes an inflammatory response and repair
+ Often affects solid mass of tissue
What types of necrosis are there?
What are features of coagulative necrosis?
+ The most common type
+ Involves coagulation of cellular proteins
+ Initially firm but later soft
-appearances develop over time
- ghost outlines of cells
- inflammatory response
What are features of colliquative necrosis?
+ In the brain
+ Liquefaction with formation of cystic spaces occurs
+ Proteolysis dominates over coagulation
What is caseous necrosis?
+ Characteristic of tuberculosis
+ There is pale yellow semi-solid material
What are features of gangrenous necrosis?
+ Necrosis with putrefaction
- wet and dry forms
- gas gangrene due to C perfringens
+ Follows vascular occlusion or certain infections
What are features of fibrinoid necrosis?
+ Microscopic feature in arterioles
+ Most commonly associated with 'malignant' hypertension
+ Histological phenomenon
What are features of fat necrosis?
+ 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
When does necrosis occur?
Necrosis occurs when a cell is damaged by an external force such e.g toxins, trauma, infection or ischaemia
What is apoptosis/PCD
The death of cells which occurs as a normal and controlled part of an organism's growth or development.
How does apoptosis differ from necrosis?
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
What's the difference between apoptosis and Programmed Cell Death (PCD)?
Apoptosis is morphological; PCD is intent
Name some examples of apoptosis/PCD
+ 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
What are the types of abnormal apoptosis?
+ Reduced apoptosis
+ Increased apoptosis
Give examples of reduced apoptosis
+ Autoimmune disease
+ Viral infection
Give examples of increased apoptosis
+ Neurodegenerative disorders
+ HIV infection of T lymphocytes
Apoptosis vs Necrosis: Induction
Apoptosis: physiological or pathological
Apoptosis vs Necrosis: Extent
Apoptosis: single cells
Necrosis: cell groups
Apoptosis vs Necrosis: Biochemical Events
Apoptosis: energy-dependent fragmentation of DNA
Necrosis: abnormal ion homeostasis
Apoptosis vs Necrosis: Cell Membrane Integrity
Apoptosis vs Necrosis: Morphology
Apoptosis: cell shrinkage and fragmentation
Necrosis: cell swelling and lysis
Apoptosis vs Necrosis: Inflammatory Response
Apoptosis vs Necrosis: Fate of dead cells
Apoptosis: phagocytosed by neighbouring cells
Necrosis: phagocytosed by inflammatory cells
What is pyroptosis?
+ Highly inflammatory form of programmed cell death
+ Occurs most frequently upon infection with intercellular pathogens
+ Likely to form part of the
+ Part apoptosis but then necrosis
+ Associated with Salmonella infection
What happens to cells after injury?
What is healing?
The restitution with no/minimal residual defect
E.g superficial skin abrasion, incised wound healing by first intention
What is the difference between hearing and repair?
+ Healing is complete resolution
+ Repair is necessary when there is tissue loss: healing by second intention (second best option)
What three types of cell populations are there?
What are features and examples of labile cells?
+ continuous regeneration
+ short lifespan
+ Skin, blood, gut
What are features and examples of stable cells?
+ 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
What are features and examples of permanent cells?
+ Cannot regenerate once injured
+ Brain/neurones, skeletal muscle
What is organisation?
+ Repair of specialised tissue by formation of a scar
What does organisation involve?
+ Formation of granulation tissue
+ Removal of dead tissues by phagocytosis
+ Wound contraction and scarring
Describe the process of healing by first intention (wound with opposed edges)
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
What happens during the second week of healing by first intention? (Wound with opposed edges)
+ Proliferation of fibroblasts
+ Collage accumulation
+ Leucocytes infiltrate, oedema reduced
+ Vascularity virtually disappeared
What happens by the end of the first month of healing by first intention? (Wound with opposed edges)
+ Scar consists of cellular connective tissue
+ Tensile strength now increases
Describe healing by second intention (wounds with separated edges) compared to first intention
+ 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
What most clearly differentiated healing by first intention and healing by second intention?
What are the stages of bone healing?
What are the steps involved in liver healing/repair?
+ Fibrous scarring
+ Architectural disruption
What is the wound strength process?
+ 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
What are the systemic factors that influence wound healing?
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
What are the local factors that influence wound healing?
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
What are some types of abnormal wound repair?
+ Deficient scar formation
+ Excessive formation of repair components
- keloid scar
+ Formation of contractures
- exaggerated contraction
- deformity if the wound and surrounding tissues
What are the effects of scarring?
+ Functionally imperfect
+ Provides permanent patch
+ Allows surrounding tissue to continue to function
What sort of problems might scarring cause?
- site e.g stricture
- size e.g healed myocardial infarct
Define keloid scars.
Excessive fibroblast proliferation and collagen production.