Necrosis Flashcards
(30 cards)
What are the causes of cell injury?
- hypoxia due to ischaemic, inadequate oxygenation and anaemia
- living irritants like bacteria, fungus, virus and parasites
- physical irritant
- chemical irritant
- immunological reactions
- nutritional deficiencies
- genetic and enzymatic abnormalities
What causes necrosis AND inflammation?
- chemical irritant
- physical irritant
- living irritant
- immunological reactions
What is the definition of necrosis?
local death of cells ir tissues in the living body
What are the causes and pathogenesis of necrosis?
same as reversible cell injury
What is the gross picture of necrosis?
necrotic tissue appears opaque, white or yellow area surrounded by red zone of acute inflammation even if the cause does not cause inflammation
What is the microscopic picture of necrosis?
immediately after necrosis, dead cells appear more or less normal then followed by autolytic (post-necrotic) changes that take place due to the effect of lysosomal enzymes (after 6 hours)
What are the autolytic changes that take place during necrosis?
- nuclear changes
- cytoplasmic changes
What are the nuclear changes that take place in necrosis?
- pyknosis
- karyorrehxis
- karyolysis
What is pyknosis?
nucleus becomes small, irregular and deeply stained
What is karyorrehxis?
fragmentation of nucleus into small pieces
What is karyolysis?
dissolution of nuclear fragments
What are the cytoplasmic changes that take placeduring necrosis?
- the cells swell (except nucleus) (cytomegaly), the cytoplasm becomes homogenous and the cells lose their cell membrane
- necrotic cells now appear as homogenous structureless area
What are the types of necrosis?
- coagulative necrosis
- liquefactive necrosis
- caseous necrosis
What happens in coagulative necrosis?
- necrotic tissues appear firm and dry
- caused by cut of blood supply
- at first, there is loss of cellular details and preservation of architecture for some time
- later on, there is loss of both
What happens in liquefactive necrosis?
- necrotic tissue appears as liquid
- not found in all tissues
- in case of CNS infarction, the cause of liquefaction is the high lipid and fluid content
- in case of pyogenic abscess, the cause of liquefaction is the lysosomal enzymes released from dead polymorphs (pus cells)
What happens in caseous necrosis?
- begins as coagulative necrosis followed by slow partial liquefaction
- necrotic area appears semi-solid semi-fluid like casein of milk
- commonly seen in tuberculosis and syphilis
- the cause of necrosis is antigen-antibody reaction
- there is loss of cellular details followed by loss of architecture
What are the types of fat necrosis?
- enzymatic fat necrosis
- traumatic fat necrosis
How does enzymatic fat necrosis occur and when does it occur?
- occurs in acute haemorrhagic liquetising pancreatitis
- lipase enzyme escapes from ruptured pancreatic ducts and acts on fat in abdominal cavity, splitting it into fatty acids and glycerol
- glycerol is absorbed and fatty acids combine with calcium from blood plasma and become deposited as opaque white patches
- a person can die from hypocalcaemia
- affected fat cells are swollen and surrounded by foreign body giant cell reaction and fibrosis
How does traumatic fat necrosis occur and when does it occur?
- occurs as a result of trauma to fatty areas as the female breast or any tissue that has fat and trauma
- self digestion of fat splits it into fatty acid and glycerol
- glycerol is absorbed and fatty acids combine with calcium and become deposited and induces fibrosed hard mass
- malignant tumours occur in dry and hard mass in breast
- affected fat calls are swollen and surrounded by foreign body giant cell reaction and fibrosis
What is the definition of apoptosis?
a special type of death affecting a single cell or a small group of cells and is sometimes referred to as cell suicide
What are the morphological changes that take place during apoptosis?
- shrinkage of nucleus
- condensation and fragmentation of chromatin
- chromatin fragments are enclosed in parts of cell membrane to form apoptotic bodies and are phagocytosed by macrophages or adjacent phagocytic cells
Why does apoptosis occur?
- normal cell turn over (all tissues except brain CNS)
- programmed cell death during embryonic development
- endocrine dependent tissue involution: menstrual cycle (endometrial involution)
- in some pathologic conditions
What are the pathologic conditions that lead to apoptosis?
- cell death by cytotoxic lymphocytes (no inflammation)
- liver cells in viral hepatitis
- radiation cell injury
- pathological atrophy
What are the types of pathological calcification?
- dystrophic calcification
- metastatic calcification
