Pathology
Inflammatory Responses
Question 121 of 180
Fat necrosis is typically seen in which of the following:
Answer:
Fat necrosis typically occurs following either direct trauma or from enzymatic lipolysis in acute pancreatitis, where release of triglyceride elicits a rapid inflammatory response and fat is phagocytosed by neutrophils and macrophages with subsequent fibrosis.Cellular Pathology
Pathology / Inflammatory Responses
Last Updated: 27th April 2019
Cellular Adaptations
Atrophy:
- A reduction in size of a tissue or organ; this may occur through a reduction in cell number be deletion (apoptosis) or a reduction in cell size through shrinkage
- Examples of physiological atrophy include: thymic atrophy during adolescence and post-menopausal ovarian atrophy
- Examples of pathological atrophy include: muscle atrophy following denervation and cerebral atrophy due to cerebrovascular disease
Hypertrophy:
- An increase in size of individual cells due to an increase in cell proteins and organelles; seen in organs containing terminally differentiated cells that cannot multiply e.g. cardiac and skeletal cells
- Examples of physiological hypertrophy include: hypertrophy of the myometrium of the uterus in pregnancy and muscles of a bodybuilder
- Examples of pathological hypertrophy include left ventricular hypertrophy due to hypertension
Hyperplasia:
- An increase in cell number
- Examples of physiological hyperplasia include endometrial and breast lobules in response to cyclical oestrogen exposure
- Examples of pathological hyperplasia include benign prostatic hyperplasia (BPH)
Metaplasia:
- A change in which one cell type is switched for another; thought to be the result of progenitor cells differentiating into a new type of cell rather than a direct morphogenesis of cells from one type to another; seen almost exclusively in epithelial cells, often in response to chronic injury; may develop into epithelial dysplasia and eventually carcinoma
- Common sites of squamous metaplasia include the endocervix (creating the transformation zone where cervical neoplasia occurs) and the bronchi of smokers
- Common sites of glandular metaplasia include the lower oesophagus in severe reflux disease
Reversible vs Irreversible Cell Damage
Cells may be damaged either reversibly or irreversibly. There are no absolute ultrastructural criteria by which reversible and irreversible cellular damage can be distinguished, and there is a continuum from a reversible injured cell through to an irreversibly damaged cell. Cell recovery is associated with removal of damaged components by autophagy.
Features of cell damage that tend to be reversible include:
- swelling of endoplasmic reticulum and some mitochondria
- loss of ribosomes
- cell stress response
Features of cell damage that tend to be irreversible include:
- loss of nucleolus
- no ribosomes
- swelling of all mitochondria
- nuclear condensation
- membrane blebs and holes
- lysosome rupture
- fragmentation of all inner membranes
- nuclear breakup
Cellular Death
Apoptosis:
- A controlled form of cell death in which no cellular contents are released from the dying cell, and thus no inflammatory reaction is seen
- Apoptosis may occur physiologically or pathologically
- Apoptosis may be induced in two main ways: by the engagement of surface death receptors e.g. TNF-alpha (extrinsic pathway) or through cellular injury (intrinsic pathway)
- The end result is the activation of proteases enzymes called caspases which dismantle the cell cytoplasm and nucleus
- Apoptotic cells shrink down and fragment into apoptotic bodies, each of which retains an intact cell membrane; apoptotic bodies are then targeted or rapid removal by adjacent cells
- Disordered apoptosis is thought to be central to a number of important disease processes, particularly carcinogenesis
Necrosis:
- A poorly controlled form of cell death in which membrane integrity is lost with leakage of cellular contents and an inflammatory response
- Coagulative necrosis is the most common form of necrosis characterised by the loss of cell nuclei, but with general preservation of the underlying architecture. Dead tissue is macroscopically pale and firm. This is the classic pattern seen in myocardial infarction.
- Liquefactive necrosis leads to complete loss of cellular structure and conversion into a soft, semi-solid mass. This is typically seen in the brain following cerebral infarction.
- Caseous necrosis is most commonly seen in tuberculosis. Histologically, the complete loss of normal tissue architecture is replaced by amorphous, granular and eosinophilic tissue with a variable amount of fat and an appearance reminiscent of cottage cheese.
- Fibrinoid necrosis occurs in malignant hypertension where increased arterial pressure results in necrosis of smooth muscle wall. Eosinophilic and fibrinous deposits are seen.
- Fat necrosis typically occurs following either direct trauma or from enzymatic lipolysis in acute pancreatitis, where release of triglyceride elicits a rapid inflammatory response and fat is phagocytosed by neutrophils and macrophages with subsequent fibrosis.
- Gangrenous necrosis is necrosis with putrefaction of tissues due to exposure to air (dry gangrene) or infection (wet gangrene). The tissue is black due to iron sulphide from degraded haemoglobin.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
