Introductory Pathology 5-13 Flashcards
What is Pitting Oedema?
With severe diffuse subcutaneous oedema, a finger pushed into the expanded interstitium leaves an indentation.
Describe Dependent Oedema
In generalised oedema, the fluid tends to sink with gravity so that the ventral abdomen and limbs are mainly affected.
What is Hydrothorax/ hydropericardium?
Accumulation of oedema fluid in the pleural cavity/ pericardial sac
What is Ascites?
Accumulation of oedema fluid in the peritoneal cavity
Describe Anasarca?
Severe, generalised oedema involving cavities and subcutis
Name the four main mechanisms which underpin the development of oedema?
Increased blood hydrostatic pressure,, increased vascular permeability, decreased plasma colloidal-osmotic pressure, lymphatic obstruction.
Describe the main differences between transudate and excudate
Transudate: clear or pale yellow, thin and serous, 0.05-0.5% protein, no coagulation as no fibrinogen, very low cell content, mesothelial cells, some macrophages/lymphocytes
Exudate: Dark yellow, red or brown, often cloudy, viscous, usually 2-4% protein but can be higher, contains fibrinogen so will coagulate, more macrophages/lymphocytes/neutrophils, usually caused by inflammation.
Describe the most common cause of septic shock.
Mediated by vascular and inflammatory mediators released in response to bacteria or fungal elements The most common cause is endotoxin, a lipopolysaccharide (LPS) in the cell wall of gram negative bacteria. LPS is a pattern associated molecular pattern (PAMP). It binds CD14 and toll like receptor 4. TLRs are membrane molecules that allow a wide range of microbes to activate cells. Effect of LPS is to activate macrophages and release of TNF, Il-1, Il-6, IL-8, and activate factor XII.
Describe the Clinical and morphological Features of shock
Hypotension, Weak pulse and tachycardia, hyperventilation, decreased urine production, hypothermia. Lesions depend on initiating trigger, congestion and pooling of blood, oedema and haemorrhageg, thrombosis, cellular necrosis.
Describe the Non progressive stage of Shock.
The body compensates by increasing sympathetic nervous output, leading to increased cardiac output and arteriolar vasoconstriction, raising blood pressure. Blood flow maintained to critical organs, heart kidneys and brain. Renin angiotensin system stimulated.
Describe the progressive stage of shock.
Progressive Stage: prolonged or severe hypovolaemia overcomes compensatory mechanisms. There is blood pooling, tissue hypoperfusion and cellular injury. The cell shifts to anaerobic respiration leading to lactic acid production and decreased ATP production, cell membranes damaged, lysosomal enzymes released and necrois.
Describe Irreversible shock
Irreversible: mechanisms aimed at vasoconstriction are overcome, widespread vasodilation and multiorgan failure.
Describe a thromboembolism
The most common type - fragments of thrombi detach and spread throughout the circulation. Examples include in bacterial endocarditis of heart valves in large animals fragments break off the infected valvular thrombus - infective emboli in the circulation - multifocal abscesses in other organs eg kidneys.
Describe a Gas embolism
If a large enough volume of air is injected into the circulation it can accumulate in the pulmonary trunk and form a fatal airlock.
Describe a fat embolism.
Adipocytes from the bone marrow may be released into the circulation following bone fractures. Especially affects the CNS and pulmonary circulation.
Describe a tumour cell embolism.
Malignant neoplasms may erode into the veins and lymphatics forming friable thrombi and embolic fragments breakoff and circulate to other sites (metastasis) tumour emboli lodge in capillary beds such as lung, spleen, liver and kidney where they grow to produce secondary tumours.
Describe how parasites can be a type of emboli.
Heartworms in dogs may embolize into the pulmonary trunk when they die following anthelmintic treatment. Strongyle larvae in horses, filarial worms in cattle and cats and aberrant fluke larvae in cattle and sheep may all embolise and the significance depends on their final location.
How may a foreign body act as an emboli?
Fragments of skin/hair; fibrocartilagenous emboli of degenerate disc material etc.
What is ischaemia?
Ischaemia is reduced blood flow to a tissue/organ and results in tissue hypoxia. Usually arteries or arterioles are involved. Venous thrombosis may cause infarction but typically causes congestion. Arteriospasm - arterial trauma, ergotism. Compression of vessels - ligatures, tumours, torsion. Thromboembolism - obstruction by embolic fragments.
The extent and consequences of Ischaemia depend on several factors such as;
Degree of occlusion (partial or complete), speed of occlusion (sudden onset or gradual), presence of collateral circulation and vulnerability of tissues to ischaemia (eg neurones and cardiac mycocytes more susceptible than fibrous tissue).
What is Infarction?
A segmental or localised area of ischaemic necrosis due to occlusion of the blood supply. The embolus may be bland, infective or neoplastic. The affected area typically has a wedge shape. The colour depends on the degree of vascular engorgement and co-existing inflammation or infection.
Describe the microscopical process of Infarction.
Coagulative necrosis occurs so the outline of the coagulated cells is preserved, there is increased eosinphilia of affected area and loss of cellular detail. Denaturation of the structural proteins and enzymes is the primary cause of necrosis and there is no proteolysis of the cell. Necrotic tissue is removed and replaced by either regeneration or fibrosis which forms a scar. In the brain infarcts cause liquefactive necrosis and necrotic tissue is digested.
What is Disseminated intravascular Coagulation?
DIC is characterised by the activation of coagulation within the vascular system resulting in deposition of fibrin in the small blood vessels and consumption of coagulation factors and platelets. The fibrin deposition within blood vessels lads to vascular obstruction and microinfarction. The fibrinolytic system is activated which removes some fibrin but also uses up clotting factors and forms fibrin degradation products. The process begins as hypercoagulability with a tendency to infarction which progresses to a severe, bleeding tendency. (haemorrhagic diathesis).
What is Dysplasia?
An abnormal pattern of tissue growth
Describe Benign neoplasia vs malignant neoplasia.
Benign is well differentiated, uniform cell size and shape, normal nuclear morphology, few mitosis, encapsulated, no metastases. Malignant are poorly differentiated, variable cell size and shape (pleomorphic), abnormal nuclear morphology, increased mitoses, some bizzarre, non-encapsulated and infiltrative, metastasises.
Describe Ovine pulmonary Adenocarcinoma
This is a lung neoplasm in sheep which is caused by infection with a virus known as Jaagsiekte sheep retrovirus. The neoplastic cell is either the clara cell found in the terminal bronchioles of the lung or the type II pneuomocyte which lines the alveoli of the lung. Both of these are surfactant producing cells - overproductino of surfactant is one of the obvious clinical signs of the disease. Grossly the tumour forms firm grey nodules in the lungs. Histologically the neoplastic epithelial cells form clusters of papillary and acini structures within the lungs. They rarely metastasise. JSRV has its own oncogene which causes a cell to become neoplastic.
Describe Squamous Cell Carcinoma
This is malignant neoplasm of squamous epithelium. It can be found in different organs including the skin, oral cavity, larynx, oesophagus, stomach, urinary tract, penis and vulva. They are locally invasive and do metastasise, usually to the draining lymph nodes. They are nodular, proliferative and sometimes ulcerated lesions. Histologically they are made up of cords or whorls of pleomorphic epithelial cells. Sometimes they have keratin pearls at the centre o f the whorls. They are normally found on nonpigmented or sparsely haired skin, as UV light is an important cause of genetic damage to epithelial cells.
Describe Feline Vaccine Associated Sarcoma
This neoplasm occurs at vaccine sites in cats, in the interscapular region and lateral thorax. The neoplasms can be fibroblastic, myoblastic, chondroblastic, or osteoblastic. They are malignant, spread into surrounding tissue and can metastasise. They can b e very difficult to remove from interscapular region.
What is the Tasmanian Devil facial tumour?
Malignant neoplasms were found on the face and mouth of Tasmanian devils, they consisted of poorly differetiated highly pleomorphic, malignant schwann cells. The neoplasm seemed to be transmitted between devils. (an allograft). The tumour cells from another animal were not being recognised as non self - may be because Tasmanian devils lack genetic diversity and have very similar MHCs.
