Hyperemia Congestion The terms hyperemia congestion both indicate
Hyperemia & Congestion The terms hyperemia & congestion both indicate: a local increased volume of blood in a particular tissue. Hyperemia is an active process resulting from increased arterial blood inflow because of arteriolar dilatation. - The affected tissue is red in color because of engorgement of tissues with oxygenated blood. Congestion is a passive process resulting from impaired venous outflow from a tissue. - The tissue has a red-blue color due to accumulation of deoxygenated blood.
• HYPEREMIA • Definition: Increase in blood flow to an organ as result of active dilatation of its arterioles. It is an active process, involving change in the muscle tone of the arterioles (active hyperemia). • Types: 1 - Physiological: - hyperemia in skeletal muscles during exercise. - hyperemia in the gut following a meal. 2 - Pathological: e. g. in acute inflammation.
VENOUS CONGESTION (Passive Hyperemia) • Definition: Increase in venous blood in an organ as result of obstruction of venous outflow. - the veins, venules, & capillaries in the organ become passively dilated (passive hyperemia). - although there is excess blood in the tissue, the blood flow is slow & reduced. • Types: → Localized: Generalized: acute and chronic
Acute localized venous congestion • Causes: Sudden complete venous obstruction by: thrombosis, ligature, strangulation, or twisting of the pedicle of a movable organ. • Effects: 1 - Rapid severe distention of the veins and capillaries which may rupture → hemorrhage. 2 - Edema occurs rapidly in the tissues. 3 - In intestines: infarction & gangrene may occur
Chronic localized venous congestion Causes: Gradual incomplete venous obstruction by: 1 - Venous compression by: a tumor, enlarged lymph node or pregnant uterus. 2 - Liver cirrhosis or fibrosis → congestion in mesenteric & splenic veins. 3 - Left ventricular failure → congestion of pulmonary veins • Effects: Chronic dilatation of the veins, venules and capillaries proximal to the obstruction resulting in: 1 - Edema. 2 - Stasis predisposes to thrombosis 3 - Gradual opening of the collateral veins. 4 - Development of varicoses (e. g. oesophageal varices)
Acute generalized venous congestion • Causes: - occurs in acute heart failure • Effects: All viscera show acute congestion (rapid generalized congestion)
Chronic generalized venous congestion • Definition: Gradual congestion affecting the whole venous system in the body. • Causes: Right sided heart failure • Effects: Hypoxia & cyanosis. - Dyspnea (due to pulmonary Congestion). 3 - Generalised oedema. 4 - C. V. C in different organs. 12
Effects of chronic generalized venous congestion • Hypoxia & Cyanosis: - Hypoxia is due to defective oxygenation of blood in the congested lungs. - Cyanosis is due to increased amounts of reduced hemoglobin (due to stasis). • Dyspnea: due to pulmonary congestion. • Generalized edema (cardiac edema). • Effects in different organs.
Definition of thrombosis • Thrombosis is: - The formation of a solid mass (compact mass) - Composed of the blood elements. - In a blood vessel or heart. - In circulating blood. - During life.
Causes of thrombosis There are 3 major factors which predispose to thrombosis (Virchow’s triad) 1 - Endothelial damage 2 - Slowing & turbulence of blood flow 3 - Changes in blood composition
1 - Endothelial damage: - This is the most important factor in thrombus formation. - Endothelial damage may be: Mechanical, inflammatory, or degenerative. The injured endothelium becomes swollen with rough surface. 2 - Stasis: There is slowing of blood flow in the heart as in mitral stenosis and in blood vessels as in varicose veins. 3 - Changes in composition f blood: - ↑ platelets e. g. after operations. - ↑ fibrinogen as in pregnancy. - ↑ R. B. Cs. (polythycaemia) → ↑ viscosity of blood → staisis → thrombosis. - ↑ W. B. C. as in leukaemia → ↑ viscosity of blood → staisis → thrombosis
Pathogenesis (Mechanism) of thrombosis: - Platelets leave the blood stream, agglutinate and adhere to the damaged endothelium. - They form laminae, which are arranged vertical to the blood stream and called lines of Zhan. - Soon, fibrin accumulates around them with red and white blood cells.
Classification: According to the color & composition of thrombi: 1 - Pale thrombus: formed only of platelets and fibrin. 2 - Red thrombus: formed mainly of red cells and fibrin. 3 - Mixed thrombus: containing all blood elements.
• According to the site of thrombus: 1 - Venous thrombus (the most common): formed in veins as in varicose veins and after major abdominal operations. 2 - Arterial thrombus: found in atherosclerosis and aneurysm. 3 - Cardiac thrombus: found in the heart, either in the heart chambers called mural thrombus or on the heart valves called vegetations. 4 - Capillary thrombi
• According to presence or absence of bacteria: 1 - Septic thrombus: containing pyogenic bacteria. 2 - Aseptic thrombi: without bacteria
• 1 - Venous thrombosis Thrombosis in veins is more common than other sites because of their slow blood, and thin wall. Thrombosis in veins may be either: I. Thrombophlebitis II. Phlebothrombosis
Thrombophlebitis Thrombosis is initiated by inflammation of venous wall. - Occurs in veins draining septic lesions. - e. g. : appendicular vein in case of acute appendicitis. - suppuration of the thrombus causes its softening - fragments of infected thrombus may break away → pyaemia Phlebothrombosis • This is thrombosis in non-inflamed veins. • may fragment causing embolism and infarction. • Examples include: 1 - Thrombosis in varicose veins due to stasis. 2 - Thrombosis in calf veins (DVT) in chronic cardiac pts confined to bed (stasis & compression of calf ms). 3 - Thrombosis in pelvic & femoral veins after labour or perations (↑platelets, bed recumbence, surgical injury).
• 2 - Arterial thrombosis Less common than venous thrombosis because of the rapid blood flow in the arteries and the thick elastic arterial wall which resists injury. ● Thrombosis occurs in arteries affected by: atherosclerosis, arteritis, & aneurysms (due to stasis, disordered blood flow & roughness of the intima). ● Arterial thrombosis → ischemia.
• Fate of thrombi It depends upon its size & whether it is septic or aseptc. ● Septic thrombi: Fragments by proteolytic enzymes into septic emboli → pyaemic abscesses. ● Aseptic Thrombi: may undergo: - Small thrombi is dissolved and absorbed. - Large thrombus undergoes: 1 - Organization (fibrosis) 2 - Organization & canalization 3 - Calcification 4 - Fragmentation and embolism→infarction
• Blood Clot A mass of blood elements formed by transformation of fibrinogen to fibrin, in stagnant blood. The clot is dark red with a glistening smooth surface, and is not adherent to the vessel wall. Thrombus • 1 - Occurs in circulating blood during live 2 - Firmly attached 3 - Friable and dry 4 - Pale, pale red or red 5 - May show lines of Zhan Clot 1 - Occurs in stagnant blood during life or after death 2 - Loosely attached 3 - Soft and moist 4 - Red and yellow 5 - No lines of Zhan •
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