七年制医学课件 病理生理

CHAPTER 2,EDEMA,EDEMA,Edema, like most other symptoms / pathological process, merely reflects disturbed physiologic functions caused by diseases rather than a disease entity itself.,1. Concept, Edema refers to the accumulation of an abnormally large amount of fluid in : the interstitial space or cavities - hydrothorax, hydroperitoneum (ascites). Presence of an abnormal accumulation of fluid within cells is referred to as cellular edema.,Classification of edema,Characteristics & Effects of Edema,Properties of Edema Fluid Edema fluid can be placed in two categories: A. Exudates B. transudates,Main Differences between Exudates and Transduates,Effects of Edema,Effects of edema on body depend on : type location extent rate of development lasting time of edema. Can be divided into two aspects: beneficial & harmful,Beneficial & Harmful Effects,Beneficial & Harmful Effects,Structures & functions of capillaries,Formation of Interstitial fluid,1). Normally , effective colloid osmotic pressure =difference between and plasma interstitial fluid colloid osmotic pressure colloid osmotic pressure which tends to draw water into the vessels. 2). Capillary blood pressure (hydrostatic pressure) is the force that drives water through the capillary membrane into the tissue spaces. Hdrostatic pressure of interstitial fluid (tissue tension), which is much smaller, tends to oppose that in the capillaries.,A: Blood pressure is greater than the colloid osmotic pressure, so that fluid is filtered from the plasma into the interstitial spaces.,V: Hydrostatic pressure within the capillary is lower than the colloid osmotic pressue, and reabsorption of fluid into the plasma occurs.,V,A,H2O,between the vessels and the extravascular spaces is determined by the balance of the hydrostatic and osmotic forces acting upon it.,15.5,Formation of tissue fluid : (35 -25) (25 15.5)=10 -9.5=0.5 mmHg,Movement of fluid,Filtration pressure,The difference between the two is the effective filtration pressure, which forces fluid through the capillary wall .,a. tissue fluid reabsorbed directly into the blood, b. filters through the lymphatic vessels, by which route it is returned to the venous circulation.,Venous circulation,Anchoring 10% water of the body 10%: pitting (frank) edema,2. Pathogenesis of Edema,Safety Factors against Edema Human-being has tremendous capability for resisting the development of edema.,Interstitial fluid pressure rises - lymph flow increases. - movement of fluid through interstitial spaces toward lymph vessels - washes protein out of interstitial spaces - decrease colloid osmotic pressure in interstitial fluid. 2) There is a clinical state called “pre-edema“, which means a condition in which much of the above mentioned safety factors has been dissipated even though the edema state itself has not yet been reached.,3. Basic Mechanisms of Edema,Imbalance of exchange : A). between intra- B). between intra- & extra- body fluid.,3.1 Imbalance of exchange between intra- & extra- vascular fluid - formation of tissue fluid more than back-flow of tissue fluid,Fluid exchange between both sides of capillary membrane is in dynamic equilibrium, the process is controlled by many factors inside & outside blood vessels. When these factors alter, more formation of tissue fluid & less back-flow of it may occur, leading to edema( excess accumulation of fluid in the interstitial space),Factors are related to edema: 1). Increased capillary blood pressure (CBP),This edema is caused by : (1) arteriolar dilation ( acute inflammation, allergic responses ) (2) venous obstruction ( thrombo-phlebitis, constrictive pericarditis, hepatic obstruction) (3) increased vascular volume ( in heart failure, pregnancy, increased level of adrenal cortical hormone) (4) effect of gravity ( prolonged standing).,arteriolar dilation : (acute inflammation, allergic responses ),(2) venous obstruction,Thrombo-phlebitis,congestive heart failure constrictive pericarditis,hepatic obstruction,(3) increased vascular volume,as in : increased level of adrenal cortical hormone,heart failure,Prenancy,(4) effect of gravity,prolonged standing,2) Decreased plasma colloid osmotic pressure (PCOP).,Main causes a. Liver function insufficiency - production of proteins - concentration of plasma albumin decreases - PCOP reduces, (PCOP tends to retain fluid in capillaries) resulting in edema,PCOP depends mainly on the concentration of plasma albumin whose concentration normally is about 4-5g/dl.,intake of proteins ( starvation / severe protein deficiency),c. loss of plasma proteins,extensive burns,nephrontic syndrome,d. consumption of proteins,chronic consumptive diseases : malignant tumours, chronic infections,3) capillary permeability,burns, trauma, radiation damage, acidosis, anoxia, infection, direct injury of capillary walls release of inflammatory mediators ( histamine, kinins). - increased capillary permeability - salt & water filter out of capillaries, specially leakage of plasma albumin into interstitial space -leading to an increase of colloid osmotic pressure in interstitial fluid - accelerates the accumulation of fluid in interstitial space.,4) lymphedema -Obstruction of lymph flow,Lymph flow is obstructed, - backflow (into the circulatory system) of interstitial fluid blocked - Plasma proteins leaking into interstitial space - colloid pressure in interstitial fluid increases, - lymphedema occurs. ,Parasitic infestation : Elephantiasis,Malignant involvement of lymph structures, removal of lymph nodes in radical operation of mammary cancer ,Common causes of lymphedema are:,(2) Imbalance of exchange between intra- & extra- body fluid -retention of H2O and Na+ in body,Normally , kidneys play an important role: intake/ excretion of H2O and Na+ is in dynamic balance . Under pathologic conditions, kidneys fail to maintain balance of H2O and Na+ metabolism - resulting in retention of H2O and Na+ in body.,1) Decreased glomerular filtration rate,GFR depends on : filtration pressure, surface area , permeability of glomerular membrane. Alterations of these factors can affect GFR: GFR decreases-excretion of H2O and Na+ reduces - accumulation of H2O and Na+ in body. eg. congestive heart failure, liver cirrhosis with ascites - glomerular blood flow (constriction of afferent arterioles ) - filtration pressure,Glomerulonephritis,acute : swelling of capillary membrane of glomeruli - blood flow through glomeruli - filtration pressure - GFR Chronic: a. proliferative changes in mesangium b. progressive thickening of the glomerular wall on epithelial side - surface area / permeability of glomerular membrane - GFR .,2) H2O and Na+ reabsorption in renal tubules,( Normal : 99% of H2O and Na+ ) Strengthened re-absorption of H2O and Na+ in renal tubules may be more important than the reduced GFR. Factors causing are as follows: Glomerular-tubular imbalance.,Glomerular-tubular imbalance - filtration fraction ( FF ) ,When GFR falls, re-absorption of H2O and Na+ in proximal tubules does not reduce correspondingly, on the contrary, there is even an increased re-absorption! FF = GFR / RPF ( renal plasma flow) With the fall of GFR, efferent arteriolar resistance - filtration fraction ( FF ) = GFR / RPF Because : FF -Non-filtered blood through glomeruli is concentrated - 1). colloid osmotic pressure & 2). hydrostatic pressure in the capillaries around proximal tubules - reabsorption of H2O and Na+ .,3) Redistribution of renal blood flow,Normally: 90 % of renal blood flow - supplies the renal cortex ; 10 % - goes to renal medulla . Two types of nephrons,Heart failure : - renal blood flow shifts from cortical nephrons to juxta-medullary nephrons. - reabsorption of H2O and Na+ by kindeys,4) secretion of aldosterone,zona glomerulosa of the adrenal cortex secreted aldosterone -absorption of Na+ & simultaneous excretion of K+ in both the distal tubules and the collecting ducts. - osmosis of H2O through the tubular epithelium - H2O reabsorption . - H2O and Na+ to be conserved in interstitial fluid,5) secretion of anti-diuretic hormone (ADH),When re-absorption of Na+ - osmotic pressure of blood - stimulating the secretion of ADH - promoting reabsorption of water, followed by retention of water in body. Heart failure: Diminution of cardiac output / effective circulating blood volume (ECBV) - stimulation of ADH secretion,6) activities of prostaglandin / kinin (激肽) systems in kidneys,1. PGA2 & PGE2 (produced in renal medulla) 2. Kallidin / bradykinin (缓激肽） (formed in renal cort