NU608 Edema.pdf

1 Water is a major component of the body and is Found within and outside the cell. The maintenance of a relatively constant volume & stable composition of body fluids is essential for homeostasis. Water is the medium within which metabolic reactions and processes take place. Fluid is distributed w...

1 Water is a major component of the body and is Found within and outside the cell. The maintenance of a relatively constant volume & stable composition of body fluids is essential for homeostasis. Water is the medium within which metabolic reactions and processes take place. Fluid is distributed with the body into compartments Total Body water (TBW) is distributed into two compartments: Intracellular fluid Extracellular fluid Intracellular Fluid (ICF) Consists of fluid inside the cells of the body and is ~ 2/3 of total body water Estimated as the difference between total body water and extracellular fluid Barrier separating ICF & ECF is the cell membrane Potassium (K+) is the principal cation (major intracellular electrolyte) Phosphates and proteins the principal anions Extracellular fluid (ECF) 1/3 of the total body water divided into two components: plasma volume (also referred to as intravascular fluid)  is the non-cellular component of blood. interstitial fluid (also referred to as extravascular fluid) 3/4 of ECF Sodium (Na+) is the principal cation (major extracellular electrolyte) Chloride (Cl-) and bicarbonate (HCO3-) are the principal anions Regulation of Na & CL are by mechanisms in the kidney (which were discussed in last week’s module) 2 Another compartment (usually minor & considered a subdivision of the ECF compartment) is called Transcellular: which includes fluid in synovial, peritoneal, pleural, pericardial, intraocular fluid and CSF. transcellular compartment makes up ~ 1% of ECF This amount can increase significantly in conditions such as ascites (fluid within the peritoneal space) When transcellular compartment enlarges considerably this is called “third spacing” Fluid in transcellular space not readily available for exchange with rest of ECF 3 4 What do you think? 5 6 Edema refers to an excessive amount of fluid in the interstitial compartment, which causes a swelling or enlargement of the tissues. Remember that edema can be localized in one area (for example – in the ankles) or generalized throughout the body (anasarca). Depending on the type of tissue and the area of the body, edema may be highly visible (such as facial edema) or relatively invisible (such as the edema seen in the organs – liver edema, in the lungs pulmonary edema) 7 There are four general causes of edema:  must know these four causes and identify how they contribute to edema formation 1. Increased capillary hydrostatic pressure 2. Decreased capillary oncotic pressure 3. Increased capillary permeability 4. Lymph obstruction 8 The first cause is increased capillary hydrostatic pressure (think increased volume or increased pressure) in which the increased pressure forces excessive amounts of fluid out of the capillaries into the tissues. Just remember it’s the force that “pushes” fluid out. An example would be pulmonary edema in which excessive pressure in the vascular bed (often due to increased volume –hypervolemia) forces fluid from the pulmonary capillaries into the alveoli which then interferes with respiratory function. Other causes of increased hydrostatic pressure due to hypervolemia are those related to heart failure, renal failure and pregnancy. 9 10 Edema can be related to a loss of plasma proteins (mainly albumin) which results in a decrease in plasma osmotic pressure. Plasma proteins usually remain inside the capillary – however whenever there is the presence of fewer protein – whether they aren’t being produced or they are being lost – the decreased protein levels allows more fluid to leave the capillary and go into the interstitium. Proteins may be lost in the urine because of kidney disease (patient is literally “peeing” out protein) as can be seen in glomerulonephritis or nephrotic syndrome. Proteins can also be decreased as synthesis of proteins may be impaired in patients with malnutrition or with liver disease (as the liver produces protein). 11 Increased capillary permeability usually causes a localized edema and may result from an inflammatory response or infection. Usually the release of histamine and other chemical mediators released from injured cells cause increased cell wall permeability allowing proteins and fluid movement out of the vascular bed into the interstitium. (You’re right it’s one of those pesky mediator things we learned about early in the semester). 12 Edema may result from obstruction of the lymphatic circulation. Such an obstruction usually causes a localized edema because excessive fluid and protein are not returned to the general circulation. This may develop if a tumor or infection damages a lymph node or if lymph nodes are removed, as they may be in cancer surgery. 13 What do you think? 14 15 No, not yet…but we are over half-way through the semester. 16