Water & Electrolytes PDF

Water & electrolytes  The average water content of the human body varies from 60% to 75% of total body weight.  Function of water Solvent for electrolytes Transport media Determine cell volume Urine Body coolant control body temperature Lubricant for tissue  Sources of...

Water & electrolytes  The average water content of the human body varies from 60% to 75% of total body weight.  Function of water Solvent for electrolytes Transport media Determine cell volume Urine Body coolant control body temperature Lubricant for tissue  Sources of water: Drinking water 1000-1500 ml Endogenous source : Metabolic water (400 ml ) produced during metabolic oxidation  Water disribution Intracellular fluid(ICF) is the fluid inside the cells = two thirds of total body water. Extracellular fluid (ECF)= one third of total body water Subdivided into the : intravascular fluid (plasma) and the interstitial fluid and trans cellular fluid Normal plasma is about 93% water.  Water input and out put Body input : Ingestion (2300 ml) Metabolic ( 200 ml / day ) Water output : Kidneys ( 1500 ml) Evaporation from Skin ( 600ml/day) Exhalation from lung (300 ml/day) Feces ( 100 ml / day )  Movement of water & E Diffusion : movement of water down its concentration gradient Osmosis :diffusion of water across electively permeable membrane Osmolarity: the number of solutes per liter Osmolality : number of solutes per kg of solvent  Osmolality Osmolality is a physical property of a solution that is based on the concentration of solutes (expressed as millimoles) per kilogram of solvent (w/w). measured by Freezing point depression and vapor pressure decrease.  Osmolarity is reported in milliosmoles per liter (w/v) it is inaccurate in cases of hyperlipidemia or hyperproteinemia Osmolality is regulated by thirst and arginine vasopressin hormone AVP (ADH). Regulation of osmolality affects the sodium concentration.  Normal plasma osmolality (275–295 mOsm/kg) A 1%–2% increase causes four fold increase in ADH secretion 1%–2% decrease in osmolality shuts off AVP production  Determination of Osmolality Serum or urine Change in colligative properties Turbid serum and urine samples should be centrifuged Osmometers are standardized using sodium chloride reference solutions.  Calculation of osmolality Osmolal gap is the difference between the measured osmolality and the calculated osmolality, if increased it indicates the presence of osmotically active substances other than Na, urea, or glucose, such as ethanol,methanol, ethylene glycol, lactate, or -hydroxybutyrate.  2 Na+ glucose(mg/dl)+BUN(mg/dl) 20 3 1.86Na+ glucose(mg/dl)+BUN(mg/dl) +9 18 2.8  Disorders Water Load over hydration Water Deficit dehydration  Dehydration is case of water imbalance the output exceed input Causes : No water intake Excessive loss Diabetis insipidus Defect in hypothalmus  Feature of dehydration Low body water Low blood volume Disturbance of electrolytes Body electrolytes  Electrolytes Substance dissolved in solution and dissociate to ions carry electrical charge Cation positively charged Anions Negatively Intracellular Extracellular Potassium Sodium Magnesium Chloride Phosphate Bicarbonate  Sodium Na is the most abundant cation in the ECF, representing 90% of all extracellular cations, and largely determines the osmolality of the plasma.  Regulation (1)the intake of water in response to thirst (neural mechanism) (2) the excretion of water, largely affected by AVP ( ADH) release in response to changes in either blood volume or osmolality from hypothlamus and stored in posterior pitutary (3) the blood volume status, which stimulate atrial natriuritic peptides (4) Kinins increase salt and water secretion  ADH act on collecting ducts to reabsorbe water Renin angiotensin relased from kidneys in response to decrease blood volume Also control aldosterone Aldosterone steroid hormone produced by adrenal cortex Increase Na reabsorption and CL and increase K loss through urine  ANP cardiac hormone secreted by right atrium Released in resopnse to increase blood pressure oppose renin angiotensin aldosterone system Increase Na loss by urine Kinins are protiens in blood cause inflamation ; lower blood pressure Increase water and salt excretion  Hyponatremia  INCREASED SODIUM LOSS Hypo-adrenalism Potassium deficiency Diuretic use Prolonged vomiting or diarrhea Severe burns  INCREASED WATER RETENTION Renal failure Hepatic cirrhosis Congestive heart failure  WATER IMBALANCE Excess water intake SIADH Pseudohyponatremia  Hypernatremia EXCESS WATER LOSS Diabetes insipidus Prolonged diarrhea Profuse sweating DECREASED WATER INTAKE Older persons Infants Mental impairment INCREASED INTAKE OR RETENTION Hyperaldosteronism  Potassium Potassium (K) is the major intracellular cation in the body, with a concentration 20 times greater inside the cells than outside Regulation of neuromuscular excitability, contraction of the heart, ICF volume, and H concentration.  Regulation Aldosteron  Hypokalemia GI LOSS Vomiting Diarrhea RENAL LOSS Diuretics Hyperaldosteronism CELLULAR SHIFT Alkalosis Insulin overdose DECREASED INTAKE  Hyperkalemia DECREASED RENAL EXCRETION Acute or chronic renal failure Hypoaldosteronism CELLULAR SHIFT Acidosis Muscle/cellular injury Leukemia Hemolysis INCREASED INTAKE Oral or IV potassium replacement therapy ARTIFACTUAL Sample hemolysis Thrombocytosis Prolonged tourniquet use or excessive fist clenching  Chloride Major extracellular anion Maintains blood osmolality, volume and electroneutrality Absorbed in GIT Reabsorbed with sodium Excess excreted in urine and sweat  Hyperchloremia may also occur when there is an excess loss of HCO3 result of GI losses, RTA, or metabolic acidosis. Hypochloremia may also occur with excessive loss of Cl− from prolonged vomiting, diabetic ketoacidosis, aldosterone deficiency, or salt-losing renal diseases such as pyelonephritis.  Bicarbonate Bicarbonate is the second most abundant anion in the ECF. Total CO2 comprises the bicarbonate ion (HCO3−) accounting for more than 90% of the total CO2 at physiologic pH HCO3 is the major component of the buffering system in the blood. −.  Acid–base imbalances cause changes in HCO3 and CO2 levels. A decreased HCO3 may occur from metabolic acidosis The typical response to metabolic Acidosis is compensation by hyperventilation Elevated totalCO2 concentrations occur in metabolic alkalosis as HCO3 is retained, often with increased pco2 as a result of compensation by hypoventilation