Water and Electrolytes PDF

Water and electrolytes Functions of Body Fluid Provides a medium for transporting nutrients to cells and wastes from cells and for transporting substances such as hormones, enzymes blood plates, and red and white blood cells. Solvent for electrolytes and other constituents Helps maintain body temper...

Water and electrolytes Functions of Body Fluid Provides a medium for transporting nutrients to cells and wastes from cells and for transporting substances such as hormones, enzymes blood plates, and red and white blood cells. Solvent for electrolytes and other constituents Helps maintain body temperature Functions of Body Fluid Facilitates digestion and promotes elimination Acts as a tissue lubricant Facilitates cellular metabolism and proper cellular chemical functioning To be in balance, the quantities of fluids and electrolytes leaving the body should be equal to the amounts taken in Mechanisms of Fluid Gain and Loss Gain Fluid intake 1500ml Food intake 1000ml Oxidation of nutrients 300ml (10ml of H20 per 100 Kcal) Loss “Sensible” Can be seen. Urine 1500ml Sweat 100ml “Insensible” Not visible. Skin (evaporation) 500ml Lungs 400ml Feces 200ml Fluid Compartments Intracellular fluid (ICF) Fluid inside the cell Most (2/3) of the body’s H20 is in the ICF. 40% of BODY WEIGHT = ICF fluid Extracellular Fluid (ECF) Fluid outside the cell. 1/3 of body’s H20 More prone to loss 3 types: Interstitial- fluid around/between cells Intravascular- (plasma) fluid in blood vessels Transcellular –CSF, Synovial fluid etc 20% of BODY WEIGHT = ECF fluid VARIATIONS IN FLUID CONTENT Age Sex Amount of body fat Water as a percent of body weight – Infants = 77% – Adult male=60% – Adult female= 50% – Elderly person =45% Distribution of Body Fluids – The intracellular fluid compartment includes all the water and electrolytes within cells. – The extracellular fluid compartment includes all water and electrolytes outside of cells (interstitial fluid, plasma, and lymph). – Transcellular fluid includes the cerebrospinal fluid of the central nervous system, fluids within the eyeball, synovial fluid of the joints, serous fluid within body cavities, and exocrine gland secretions. 9 Distribution of Body Fluids Body Fluid Composition – Extracellular fluids have high concentrations of sodium, chloride, and bicarbonate ions, and lesser amounts of potassium, calcium, magnesium, phosphate, and sulfate ions. – Intracellular fluid has high concentrations of potassium, phosphate, and magnesium ions, and lesser amounts of sodium, chloride, and bicarbonate ions. 10 Distribution of Body Fluids Movement of Fluid between Compartments – Hydrostatic pressure and osmotic pressure regulate the movement of water and electrolytes from one compartment to another. 11 Water Balance Water balance exists when water intake equals water output. – Water Intake The volume of water gained each day varies from one individual to the next. About 60% of daily water is gained from drinking, another 30% comes from moist foods, and 10% from the water of metabolism. – Regulation of Water Intake The thirst mechanism is the primary regulator of water intake. 12 Water Balance – Water Output Water is lost in urine, feces, perspiration, evaporation from skin (insensible perspiration), and from the lungs during breathing. The route of water loss depends on temperature, relative humidity, and physical exercise. – Regulation of Water Output The distal convoluted tubules and collecting ducts of the nephrons regulate water output. Antidiuretic hormone from the posterior pituitary causes a reduction in the amount of water lost in the urine. 13 Electrolytes Electrolytes are substances whose molecules dissociate or split into ions when placed in water Work with fluids to keep the body healthy and in balance They are solutes that are found in various concentrations and measured in terms of milliequivalent (mEq) units Can be negatively charged (anions) or positively charged (cations) For homeostasis body needs: Total body ANIONS = Total body CATIONS Electrolytes Cations Positively charged  Sodium Na+  Potassium K+  Calcium Ca++  Magnesium Mg++ Anions Negatively charged Chloride Cl Phosphate PO4 Bicarbonate HCO3- Electrolyte Functions Regulate water distribution Muscle contraction Nerve impulse transmission Blood clotting Regulate enzyme reactions (ATP) Regulate acid-base balance Electrolyte Balance An electrolyte balance exists when the quantities of electrolytes gained equals the amount lost. – Electrolyte Intake The electrolytes of greatest importance to cellular metabolism are sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, and hydrogen ions. Electrolytes may be obtained from food or drink or produced as a by-product of metabolism. 17 Electrolyte Balance – Regulation of Electrolyte Intake A person ordinarily obtains sufficient electrolytes from foods eaten. – Electrolyte Output Losses of electrolytes occur through sweating, in the feces, and in urine. 18 FLUID AND ELECTROLYTE MOVEMENT Diffusion Facilitated diffusion Active transport Osmosis Hydrostatic pressure Oncotic pressure (reabsorption) “keeping the fluid in” Diffusion Movement of solutes from high concentration to low concentration It is a PASSIVE movement DOWN the concentration gradiant. (requires no energy) Many body processes use diffusion. Example: O2 and CO2 exchange Rate is affected by: concentration gradiant, permeability-surface area-thickness of membranes, and size of particles. Active transport requires energy (ATP) to move from low concentration to high concentration Example: Na / K pump May be enhanced by carrier molecules with binding sites on cell membrane Example: Glucose (Insulin promotes the insertion of binding sites for Glucose on cell membranes). Osmosis: diffusion of solvent molecules (water) into region in which there is a higher concentration of a solute (electrolyte) to which the membrane is impermeable Oncotic pressure (colloid osmotic pressure): the pressure necessery to prevent diffusion of solvent molecules (water) into region in which there is a higher concentration of a colloid to which the membrane is impermeable ORGANS OF REGULATION KIDNEYS LUNGS HEART BLOOD VESSELS PITUITARY ADRENAL CORTEX PARATHYROIDS Hyponatraemia Serum Na < 135 mmol/l Causes: – Water problem (excess of water relative to sodium) – Water excretion by the kidney is impaired – Pseudohyponatraemia (hyperlipidaemia, hyperproteinaemia) Symptoms: – Cerebral oedema – Nausea, vomiting, lethargy, confusion, seizures, coma Therapy: – Hypertonic saline – Isotonic saline Hypernatraemia Se Na > 145 mmol/l Causes: inadequate water intake and increased free water loss; intake of hypertonic sodium solution Symptoms: – Increased thirst – Central nervous system abnormalities (confusion, weakness, lethargy, seizures, coma) Therapy: water repletion, correction rate of Na level should be no greater than 2 mmol/h Potassium Most abundant cation of ICF, helps maintain ICF volume Key role in the resting membrane potential and action potential of neurons and muscle fibers K+ level is controlled by aldosterone Hydrogen-potassium exchange in cell membrane Minimal potassium intake: 1 mmol/kg Hyperkalaemia Se K > 5 mmol/l Causes – Impaired excretion Renal failure, mineralocorticoid deficiency, pseudohypoaldosteronism, drugs (potassium sparing diuretics, ACE-inhibitors ,NSAID, cyclosporin) – Shifts of K out of cells Tissue breakdown, acidosis, insulin deficiency Hyperkalaemia Symptoms: Cardiac (peaked T waves, loss of P waves, heart blocks, ventricular arrhytmias, widening of QRS complexes, asystole) Paresthesias, weakness, paralysis Acidosis Therapy – Direct antagonism of hyperkalemic effect on cell membrane polarization Calcium gluconate – Movement of extracellular K into intracellular compartment Insulin (+glucose) Sodium bicarbonate β2-adrenergic agonists Hyperkalaemia Therapy – Removal K from the body Loop diuretics Dialysis Hyperkalaemia Therapy – Removal K from the body Loop diuretics Dialysis Hypokalaemia Se K < 3,5 mmol/l Causes: – Increased excretion: diarrhoea, renal losses, mineralocorticoid excess, magnesium depletion – Shifts of K into cells: drugs (insulin, β2-adrenergic agonists, theophylline, caffeine), alkalosis, hyperthyreoidism Symptoms: – Cardiac: flat t waves, ST depression, U wave, QT interval prolongation, arrhytmias – Muscle paralysis, rhabdomyolysis – Coma – Metabolic alkalosis Hypokalaemia Therapy – Supplementation of K Calcium Ca++ 4.5-5.5mEq/L Most abundant in body but: 99% in teeth and bones Needed for nerve transmission, vitamin B12 absorption, muscle contraction & blood clotting Inverse relationship with Phosphorus Vitamin D needed for Ca absorption Calcium metabolism Source of calcium is milk and milk product. Absorbed in the small intestine. >99% of Calcium in the body is bone. Regulates by (PTH, Calcitonine and VitD). PTH Stimulated by decrease in ionized ca. The effect of it activates bone resorption, increase tubular reabsorption of ca and stimulate formation of vit D. Promote phosphaturia ,decrease reabsorption of filtered phosphate. Vit D Cholecalciferol from diet or sun light. Converted into 25- hydroxycholecalciferol in liver. Hydroxylated ----1:25 di hydroxycholecalciferol in kidney---------increases ca absorption in intestine and enhances the effect of PTH on bone resorption. In gut stimulate absorption of phos. Causes of hypocalcemia: Hypoparathyroidism Idiopathic. pancreatitis. Magnesium deficiency. Vit D deficiency(malabsortion ). Renal disease Pseudohypoparathyroidim. Clinical features Neurological features (tingling , tetany and mental changes. Chovstek sign-Tap facial nerve in front of ear= facial spasm Trousseau- carpal spasm after BP cuff inflated due to increased neuromuscular excitability Cardiovascular signs ( arrhythmia by ECG) Cataract. Chovstek Trousseau Hypercalcaemia Primary hyperparathyroidism. Malignancy. Hyperthyroidism. Multiple myloma. Increased vit D. Thiazide diuretics. Prolonged immolization. Clinical features Neurologic symptom: Mild drowsiness ,depression and lethargy. GIT symptom: nausea ,vomiting ,anorexia ,constipation and peptic ulcer. Renal symptom: Stones Nephrocalcinosis. Nephrogenic diabetes insipidus. Phosphate Acts as urinary buffer. Found in bone.PTH reabsorption. Normal range 0.80-1.4 mmol/l. Hyperphosphataemia: Causes: Renal failure. Hypoparath. Haemolysis. Peudohypoparath. Hypophosphataemia Cause muscle weakness ----respiratory impairment. Causes: Hyperparathyrodism. Fanconi syndrome affect reabsorption of phos in tubule due to congenital defect. Use of anti acid (aluminum hydroxide). Treatment of diabetic ketoacidosis. Sever dietary deficiency. Magnesium 2nd intracellular cation after potassium. about 300 enzymes system are activated by it. Causes of hypomagnesaemia: Renal failure. Causes of hyperMg: Dietary insufficiency and malabsorption. Osmotic diuresis (diabetic). Prolonged use of diuretic. Prolonged nasogastric suction. Clinical features are same like hypoca. Investigation of hypomg: less than 0.7mmol/l