Fluid and Electrolyte Balance PDF

Electrolyte and Body Fluid Regulation Dr. Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Learning Objectives State the distribution of body water Describe the renal regulatory mechanis...

Electrolyte and Body Fluid Regulation Dr. Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Learning Objectives State the distribution of body water Describe the renal regulatory mechanisms of water balance Enlist the main sensors that help to control water balance Enlist the disorders of water and describe the regulatory mechanisms Describe Na+, K+, Ca++ and PO4+ homeostasis. Body Water content  Body Water content In healthy males –60 % of body weight (around 40 liters) In healthy females – 55 % of body weight  Fluid compartments Water occupies two main fluid compartments in the body 1.ICF( Intra cellular fluid) – two third of total body water 2.ECF(extra cellular fluid)- one third of total body water. ECF include, ✓ Plasma ✓ Interstitial fluid ✓ Trans cellular fluid (CSF, aqueous humor, synovial fluid, GI secretions)  Distribution of Electrolytes in ECF and ICF ECF - Na+ is the main cation Cl- is the main anion ICF - K+ is the main cation PO4 – is the main anion Water Balance (homeostasis) Water gain = Water loss  Water loss : Kidneys Regulation The distribution of the TBW between the ECF and the ICF is determined by the ECF [Na+]. Therefore, regulation of water balance and Na+ balance is integrated. Kidney regulate water through it effect on diuresis (increase urinevolume) and natriuresis (increase Na+ secretion)  How the kidney regulates water loss Vasopressin( ADH) Auto regulation of RBF & GFR Glomerulotubular Balance Intrinsic Pressure-Volume Control System Tubular concentrating ability Renin- Angiotensin- Aldosterone system Natriuretic peptides ✓ Glomerulotubular Balance Glomerulotubular balance is a strictly local renal mechanism. The effect of this is to minimize the effect of changes in GFR on sodium and water excretion. ✓ Intrinsic Pressure-Volume Control System The pressure-volume control system is the intrinsic control system for maintaining a constant blood volume. Pressure diuresis Pressure natriuresis The kidney excretes more Na+ and water when arterial blood pressure rises, and this helps to maintain volume and blood pressure. Disorders of Kidney that affect water balance Central Diabetes Nephrogenic Insipidus Diabetes Insipidus DCT, CD unresponsive to ADH Due to deficiency of ADH ADH receptor gene mutation Aquaporin 2 channel protein gene mutation Water gain: Sensors for body water gain The main sensors that are involved in control of water balance are: ✓Osmoreceptors (Hypothalamus) ✓Thirst center (Hypothalamus) ✓Volume receptors (Atria) ✓High pressure baroreceptors (carotid sinus & aortic arch) Factors affecting thirst The 4 major stimuli to thirst are: 1. Hypovolemia 2. Hypertonicity (osmolality) 3. Hypotension 4. Angiotensin II  Disorders of water balance Dehydration Overhydration  Dehydration Excessive loss of body water  Dehydration Compensatory mechanisms: ✓Stimulation of Thirst -  water intake ✓Secretion of ADH- less urine volume ✓ Inhibition of High pressure baroreceptors- ✓  Sympathetic tone-  GFR & RBF-  urine output ✓Stimulation of Renin- angiotensin – Na+ reabsorption, thirst, vasoconstriction ✓Secretion of Aldosterone-  Na+ reabsorption Over-hydration  Over-hydration Compensatory mechanisms: ✓Inhibition of thirst- less water intake ✓Stimulation of high pressure baroreceptors- sympathetic tone , RBF & GFR  , Urine output  ✓Inhibition of ADH, Renin- angiotensin, aldosterone secretions-  urine output ✓Stimulation of ANP- Natriuresis (Na+ excretion in the urine)  Regulating Na+ Balance Normal Na+ level : 135 to 145 mmol/L Hypernatremia(excess Na+) while Hyponatremia (Low Na+) Na+ regulation is affected by: 1- Aldosterone Effects When Stimulated → Na+ reabsorption increased Decrease urinary output (concentrated urine) and increase blood volume When Inhibited → Na+ reabsorption reduced so excreted diluted urine Renin-angiotensin mechanism JG apparatus releases renin → stimulates aldosterone release 2- Atrial natriuretic peptide (ANP) Atrial stretch stimulates its release ANP opposes Effect: Reduces BP and blood volume the action of Inhibits vasoconstriction Aldosterone Inhibits Na+ and H2O retention Inhibit collecting duct Na+ reabsorption (Natriuresis) Suppresses ADH, renin, and aldosterone release Other Hormones Regulating Na+ Balance Estrogens Enhance NaCl reabsorption by renal tubules Enhance H2O retention during menstrual cycles Cause edema during pregnancy Progesterone Promotes Na+ and H2O loss Blocks aldosterone effects at renal tubules → diuretic Glucocorticoids Enhance Na + reabsorption Increase GFR Promote edema  Regulating K+ Balance [K+] in plasma High K+ in ECF (hyperkalemia) increases its secretion Stimulates adrenal cortical release of aldosterone Aldosterone enhances K+ secretion High ECF K+ stimulates adrenal cortex to release aldosterone Renin-angiotensin mechanism  Regulating Ca2+ and PO42- Parathyroid hormone (PTH) from parathyroid gland Increase renal calcium reabsorption and phosphate excretion Increases blood calcium level Calcitonin from thyroid gland Lowers blood calcium level  Learning Resources Text Book: Vander’s Human Physiology, 13th Edition, USA: McGraw- Hill; 2014. ISBN-13: 978-0073378305, chapter 14, pp 506-520 Guyton and Hall: Textbook of Medical Physiology Power-point presentation in the moodle www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES