Body Fluid Balance Lecture Notes PDF

Good afternoon Body Fluid Balance Prof. Dr. Faten Mahmoud A. Diab Professor of Medical Physiology Egypt  Learning objectives List sources of water intake & water loss. Outline disturbance in water balance. Describe body regulatory mechanisms for dehydration....

Good afternoon Body Fluid Balance Prof. Dr. Faten Mahmoud A. Diab Professor of Medical Physiology Egypt  Learning objectives List sources of water intake & water loss. Outline disturbance in water balance. Describe body regulatory mechanisms for dehydration. Describe body regulatory mechanisms for over-hydration. Outline hazards of change tonicity of the plasma: hypotonicity or hypertonicity on body cells and different body water compartments.  Total Body Water 3/4 1/4 9/25/2024 3  How it can be measured?? 9/25/2024 4  But we should know how to estimate (or calculate) the volume of each compartment A 30-year-old man, his body weight is 80 Kilograms. Calculate his: a. Total body water b. ECF volume c. Intravascular volume (plasma volume) TBW = 60 % of the body weight. So, TBW= 80 × 60/100 = 48 liters ECF = 1/3 of the TBW. So, ECF = 48 × 1/3 = 16 liters ICF Plasma volume = 1/4 ECF. So, Plasma volume= 16 x 1/4 = 4 liters ISF 9/25/2024 5 Case scenario 9/25/2024 6  Electrolyte Balance Sodium balance Na+ Why it is important?  Na+ is the most abundant extracellular ion.  Water reabsorption occurs by osmosis, is dependent on Na+ reabsorption. Na+ Water follows Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+  Osmosis??  Osmosis:  It is the passive transport of water across the selectively semi-permeable membrane. From area of higher water To the area of lower water conc. conc. (or from pure water) (to the solution) Along water concentration gradient. From area of lower solute To an area of higher solute conc. concentration (weak = diluted (strong = concentrated solution) to MORE WATER solution) which membrane is impermeable (low solutes = (High solutes = low tonicity) high tonicity) Some roles: Therefore, regulation of water balance and Na+ balance is integrated, If there is disturbance in one, the regulation of the other is affected. The distribution of the TBW between the ECF and the ICF is determined by mainly ECF [Na+]. Water Balance Water Water gain loss  Sources of water Sources of water gain loss Drinking (1200 ml) Urine (1500 ml) Water contained in solid food (800 ml) Insensible water loss via respiratory tract & skin sweating (800 ml) Water derived from oxidative metabolism in our body (400 ml) Stool (100 ml). 2300 – 2500 ml/day 2300 – 2500 ml/day  Fluid output (loss) If water loss > water gain Dehydration If water gain > water loss Over-hydration Disturbance in Body Water Balance Dehydration Overhydration  Dehydration Causes of dehydration:  Insufficient water intake.  Excessive water loss: (vomiting, diarrhea, sweating) There is less water than solutes (i.e. Person develop ECF hypertonicity)  Dehydration Body correction of dehydration: When ECF osmolarity increase (hypertonicity): increase water intake: As the hypertonicity stimulates the thirst center in the hypothalamus. decrease water loss in urine: As hypertonicity stimulates the secretion of anti-diuretic hormone (ADH). ADH decreases urine volume by increasing water reabsorption in the kidney to increase blood volume = secretion of concentrated urine. 25/09/2024 16 Correction of dehydration by ADH 9/25/2024 17  Overhydration Causes of overhydration:  Rapid ingestion of water  There is more water than solutes (i.e. Person develop ECF hypotonicity)  Overhydration Body correction of overhydration: Conversely, when osmolarity decrease (hypotonicity = low serum osmolarity): decrease water intake: As hypotonicity inhibits the thirst center. increase loss of water in urine: As hypotonicity inhibits ADH secretion so, there is increase in excretion of water in urine = secretion of diluted urine. 25/09/2024 19 (summary) Regulation of body water disturbance + - + - 25/09/2024 20  What Controls What controls thirst ADH secretion?? sensation?? 9/25/2024 21  Both Overhydration & dehydration are serious conditions.  What are the What are the hazards of ECF hazards of ECF hypertonicity? hypotonicity? Water moves from the ECF to cells Water moves out from the cells, leading to swelling of cells and leading to shrinkage of cells called water intoxication. The most rapidly affected cells are the brain cells with altered neurological functions with nausea, malaise, headache, confusion, lethargy, seizures, and coma & death. 25/09/2024  Clinical Application ?!! 9/25/2024 24  isotonic An isotonic solution has the same osmolality as that of plasma, solutions about 290 mOsm/kg. An isotonic solution of NaCl (also known as 0.9% saline or normal saline solution) Hypotonic A hypotonic solution has lower osmolality than plasma: e.g., solutions 5% dextrose. If we inject 5% dextrose, the dextrose is immediately metabolized, leaving only free water behind. Hypertonic A hypertonic solution has a higher osmolality than plasma. If a solutions hypertonic solution (e.g., 3% saline, osmolality = 1027 mOsm/kg) 9/25/2024 25  Hypotonic solution Hypertonic solution left right (low solutes) = (low tonicity) (High solutes) = (high tonicity) 9/25/2024 26  ECF Inject Normal isotonic Cell = solution in (isotonic The medical team decided to infuse the as ECF) patient with dehydration with normal Normal Saline the ECF saline (0.9% sodium chloride) to replace the lost fluids, quickly restore his fluid levels (ECF) and stabilize his condition. Normal Cell volume 9/25/2024 27  What is the effect of infusion of an isotonic solution? The infused isotonic NaCl (isotonic saline) will be distributed into the ECF but not into the ICF (because the water will stay with the sodium). It will then distribute throughout the ECF, including the interstitial and intravascular spaces with the same ratio (1/4 intravascular & 3/4 interstitial fluid). So, for every liter (1000 ml) of normal saline infused, 250 mL will remain intravascular, and 750 mL enters the interstitium.  ECF HYPERTONIC - WATER DEHYDRATION Inject CELLS SHRINK OSMOLARIT INCREASES Normal Cell = Hypertonic isotonic solution in the ECF So, water moves (3%) Administration of 3% NaCl is primarily out of the cell indicated to treat symptomatic hyponatremia to decrease the development of hyponatremic Cell encephalopathy and brain edema. shrinks EXCESS TOTAL BODY WATER FOR CASES LIKE EDEMA WHEN THE CELLS ARE SWELLED UP. HYPO-CASES WE USE HYPERTONIC SOLU LIKE 5% NACL TO ADMISNITRATE AND CAUSE THE CELL TO SHRINK. 9/25/2024 29  What is the effect of hypertonic solution infusion? If hypertonic saline solution is infused into the ECF, this would result in an increase in osmolality of the ECF. So, water would move from the intracellular space (ICF) to the extracellular space (ECF) to maintain equal osmolality inside and outside cells. Although this is good in terms of ECF expansion, it comes at the expense of ICF contraction. 9/25/2024 30  ECF Inject Hypotonic Normal solution in Cell = Isotonic Hypotonic solutions e.g., hypotonic the ECF NaCl (e.g., 0.45% NaCl or 5% dextrose in water is prescribed for patients whose So, water moves into the cell body fluids are hyperosmotic. Cell swelling 9/25/2024 31  What is the effect of infusion of hypotonic solution?  Following an infusion of 5% dextrose into the ECF, there is an acute drop in ECF osmolality (hypo). This results in water moving from the ECF to the intracellular space (ICF) in an attempt to equilibrate the osmotic difference.  When 1 L of 5% dextrose is given, it distributes into the TBW space. This means it is distributed equally throughout the ECF and ICF. 9/25/2024 32 If we infuse the patient with 1 liter of 5 % dextrose: How it will be How much will distributed in remain in the different body intravascular compartment? compartment? 1000 x 1/3 = 333.33 ml. in the ECF 333.33 x 1/4 = 83.33 ml in intravascular 1000 x 2/3 = 666.66 ml. in the ICF 333.33 x 3 /4= 249.9 ml in interstitium 9/25/2024 33 Q & A: In overhydration, the thirst center is: a. stimulated b. Inhibited. The hypertonicity of the ECF induces: a. Cell swelling b. Cell shrinking. In dehydration, the anti-diuretic hormone secretion is: a. Stimulated. b. Inhibited 25/09/2024 34  Learning Resources  Textbook: Hall, J. and Hall, M. Guyton and Hall textbook of medical physiology, Fourteenth Edition, Elsevier 2021. ISBN: 978-0-323-59712-8. International Edition ISBN: 978-0-323-67280-1. Chapter 25, 310-320  https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0- B9780323597128000254  Power-point presentation in the moodle.  Brick Exchange Brick (scholarrx.com) 9/25/2024 35 36