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Fluid, Electrolyte & Ph Balance

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Fluid, Electrolyte & Ph Balance Fluid / Electrolyte / Acid-Base Balance Fluid, Electrolyte Body Fluids: & pH Balance Cell function depends not only on continuous nutrient supply / waste removal, but also on the physical / chemical homeostasis of surrounding fluids 1) Water: (universal solvent) Body water varies based on of age, sex, mass, and body composition H2O ~ 73% body weight Low body fat Low bone mass H2O (♂) ~ 60% body weight H2O (♀) ~ 50% body weight ♀ = body fat / muscle mass H2O ~ 45% body weight Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance Body Fluids: Clinical Application: Cell function depends not only on continuous nutrient supply / waste removal, but also on the physical / chemical homeostasis of surrounding fluids The volumes of the body fluid compartments are measured by the dilution method 1) Water: (universal solvent) Total Body Water Step 1: Step 2: Step 4: Volume = 40 L (60% body weight) Identify appropriate marker Inject known volume of Calculate volume of body substance marker into individual fluid compartment Plasma Total Body Water: Amount Volume = A marker is placed in (L) Concentration the system that is distributed (mg) Intracellular Fluid (ICF) Interstitial wherever water is found Volume = 3 = 3 Volume Volume = 25 L Fluid Amount: Marker: D2O (40% body weight) Volume = 12 L Step 3: Amount of marker injected (mg) – Amount excreted (mg) L Extracellular Fluid Volume: Let marker equilibrate and A marker is placed in measure marker Concentration: the system that can not cross • Plasma concentration Concentration in plasma (mg / L) cell membranes Extracellular Fluid (ECF) • Urine concentration Volume = 15 L Marker: Mannitol Note: (20% body weight) ICF Volume = TBW – ECF Volume Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance Electrolytes have great osmotic power: Body Fluids: 2+ - - Fluid Movement Among Compartments: MgCl2 Mg + Cl + Cl Cell function depends not only on continuous nutrient supply / waste removal, The continuous exchange and mixing of body fluids are regulated but also on the physical / chemical homeostasis of surrounding fluids by osmotic and hydrostatic pressures 2) Solutes: Plasma 300 mosm A) Non-electrolytes Hydrostatic Pressure (do not dissociate in solution – neutral) • Mostly organic molecules Interstitial 300 mosm (e.g., glucose, lipids, urea) Fluid Osmotic Pressure B) Electrolytes Intracellular 300 mosm (dissociate into ions in solution – charged) Fluid Osmotic Osmotic • Inorganic salts Pressure Pressure • Inorganic / organic acids • Proteins In a steady state, Although individual [solute] are different The volume of a particular The shift of fluids between intracellular osmolarity between compartments, the osmotic compartment depends on compartments depends on is equal to concentrations of the ICF and amount of solute present osmolarity of solute present ECF are usually identical… extracellular osmolarity Marieb & Hoehn (Human Anatomy and Physiology, 8th ed.) – Figures 26.2 1 Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance Water Balance: Water Balance: ICF functions as a reservoir For proper hydration: Waterintake = Wateroutput Thirst Mechanism: osmolarity / volume Water Output (-) Water Intake of extra. fluid Feces (2%) < 0 Metabolism (10%) Sweat (8%) Osmolarity rises: Osmoreceptors stimulated • Thirst (Hypothalamus) Solid foods (30%) Skin / lungs (30%) • ADH release volume / osmolarity of Sensation Drink > 0 extracellular fluid of thirst Osmolarity lowers: Ingested liquids (60%) Urine (60%) • Thirst • ADH release saliva Dry mouth secretion 2500 ml/day 2500 ml/day = 0 (-) Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance Pathophysiology: Pathophysiology: Disturbances that alter solute or water balance in the body can Disturbances that alter solute or water balance in the body can cause a shift of water between fluid compartments cause a shift of water between fluid compartments Water intoxication Volume Contraction: A decrease in ECF volume Volume Expansion: An increase in ECF volume 300 mOsm < 300 mOsm NaCl not reabsorbed Greater than normal from kidney filtrate 300 mOsm NaCl water reabsorption IV bag Water Aldosterone Diarrhea deficiency insufficiency Osmotic IV Yang’s lunch SIADH 300 mOsm 300 mOsm > 300 mOsm < 300 mOsm 300 mOsm 300 mOsm > 300 mOsm < 300 mOsm Extracellular Extracellular Extracellular Extracellular Extracellular Extracellular Extracellular Extracellular Fluid Fluid Fluid Fluid Fluid Fluid Fluid Fluid 300 mOsm 300 mOsm > 300 mOsm < 300 mOsm 300 mOsm 300 mOsm > 300 mOsm < 300 mOsm Intracellular Intracellular Intracellular Intracellular Intracellular Intracellular Intracellular Intracellular Fluid Fluid Fluid Fluid Fluid Fluid Fluid Fluid Isomotic Contraction Hyperosmotic Contraction Hyposmotic Contraction Isomotic Expansion Hyperosmotic Expansion Hyposmotic Expansion ECF volume = Decrease ECF volume = Decrease ECF volume = Decrease IV bags of varying solutes ECF volume = Increase ECF volume = Increase ECF volume = Increase ECF osmolarity = No change ECF osmolarity = Increase ECF osmolarity = Decrease allow for manipulation of ECF osmolarity = No change ECF osmolarity = Increase ECF osmolarity = Decrease ECF / ICF levels… ICF volume = No change ICF volume = Decrease ICF volume = Increase ICF volume = No change ICF volume = Decrease ICF volume = Increase ICF osmolarity = No change ICF osmolarity = Increase ICF osmolarity = Decrease ICF osmolarity = No change ICF osmolarity = Increase ICF osmolarity = Decrease Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance Acid-Base Balance: Acid-Base Balance: Acid-base balance is concerned with maintaining a normal Acid production in the human body has two forms: hydrogen ion concentration in the body fluids volatile acids and fixed acids Compatible range for life + 1) Volatile Acids: Acids that leave solution and enter the atmosphere pH = -log10 [H ] -9 pH = -log10 [40 x 10 ] Normal H CO HCO - + H+ [H+] pH = 7.4 CO2 + H2O 2 3 3 End product of carbonic Note: aerobic metabolism acid (13,000 – 20,000 mmol / day) Eliminated via the lungs 1) [H+] and pH are inversely related 2) Relationship is logarithmic, not linear [H+] = 40 x 10-9 Eq / L 2) Fixed Acids: Acids that do not leave solution (~ 50 mmol / day) Normal range of arterial pH = 7.37 – 7.42 Products of normal Products of extreme Ingested (harmful) Problems Encountered: catabolism: catabolism: products: 1) Disruption of cell membrane stability Diabetes mellitus 2) Alteration of protein structure • Sulfuric acid (amino acids) • Acetoacetic acid • Salicylic acid (e.g., aspirin) (ketobodies) 3) Enzymatic activity change • Phosphoric acid (phospholipids) • B-hydroxybutyric acid • Formic acid (e.g., methanol) • Lactic acid (anaerobic respiration) • Oxalic acids (e.g., ethylene glycol) Eliminated via the kidneys Costanzo (Physiology, 4th ed.) – Figure 7.1 2 Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance For the human body, the Acid-Base Balance: Acid-Base Balance: most effective physiologic buffers will have a pK at 7.4 1.0 H+ Gain: Distant from H+ Loss: one another The Henderson-Hasselbalch equation is used to calculate • Across digestive epithelium • Release at lungs the pH of a buffered solution • Cell metabolic activities • Secretion into urine Chemical Buffer: A mixture of a weak acid and its conjugate base or a weak base and Henderson-Hasselbalch Equation: Most effective its conjugate acid that resist a change in pH -1 +1 [A-] buffering Robert Pitt: pH = pK + log [HA] + 150 mEq H 150 mEq H+ Brønsted-Lowry Nomenclature: + Weak acid: pH = -log10 [H ] Acid form = HA = H+ donor pK = -log10 K (equilibrium constant) [A-] = Concentration of base form of buffer (mEq / L) - + Base form = A = H acceptor [HA] = Concentration of acid form of buffer (mEq / L) 11.4 L Weak base: pK is a characteristic value for a buffer pair 11.4 L + + Acid form = BH = H donor (strong acid = pK; weak acid = pK) Base form = B = H+ acceptor 7.44 7.14 7.00 1.84 Costanzo (Physiology, 4th ed.) – Figure 7.2 Fluid / Electrolyte / Acid-Base Balance pK = 6.1 Fluid / Electrolyte / Acid-Base Balance - [HCO3 ] = 24 mmol / L Acid-Base Balance: Solubility = 0.03 mmol / L / mm Hg Acid-Base Balance: PCO2 = 40 mm Hg The major buffers of the ECF are bicarbonate and phosphate The major buffers of the ECF are bicarbonate and phosphate - - 1) HCO3 / CO2 Buffer: 1) HCO3 / CO2 Buffer: - + CO2 + H2O H2CO3 HCO3 + H Acid-base map: (HA) (A-) Shows relationship between the acid and base forms of a buffer and the pH of the solution Utilized as first line of defense when H+ enters / lost from system: - (1) Concentration of HCO3 normally high at 24 mEq / L - Ellipse: (2) The pK of HCO3 / CO2 buffer is 6.1 (near pH of ECF) Normal values for (3) CO is volatile; it can be expired by the lungs 2 arterial blood Note: The pH of arterial blood can - HCO3 24 Abnormal combinations of PCO2 be calculated with the pH = pK + log pH = 6.1 + log - Isohydric line and HCO3 concentration can Henderson-Hasselbalch equation 0.03 x PCO2 0.03 x 40 yield normal values of pH (‘same pH’) (compensatory mechanisms) pH = 7.4 Costanzo (Physiology, 4th ed.) – Figure 7.4 Fluid / Electrolyte / Acid-Base Balance Fluid / Electrolyte / Acid-Base Balance H+ enters cells via a build up of Acid-Base Balance: Acid-Base Balance: CO2 in ECF, which then enters cells, or to maintain electroneutrality The major buffers of the ECF are bicarbonate and phosphate The major buffers of the ICF are organic phosphates
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