Acid base balance - Lecture notes 7 PDF

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online lecture taught by elita partosoedarso. In depth lecture on acid base balance in the blood and urinary system...

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ANATOMY AND PHYSIOLOGY 2 – ACID BASE BALANCE In arterioles and blood, 7.4 is neutral. Homeostasis = 7.35 to 7.45  Below is acidic (acidosis) and above is basic (alkalosis)  Lungs remove acid by expiration of CO2 (>30L a day) Problems that unbalanced pH can cause  If Na+ pump doesn't work, it accumulates in the cell drawing water in, which damages the membranes of the cells  Functional protein changes shape: lose shape, lose function Sources of Acids and Bases  From absorbed food and the metabolism of nutrients at the cellular level  Carbonic acid = by aerobic glucose metabolism  Lactic acid = by anaerobic glucose metabolism  Sulfuric acid = oxidation of sulfur-containing amino acids  Phosphoric acid = accumulates when phosphoproteins and ribonucleotides are broken down  Ketone bodies = accumulate during incomplete breakdown of fats (diabetic ketoacidosis)  Acid-forming minerals = remain after protein is metabolized  Base-forming minerals = remain after fruits and veg are metabolized HOMEOSTATIC CONTROL MECHANISM OF PH Three mechanisms 1. Initial Control Mechanism: RAPID-ACTING CHEMICAL BUFFERS  Immediately combines with any added acid or alkali that enters the body fluids to counteract drastic changes in H+ ion concentrations and pH 2. Secondary Control Mechanism: RESPIRATORY MECHANISMS  Changes in the rate and depth of breathing only if chemical buffers aren't enough (in hours)  If blood is TOO ACIDIC, breathing rate and depth with increase 3. Tertiary Control Mechanism  More POWERFUL, but slower-acting renal physiological buffer system  Excretion either acid or alkaline urine starts within 24 hours ACID BASE BALANCE RATIO  BASE BICARBONATE TO CARBONIC ACID (BB-CA) Rapidly acting chemical buffers: 1. Buffer: prevents parked changes in pH of a solution when an acid or base is added to it, minimize pH changes  swap strong base with weaker base or strong acid with a weaker acid  Buffer pairs: plasma + protein, hemoglobin + potassium, 2. Sodium BiCarbonate Mechanism  Adding strong acid = more H+ in the blood  Buffer pair: sodium bicarbonate  H+ and Na swap places - forming carbonic acid (weak acid; less dissociation of protons in the blood) and sodium chloride

Doesn't make pH drop so far; if small pH, other mechanisms will balance it 3. Carbonic acid  Adding strong base = more OH- in the blood  Na and H+ swap places so that sodium bicarbonate and water forms (dissociates less, so pH doesn't go up so drastically) 4. Buffering of CO2 in blood  Carbonic acid is buffered by the K+ salt of hemoglobin to form potassium bicarbonate  The bicarbonate ion then diffuses out into the plasma, causing Cl- to go in to replace that bicarbonate ion = chloride shift (for electrical balance to be maintained) 

Respiratory Mechanisms As CO2 leaves, it's a form for acid to leave the lungs as well CO2 + H2O --- carbonic anyhandrase---> H2CO3 -----> H+ + HCO31. Decrease in pH is detected carotid chemoreceptors 2. Sends a signal to the respiratory center IN BRANSTEM to activate the carotid chemoreflexes 3. HYPERVENTILATION starts, this increases loss of CO2 (too prolonged = alkalosis) Urinary Mechanisms  NH3 (ammonia) is formed by metabolism of amino acid  Combines with H+ to form NH4+  This displaces NA+ to produces ammonium salt (NH4Cl) which is excreted in urine  The leftover Na+ combines with HCO3- to form basic salt NaHCO3 which is reabsorbed back into the blood ARTERIAL BLOOD/GAS ANALYSIS Acidosis  blood pH drops below normal (below 7.35)  Pco2 = above 45 mmHg (compensation (switches/ blow 35 mmHg) - drives bicarbonate concentration above normal range)  HCO3- metabolic below 22 mEq/L  Compensation switches (above 26 mEq/L) Metabolic Acidosis BB:CA ratio maybe 10:1 (normal is 20:1) Compensation - increase in respiration to remove excess H+ as CO2 Metabolic Alkalosis  Increases above homeostatic range  Decreases depth of respiration so CO2 is conserved  Improper use of antacids or excessive vomiting  BB:CA ratio is 40:1  Tetany, convulsions, death Respiratory Acidosis

= CO2 accumulates due to pneumonia, emphysema, or drug overdose that inhibits respiration Compensation - kidneys increase HCO3- reabsorption and increase H+ excretion Infusion of sodium lactate offsets this Respiratory Alkalosis  Hyperventilation due to fever or mental illness (loss of carbonic acid) Compensation: Excretion of HCO3- while conserving H+ loss Solution containing Cl- replaces lost HCO3- ions will fix the problem...