Acid Base Balance I-II, GULF MEDICAL UNIVERSITY, PDF

Acid base balance I and II Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF  Define pH and how its calculated & its normal range that is compatible with life.  State di...

Acid base balance I and II Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF  Define pH and how its calculated & its normal range that is compatible with life.  State different regulatory mechanisms for acid-base balance.  Outline different acid base disorders.  State role of respiratory compensation in cases of metabolic acidosis & alkalosis.  List the causes underlying respiratory acidosis and alkalosis.  Describe the role of renal compensations for respiratory acidosis and alkalosis.  Outline how to diagnose a case of respiratory acidosis and respiratory alkalosis.  Definitions Acid: is a molecule that can function as a H+ donor. Strong acid: has a strong tendency to dissociate in the solution and discharge H+ like HCl. Weak acid: has a weak tendency to dissociate in the solution and discharge H+ like H2CO3. A base is a molecule that can function as a H+ acceptor. Strong base : reacts powerfully with H+ like OH- Weak base: reacts weakly with H+ like HCO3-. An alkali combination of one alkaline metal (Na+ or K+) with strong base (OH-) forming NaOH or KOH. In the body , week base, HCO3-and weak acid, H2CO3 is concerned with acid-base balance  pH of the body N.B: pH= potential of H+ or power of H+. Excess H+= low pH = acidosis. Low H+= high pH = alkalosis. pH = Normal pH = 7.4 Normal pH range = 7.35 – 7.45 pH below 6.8 Deat pH Above 8 h  Acid base balance Definition: Regulation of H+ concentration. Why it is important??? Because slight change in H+ causes marked alteration of the chemical reaction in the body Excess H+ (acidosis) → Decreased H+ (alkalosis) → depress chemical reaction accelerates chemical reaction Body defense against changes in H+ concentration Acid-base buffer system Respiratory system Kidney  Body defense against changes in H+ concentration Buffer system Respiratory system Kidney acts within a fraction of acts within mins (1- Requires minutes to 15mins). several days. seconds. It acts by controlling level of It depends on the ability of Formed of a mixture of CO2 in blood through the kidney to control H+ weak acid and its base. adjustment of pulmonary secretion and HCO3 ventilation It is the first defense reabsorption. It is the second defense It is the 3rd defense against pH change. against pH change. against pH change. Less powerful moderate power. Most powerful  Body defense against changes in H+ concentration Buffer system acts within a fraction of seconds. Types: 1. Bicarbonate buffer system: Formed of H2CO3 and NaHCO3: it buffers strong acid converting it to weak acid (HCl + NaHCO3 → NaCl + H2CO3) it buffers strong base converting it to weak base with minimal change in pH (NaOH + H2CO3 →H20 + NaHCO3) 2. Phosphate buffer system Formed of H2PO4 and HPO4-. It is found in the renal tubules 3. Protein buffer system: formed of proteinic acid and Na proteinate Plasma proteins. Hemoglobin  Body defense against changes in H+ concentration Respiratory system acts within mins (1-15mins). The respiratory system controls the pH by controlling PCO2 of the arterial blood through changes in the rate of ventilation. Decrease pH (↑H+) → stimulates respiratory centre → increase rate of ventilation → washing out of CO2 → increase pH back to normal. increase pH (↓ H+) → inhibits respiratory centre → decrease rate of ventilation → increase PCO2 → decrease pH back to normal. The efficiency of Respiratory Control of H + Concentration is 50% to 75% effective because respiratory control cannot return the H + concentration all the way back to normal when a disturbance outside the respiratory system has altered the pH.  Body defense against changes in H+ concentration Kidney Requires minutes to several days. Most powerful The kidneys control acid–base balance by excreting acidic or alkaline urine. Excreting acidic urine reduces the amount of acid in extracellular fluid, whereas excreting alkaline urine removes alkali from the extracellular fluid. In acidosis (low pH, high H+), the kidneys secrete additional H + and reabsorb all the filtered HCO 3 − and produce new HCO 3 − →reduces H + concentration in extracellular fluid back toward normal. In alkalosis (high pH, low H+), the kidneys do not secrete H + and inhibit reabsorption of HCO3 − → excretion of HCO3 → increases H + concentration in extracellular fluid back toward normal.  Acid- base disorders Metabolic Respiratory Metabolic Metabolic Respiratory Respiratory Acidosis Alkalosis Acidosis Alkalosis  Acid- base disorders Respiratory Acidosis Increased PCO 2 Causes: Decreased ventilation → increased PCO 2 → increase H+ concentration → acidosis. as in 1. Voluntary breath apnea. 2. Damage to the respiratory centre. 3. Obstructive lung disease, asthma, emphysema. 4. Any factors interfere with gas exchange like Lung fibrosis.  Acid- base disorders Respiratory Alkalosis Decreased Causes: PCO 2 increased ventilation → washout of CO2 from the lung → decrease H+ concentration → alkalosis. as in 1. Voluntary hyperventilation. 2. Physiological: high altitude. 3. Pathological: psychoneurosis that causes hyperventilation. 4. Pulmonary embolism leads to hyperventilation. Compensation of respiratory acidosis and respiratory alkalosis: 1. the buffers of the body fluids. 2. the kidneys, which require several days to compensate for the disorder.  Acid- base disorders Metabolic Acidosis Decreased HCO3 Causes: Decreased Extracellular Fluid HCO 3 Concentration 1. failure of the kidneys to excrete metabolic acids normally formed in the body 2. formation of excess quantities of metabolic acids in the body. 3. addition of metabolic acids to the body by ingestion or infusion of acids 4. loss of base (alkali) from the body fluids  Acid- base disorders Metabolic Acidosis Decreased HCO3- Specific condition causing metabolic acidosis 1. Diarrhea: due to loss of excess HCO3 in stool. 2. Renal failure (uremia). 3. Diabetes mellitus: Fat are used as a source of energy , Fat metabolism → ketone bodies (acetone, acetacetic acid, and B- hydroxybutyric acid) → metabolic acidosis. 4. Carbonic anhydrase inhibitors(acetazolamide diuretic): prevent reabsorption of HCO3- → alkaline urine.  Acid- base disorders Metabolic Alkalosis Increased HCO3- Causes: 1. All diuretics except carbonic anhydrase inhibitors (acetazolamide). 2. Excessive ingestion of alkaline drugs: for treatment of gastritis and peptic ulcer. 3. Vomiting : loss of HCl. 4. Excess aldosterone secretion: stimulation of Na+ reabsorption is coupled with H+ secretion → alkalosis. Compensation of metabolic acidosis and metabolic alkalosis: 1. the buffers of the body fluids. 2. Respiratory system 3. the kidneys. Diagnosis of simple acid-base disorder  Acid- base disorders Diagnosis of simple acid-base disorder 1- Measure pH Low pH = acidosis High pH = alkalosis 2- Measure plasma PCO2 and HCO3- concentration Normal PCO2 =40mmHg , HCO3- = 24mEq/L Respiratory Respiratory Metabolic acidosis Metabolic alkalosis acidosis alkalosis Low pH. High pH. Low pH. High pH. Decreased HCO3- Increased HCO3- Increased PCO2 Decreased PCO2 due to Increased PCO2 due to Decreased PCO2 Increased HCO3- respiratory respiratory due to renal Decreased HCO3- due compensation compensation compensation to renal compensation (Hyperventilation) (Hypoventilation)  Review question A 45-year-old woman presents to the emergency department with weakness, dizziness, and muscle cramps. She reports frequent vomiting over the past three days due to food poisoning. Laboratory tests reveal: pH: 7.50 HCO₃⁻: 34 mEq/L pCO₂: 47 mmHg Which of the following is the most likely cause of this case? A. Metabolic acidosis B. Metabolic alkalosis C. Respiratory acidosis  Summary  Define pH and how its calculated & its normal range that is compatible with life.  State different regulatory mechanisms for acid-base balance.  Outline different acid base disorders.  State role of respiratory compensation in cases of metabolic acidosis & alkalosis.  List the causes underlying respiratory acidosis and alkalosis.  Describe the role of renal compensations for respiratory acidosis and alkalosis.  Outline how to diagnose a case of respiratory acidosis and respiratory alkalosis.  Learning Resources  Hall JE, Hall ME. Guyton and Hall textbook of medical physiology e-Book. 14ed, Elsevier Health Sciences; 2021. Chapter 31, https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0-B9780323 59712800031X  https://exchange.scholarrx.com/brick/respiratory-acidosis-and-alkalosis  Power-point presentation in the Moodle. www.gmu.ac.ae COLLEGE OF Thank you