![Measuring acidity
• Concentration of H+ ions in solution - [H+]
• Actual numbers not helpful!
• Range 0.1 - 0.00000000000001 M
• Taking negative base10 logarithm gets rid of zeroes
• Number known as pH & gives range of 0 - 14](https://image.slidesharecdn.com/acidbaseinpractice-221212035731-936d73c7/85/acid_base-in-Practice-ppt-6-320.jpg)
![Measuring acidity
• For example - water has [H+] = 0.0000001 M
• - log10 (0.0000001) = 7 (neutral pH)
• Acids have pH values less than 7
• Bases have pH values greater than 7](https://image.slidesharecdn.com/acidbaseinpractice-221212035731-936d73c7/85/acid_base-in-Practice-ppt-7-320.jpg)
![Why is maintaining pH important?
• Changes in acidity profoundly affect proteins
• Protein function relies entirely on their shape
• If pH changes, so does the shape of proteins
• Narrow limits of normal pH 7.35 - 7.45
• Remember a 1 unit pH change = 10 fold [H+] change](https://image.slidesharecdn.com/acidbaseinpractice-221212035731-936d73c7/85/acid_base-in-Practice-ppt-9-320.jpg)
acid_base in Practice.ppt
- 1. Introduction to Physiology Acid & Base
- 2. Acid & Base • What are acids and bases ( for non-chemists) • Why is keeping acid / base balance important • How does the body manage this balance • How can we look at what is going on in the body?
- 3. What are acids? • Acids donate protons (H+ ions) Eg. Hydrochloric acid contains 1 hydrogen atom and 1 chlorine atom In solution HCl splits into ions (charged particles) HCl H+ + Cl- HCl is a strong acid, and almost all dissociates into H+ and Cl-
- 4. What are bases? • Bases can accept protons (H+ ions) Eg. sodium hydroxide (NaOH) splits in solution to form Na+ and OH- NaOH ↔ Na+ + OH- OH- ions can accept protons (H+) to form water OH- + H+ ↔ H20
- 5. Strong vs. weak • In chemistry, we meet many strong acids & bases • In biology, most acids and bases are much weaker • Strong acids dissociate almost completely • Weaker acids do not… • CH3-COOH ↔ CH3COO- + H+ (cf. HCl ↔ H+ + Cl-)
- 6. Measuring acidity • Concentration of H+ ions in solution - [H+] • Actual numbers not helpful! • Range 0.1 - 0.00000000000001 M • Taking negative base10 logarithm gets rid of zeroes • Number known as pH & gives range of 0 - 14
- 7. Measuring acidity • For example - water has [H+] = 0.0000001 M • - log10 (0.0000001) = 7 (neutral pH) • Acids have pH values less than 7 • Bases have pH values greater than 7
- 8. • Acids have pH values less than 7 • Bases have pH values greater than 7
- 9. Why is maintaining pH important? • Changes in acidity profoundly affect proteins • Protein function relies entirely on their shape • If pH changes, so does the shape of proteins • Narrow limits of normal pH 7.35 - 7.45 • Remember a 1 unit pH change = 10 fold [H+] change
- 10. What disturbs the body’s pH? • CO2 production (respiration) – CO2 is a weak acid when in solution – Produced when glucose metabolised via glycolysis – Occurs in all cells, all the time
- 11. What disturbs the body’s pH? • Metabolic acids – Under strenuous exercise, anaerobic metabolism occurs – Lactic acid produced – Also commonly accumulates in shock (poor perfusion state) – Protein breakdown produces acids
- 12. How does the body prevent pH changes? 1. Buffers – Buffers allow acid to be ‘stored’ temporarily – Bicarbonate / CO2 is the most important: H+ + HCO3 - ↔ CO2 + H2O – Excess acid (H+) drives the reaction to the right – CO2 produced can be excreted by the lungs
- 13. How does the body prevent pH changes? Buffers – Other buffer systems: – Proteins - can reversibly accept H+ ions – Intracellular phosphate - HPO4 2- + H+ ↔ H2PO4 -
- 14. How does the body prevent pH changes? • Short term buffering requires a final solution • Respiratory acid (CO2) is excreted by the lungs • Metabolic acids are excreted by the kidneys
- 15. Acid & Base in practice • Within the body, excess acid produces an acidosis • Excess base produces an alkalosis • Acidosis & alkalosis can be produced from either a respiratory or metabolic source
- 16. Acid & Base in practice • CO2 too high = respiratory acidosis • CO2 too low = respiratory alkalosis • Metabolic acids too high = metabolic acidosis • Metabolic acids too low = metabolic alkalosis
- 17. Acid & Base in practice - Blood gases • Arterial blood gas analysis reveals oxygenation & acid base status of the body • The analysis usually includes: pH PaO2 PaCO2 BE Pa = Partial arterial pressure of O2 or CO2
- 18. Acid & Base in practice - Blood gases Some normal values – pH 7.35 – 7.45 (no units) – PaO2 10 – 13 KPa – PaCO2 4 – 4.5 KPa – BE -2 - +2 mmol/l -ve = acidosis, +ve=alkalosis
- 19. Blood gases 1 - Oxygenation • To interpret PaO2 result, you need to know what oxygen concentration the patient is breathing – PaO2 9 (10 – 13 KPa) – pH (7.35 – 7.45) – PaCO2 (4 – 4.5 KPa) – BE (-2 - +2 mmol/l) • %age O2 is often given as Fractional inspired O2 • eg. 21% O2 = FiO2 0.21
- 20. Blood gases 2 - Acid & Base This patient has severe sepsis – PaO2 10 (10 – 13 KPa) – pH 7.0 (7.35 – 7.45) low pH= acid – PaCO2 4.2 (4 – 4.5 KPa) high CO2= acid – BE -19 (-2 - +2 mmol/l) -ve = acid • First look at pH - it tells you what the overall problem is • Next look at the PaCO2 - it tells you what the respiratory side of things is doing • Then look at the base excess (BE) which tells you about the metabolic component • Here there is a metabolic acidosis (eg. severe sepsis)
- 21. Blood gases 3 - Compensation • This patient has diabetic ketoacidosis – PaO2 10 (10 – 13 KPa) – pH 7.3 (7.35 – 7.45) low pH= acid – PaCO2 2.1 (4 – 4.5 KPa) high CO2= acid – BE -19 (-2 - +2 mmol/l) -ve = acid • The body NEVER over compensates for disturbances • Here there is a respiratory alkalosis trying to compensate for a metabolic acidosis
- 22. Blood gases 4 - Compensation • The lungs can compensate for disturbances QUICKLY • The kidneys can only compensate for metabolic disturbances SLOWLY BUT… • When things go wrong in the body, a metabolic acidosis can build up FAST
- 23. Acid / Base • Don’t worry if this is clear as mud! • More blood gas work in group session