Carbon Dioxide transport and blood buffers

Carbon Dioxide transport and blood buffers

1. Carbon Dioxide in blood

   • Dissolved
     • Like Dissolved gas in water.
   • Bicarbonate
     • Bicarbonate is formed in blood in the following reactions, water and carbon dioxide is combined to form hydrogen bicarbonate and it dissociates to hydrogen ion and Hco3. 1st Reaction is very slow in plasma and fast in RBC contains enzyme carbonic anhydrase. 2nd reaction does not need any factors. This case a rise in intracellular concentrations of HCo3 and H and HCo3 is forced to leave with chloride shift via membrane transported Increased osmolar content cause water to enter RBC.
   • Carbamino Compounds
     • Formed by the combination of Carbon dioxide with amines in the blood proteins. Like Haemaglobin

2. Haldane Effect

   • Deoxygenated blood can carry more carbondioxide than oxygenated blood. Haldane effect, unloading of the O2 in tissues help blood carry more Co2 while loading of O2 in the lungs help blood to give CO2 to lungs.
   • Amount of Co2
     • Arterial blood consists of Pco2 of 40mmHg contains 22mM of Co2 90% Hco3 5% dissolved 5% carbamino compounds Venous blood consists of Pco2 of 47mmHg and 23.9mM of Co3 Difference is around 1.9mM. 60% from HCo3 30% carbamino compounds 10% dissolved.

3. Blood Co2 Equilibrium Curve

   • Carbon dioxide curve is more linear than oxygen curve Blood carries more Co2 than o2

4. pH

   • Measure of acidity. Check chemistry: pH= - log(H+) Normal pH 7.4
   • Weak Acids
     • Carboxyl groups are weak acids The stronger the acid the Higher the KA Ka= [H+][A-]/[HA]
     • Henderson-Hasselbalch
       • pH = pKa + log10 ( [a-]/[HA])

5. Blood Buffering System

   • Body acid-base balance
     • Balance is maintained by buffering, respiratory regulation of pH and renal regulation of pH.
     • Carbonic acid-bicarbonate system
       • Co2 and bicarbonate can be regulated by the body. I.e Co2 from lungs and bicarbonate in kidneys. It's present in high concentrations (24 mM)
     • Phosphates
       • pKa of 6.8 Closer to plasma pH but it consists of very little inorganic phosphates in blood (0.8 to 1.6mM)
     • Protein Buffering
       • Major buffer. Buffer by accept/release a protein by a side chain of an amino acid residue usually histidine. Accept/release a proton by terminal amino or carbonate side groups.
     • Haemoglobin
       • 6X buffering capacity of plasma proteins. Present in high concentrations and rich in histidine residues.
   • Isohydric Principle
     • When a solution contains more than one buffer all buffer pairs are in equilibrium with same protons. Any changes will balance all buffer systems.
   • Respiratory Regulation
     • Hyperventilation PCo2 can be reduced from 40 to mmHg Hypoventilation limited by hypoxia.
   • Renal Regulation
     • Bicarbonate is important but limited. Kidneys will generate more/new bicarbonate. To lower pH, kidney will generate more bicarbonate

6. Acid-Base Disorders

   • Acidocis: Plasma pH less than 7.35 Alkalosis: Plasma pH greater than 7.45
   • Respiratory Acidosis
     • low pH and increased pCO2 Caused by failure to eliminate Co2 Due to inadequate ventilation or inadequate gas exchange. Renal compensation will over several days if sustained Therefore respiratory acidosis is commonly divided into acute and chronic phase
   • Respiratory alkalosis
     • High pH and low PCo2 Caused by hyperventilation
   • Metabolic Acidosis
     • low pH and low plasma bicarbonate Caused by addition of non-volatile acid to body. like diabetic ketoacidosis or ingestion of ammonium chloride. Or renal flailure.
   • Metabolic Alkalosis
     • High pH and High plasma bicarbonate Caused by addition of non-volatile alkali Or loss of non-volatile acid (vomit)