Identify and understand the buffer systems in the body Buffer Systems in the Body The buffer systems in the human body are extremely efficient, and different systems work at different rates. It takes only seconds for the chemical buffers in the blood to make adjustments to pH. The respiratory tract can adjust the blood pH upward in minutes by exhaling CO 2 from the body. The renal system can also adjust blood pH through the excretion of hydrogen ions (H + ) and the conservation of bicarbonate, but this process takes hours to days to have an effect. The buffer systems functioning in blood plasma include plasma proteins, phosphate, and bicarbonate and carbonic acid buffers. The kidneys help control acid-base balance by excreting hydrogen ions and generating bicarbonate that helps maintain blood plasma pH within a normal range. Protein buffer systems work predominantly inside cells. Phosphate Buffer Phosphates are found in the blood in two forms: sodium dihydrogen phosphate (Na 2 H 2 PO 4 − ), which is a weak acid, and sodium monohydrogen phosphate (Na 2 HPO 4 2 - ), which is a weak base. When Na 2 HPO 4 2 - comes into contact with a strong acid, such as HCl, the base picks up a second hydrogen ion to form the weak acid Na 2 H 2 PO 4 − and sodium chloride, NaCl. When Na 2 HPO 4 2 − (the weak acid) comes into contact with a strong base, such as sodium hydroxide (NaOH), the weak acid reverts back to the weak base and produces water. Acids and bases are still present, but they hold onto the ions. HCl + Na 2 HPO 4 → NaH 2 PO 4 + NaCl (strong acid) + (weak base) → (weak acid) + (salt) NaOH + NaH 2 PO 4 → Na 2 HPO 4 + H 2 O (strong base) + (weak acid) → (weak base) + (water) Bicarbonate-Carbonic Acid Buffer Maintaining a constant blood pH is critical for the proper functioning of our body. The buffer that maintains the pH of human blood involves a carbonic acid (H 2 CO 3 ) - bicarbonate ion (HCO 3 - ) When any acidic substance enters the bloodstream, the bicarbonate ions neutralize the hydronium ions forming carbonic acid and water. Carbonic acid is already a component of the buffering system of blood. Thus hydronium ions are removed, preventing the pH of blood from becoming acidic. On the other hand, when a basic substance enters the bloodstream, carbonic acid reacts with the hydroxide ions producing bicarbonate ions and water. Bicarbonate ions are already a component of the buffer. In this manner, the hydroxide ions are removed from blood, preventing the pH of blood from becoming basic. As depicted below, in the process of neutralizing hydronium ions or hydroxide ions, the relative concentrations of carbonic acid (H 2 CO 3 ) and bicarbonate ions (HCO 3 - ) fluctuate in the bloodstream. But this slight change in the concentrations of the two components of the buffering system doesn’t have any adverse effect; the critical thing is that this buffering mechanism prevents the blood from becoming acidic or basic, which can be detrimental. The pH of blood is maintained at ~ 7.4 by the carbonic acid–bicarbonate ion buffering system. Disorders of Acid-Base Balance Respiratory Acidosis: Primary Carbonic Acid/CO 2 Excess Respiratory acidosis occurs when the blood is overly acidic due to an excess of carbonic acid, resulting from too much CO 2 in the blood. Respiratory acidosis can result from anything that interferes with respiration, such as pneumonia, emphysema, or congestive heart failure. Respiratory Alkalosis: Primary Carbonic Acid/CO 2 Deficiency Respiratory alkalosis occurs when the blood is overly alkaline due to a deficiency in carbonic acid and CO 2 levels in the blood. This condition usually occurs when too much CO 2 is exhaled from the lungs, as occurs in hyperventilation, which is breathing that is deeper or more frequent than normal. An elevated respiratory rate leading to hyperventilation can be due to extreme emotional upset or fear, fever, infections, hypoxia, or abnormally high levels of catecholamines, such as epinephrine and norepinephrine. Surprisingly, aspirin overdose—salicylate toxicity—can result in respiratory alkalosis as the body tries to compensate for initial acidosis. Respiratory Compensation Respiratory compensation for metabolic acidosis increases the respiratory rate to drive off CO 2 and readjust the bicarbonate to carbonic acid ratio to the 20:1 level. This adjustment can occur within minutes. Respiratory compensation for metabolic alkalosis is not as adept as its compensation for acidosis. The normal response of the respiratory system to elevated pH is to increase the amount of CO 2 in the blood by decreasing the respiratory rate to conserve CO 2 . There is a limit to the decrease in respiration, however, that the body can tolerate. Hence, the respiratory route is less efficient at compensating for metabolic alkalosis than for acidosis. Key Takeaway