Anatomy Physiology

In this article, I will discuss how the pH of the blood is regulated in addition to the mechanisms that stand this regulation.  The pH of the blood is tightly regulated and is kept within a narrow range that does not change even with the addition of substantial amount of acid or base to the body. 

The main mechanism for keeping the pH of the blood constant is called buffers.  Buffers are by definition solutions of weak acid and its conjugate base.  They function usually by reacting with the added acid through the conjugate base which neutralizes and gets rid of the excess acid.  It also reacts with the added base through the weak acid.  Thus neutralizing it and getting rid of the excess base that was added to the solution.  This maintains the pH and does not change it. 

In the body there are two important buffers with a third one that is less significant than the other two buffers.  They will be discussed sequentially one after the other.  The main extracellular buffer is the bicarobate / carbonic acid buffer.  It is the main buffer in the blood due to the fact that the concentration of of the bicarbonate ions in the extracellular space is higher or more significant than its concentration inside the cell.

Carbonic anhydrase is an enzyme which catalyzes the formation of water and carbon dioxide from carbonic acid.  It stimulates the secretion of bicarbonate ions in the urine while conserving protons or acids.  Its inhibition is important in the medical condition that is called glaucoma in which the amount of water produced in the eye ball is lowered due to the inhibition of the carbonic anhydrase inhibition. 

The other buffer that is discussed here is the phosphate buffer.  This buffer is only important inside the cell.  This is so due to the fact that the phosphate ions concentration outside the cell is much lower than its concentration inside the cell.  In addition to phosphate ions that function buffers, proteins also can function as buffers due to the presence of charged residues of amino acids in its structure.  They are important also inside the cell.  Especially important is the hemoglobin buffer.

The third and less important buffer than the others that were discussed so far is the ammonia buffer.  Ammonia is a nitrogenous base that is generated from the metabolism of amino acids in which it is deaminated expelling an ammonia molecule.  Ammonia is a toxic compound which is converted in the liver to the less toxic compound of urea.

In one pathology of the liver, in which it is unable to get rid or detoxify the ammonia base there is accumulation of ammonia in the body fluids.  Thus causing toxicity.  This is especially manifested in the medical condition and which is called hepatic encephalopathy which affects the brain tissue. 

Other than the buffers that were discussed so far two important organs in the body function also by regulating the amount of acid and base in the blood.  They work together and synchronously to adjust the pH of the blood.  These two organs are the two kidneys and the lungs.

The kidney usually functions by by filtering the blood from its waste products.  Many compounds are filtered in the glomerulus of the nephron such as amino acids which are reabsorbed in the most part in the kidney tubules.  In addition acid in the form of protons as well as bases in the form of bicarbonate are also filtered in the glomeruli. 

The amount of acid or base that is filtered is dependent on the pH of the blood.  In renal failure the urine is usually basic due to the conservation of acid in the kidney.  Passing acidic urine signifies an acidic blood with metabolic acidosis.

The other organ which functions also by regulating the pH of the blood is the lungs.  Carbonic acid is converted in the blood to water and carbon dioxide.  Carbon dioxide is exhaled in the lungs in a usual process.  Acidic blood usually stimulates the rate of pulmonary respiration.  Thus causing exhalation of increased amount of CO2.  A high or basic pH on the other hand depresses the pulmonary respiration rate.  Thus causing retention of CO2 in the blood.  This subsequently contribute to lowering of the pH of the blood by increasing the proton concentration.