The regulation of hydrogen ions is just like the regulation of other ions. For the acid base homeostasis, the production and the removal of the hydrogen ions should be in balance. The kidneys play an important role in the regulation of hydrogen ions. Our body has multiple buffering mechanisms involving blood cells and lungs to main the hydrogen ion concentration in intracellular and extracellular fluid. All the enzymes in our body needs a strict control of pH to work properly so any change in pH greatly affects the cell functions.
Hydrogen ion is a free proton which is released from hydrogen atom. Acids have the ability to release the hydrogen ions in solutions. For example, HCL gives hydrogen ion and chloride ions when ionized in the water. Base is an ion that accepts the proton. For example HCO3 can combine with Hydrogen ion to form H2CO3. The proteins in our body acts as a base. Hemoglobin protein is the most important base in our body. The concentration of Hydrogen ions is tightly regulated around a normal value of 0.00004mEq/L.
The normal arterial blood pH is 7.4 whereas the pH of venous blood is 7.35. The pH of venous blood is low because the tissue releases extra amount of carbon dioxide to form H2CO3 in fluids. The pH of intracellular environment is low as compared to plasma because metabolism of the cells produces acids. Decreased blood supply to the tissues cause acid accumulation in the tissues and decrease intracellular pH.
Defenses against pH changes:
There are three main systems that regulate the pH balance.
- Chemical acid base buffer system of body fluids.
- Respiratory system
- The kidneys
In the chemical acid base buffer system, the hydrogen ions immediately combine with acids or bases to prevent changes in pH. This system doesn’t eliminate or add the hydrogen ions but keep them tied up until the normal balance is established. The respiratory system removes the CO2 and therefore H2CO3 from the extracellular fluids and the kidneys readjust the extracellular pH by excreting either acidic or alkaline urine. The response of the kidneys is usually slow as compared to the other defenses.
Proteins are important intracellular buffers:
Proteins are very important part of buffer system because of their high concentration. This buffer system needs several hours to effectively prevent the changes in the pH of extracellular. There is a slight amount of diffusion of hydrogen ions and HCO3 through the cell membrane. This may take several hours to reach equilibrium except in red blood cells.
Respiration Regulation of Acid Base Balance:
It is the second line of defense against acid base disturbance. Hyperventilation removes the CO2 from extracellular fluid which reduces the hydrogen ion concentration. Carbon dioxide is continually excreted from the cells which diffuses into the interstitial fluids and blood. From blood it transported into the lungs.
Renal production of acid base balance.
The kidneys regulate the acid base balance by excreting acidic or a basic urine. If the amount of acid in extracellular fluid increases, the kidney excretes an acidic urine. The reabsorption of HCO3 is occurs in the proximal tubule. Fixed Hydrogen ions are produced from the catabolism of proteins and can be excreted in the form of titratable acids and NH4.