Dear Sudip Saha,

As often a question like yours can be answered in a simple or more complex way.

The simple version is that the most important buffer for maintaining acid-base balance in the blood is the carbonic-acid-bicarbonate buffer. In other words the well-known equilibrium between CO2 and carbonic acid (H2CO3). It comes down to:

H+(aq) + HCO3-(aq) ↔ H2CO3 (aq) ↔ H2O (l) + CO2 (g)

Other buffers play a role too in regulating the pH of the blood. Think about buffer systems like the phosphate buffer that consists of phosphoric acid (H3PO4) in equilibrium with dihydrogen phosphate ion (H2PO4-) and H+. The phosphate buffer is believed to play a less prominent role in the blood, because H3PO4 and H2PO4- are found in low concentrations in the blood. Proteins play an important role in the body when it comes to buffer function, in the blood this is obviously Hemoglobin that also acts as a pH buffer in the blood. Hemoglobin protein can reversibly bind either H+ (to the protein) or O2 (to the Fe of the heme group).

For a more complex and obviously more complete description see for example:

https://www.khanacademy.org/test-prep/mcat/chemical-processes/acid-base-equilibria/a/chemistry-of-buffers-and-buffers-in-blood

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/bicarbo.htm

http://library.open.oregonstate.edu/aandp/chapter/26-4-acid-base-balance/

Hope this answers your question.

Please have a look at these useful links.

https://sciencing.com/ph-buffers-work-5007354.html

Good question.. following

Perhaps the most basic answer to your question is that a buffer is a mixture that contains a weak acid and its conjugate base. The carbonic acid - bicarbonate system has already mentioned. Regulation of pH is described by the Henderson-Hasselbach equation ( pH = pKa + log(10) ([conjugate base]/[weak acid]) ). To add to this information, the two primary organ systems for regulation of the pH in human blood are the kidney and the lung. The lung expels carbon dioxide and the kidney reabsorbs nearly all filtered bicarbonate. In addition, the kidney may excrete other acids. Note that carbonic acid is the dissolved form of carbon dioxide (H20 + CO2 -> H2CO3, bicarbonate is HC03-, and carbonate is C03--. Little or not carbonate is present at the pH of in blood, as described above. pKa values for carbonic acid are something like 2.3 and 7.4. The system might involve two Henderson - Hasselbach equations that need a simultaneous solution. It helps that the carbonate concentration is small.)

In short When H+ is added to the blood as a result of metabolic processes, the amount of HCO3- (relative to the amount of CO2) decreases; however, the amount of the change is tiny compared to the amount of HCO3- present in the blood. This optimal buffering occurs when the pH is within approximately 1 pH unit from the pK value for the buffering system, i.e., when the pH is between 5.1 and 7.1.