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The bicarbonate buffer system is an acid-base homeostatic mechanism involving the balance of carbonic acid (H 2 CO 3), bicarbonate ion (HCO − 3 ), and carbon dioxide (CO 2 ) in order to maintain pH in the blood and duodenum , among other tissues, to support proper metabolic function. [ 1 ]
Albumin, carries thyroid hormones and other hormones, particularly fat soluble ones, fatty acids to the liver, unconjugated bilirubin, many drugs and Ca 2+ Ceruloplasmin, carries copper; Transcortin, carries cortisol, aldosterone and progesterone; Haptoglobin, carries free hemoglobin released from erythrocytes
The bicarbonate buffer, consisting of a mixture of carbonic acid (H 2 CO 3) and a bicarbonate (HCO − 3) salt in solution, is the most abundant buffer in the extracellular fluid, and it is also the buffer whose acid-to-base ratio can be changed very easily and rapidly. [15]
Hemoglobin can bind protons and carbon dioxide, which causes a conformational change in the protein and facilitates the release of oxygen. Protons bind at various places on the protein, while carbon dioxide binds at the α-amino group. [71] Carbon dioxide binds to hemoglobin and forms carbaminohemoglobin. [72]
Hemoglobin's oxygen binding affinity (see oxygen–haemoglobin dissociation curve) is inversely related both to acidity and to the concentration of carbon dioxide. [1] That is, the Bohr effect refers to the shift in the oxygen dissociation curve caused by changes in the concentration of carbon dioxide or the pH of the environment.
This releases hydrogen ions from hemoglobin, increases free H + concentration within RBCs, and shifts the equilibrium towards CO 2 and water formation from bicarbonate. The subsequent decrease in intracellular bicarbonate concentration reverses chloride-bicarbonate exchange: bicarbonate moves into the cell in exchange for chloride moving out.
The bicarbonate ion (hydrogencarbonate ion) is an anion with the empirical formula HCO − 3 and a molecular mass of 61.01 daltons; it consists of one central carbon atom surrounded by three oxygen atoms in a trigonal planar arrangement, with a hydrogen atom attached to one of the oxygens.
The average red blood cell contains 250 million hemoglobin molecules. [7] Hemoglobin contains a globin protein unit with four prosthetic heme groups (hence the name heme-o-globin); each heme is capable of reversibly binding with one gaseous molecule (oxygen, carbon monoxide, cyanide, etc.), [8] therefore a typical red blood cell may carry up to one billion gas molecules.