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Carbon dioxide, a by-product of cellular respiration, is dissolved in the blood, where it is taken up by red blood cells and converted to carbonic acid by carbonic anhydrase. Most of the carbonic acid then dissociates to bicarbonate and hydrogen ions.
When the tissues release carbon dioxide into the bloodstream, around 10% is dissolved into the plasma. The rest of the carbon dioxide is carried either directly or indirectly by hemoglobin. Approximately 10% of the carbon dioxide carried by hemoglobin is in the form of carbaminohemoglobin.
Carbon dioxide (CO 2) is produced in tissues as a byproduct of normal aerobic metabolism. It dissolves in the solution of blood plasma and into red blood cells (RBC), where carbonic anhydrase catalyzes its hydration to carbonic acid (H 2 CO 3). Carbonic acid then spontaneously dissociates to form bicarbonate Ions (HCO 3 −) and a hydrogen ion ...
CO 2 is excreted from the cell via diffusion into the blood stream, where it is transported in three ways: Up to 7% is dissolved in its molecular form in blood plasma. About 70-80% is converted into hydrocarbonate ions, The remainder binds with haemoglobin in red blood cells, is carried to the lungs, and exhaled. [11]
Histidine residues in hemoglobin can accept protons and act as buffers.Deoxygenated hemoglobin is a better proton acceptor than the oxygenated form. [1]In red blood cells, the enzyme carbonic anhydrase catalyzes the conversion of dissolved carbon dioxide to carbonic acid, which rapidly dissociates to bicarbonate and a free proton:
One of the main roles of extracellular fluid is to facilitate the exchange of molecular oxygen from blood to tissue cells and for carbon dioxide, CO 2, produced in cell mitochondria, back to the blood. Since carbon dioxide is about 20 times more soluble in water than oxygen, it can relatively easily diffuse in the aqueous fluid between cells ...
Hence, blood with high carbon dioxide levels is also lower in pH (more acidic). 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]
The dissolved gas in the alveolar blood is transported to the body tissues by the blood circulation. There it diffuses through the cell membranes and into the tissues, where it may eventually reach equilibrium. The greater the blood supply to a tissue, the faster it will reach equilibrium with gas at the new partial pressure. [3] [18]