Question

Isohydric transport of carbon dioxide from tissues to lung refers to A. free \(\mathrm{CO}_{2}\) dissolved in plasma. B. \(\mathrm{HCO}_{3}^{-}\) in plasma. C. carbamino compounds. D. the Bohr effect. E. the presence of carbonic anhydrase in plasma.

Short answer

Answer: B. HCO₃⁻ in plasma

Step-by-step solution

Understand the concept of isohydric transport of carbon dioxide

Isohydric transport of carbon dioxide refers to the way in which carbon dioxide is transported in the blood, maintaining a constant pH value. This is important for maintaining the optimal pH level in the body.

Analyze the options given

We will go through each option and check if it is a correct definition for isohydric transport of carbon dioxide. A. The free \(\mathrm{CO}_{2}\) dissolved in plasma plays a role in the transport of carbon dioxide, but it is not sufficient to maintain the pH constant in blood. B. \(\mathrm{HCO}_{3}^{-}\) in plasma is the correct option. When the blood reaches tissues, high levels of \(\mathrm{CO}_{2}\) result in \(\mathrm{CO}_{2}\) combining with \(\mathrm{H}_{2}\mathrm{O}\) (water) to form carbonic acid (\(\mathrm{H}_{2}\mathrm{CO}_{3}\)), which dissociates into \(\mathrm{H}^{+}\) and \(\mathrm{HCO}_{3}^{-}\). The \(\mathrm{H}^{+}\) ion combines with hemoglobin, and \(\mathrm{HCO}_{3}^{-}\) is released into the plasma. This process helps maintain the pH constant as \(\mathrm{CO}_{2}\) is transported from the tissues to the lungs. C. Carbamino compounds are formed when \(\mathrm{CO}_{2}\) binds to the amino groups of proteins (mainly hemoglobin), but they are not sufficient to maintain the pH constant in blood. D. The Bohr effect refers to the effect of \(\mathrm{CO}_{2}\) and H+ concentration on the affinity of hemoglobin for oxygen, which contributes to oxygen release at the tissue level but is not directly involved in isohydric transport of carbon dioxide. E. The presence of carbonic anhydrase in plasma refers to the enzyme that catalyzes the reversible conversion of carbon dioxide and water to carbonic acid. However, it does not define isohydric transport.

Conclusion

Therefore, the correct answer for the isohydric transport of carbon dioxide from tissues to lung is B. \(\mathrm{HCO}_{3}^{-}\) in plasma.