Chapter 10: Final Examination

Chapter 10. Final Examination

Nitrous oxide (N₂O) is a lipid soluble anesthetic gas. A 14-year-old girl was sedated with N₂O to relieve pain during an intra-articular injection. The N₂O concentration in her blood quickly equaled, but never exceeded, the alveolar N₂O concentration. What membrane transport mechanism is most likely to account for the uptake of N₂O from inspired air into her blood?

A Antiport with CO₂

B Cotransport with O₂

C Endocytosis

D Primary active transport

E Simple diffusion

E. Small lipid soluble gas molecules such as N₂O readily diffuse through biological membranes. The inability to increase blood N₂O concentration above that in the lung alveolus is consistent with simple diffusion and the absence of any primary or secondary active transport process.

Nitrous oxide (N₂O) is a lipid soluble anesthetic gas. A 14-year-old girl was sedated with N₂O to relieve pain during an intra-articular injection. The N₂O concentration in her blood quickly equaled, but never exceeded, the alveolar N₂O concentration. The rate of N₂O uptake would increase if the:

A body temperature decreased

B diffusion distance from alveolus to blood increased

C inspired N₂O concentration increased

D rate of alveolar ventilation decreased

E rate of pulmonary blood flow decreased

C. According to Fick's law of diffusion, the rate of simple diffusion of N₂O is proportional to its membrane permeability and to its concentration gradient. The N₂O concentration gradient is increased if the inspired N₂O concentration is increased, but is decreased if alveolar ventilation or pulmonary blood flow are decreased. The rate of simple diffusion is slower at colder temperatures or if the diffusion distance is increased.

What change in ion channel activity is most responsible for the rapid depolarization of the neuronal membrane potential at position 2 (shown in the above figure)?

A Opening of K⁺ channels

B Closure of K⁺ channels

C Inactivation of K⁺ channels

D Opening of Na⁺ channels