Ultrasound has what effect on membrane permeability?

• A. No change
• B. Alternating
• C. Decrease
• D. Increase

Answer: (D)

The main concept being tested is how ultrasound interacts with cellular membranes to change their permeability. When tissue is exposed to ultrasound, the energy causes mechanical effects in the fluid and around membranes. Cavitation and the resulting microstreaming create transient disruptions in the lipid bilayer, forming short-lived pores—a phenomenon known as sonoporation. These temporary pores allow ions and small molecules to cross the membrane more readily, so permeability increases for a period after exposure. That’s why the correct answer is that ultrasound increases membrane permeability. It doesn’t imply there’s no change, alternating permeability, or a decrease, all of which wouldn’t match the mechanical disruption that creates those transient pores.