Describe absorption in the oral cavity.

• A. Small surface area; highly vascularized; thin lining; goes directly to blood; lacks first-pass; must be in contact with mucosa
• B. Large surface area; thick lining; goes via liver
• C. Absorption occurs in stomach
• D. Only via endocytosis

Answer: (A)

Absorption in the oral cavity happens across the oral mucosa, especially via the sublingual and buccal routes. The mucosa is thin and well supplied with blood, so drugs can diffuse directly into the capillaries and reach systemic circulation quickly. Because this pathway bypasses the liver, there’s little or no first-pass metabolism for drugs absorbed this way. For efficient uptake, the drug needs to stay in contact with the mucosa long enough to diffuse—saliva flow or swallowing can reduce absorption if contact is lost.

That’s why the best description emphasizes a small surface area relative to the GI tract but a very vascular, thin barrier, direct entry into blood, lack of first-pass metabolism, and the necessity of remaining in contact with the mucosa.

The other ideas don’t fit the oral-cavity route as well: a large surface area with a thick lining implies absorption through the GI tract with liver metabolism; absorption in the stomach isn’t through the oral mucosa; and endocytosis is not the general mechanism for most drugs absorbed in this region.