Which pathway allows a substance to enter the bloodstream via the lungs?

Which pathway allows a substance to enter the bloodstream via the lungs?

• A. Inhalation
• B. Ingestion
• C. Dermal absorption
• D. Injection

Answer: (A)

Inhalation is the route that delivers substances to the bloodstream through the lungs. When you breathe in, the substance enters the lungs and must cross the very thin walls of the alveoli into the surrounding capillaries. The alveolar-capillary interface is designed for rapid diffusion of gases, so airborne substances that are small enough or soluble can move from the air into the blood, making inhalation the pathway that brings them into circulation via the lungs. Ingestion takes substances into the digestive tract, not the lungs; dermal absorption occurs through the skin; and injection delivers something directly into tissues or the bloodstream, bypassing the lungs entirely.

Inhalation is the route that delivers substances to the bloodstream through the lungs. When you breathe in, the substance enters the lungs and must cross the very thin walls of the alveoli into the surrounding capillaries. The alveolar-capillary interface is designed for rapid diffusion of gases, so airborne substances that are small enough or soluble can move from the air into the blood, making inhalation the pathway that brings them into circulation via the lungs. Ingestion takes substances into the digestive tract, not the lungs; dermal absorption occurs through the skin; and injection delivers something directly into tissues or the bloodstream, bypassing the lungs entirely.