In the digestive tract, what does the lumen contain during digestion?

• A. Digestive contents such as chyme.
• B. Blood.
• C. Bone tissue.
• D. Muscle fibers.

Answer: (A)

The lumen is the hollow interior of the digestive tract where the contents move and are processed during digestion. The correct idea is that it contains digestive contents such as chyme— the semi-fluid mass formed when swallowed food mixes with stomach acid and digestive enzymes, and then travels through the stomach and into the intestines. Blood runs through vessels outside the lumen, not inside this hollow space. Bone tissue and muscle fibers are tissues of the body’s organs and skeletal system; muscle fibers make up the walls of the tract to help move contents, but they are not what fills the lumen during digestion.