Most water absorption occurs via osmotic movement driven by solute absorption through aquaporins and paracellular pathways in which part of the GI tract?

Most water absorption occurs via osmotic movement driven by solute absorption through aquaporins and paracellular pathways in which part of the GI tract?

• A. Esophagus
• B. Large intestine
• C. Stomach
• D. Small intestine

Answer: (D)

Water absorption in the gut happens mainly by osmosis following solute movement. The small intestine provides by far the largest absorptive surface area because of its villi and microvilli, so lots of solutes—especially sodium and other nutrients—are actively transported across the epithelium there. This creates an osmotic gradient that pulls water either directly through aquaporin channels in the enterocytes (transcellular path) or between cells through tight junctions (paracellular path). Because of these reasons, most water reabsorption occurs in the small intestine. The esophagus and stomach absorb little water, and the large intestine reabsorbs water mainly from what's left to form stool.

Water absorption in the gut happens mainly by osmosis following solute movement. The small intestine provides by far the largest absorptive surface area because of its villi and microvilli, so lots of solutes—especially sodium and other nutrients—are actively transported across the epithelium there. This creates an osmotic gradient that pulls water either directly through aquaporin channels in the enterocytes (transcellular path) or between cells through tight junctions (paracellular path). Because of these reasons, most water reabsorption occurs in the small intestine. The esophagus and stomach absorb little water, and the large intestine reabsorbs water mainly from what's left to form stool.