[Campbell Biology P.1054] In the simple endocrine pathway of secretin signaling, what is the ... | Practice Question

In the simple endocrine pathway of secretin signaling, what is the direct stimulus that triggers the S cells of the duodenum to secrete secretin?

  • A: High pH in the stomach.
  • B: Presence of bicarbonate in the duodenum.
  • C: Low pH in the duodenum.
  • D: Secretin hormone circulating in the blood.

Explanation

Figure 45.9 and the accompanying text clearly state, 'The low pH of partially digested food entering the small intestine is detected by S cells, which are endocrine cells in the lining of the duodenum.' This low pH is the initial stimulus.