Which structure releases \(\mathrm{HCO_3^-}\) (bicarbonate) in response to the hormone secretin?

• A. Liver
• B. Stomach
• C. Gallbladder
• D. Pancreas

Answer: (D)

Verified step by step guidance

1. Understand the role of the hormone secretin: Secretin is a hormone released by the small intestine in response to acidic chyme entering from the stomach. Its primary function is to regulate pH in the small intestine by stimulating the release of bicarbonate (\(\mathrm{HCO_3^-}\)).
2. Identify the organ responsible for releasing bicarbonate (\(\mathrm{HCO_3^-}\)): The pancreas is the organ that responds to secretin by releasing bicarbonate into the small intestine to neutralize the acidic chyme.
3. Clarify why other options are incorrect: The liver produces bile but does not release bicarbonate in response to secretin. The stomach secretes gastric acid and enzymes but does not neutralize acid with bicarbonate. The gallbladder stores bile but does not release bicarbonate.
4. Connect the function of bicarbonate (\(\mathrm{HCO_3^-}\)) to the pancreas: Bicarbonate is released by the pancreas into the duodenum (the first part of the small intestine) to maintain an optimal pH for enzymatic digestion.
5. Summarize the process: Secretin stimulates the pancreas to release bicarbonate (\(\mathrm{HCO_3^-}\)), which neutralizes the acidic chyme and creates a suitable environment for digestive enzymes to function effectively.