Which of the following is TRUE?
a. Glucagon is released by the beta cells of the pancreatic islets of Langerhans.
b. Bile only flows in one direction in the cystic duct.
c. Pepsinogen is converted into pepsin by hydrochloric acid.
d. Intrinsic factor is secreted by parietal cells and is necessary for vitamin K absorption in the ileum.
e. Mechanical digestion does not occur in any organs found below the diaphragm

a. Glucagon is released by the beta cells of the pancreatic islets of Langerhans.

Explanation:

When the body is fasting, the pancreas releases glucagon so that your body can produce glucose. Glucagon is a protein hormone made and secreted by alpha cells from pancreatic islets (or islets of Langerhans).

The islets of Langerhans are a special group of cells in the pancreas that produce not only glucagon, but also insulin. These substances act as important regulators of sugar metabolism.

b.