Question

If you put the following events in the order they occur in the human digestive system, the third event in the series would be

(A) Cells in gastric pits secrete protons.

(B) Pepsin activates pepsinogen.

(C) HCl activates pepsinogen.

(D) Partially digested food enters the small intestine.

Short answer

(A) The statement “Cells in gastric pits secrete protons” is false.

(B) The statement “Pepsin activates pepsinogen” is true.

(C) The statement “HCl activates pepsinogen” is false.

(D) The statement “partially digested food enters the small intestine” is false.

Step-by-step solution

Human digestive system

The series of structures involved in the process of digestion is coined the human digestive system. The human digestive system is complete; it starts from the mouth and ends at the anus. The grinding occurs in the mouth with the help of teeth.

As the food moves inside the digestive tract, enzymatic action leads to chemical digestion.

Explanation of option ‘(A)’ 

The cells in gastric pits, such as parietal cells, secrete HCl, and it causes a low pH environment in the stomach. The cells do not secrete protons. The proton pump of the parietal cells decreases proton to create an acid medium in the stomach.

Therefore, cells of gastric cells do not secrete protons; they secrete enzymes.

Thus, the given option is false.

Explanation of option ‘(B)’

The gastric chief cells secrete pepsin in its inactive form called pepsinogen. This mechanism stands in the third step of digestion events. The performed pepsin converts the pepsinogen into active pepsin.

Therefore, the action of pepsin is the third step of digestion.

Thus, the given option is true.

Explanation of option ‘(C)’

The HCl acts on pepsinogen converts them to active pepsin. It is the second step of digestion in the stomach. Parietal cells release HCl.

Therefore, the action of HCl on pepsinogen is considered the second step.

Thus, the given option is false.

Explanation of option ‘(D)’

The partially digested food or chyme enters the small intestine. The final digestion process that is chemical digestion takes place small intestine by the action of enzymes.

Therefore, digestion in the small intestine is not the third step in digestion.

Thus, the given option is false.