Question

The enzyme pepsin is secreted by
A) Inner lining of oesophagus
B) Gastric lining of stomach
C) Inner lining of duodenum
D) Gallbladder

Answer 1

Hint: Pepsin is an enzyme which catalyses the breakdown of proteins into smaller peptides.

Complete Answer:
In the digestive system of humans various enzymes are found. These enzymes help in catalysing the breakdown of complex substances like proteins, carbohydrates, etc into smaller substances like peptides, sugars, etc.

Option a: The inner lining of oesophagus contains gastric glands which produce various digestive enzymes but not pepsin. It also secretes mucus and hydrochloric acid. Therefore, this is the incorrect option.
Option b: In the stomach, proteins are digested by pepsin. Pepsin in the stomach helps in digesting proteins which are found in undigested food. In the stomach, chief cells are present which are responsible for secreting pepsinogen/zymogen (inactive form of pepsin).
This pepsinogen is activated in the stomach as it contains hydrochloric acid which decreases the pH level in the stomach which is favourable for activation of pepsinogen. Pepsin then catalyses the breakdown of proteins into smaller particles peptides. Therefore, this is the correct option.
Option c: The inner lining of duodenum secretes amylase for breakdown of carbohydrates, lipase for breakdown of lipids, trypsin for protein digestion. But it does not contain pepsin. Therefore, this is the incorrect option.
Option d: In gallbladder, fats are broken down into smaller particles with the help of bile salts produced by the liver. It has no role in protein digestion and thus does not contain pepsin. Therefore, this is the incorrect option.

Thus, the correct option is b) Gastric lining of the stomach.

Note: Both stomach and duodenum are involved in protein digestion. Even though the duodenum does not contain pepsin for protein digestion, it has an enzyme called enterokinase which helps to activate the trypsinogen into trypsin. This activated trypsin is involved in the breakdown of proteins into small polypeptide chains.