Parietal cells of the stomach produce __.
A) mucin
B) pepsinogen
C) hydrochloric acid
D) rennin
The correct answer and explanation is :
The correct answer is C) hydrochloric acid.
Explanation:
Parietal cells, also known as oxyntic cells, are specialized epithelial cells found in the lining of the stomach. These cells are primarily responsible for producing hydrochloric acid (HCl), which is a key component of gastric juice. HCl plays several critical roles in the digestive process, including:
- Acidic environment for enzyme activity: The hydrochloric acid creates a highly acidic environment in the stomach (with a pH of around 1.5 to 3.5). This acidity is essential for the optimal activation and function of pepsinogen (secreted by chief cells) into its active form, pepsin, which is responsible for breaking down proteins into smaller peptides.
- Defense against pathogens: The acidic environment also acts as a defense mechanism, killing harmful microorganisms that may be ingested with food, thus preventing infections.
- Denaturation of proteins: The acid helps denature proteins in food, unraveling their complex structures and making them more accessible for enzymatic digestion by pepsin.
- Stimulation of digestion: The presence of HCl also activates the enzyme rennin (chymosin), which is involved in the coagulation of milk proteins in infants.
In addition to hydrochloric acid, the parietal cells secrete intrinsic factor, a glycoprotein necessary for the absorption of vitamin B12 in the small intestine.
Other options:
- A) Mucin: Mucin is produced by goblet cells in the stomach lining and serves to protect the stomach lining from the harsh acidic environment. It is not produced by parietal cells.
- B) Pepsinogen: Pepsinogen is produced by chief cells, not parietal cells. It is the inactive precursor of pepsin.
- D) Rennin: Rennin (also called chymosin) is primarily produced in the stomachs of infants and is involved in curdling milk, but it is not secreted by parietal cells.
Thus, parietal cells are crucial for maintaining the acidic environment necessary for digestion and protection.