Which cells are responsible for H+ or acid secretions?
A EC cells
B G cells
C Parietal cells
D Mucus cells
The correct answer and explanation is:
The correct answer is C. Parietal cells.
Explanation:
Parietal cells, found in the lining of the stomach, are primarily responsible for the secretion of hydrochloric acid (HCl). These cells play a crucial role in digestion by lowering the pH of the stomach environment, which is essential for the activation of digestive enzymes such as pepsinogen into pepsin. This acidic environment also helps kill harmful microorganisms that may enter the stomach.
Parietal cells secrete hydrogen ions (H+) through a specialized mechanism known as the proton pump. The hydrogen ions are exchanged for potassium ions in a process driven by the enzyme H+/K+ ATPase, often referred to as the proton pump. The pump actively transports H+ ions into the lumen of the stomach, which combines with chloride ions (Cl-) to form hydrochloric acid. This secretion process is regulated by several factors, including the presence of food, hormones, and neural signals.
The secretion of acid by parietal cells is stimulated by a variety of signals. The presence of food in the stomach triggers the release of gastrin, a hormone produced by G cells in the stomach lining. Gastrin binds to receptors on the parietal cells and enhances the activity of the proton pump, leading to increased acid production. Additionally, the parasympathetic nervous system, through the release of acetylcholine, also stimulates parietal cells to secrete H+.
Other cell types in the stomach also play important roles, but they are not directly responsible for acid secretion:
- A. EC cells (Enterochromaffin-like cells) release histamine, which also stimulates parietal cells to secrete acid.
- B. G cells release gastrin to stimulate parietal cells but do not secrete acid themselves.
- D. Mucus cells secrete mucus to protect the stomach lining from the corrosive effects of stomach acid, but they do not produce acid.
Thus, the parietal cells are the key players in acid secretion in the stomach.