I have a question regarding the gastric wall. Do the epithelial cells of the mucosa secrete substances directly into the lumen or do they secrete into the gastric pits then then from there the substances go into the lumen?
The epithelial cells of the gastric mucosa secrete substances into the lumen of the stomach through a two-step process. First, these cells secrete substances into the gastric pits, which are intions or small depressions on the surface of the mucosa. These gastric pits contain specialized cell types, such as mucus cells, parietal cells, and chief cells.
The mucus cells produce and secrete mucus, which forms a protective layer that coats the inner surface of the stomach, preventing damage from gastric acid and enzymes. Mucus also facilitates the movement of food in the stomach.
The parietal cells are responsible for secreting hydrochloric acid (HCl) into the gastric pit. This acid helps to create an acidic environment in the stomach, which is necessary for the activation of digestive enzymes and the breakdown of food particles.
The chief cells, present in the gastric pits, secrete pepsinogen, which is an inactive form of the enzyme pepsin. Pepsinogen is later activated to become pepsin in the presence of the acidic environment created by the hydrochloric acid secreted by the parietal cells.
After the secretion of these substances into the gastric pits, they then pass from the pits into the lumen of the stomach. This transfer occurs through small channels known as gastric glands, which connect the gastric pits to the stomach lumen.
Overall, the gastric mucosa epithelial cells secrete substances into the gastric pits first, and then these substances flow into the stomach lumen through gastric glands.