Luminal or Gland pH?

Gastrin indirectly stimulates Enterochromaffin-like cells to release H+ (acid) and gastrin has a direct effect on Parietal cells via the CCK-B receptor to release H+, thus lowering the pH. These cells are located in the gastric gland area, which is like a dip or a pocket within the lumen, like a sink hole, but for your gastric lining. If there is a lower pH, then the D-cells would secrete Somatostatin to inhibit G-cells to stop the actions of Gastrin. Basically, it’s saying, “Woah there. There is too much acid going around, we need slow ya’ll down.” By ya’ll, D-cell means G-cells, ECL cells, and Parietal Cells. How D-cells do that is by secreting Somatostatin, which inhibits G Cells, ECL cells, and Parietal cells (Somatostatin directly suppresses H+ secretion on Parietal cells).

So wouldn’t D-cells sense the acid right in the Gastric Pit or Gastric Gland and not the lumen?

No, absolutely not.

I would know this because I got a question on my GI Exam 2 regarding this concept wrong. I checked my professor’s lecture video and he mentioned that the mechano- and chemoreceptors from the Enteric Nervous System. These receptors send signals to the ENS and that sends signals into the D-cells (other cells as well, but for this context, we are focused on D-cells). D-cells will then secrete Somatostatin.

The answer is that acidity is sensed in the lumen, even though D-cells are in the gastric pits.

This is due to the ENS sensing chemo receptors in the lumen and sending signals in to the D-cells, located in the gastric gland.