Parietal Cells

00:01 The parietal cells, as you have seen before, are in the middle component or the middle section of the gastric glands. They are easily identified in H&E sections because they have a beautiful pink-stained cytoplasm and a nice prominent round nucleus. Sometimes, if you look very carefully, you'll even find these two nuclei in these cells. They secrete hydrochloric acid, which is a very important component that breaks down food. They also secrete intrinsic factor. This intrinsic factor is extremely important because it binds in the lumen of the stomach and also the duodenum. It binds the Vitamin B12, and Vitamin B12 cannot be absorbed by the ileum, by a lower part of the small intestine without being, first of all, attached or combined with this intrinsic factor. So that's an important job of the stomach. The major role here though in digestion is to secrete hydrochloric acid. They are very eosinophilic.

01:17 They stain very pink, and that reflects their affinity for eosin that's probably the enormous number of mitochondria in these cells. Have a look at the diagram on the right-hand side.

01:35 And just so that I don't forget when I'm explaining this cell structure to you, have a look down the base of the diagram, the base of the cell, and you'll see there are a number of receptors there for histamine, for acetylcholine, and for gastrin. That means that these cells can be stimulated or even inhibited by the activity of other hormones such as gastrin, and also by the activity of cholinergic nerve fibers. So, I'm not going to go into details of these sets.

02:14 Again, something you'll learn in your physiology course, but I just want you to be aware that all the cells we're going to be looking at are influenced by both hormones and also by components of the autonomic nervous system. What a wonderful looking cell this is, in reality, even though we don't appreciate it when we look at histological sections. If you look at the diagram, there's two major differences you see compared to other cells. There's a lumen or an apical border surrounded by microvilli which you see in many secretory cells, but then you have this canaliculi, these spaces, corridor if you like, very membranous corridors extending into the body of the cell, the secretory canaliculi.

03:11 And then, in the cytoplasm itself are an enormous number of these little tubular vesicles, and again, mitochondria.

03:23 These are structural evidence that these cells are very very important and very active in secreting hydrochloric acid. These canaliculi can vastly expand with membranes because what happens is that the tubular vesicles fuse with the plasma or cell membrane of the parietal cell and these canaliculi expand greatly. And therefore, they increase the surface area for proton pumps that are needed to make acid. And the mitochondria provide the energy, the high energy requirement to have these proton pumps working and producing the hydrochloric acid. So that's why you see this very specialized structure in these parietal cells. The chief cell lies, as I mentioned, at the base of these gastric glands.

04:30 In the central image where the label of the chief cell indicates the bluish stained cluster of cells, you can also see some parietal cells. As I mentioned before, often, some will sneak down into those lower ends of the gastric glands.

04:51 These chief cells secrete pepsinogen to fairly weak lipase. And when that pepsinogen is secreted from these cells and moves through the gland lumen, through the surface, it's converted to a proteolytic enzyme pepsin by interaction with hydrochloric acid. So that's another role that hydrochloric acid is, has been produced by these parietal cells. And there are different sort of a cell, they've got different sort of factory inside them. Often, when the granules appear, the zymogen granules, zymogen granules are just enzyme precursors, when they appear containing their pepsinogen as well, then they would have an eosinophilic type stain, a pinky little stain. You'd see little red granules at the apex of the cells. Perhaps, they're all being released here in this section so you don't see them. The bluey tinge, the basophilia that you see reflects the enormous protein factory you have in these cells to produce the protein components of the secretory products, the pepsinogen.

06:12 And again, at the base of the cell on the diagram, you can see an acetylcholine receptor.

06:18 The acetylcholine receptor obviously is there to allow the communication of nerve fibres to this cell, or perhaps, the interaction of hormones, etc, interacting with receptors on this cell as well. Again, emphasize that these cells are controlled by both hormonal and neural input. And on the diagram, it just summarizes what I mentioned about having granules and also lots and lots of endoplasmic reticulum, and mitochondria, of course, to provide the energy.