Acid reducing medications

Acid reducing medications include antacids that directly lower the acidity of stomach contents, and antisecretory medications that act on parietal cells in the stomach to decrease acid secretion. They are used to treat conditions like gastroesophageal reflux disorder and peptic ulcer disease by decreasing the acidity of the stomach and allowing the epithelial linings to heal.

Now, the stomach is composed of four regions: the cardia, the fundus, the body, and the pyloric antrum. There’s also a pyloric sphincter, or valve, at the end of the stomach, which closes while eating, keeping food inside for the stomach to digest. The epithelial layer of the stomach contains different gastric glands which secrete a variety of substances.

Starting with the cardia, it contains mostly foveolar cells that secrete a protective mucus, which is mostly made up of water and glycoproteins. The fundus and the body contain both the parietal cells and enterochromaffin-like cells, and the antrum and pyloric areas contain G-cells. Now gastric acid is mainly composed of HCl, or hydrochloric acid, which is mainly secreted by the parietal cells. Parietal cells have M3, CCK2, and H2 membrane receptors, which modulate their secretory behavior. When food enters the stomach, it causes the stomach walls to expand, which leads to the activation of these receptors.

First, stomach expansion causes the branches of the vagus nerve that innervates the stomach to release acetylcholine, which activates M3 receptors. Next, the G cells in the antrum of the stomach release gastrin, which activate the CCK2 receptors. Gastrin and acetylcholine activate the enterochromaffin-like cells, which release histamine, that then activates H2 receptors.

Activation of M3, CCK2, and H2 receptors increases the conversion of H20 and CO2 to H+ and HCO3- by carbonic anhydrase. The H+ is then pumped out of the cell and into the stomach via the H+/K+-ATPase pump. These H+ ions combine with Cl- ions to form hydrochloric acid and decrease the pH in the stomach.

Normally, the stomach is protected from the acidic environment by the mucus secreted by foveolar cells. However, if there’s an imbalance between mucus and acid secretion, like in Zollinger-Ellison syndrome, which is caused by a gastrin secreting tumor, it could lead to damage of the stomach. This could manifest as chronic gastritis and gastric, or peptic ulcers. Now, in the esophagus, the lower esophageal sphincter prevents most of the gastric acid from coming back up when the stomach is full or when you’re laying down. If this sphincter is loose, the acid could reflux into the lower esophagus and erode the esophageal lining. This is called GERD, or gastroesophageal reflux disease, most commonly known as heartburn. One way to mitigate the harmful effects of gastrin in these disorders is to decrease its acidity through medications.