The Stomach
The Stomach
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Following the esophagus, as it enters through the cardiac sphincter, is the stomach. The stomach is split into four main sections - the cardia, fundus, body, and pylorus (from top to bottom). Two notches can be found on the stomach, the cardiac and angular notch. The curve of the stomach is can also be split into a lesser curvature and greater curvature, similar to minor and major arcs.
Cardia - Contains the cardiac sphincter which prevents backflow into the esophagus.
Fundus - Stores any gas created from digestion.
Body - The main portion for digestion, contracting and mixing food.
Pylorus - Holds food until it's ready to enter the small intestine, also has the pyloric sphincter to prevent food in the small intestine from re-entering the stomach.
Figure 1 - Stomach's Position Within the Digestive System
Figure 2 - Specific Terminology Displayed on Diagram of Stomach
The stomach has a special mucosa layer that, when empty, has ridges called rugae. However, when the stomach is full, the mucosa expands and ridges flatten. The rugae helps the stomach have more surface area for absorbing food as well as having a flexible volume for containing food. The stomach has a strong muscularis and is the major muscle to allow it to churn and contract.
On the lining of the stomach are numerous gastric glands that produce gastric juice. Gastric juice is a mix of enzymes that works at an optimum environment of pH 1-3. Glands are differentiated by their location in the stomach - the cardiac gastric glands, intermediate gastric glands, and the pyloric gastric glands.
As seen on the right, there are five main types of cells - surface mucus cells, mucus neck cells, parietal cells, chief cells, and G-cells.
Surface mucus cells and mucus neck cells secretes mucus as a viscous protective barrier to protect the stomach from self-digestion.
Parietal cells secrete hydrochloric acid and intrinsic factor. Intrinsic factor is a protein that helps the intestines absorb vitamin B12 later on. Vitamin B12 is to help blood/nerve cells healthy and in the synthesis of DNA. HCL creates the acidic environment for large foods to be broken down and to fight antibodies.
Chief cells secrete pepsinogen that collaborate with the aforementioned HCL. Pepsinogen is the unactivated form of the protease known as pepsin, but when HCL and pepsinogen coexist, pepsinogen turns into pepsin. Pepsin is able to break amino acid bonds (proteolysis). Chief cells also secretes gastric lipase, an enzyme that breaks down triglycerides.
Lastly, G-cells secrete a hormone called gastrin to stimulate the stomach.
Figure 3 - Histology of the Gastric Glands in the Stomach
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