Epithelium of the eye
The stomach is internally lined by the gastric mucosa, the innermost layer of which forms a single-layered, highly prismatic epithelium. This means that the epithelial cells have an elongated shape. The individual cells are connected to each other by special connections, so-called tight junctions. The epithelium and the adjacent layers form gastric pits (foveolae gastricae) into which the stomach glands end. The epithelium contains many secondary cells that produce mucus, which is very important for the protection of the stomach.
Epithelium of the esophagus
The esophagus is lined by multi-layered unkeratinized squamous epithelium. This can be divided into four layers. The basal membrane is covered by the so-called stratum basale, from which the regeneration of the cells starts.
This is followed by the stratum parabasale, stratum spinosum (intermedium) and stratum superficiale. The cells of the inward-facing stratum superficiale perish due to the mechanical stress caused by food and are regularly sheared off. In addition, the excretory ducts of glands open into the interior of the esophagus and can be found in the epithelium. The mucosa then regenerates from basal to luminal (i.e. directed towards the lumen of the esophagus). The same epithelium can be found in the oral cavity.
Epithelium of the intestine
The intestine, just like the stomach, is lined by a single-layered cylindrical epithelium. This applies to the large intestine as well as to the small intestine. However, the exact structure of the mucous membrane differs somewhat in the individual sections of the digestive tract, as each section has special functions to fulfil.
The epithelial cells of the intestine are called enterocytes and have so-called microvilli on the side facing the inside of the intestine (lumen). These are small protuberances that serve to increase the surface area and are also called brush border. The large surface area offers plenty of space for the absorption of food components from the intestine. In addition, the mucous membrane of the intestine has many glandular cells that produce hormones to control digestion.
