Mucosa of stomach

The mucosa of stomach is the innermost layer of the gastric wall and is specialised for the secretion of mucus, acid, digestive enzymes, and hormones. It consists of three components: a surface simple columnar epithelium, the lamina propria, and the muscularis mucosae.

1. Mucosal epithelium (surface mucous cells)

The gastric luminal surface is lined by mucus-secreting simple columnar epithelial cells, also known as the surface mucous cells.

--- Mucus-bicarbonate barrier

• These cells have a basally located nucleus and an apical cytoplasm filled with mucin granules, which are released continuously to produce a thick, viscous mucus layer.

• In addition to mucus, surface mucous cells secrete bicarbonate ions that become trapped within the mucus, creating a protective alkaline micro-environment at the epithelial surface. This mucus-bicarbonate barrier is essential for protecting the gastric mucosa from the corrosive effects of hydrochloric acid, the proteolytic action of pepsin, and mechanical injury caused by ingested food.

Gastric pits and gastric glands

The surface epithelium (or surface mucous cells) of gastric mucosa is thrown into numerous small microscopic invaginations that extend from the luminal surface of the stomach into the underlying mucosa. These are known as gastric pits, into which the gastric glands open and pour their secretions into the gastric lumen.

--- Gastric glands

Gastric glands are branched tubular secretory glands located within the lamina propria of the gastric mucosa. They extend from the base of the gastric pits to the muscularis mucosae and open into the lumen of the stomach through the gastric pits. Structurally, they comprise of an isthmus, a neck, and a base region.

These glands are responsible for producing the various components of gastric juice required for digestion and protection of the stomach lining.

2. Lamina propria

The lamina propria is composed of loose connective tissue containing blood vessels, lymphatics, immune cells, and the gastric glands.

3. Muscularis mucosae

Deep to the lamina propria lies the muscularis mucosae, a thin layer of smooth muscle that produces local movements of the mucosa, facilitating glandular secretion and improving contact between the mucosal surface and gastric contents.

Gastric rugae (gastric folds), gastric pits, and gastric glands

Gastric rugae are large folds of the mucosa and submucosa visible to the naked eye, which allow the stomach to expand when filled with food and flatten in a distended stomach. Within the mucosa, that is covering these rugae, there are numerous microscopic gastric pits, which are invaginations of the surface simple columnar epithelium (i.e. the surface mucous cells). The gastric pits open into deeper tubular gastric glands located within the lamina propria. These glands contain specialized secretory cells, which produce the various components of gastric juice.

• In summary, the gastric pits extend from the lumen to end inner to the muscularis mucosae, while the gastric folds (or gastric rugae) go deeper and end inner to the muscularis externa.