Mucosa

The mucosa, which lines the lumen of the GI tract, is the absorptive and major secretory layer. It consists of a simple columnar epithelium supported by the lamina propria, a thin layer of areolar connective tissue containing numerous lymph nodules, which are important in protecting against disease (fig. 18.3b). External to the lamina propria is a thin layer of smooth muscle called the muscularis mucosae. This is the muscle layer responsible for the numerous small folds in certain portions of the GI tract. These folds greatly increase the absorptive surface area. Specialized goblet cells in the mucosa secrete mucus throughout most of the GI tract.

Artery

Mesentery

Artery

Mesentery

Mucosa Submucosa

Muscularis externa

Plica circularis

Myenteric plexus

Submucosal plexus

Lymph nodule

Lacteal

Epithelium

Plica circularis

Mucosa Submucosa

Longitudinal muscle

Circular muscle

Muscularis externa

Myenteric plexus

Submucosal plexus

Lymph nodule

Lacteal

Epithelium

■ Figure 18.3 The layers of the digestive tract. (a) An illustration of the major tunics, or layers, of the small intestine. The insert shows how folds of mucosa form projections called villi in the small intestine. (b) An illustration of a cross section of the small intestine showing layers and glands.

The Digestive System Submucosa

The relatively thick submucosa is a highly vascular layer of connective tissue that serves the mucosa. Absorbed molecules that pass through the columnar epithelial cells of the mucosa enter into blood and lymphatic vessels of the submucosa. In addition to blood vessels, the submucosa contains glands and nerve plexuses. The submucosal plexus (Meissner's plexus) (fig. 18.3ft) provides an autonomic nerve supply to the muscu-laris mucosae.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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