Histology – Digestive System

Histology – Digestive System

# Official Digestive Tract

The official digestive tract begins at the esophagus and ends at the anal canal.

The wall of the official digestive tract consists of 4 layers:

1. Mucosa:

– Composed of the epithelium, lamina propria, and muscularis mucosae.

– Epithelium originates from the endoderm and is classified according to each part of the digestive tract.

– The lamina propria is loose connective tissue containing blood vessels, lymphatic vessels, nerve fibers, and Meissner’s nerve plexus.

– The muscularis mucosae is composed of smooth muscle, except for the upper 1/4 of the esophagus, which is striated muscle. This layer helps to contract and move food.

2. Submucosa:

– Composed of elastic connective tissue, blood vessels, lymphatic vessels, nerve fibers, and Auerbach’s nerve plexus.

– This layer connects the mucosa to the muscle.

3. Muscularis propria:

– Composed of two layers of smooth muscle: the inner circular layer and the outer longitudinal layer.

– Between the two layers is Auerbach’s nerve plexus, which controls the muscle’s contraction activity.

– In the stomach, there is an additional oblique muscle layer within the circular muscle layer.

4. Serosa:

– Composed of loose connective tissue, covering the outer surface of the digestive tract.

– The outermost layer is the mesothelium.

Parts of the official digestive tract:

1. Esophagus:

– Epithelium: stratified squamous non-keratinized epithelium.

– Lamina propria: contains esophageal-gastric glands, collagen/elastic fibers, fibroblasts, lymphocytes, and lymphatic nodules.

– Muscularis mucosae: very thick.

– Submucosa: upper 1/4 is striated muscle, lower 3/4 is smooth muscle, Auerbach’s nerve plexus is located between the two layers.

– Muscularis propria: forms longitudinal folds when the esophagus is empty and stretches when swallowing food.

2. Stomach:

– Epithelium: simple columnar epithelium, with mucus-secreting cells.

– Lamina propria: contains gastric pits, pyloric glands, and cardiac glands.

– Muscularis mucosae: thin.

– Submucosa: contains 3 muscle layers: oblique, circular, and longitudinal.

– Muscularis propria: has a circular pyloric sphincter at the pylorus.

• Gastric pits:

– Secretes gastric juice, straight tubular glands with branching.

– Contains 3 sections: neck, body, and base.

– Chief cells: secrete pepsinogen, have short microvilli, and are covered with a glycocalyx layer.

– Parietal cells: secrete hydrochloric acid (HCl), react positively with PAS and muci-carmin.

– Mucous cells: secrete serotonin.

– Argentaffin cells: secrete gastrin.

• Pyloric glands:

– Similar to gastric pits, may contain argentaffin cells.

• Cardiac glands:

– Similar to the muscularis mucosae of other parts of the official digestive tract.

3. Small intestine:

– Epithelium: simple columnar epithelium.

– Lamina propria: contains absorptive cells (enterocytes), goblet cells, endocrine cells (argentaffin, chrom), and Lieberkuhn glands.

– Submucosa: contains Brunner’s glands in the duodenum.

– Muscularis propria: contains 2 muscle layers, with Auerbach’s nerve plexus.

• Absorptive cells (enterocytes):

– Oval nucleus near the base.

– Free surface has microvilli.

– Microvilli surface has a thick glycocalyx layer, alkaline phosphatase.

• Goblet cells:

– Secrete mucus.

• Endocrine cells:

– Secrete serotonin.

• Lieberkuhn glands:

– Contains absorptive cells, goblet cells, argentaffin cells, Paneth cells (exocrine gland cells).

• Brunner’s glands:

– Secrete alkaline mucus, protecting the duodenum from HCl.

4. Large intestine:

– Epithelium: simple columnar epithelium, no microvilli.

– Lamina propria: contains goblet cells, absorptive cells, endocrine cells, Lieberkuhn glands, few argentaffin cells, and no Paneth cells.

– Muscularis propria: contains 2 thin layers of smooth muscle.

– Serosa: has 3 longitudinal muscle bands protruding outward.

5. Appendix:

– Epithelium: similar to the large intestine.

– Lamina propria: contains Lieberkuhn glands, lymphatic nodules extending into the submucosa.

– Muscularis propria: thin, discontinuous, incomplete.

# Digestive Glands

Digestive glands include:

• Major salivary glands:

– Parotid gland, submandibular gland, sublingual gland.

– Exocrine glands of the acinar type.

• Liver:

– Structural and functional unit is the hepatic lobule.

– Functions: detoxification, synthesis of blood proteins, storage of glycogen, regulation of blood sugar levels.

• Pancreas:

– Includes exocrine and endocrine glands.

– Exocrine gland: secretes pancreatic juice into the duodenum.

– Endocrine gland: secretes insulin, glucagon, somatostatin, and pancreatic polypeptide into the blood.

General characteristics of digestive glands:

• Salivary glands:

– Contains 3 types of acini: serous acini, mucous acini, mixed acini.

– Each glandular unit includes a secretory portion (acini) and an excretory portion (duct).

• Liver:

– There are 3 ways to divide hepatic lobules: classical hepatic lobule (Kiernan), portal lobule (Mall), hepatic acinus (Rappaport).

• Pancreas:

– Exocrine gland contains acini, excretory ducts.

– Endocrine gland: contains islets of Langerhans.

# Notes

– BM: epithelium.

– SI: small intestine.

– LI: large intestine.

– NP: nerve plexus.

– V: vein.

– A: artery.

– BC: blood concentration.

– LY: lymph.

– C: cell.

– Golgi: Golgi apparatus.

– IC: intracellular.

– PAS: Periodic Acid Schiff reaction.

– muci-carmin: mucus stain.

– IgA: immunoglobulin A.

This article provides an overview of the histology of the digestive system. For a deeper understanding, you should refer to more specialized materials.