Alimentary Canal I Esophagus and Stomach Objectives n

Alimentary Canal (I) Esophagus and Stomach (Objectives) n By the end of this lecture, the student should be able to discuss the microscopic structure in correlation with the function of the following organs: 1. Esophagus. 2. Stomach.

Alimentary Canal n n Is the tubular portion of digestive system. Is subdivided into: esophagus, stomach, small intestine (duodenum, jejunum and ileum), and large intestine (cecum, colon, rectum, anal canal, and appendix).

General Architecture of L/M Structure of Alimentary Canal 1234 - Mucosa. Submucosa. Muscularis externa. Adventitia OR serosa. Serosa

General Architecture of L/M Structure of Alimentary Canal or Serosa

ESOPHAGUS

ESOPHAGUS Four concentric layers: 1. Mucosa: – Epithelial Lining: Non-Keratinized Str. Squamous Epith. Serosa – Lamina propria: C. T. – Muscularis mucosae: Few layers of smooth muscle fibers.

Esophagus 2. Submucosa: • Connective tissue containing blood vessels, nerves, glands & • Meissner’s plexus of nerve fibers and nerve cells. 3. Muscularis Externa: Usually 2 smooth muscle layers: • Inner circular layer. • Outer longitudinal layer. • Auerbach’s (myenteric) plexus in between the 2 layers 4. Serosa or adventitia: Serosa is C. T. covered by mesothelium (simple squamous epithelium) in the abdominal part of the esophagus. or adventitia if there is no mesothelium. Serosa

STOMACH n n It has 4 regions: cardia, fundus, body and pylorus. Mucosa has folds, known as rugae that disappear in the distended stomach. fundus cardia body pylorus

Fundus of Stomach n n Mucosa: modify to form fundic glands. The surface epithelium of the mucose is simple columnar mucus-secreting cells. Submucosa: – Connective tissue containing blood vessels & nerves. – NO glands. Muscularis Externa: – Three smooth muscle layers: • Inner oblique. • Middle circular. • Outer longitudinal. Serosa: – C. T. covered by mesothelium.

Fundus (or body) of Stomach 1. Lumen. 1 2 3 2. Surface columnar epithelium. 3. Pits of fundic glands. 4 4. Fundic glands. 5 5. Lamina propria. 7 6. Muscularis mucosae. 7. Submucosa. 8. Muscularis externa. 8 6

Mucosa of Fundus of Stomach n It is composed of: 1. Surface Columnar Epithelium: Simple columnar epithelium: Secretes mucus. 2. Fundic glands. 3. Lamina propria: invaded by numerous fundic glands. 4. Muscularis mucosae.

Fundic Glands n Fundic glands have: • Short pits: one forth of mucosa. • Simple or branched tubular glands. • Are rich in parietal & chief cells.

Fundic Glands Composed of 5 cell types: 1. Parietal (oxyntic) cells: secrete HCl and gastric intrinsic factor that helps absorption of vitamin B 12. 2. Peptic (chief) cells: secrete pepsinogen. 3. Mucous neck cells: secrete mucus. 4. Enteroendocrine (DNES) cells: secrete hormones (e. g. serotonin). 5. Stem cells: regenerative cells.

Fundic Glands

Parietal and Chief Cells 1 1 - Parietal cells 2 - Chief cells 2

PYLORUS OF STOMACH n Mucosa: modify to form pyloric glands. The surface epithelium is simple columnar mucus-secreting cells. n Submucosa: – Connective tissue containing blood vessels & nerves. – NO glands. n Muscularis Externa: – Two smooth muscle layers: • Inner circular. • Outer longitudinal. 1. 2. 3. 4. n Serosa: 5. – C. T. covered by mesothelium. 6. 7. Lumen Surface epithelium Pits of pyloric glands Lamina propria Muscularis mucosae Submucosa Muscularis externa

Pyloric glands Their pits are deep --- about half the length of mucosa. n They are branched and convoluted --- many cross sections. n The predominant cells are mucous neck cells that secrete mucus. n

Pyloric glands

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