Objectives

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

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 Architectureof L/M Structure of Alimentary Canal

Serosa

General Architectureof L/M Structure of Alimentary Canal

ESOPHAGUSFour concentric layers:

1.Mucosa: Epithelial Lining:

Non-Keratinized Str. Squamous Epith.

Lamina propria: C.T. containing blood vessels, nerves and lymphatic vessels (Peyer’s patches)

Muscularis mucosae:Few layers of smooth muscle fibers.

Serosa

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 layers4. 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

It has 4 regions: cardia, fundus, body and pylorus.

Mucosa has folds, known as rugae that disappear in the distended stomach.

fundus

body

pylorus

cardia

Fundus of Stomach Mucosa: modify to form fundic

glands. The surface epithelium 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.

Mucosa of Fundus of Stomach It is composed of:1. Surface Epithelium.2. Fundic glands.3. Lamina propria: invaded by numerous

fundic glands. 4. Muscularis mucosae.

Fundic Glands

Fundic glands Fundic glands have:have:

• Short pits—one Short pits—one fourth of mucosa.fourth of mucosa.

• Simple or Simple or branched tubular branched tubular glands.glands.

• Are rich in Are rich in parietal & chief parietal & chief cells.cells.

Fundic Glands

Composed of 6 cell types:1.Parietal cells: secrete HCl

and gastric intrinsic factor that helps absorption of vitamin B12.

2.Peptic (chief) cells:secrete pepsinogen.

3.Mucous neck cells:secrete mucus.

4.Enteroendocrine (DNES) cells:secrete hormones.

5.G cells : secrete gastrin6.Stem cells: regenerative

cells.

1- Parietal cells1- Parietal cells2- Chief cells2- Chief cells

12

Parietal and Chief Parietal and Chief CellsCells

PYLORUS OF STOMACH Mucosa: modify to form

pyloric glands. The surface epithelium is simple columnar mucus-secreting cells.

Submucosa: Connective tissue

containing blood vessels & nerves.

NO glands.

Muscularis Externa: Two smooth muscle layers:

Inner circular. Outer longitudinal.

Serosa: C.T. covered by

mesothelium.

Pyloric glands

Their pits are deep --- about half the length of mucosa.

They are branched and convoluted --- many cross sections.

The predominant cells are mucous neck cells that secrete mucus.

Clinical ApplicationClinical Application

1. Hiatus Hernia Definition: It is herniation of the stomach into the

thoracic cage through a gap in the diaphragm around the wall of the esophagus.

Background: As the esophagus passes through the diaphragm, it is reinforced by the muscle fibers of the diaphragm. In some people, development is abnormal, causing a gap in the diaphragm around the wall of the esophagus.

Clinical ApplicationClinical Application

2. Barrett’s Syndrome Definition: It is probably a pre-cancerous (pre-

malignant) condition due to gastro-esophageal reflux, leading to the replacement of part of the stratified non-keratinized squamous epithelium of the lowest region of the esophagus (at least 3 cm) by a simple columnar epithelium (metaplasia).

Treatment: Esophageal resection of the metaplastic part.

Clinical ApplicationClinical Application

3. Gastric Intrinsic Factor Background: Gastric intrinsic factor (IF) is

secreted by parietal cells in gastric glands.

It is necessary for vitamin B12 absorption from the ileum.

Effect of absence of gastric IF: it results in deficiency of vitamin B12 with consequent development of pernicious anemia.

Clinical ApplicationClinical Application

4. Atrophic Gastritis Effect of Atrophic Gastritis: Both parietal

and chief cells are much less numerous → the gastric juice has little or no acid or pepsin activity.

Clinical ApplicationClinical Application

5. Peptic Ulcer Definition: a circumscribed ulceration of the gastro-

intestinal mucosa extends to the submucosa and may include the muscle layer, occurring in areas exposed to acid and pepsin and most often caused by Helicobacter pylori infection.

NB: Gastric erosion: Damage of the gastro-intestinal mucosa that is not penetrating the muscularis mucosae.

Types of peptic ulcers: Gastric peptic ulcer. Duodenal peptic ulcer: especially in the 1st part of duodenum.

Causes of peptic ulcer:Causes of peptic ulcer: Helicobacter Pylori (H. Pylori): this type of bacteria is

responsible for most of ulcers (70-90%) Non-steroidal anti-inflammatory drugs (NSAIDs): Long term

use of these pain relievers is the second most common cause of ulcers e.g. Ibuprofen, aspirin

Pathogenesis:Pathogenesis: Break-down of the thin protective layer of mucus over the surface of epithelial cells leads to damage of the gastric mucosa by the gastric acidity.

Complications of peptic ulcer:Complications of peptic ulcer: Perforation of the wall of the stomach → peritonitis. Malignancy (in gastric peptic ulcer). Bleeding .

“The End ”

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