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).
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 .