Histology of the Gastrointestinal System Flashcards
What are the four layers of the GI tract?
1) Mucosa
2) Submucosa
3) Muscularis externa
4) Serosa OR adventitia
What are the two layers of the muscularis externa?
Inner circular layer
Outer longitudinal layer
The mucosa of the esophagus is composed of…
Stratified squamous nonkeratinized epithelium
The mucus secreting glands of the esophagus are called the…
Esophageal cardiac glands (located at either end) and submucosal glands (located throughout)
What changes occur to the epithelium in Barrett’s esophagus?
The stratified squamous nonkeratinized epithelium is replaced by simple columnar epithelium typical of the stomach due to GERD
How do esophageal varices occur?
- Hepatic portal hypertension leads to a back up of blood in the portal-systemic anastomisis between the stomach and distal esophagus
- Venous blood is diverted from the stomach, which drains to the portal system, to the distal esophagus
- This leads to esophageal vein dilation and varices
What two types of muscle does the muscularis externa of the esophagus have?
Striated muscle that transitions distally to smooth muscle
Is the esophagus surrounded by serosa or adventitia?
- Serosa below the diaphragm, since it is intraperitoneal
- Adventitia along the rest of its length
Why does esophageal cancer metastasize readily to other tissues?
- Rich lympathic plexus
- Not separated from other tissues by a serosa
Serosa vs adventitia
Digestive organs facing the peritoneal cavity have a serosa, and those that do not have an adventitia
How does the muscularis externa of the stomach differ?
It has a third innermost, oblique layer
Which layer forms the rugae of the stomach?
Submucosa
What change occurs at the esophagogastric junction?
The stratified squamous nonkeratinized epithelium is abruptly becomes simple columnar epithelium
What are gastric pits?
Invaginations of the epithelium in the stomach into the underlying LP
Opens at its neck into several gastric glands
What are the exocrine cells of the gastric mucosa and where do they secrete their products?
- Surface mucous cells
- Mucous neck cells
- Parietal cells
- Chief cells
Secrete into the lumen
What are the endocrine cells of the gastric mucosa and where do they secrete their products?
- G-cells
- D-cells
Secrete into their basal aspect into ISF of underlying lamina propria
What is the clinical relevance of atrophic gastritis?
Autoimune destruction of parietal cells reduces intrinsic factor, impairing B12 absorption and leading to pernicous anemia
What are the plicae circularis?
Transverse folds in the small intestine formed by the mucosa and submucosa in order to increase SA for nutrient absorption
What are Brunner’s glands?
Mucous-secreting glands in the duodenum
What are Peyer’s patches and where are they located?
- MALT (mucosa-associate lymphoid tissues)
- Located in the submucosa of the ileum
- Protect against bacterial infection from the colon
What are intestinal villi?
- Formed by the mucosa in the SI
- Consist of a core of LP covered by simple columnar epithelium
- Form intestinal glands/crypts at the base
- Increase SA
What cells make up the microvilli or “brush border”?
The enterocytes
What is the glycocalyx?
“Sugar coat” covering the microvilli containing enzymes that aid in digestion + absorption of carbs and proteins
What is the function of goblet cells in the villi?
Produce mucins, which combine with water to form a protective mucous over the luminal surface of the SI
What cells line the intestinal glands?
Paneth cells, enteroendocrine cells, M (microfold) cells, stem cells
What are Paneth cells?
- Secrete antimicrobial peptides as part of innate immunity
- Stain reddish-pink
What are M cells?
- Present in the ileum and overly Peyer’s patches
- Endocytose anitgens to intiate an immune response
How does the mucosa of the colon differ from the SI?
- Lacks villi
- Forms deep tubular invaginations into the LP - intestinal glands
- Epithelium is dominated by absorptive cells and goblet cells (++ goblet cells for lubricaton)
- Epithelium still has simple columnar epithelium
- Abrupt transition to stratified squamous epithelium at the rectoanal junction (pectineal line)
