Histology of the GI Tract - Part 1 Flashcards
Saliva (in the mouth) initiates the digestion of…
carbohydrates
Describe the lumen of the esophagus
It is collapsed (when food goes through, the lumen gets distended)
The lumen of th esophagus is lined by…
mucosa
Name the 3 layers of the esophageal mucosa
- Epithelium
- Lamina propria
- Muscularis mucosa (1-2 layers of smooth muscle cells)
What type of epithelium lines the esophagus?
Non-keratinized squamous stratified epithelium
The lamina propria of the esophageal mucosa contains…
mucous glands in the upper and lower 3rds
Layer of the esophagus adjacent to the mucosa
Submucosa (contains mucous glands)
The submucosa contains… (3)
- mucous glands
- loose or dense CT
- Meissner’s nerve plexus
Layer of the esophagus surrounding the submucosa
Tunica muscularis (containing internal circular and external longitudinal muscle layers)
In what direction do internal circular muscle fibres run (esophagus)?
Around the circumference of the esophagus (circular axis)
In what direction do external longitudinal muscle fibres run (esophagus)?
Parallel to the lumen of the esophagus (longitudinal axis)
Where is the esophagus in the body?
Mediastinum
The internal circular and external longitudinal muscle fibres of the esophagus, together, form…
the tunica muscularis
The connective tissue layer surrounding the external surface of the esophagus is called…
adventitia (dense irregular connective tissue)
What is the nerve plexus in the tunica muscularis?
Auerbachs plexus (between the inner and outer muscle layers)
What is the difference between the Meissner’s nerve plexus and Auerbach’s nerve plexus?
Auerbach’s plexus:
* innervates muscular layers of the tunica muscularis
* Has both sympathetic and parasympathetic inputs
Meissner’s plexus:
* innervates the glands and muscle of the mucosa
* Has only parasympathetic fibres
In the stomach and intestines, there is no adventitia. Instead, they are surrounded by…
serosa (i.e. visceral peritoneum)
The serosa (visceral peritoneum) of the stomach and intestines is formed by a layer of…
mesothelial cells and CT
How do the layers of the tunica muscularis change as we go down the esophagus?
Upper 1/3: One layer of skeletal striated muscle
Mid 1/3: One layer of smooth and one layer of skeletal striated muscle cells
Lower 1/3: Two layers of smooth muscle cells
An incompetent esophageal sphincter causes…
gastro-esophageal reflux disease (may lead to heartburn or esophagitis with erosion of mucosa)
Histologically, how can we identify the gastroesophageal sphincter
There is an enlargement of the circular internal layer of the tunica muscularis
What type of epithelium lines the stomach?
Simple columnar epithelium
What is the main action of the stomach?
To add an acidic fluid (pH 2) and enzymes to the ingested food to transform it to chyme
The stomach secretes the intrinsic factor essential to absorb…
vitamin B12
What happens if a patient does not secrete intrinsic factor?
Vitmain B12 malabsorption, which causes pernicious anemia
Name 2 hormones produced in the stomach?
Gastrin
Somatostatin
What are the 4 regions of the stomach?
- Cardia
- Fundus (considered part of the body)
- Body proper
- Pylorus
Which 2 regions of the stomach are histologically similar?
Fundus and body
Cardia and pylorus
Where are the gastric glands?
Fundus and body of stomach
What types of glands are found in the cardia and pylorus?
Cardiac glands
Pyloric glands
Describe the mucosa of the cardia and pylorus
- Lined by simple columnar epithelium
- Made up of pits that end in glands
- Surface mucous cells (line surface and pits) and secretory cells (in the glands)
Surface mucous cells and secretory mucous cells in the cardia and pylorus produce…
glycoproteins (mucins)
Describe all the layers of the cardia and pylorus
- Mucosa
* simple columnar epithelium
* lamina propria (loose CT)
* muscularis mucosa (inner circular and outer longitudinal with Meissner’s plexus) - Submucosa
- Tunica muscularis
* Internal oblique muscle
* Middle circular muscle
* External longitudinal
Auerbach plexus is between the middle and external muscle.
Outer layer of the stomach (describe it)
Serosa (mesothelial cells and CT, sometimes infiltrated by adipocytes)
What is the only difference between pits and glands of the cardia and pylorus?
Cardia: 1:1 ratio
Pylorus: 2:1 ratio (pit is much longer than the glands)
Name the 4 regions of the gastric glands (fundus and body of stomach)
- Pit
- Isthmus
- Neck
- Base
What is the gland to pit ratio in the body and fundus of the stomach?
1:3 (glands are much larger than the pits)
Epithelium of the body and fundus of the stomach
Tall columnar epithelium
What type of cells make up the isthmus of gastric glands? (2)
Stem cells (undifferentiated) - mitotic actvity
Some parietal cells
What type of cells make up the neck of gastric glands? (2)
Foamy columnar cells (filled with secretory granules)
Parietal cells
What type of cells make up the base of gastric glands? (2)
Zymogenic cells (cymogenic cells with granules) - very basophilic
Parietal cells (very acidophilic)
Surface mucous cells (fundus and body of stomach) contain…
mucous granules (containing carbohydrate-rich glycoproteins - mucins))
The mucous secreted by surface mucous cells contains a high concentration of…
bicarbonate (protects sruface of mucosa)
Mucous neck cells (body and fundus) produce…
acidic mucin (i.e. different from surface mucous cells) - also for protection
What is contained within secretory granules of zymogenic cells (base of gastric glands) (2)
pepsinogen
lipase
Pepsinogen is a pro-enzyme. Describe how it is activated.
Pepsinogen is activated by HCl to become pepsin, a powerful proteolytic enzyme
Other than columnar cells, what other cells are found in the epithelial lining of the stomach (fundus and body)
Enteroendocrine cells (argentaffin cells)
Enteroendocrine (argentaffin cells) secrete… (2)
Where are these hormones secreted?
Gastrin and somatostatin (into the bloodstream)!
What is the purpose of gastrin?
What is the purpose of somatostatin?
Gastrin: Stimulates HCl production
Somatostatin: Inhibits HCl production
What is the role of parietal cells? (2)
Secrete HCl (pH 2)
Secrete intrinsic factor
Damage to parietal cells may lead to…
B12 malabsorption and pernicious anemia
