GI System Histology Flashcards
What are the layers of the mucosa in the GI tract?
- Epithelium
- Lamina propria - connective tissue, small blood vessels and lymphatics
- Muscularis mucosa (smooth muscle)
What are the three principal functions of the GI mucosal layer?
- Secretion – provides lubrication, digestive enzymes, acidic and and alkaline fluids, and bile into the lumen of the GI tract
- Absorption – small molecules of food, water, electrolytes, vitamins, and recyclable products such as bile components and cholesterol into the blood and lymph of lamina propria
- Protection - serves as a barrier to noxious substances, antigens, and pathogenic organisms
What are the principal functions of the submucosa of the GI tract?
provide blood and lymph vessels, nerve plexus, and occasional glands
What are the principal functions of the inner circular layer of the muscularis externa of the GI tract?
compress and mix contents in the lumen
NOTE: Inner circular forms sphincters at specific locations along digestive tract!
What are the principal functions of the outer longitudinal layer of the muscularis externa of the GI tract?
propels the contents by shortening the tube
The muscularis externa of the GI tract is controlled by what?
enteric nervous system
What does the mucosa of the esophagus consist of?
1) SS nonkeratinized epithelium
2) Thin lamina propria with cardiac glands (mucous) at upper and lower ends
3) GALT
4) esophageal glands
What does the submucosa of the esophagus consist of?
mucus-secreting tubuloalveolar glands called esophageal glands proper
mucus provides protection to the mucosa layer
What can be found between the inner circular and outer longitudinal fibers of the Muscularis externa in the esophagus?
Auerbach’s plexus
The esophagus can be divided into three regions. What are these divisions based on?
the amount of skeletal and smooth muscle in the muscularis externa
What is the muscle composition of the upper third of the esophagus?
all skeletal
What is the muscle composition of the middle third of the esophagus?
mixture of skeletal and smooth
What is the muscle composition of the lower third of the esophagus?
all smooth
Skeletal to smooth muscle transition enables what?
voluntary control to involuntary control of swallowing
What layer of the muscularis externa form upper and lower esophageal sphincters?
inner circular
Incompetent inferior esophageal sphincter may cause what?
1) chronic heartburn and erosion of the mucosa or,
2) gastroesophageal reflux disease (GERD)
What is the major function of the stomach and how does it accomplish this?
digestion. It does this by adding acidic fluid and mixing digested content into a chyme
What are the layers of the mucosa of the stomach?
1) epithelium
2) lamina propria
3) muscularis mucosa (typically)
What is the epithelium of the stomach made of?
simple columnar
What does the lamina propria of the stomach contain?
CT, gastric glands, and lymphatic cells
What are rugae?
large longitudinal gastric folds in the stomach (which disappear when the stomach is distended)
What layer of the stomach forms the core of rugae?
submucosa
What are the layers of the muscularis externa of the stomach?
3 layers- an inner oblique, middle circular, and outer longitudinal
The plyoro-duodenal sphincter is formed from what?
the middle circular layer of the muscularis externa
Does the stomach have serosa or adventitia?
serosa (present on all stomach surfaces)
What can be seen in the simple columnar epithelial of the stomach?
surface mucous cells
What do surface mucous cells produce? Why?
alkaline mucous to protect stomach lining from acidic chyme
Invaginations of the stomach epithelium into the lamina propria are called what?
gastric pits
What cell types can be found in gastric glands?
1) stem cells
2) mucous neck cells
3) chief cells
4) parietal cells
5) enteroendocrine cells
What is the role of chief cells in gastric glands and what part of the gland are they primarily found in?
found in the deeper part of gland and secrete pepsinogen
What is the role of parietal cells in gastric glands and what part of the gland are they primarily found in?
most numerous in the upper part of the gland. They secrete HCl and intrinsic factor (which facilitates vitamin B12 absorption in the ileum)
What is the role of enteroendocrine cells in gastric glands and what part of the gland are they primarily found in?
all levels, secrete a variety of gastric hormones into the lamina propria
Where are stem cells found in gastric glands?
only in the isthmus region. Thus, cell division and regeneration is restricted to the isthmus region only.
What is the life span of:
a) surface mucous cells
b) parietal cells
c) enterendocrine cells
a) 3-5 days (thus, most new cells from the isthmus migrate up to this region)
b) 6 months
c) 3 months
What is the difference between rugae, mammillated folds, and gastric glands/pits?
rugae- contain mucosa and submucosa
mammillated folds- small elevations of mucosa only
gastric glands/pits- are not elevations, small holes
What are gastic ulcers?
erosions of stomach mucosa
Helicobacter pylori infection of the stomach causes which gastric ailments?
Cause of chronic gastritis, peptic ulcers, gastric carcinoma and gastric lymphoma
What part of the stomach are helicobacter pylori infections most common?
infection tend to concentrate in neck of gastric glands lined by mucus-secreting cells including the stem cells