Flashcards in 34 - GI System II Deck (69):
What are the 4 main layers of the gastrointestinal tube?
1 - Mucosa
2 - Submucosa
3 - Muscularis externa
4 - Serosa/adventitia
Describe the serosa/adventitia
- The outermost layer of the GI tube can be either serosa or adventitia
- Most of the GI is serosa
- Both have connective tissue
Serosa has an additional component. What is it?
Mesothelium - it is found external to the muscularis externa and includues visceral peritoneum
Note that the adventitia does NOT hav a mesothelium, just an outer connective tissue component
What are the three main components of the mucosa of the GI tract?
1 - Epithelium + basal lamina
2 - Lamina propria (with glands)
3 - Muscularis mucosae
What type of epithelium would you find in the mucosa of the GI tract?
The epithelium rests on the basal lamina
- Mostly simple columnar
- The esophagus and anus have stratified squamous epithelium
What is the lamina propria of the GI mucosa?
A connective tissue layer found external to the epithelium
What type of tissue and glands are found in the lamina propria of the GI mucosa?
Lymphoid tissue and glands
Where is the muscularis mucosae found?
External to the lamina propria in the mucosa of the GI tract
Note that this muscular layer in the mucosa is separate from the muscle in the muscularis externa layer (one of the main 4 layers of the GI tract)
What type of muscle layers are found in the muscularis mucosae?
Two layers of smooth muscle
- Inner CIRCULAR layer
- Outer LONGITUDINAL layer
What are the three main components of the submucosa?
1 - Dense irregular connective tissue
2 - Glands in the esophagus and duodenum (all other glands are found in the mucosa within the lamina propria)
3 - Submucosal (Meissner's) nerve plexus
What are the main components of the muscularis externa of the GI tract?
- Inner CIRCULAR layer
- Outer LONGITUDINAL layer
Note that most area of the GI tract will have smooth muscle
Skeletal muscle is also found in some areas of the GI tract... What areas are these?
Proximal esophagus and distal portion of the GI tube
What part of the GI tract can have three muscle layers in the muscularis externa instead of just two?
What are the two nerve plexuses found in the GI tube?
Submucosal plexus (Meissner's)
Myenteric plexus (Auerbach's)
Where is the submucosal (Meissner's) plexus found?
Between the circular muscle layer and the muscularis mucosae
What is the function of the submucosal (Meissner's) plexus?
- Regulate secretory cells
- Regulate blood flow within the walls of the GI tube
- Innervate the muscularis mucosae
Where is the myenteric (Auerbach's) plexus located?
Between the longitudinal and circular muscle layers
What is the function of the myenteric (Auerbach's) plexus?
What type of neurons does the submucosal (M) plexus contain? What type does the myenteric (A) plexus contain?
Both plexuses contain autonomic neurons
- Parasympathetic postganglionic neurons and processes
- Sympathetic postganglionic fibers (from outside the GI tube)
What type of epithelium is found in the esophagus?
Stratified squamous, non-keratinized epithelium
What is the function of the epithelium of the esophagus
Protects the course texture of a food bolus as it passes through the lumen of the esophagus
Where in the esophageal tissue are glands found?
- Esophageal gland proper with ducts are found in the submucosa
Are there any exceptions to where esophageal glands are located?
Yes, toward to distal and proximal ends of the esophagus, you may also find glands in the lamina propria
What would you call esophageal glands found in the lamina propria?
Cardiac esophageal glands
(NOT esophageal gland proper)
Which end of the esophagus has a more well-developed muscularis mucosae?
The distal end has a much more well-developed muscularis mucosae
We know that in the GI tract, the outer layer can be either serosa or adventitia... Which one is it in the esophagus?
Mostly adventitia, but the distal end becomes serosa as it enters the abdominal cavity
(most of the GI tract is serosa, so this makes sense)
What type of muscle composition is found in the muscularis externa of the esophagus?
Upper 5% is striated
Middle is both striated and smooth
Distal 50% is smooth
What is the Z line?
The dividing line between the esophagus and the stomach
What type of epithelium is the stomach lined with?
- Much thinner than esophagus epithelium (stratified squamous, non-keratinized)
- One cell layer thick
What is Barrett's esophagus?
An abnormal extension of stomach lining into the esophagus due to metaplasia (the epithelium underwent changes)
What other types of cells would you find in a patient with Barrett's esophagus?
Goblet cells - mucus secreted by the goblet cells has protective properties
What will happen to the lower esophageal sphincter in Barrett's esophagus?
It will become dysfunctional, which causes stomach acid to go up into the esophagus
What is a patient with a Barrett's esophagus at risk for?
Esophageal cancer - they will be placed under surveillance
What third of the esophagus is most likely to harbor an adenocarcinoma?
The distal third
How does the staging system for esophageal cancer work?
Basically, the deeper the cancer penetrates outward through the wall of the esophagus, the greater the stage
What does a higher stage of cancer mean?
The prognosis goes down
What is high grade dysplasia or HGD esophageal cancer?
The initial stage of esophageal cancer where the normal cell lining of the esophagus has an abnormal growth within the mucosa
What is meant by T1 (intramucosal) esophageal cancer?
The mass is getting larger and now penetrates deep into the mucosa, however the tumor is still confined within the mucosa
What is meant by T1 (submucosal) esophageal cancer?
The tumor has now extended past the mucosa and into the submucosa
What is meant by T2 esophageal cancer?
The tumor has penetrated through the muscularis
What is meant by T3 esophageal cancer?
The tumor has penetrated through all the layers of the esophagus
What is meant by T4 esophageal cancer?
The tumor is starting to invade a nearby organ
Why would you check the lymph nodes if you diagnose esophageal cancer?
Because they may be harboring cancer cells and if they are, the cancer is more likely to metastasize
Where are lymphatic channels most abundant in the esophagus layers?
Where else are lymphatic channels found in the esophagus layers?
What is the relationship between the penetration of cancer and the likelihood the cancer will invade the lymphatic channels?
The deeper the cancer penetrates, the more likely it will invade the lymphatic channels
Are the lymphatic channels of the esophagus oriented longitudinally or radially?
Longitudinally "up and down"
What will happen if the lymphatics in the upper 2/3 of the esophagus contain cancer cells?
They will spread cranially and will impact the lymph nodes of the neck
What will happen if the lymphatics in the lower 1/3 of the esophagus contain cancer cells?
They will most likely spread caudally and will impact the abdominal cavity and the cardiac lymph nodes
What are rugae of the stomach?
Folds of mucosa and submucosa that are temporarily present when the stomach is empty (flatten out when the stomach is extended or "full")
How many layers of muscle are found in the stomach?
Most regions have two layers, some regions have three
What layers will you find in the mucosa of the stomach
- Lamina propria
- Muscularis mucosae
Describe the lamina propria of the mucosa
- Filled with invaginations of epithelium (the epithelium penetrates into the lamina propria)
- Packed with glands
Are lymphatics well developed in the mucosa?
No - they are much more well-developed in the submucosa
If you have stomach cancer that is confined to the mucosa cells, will you find cancer cells in the lymphatics?
If you have stomach cancer that has developed into the submucosa, will you find cancer cells in the lymphatics?
We know the stomach has a mucosa... But what are all four layers?
1 - Mucosa
2 - Submucosa
3 - Muscularis externa
4 - Serosa
The muscularis externa has three muscle layers. What are they?
- O: Oblique smooth muscle layer (innermost)
- C: Circular smooth muscle layer
- L: Longitudinal smooth muscle layer
There are three types of glands in the stomach. What are they?
Cardiac glands (found in the cardiac region)
Pyloric glands (found in the pylorus region)
Gastric or fundic glands (found anywhere in between)
What are gastric pits?
- Gastric pits are formed by the invagination of the surface epithelium into the lamina propria
- Glands empty into the gastric pits
The actual glands of the stomach are divided into three parts. What are they?
1 - Isthmus
2 - Neck
3 - Fundus (base)
Describe the isthmus of the stomach glands
- Glandular portion
- Stem cells are found here
Why are stem cells necessary in the glands of the stomach?
There is tremendous turnover of the epithelium of the GI tube (7-9 days) and the stem cells are able to replace any cell type found in the epithelium of the stomach
Describe the neck of the stomach glands
- Found below the isthmus
- Parietal cells in this region secrete HCl and intrinsic factor
- More parietal cells than chief cells
Describe the fundus or base of the stomach glands
- Deepest component of the gland
- Contain chief cells that secrete pepsinogen
- More chief cells than parietal cells
What are cardiac glands?
Glands that are found deeper into the lamina propria and have a more irregular arrangement than gastric glands
What do cardiac glands secrete?
Mostly mucous (will be lightly-stained)
What do G cells of the pyloric glands secrete?
The hormone gastrin