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24 terms

GI Histo - Lecture 2 - Upper GI

What is considered the upper GI system?
The esophagus and the stomach.
For the four layers of the GI, explain how these layers are modified in the esophagus.
Mucosa - Stratified squamous epithelium. Also have in the lamina propria, mucosal glands which are called cardiac glands.

Submucosa - contains esophageal glands.

Muscularis - Upper third of the esophagus is skeletal muscle. The middle third is a mix of skeletal and smooth muscle. The lower third is smooth muscle. The skeletal muscles are associated with the voluntary act of swallowing.

Adventitia/Serosa - above the diaphragm it is adventitia, and below the diaphragm it is serosa.

Note: the mucous glands in the mucosa and submucosa both lubricate the surface of the esophagus.
Note to make for the PowerPoint.
Make sure to go through the slides since you are expected to be easily able to identify the four layers throughout the esophagus.

This is important since in some slides the lamina propria is larger than I would expect.

Also need to be able to identify glands (cardiac or esophageal) based on location on the slide. Also need to be able to identify lymphoid nodule in the lamina propria.
What type of epithelium is characteristic of the esophagus and which is characteristic of the stomach?
Stratified squamous epithelium for the esophagus and simple columnar for the stomach.
Explain Barrett's esophagus.
Esophageal erosion occurs with reflux of stomach acids into the lower esophagus. This then causes the metaplasia of columnar epithelial cells from the stomach to go into the lower esophagus.

This condition occurs as a result of the esophageal sphincter (both intrinsic and extrinsic components) being compromised and allowing the reflux of stomach acids into the esophagus.

Important to note that having Barrett's esophagus is preliminary to esophageal cancer.
What cell type causes the metaplasia in Barrett's esophagus?
Residual embryonic cells (REC) located in the stomach at the junction with the esophagus.

After the squamous epi of the esophagus gets damaged, these REC migrate and grow.
What is Schatzki's ring?
This is a pathological condition in which the mucosa reduces the lumen size of the distak esophagus. If the patient does a barium X-ray you have see a bolus of food getting hung up on a barrier in the esophagus.

Schatski's ring is the body's way of dealing with GERD.

Is the lumen becomes so narrow that it is less than 1cm, then the patient will have trouble swallowing.
For the four layers of the GI, explain how these layers are modified in the stomach.
Mucosa - Simple columnar epithelium. Contains gastric pits and gastric glands.

Submucosa - Contains no glands.

Muscularis - Contains 3 muscle layers.

Serosa - Peritoneal.
Make sure to look at PowerPoint.
Expected to be able to identify the four layers in the stomach.

Need to know that the mucosa contains gastric glands. Also need to know that the submucosa contains connective tissue, veins, and arteries.

Also need to be able to identify that the gastric pits are well above the gastric glands on a slide.
What are the four major parts of the stomach?
1. Cardia - the initial part of the stomach.
2. Fundus - extends superiorly.
3. Body.
4. Pylorus - Known as the "gate keeper" in Latin. It is the exiting portion of the stomach.
What are stomach rugae?
These are longitudinal folds of mucosa and submucosa. Thus these are deep folds.

It is important to note that when the stomach stretches out, these rugae flatten out.
Describe the anatomy of a stomach gastric pit.
The lining of the stomach is a continuous sheet of columnar epithelium. So the gastric pit is an invagination of this epithelium. The surface epithelial cells are mucus secreting cells! = TQ.

Connected to the bottom of the gastric pit is the gastric gland. These glands contain different types of cells.
List the four cells that are in the gastric gland.
The gastric gland, which is connected to the gastric pit, contains:

Mucus neck cells.
Parietal cells.
Enteroendocrine cells.
Chief cells.
Explain how different parts of the stomach have variations in glandular makeup.
The cardia of the stomach has shallow pits which contain mucous glands.

The fundus and body of the stomach have medium pits which contain fundic (gastric) glands that put out enzymes.

The pylorus of the stomach contains deep pits which contain mucous glands.
Refer to PowerPoint.
Make sure that you can identify gastric glands and ducts, even though they are unusually far from one another. The last slide in the lecture has an additional picture that will help with this.

Also make sure that you understand that the gastric ducts and or glands invaginate into the lamina propria.

Need to be able to identify chief and parietal cells on a slide based on location. You can identify these cells in the deep cells of gastric glands.
How would you identify chief cells on a slide? What about parietal cells?
Would want to make sure that are looking at gastric glands and the dark cells around the edge of the gland, dark because have RER, are the chief cells.

Parietal cells should be able to be seen on the same slide that you see chief cells. The parietal cells are more pale colored and quite large and triangular/ stretched pentagonal in shape.
What do parietal cells produce? describe the appearance and category of these cells.
HCl and intrinsic factor.

Parietal cells are simple columnar epithelial cells.

Important to note that foldings of the plasma membrane produce extensive intracellular canaliculi. This helps to pump out the large amount of protons. So have more surface membrane for proton pumps.
What happens to RBC formation in the absence of B12?
The RBC formation decreases.
What paracrine hormones stimulate HCl production by parietal cells?
Gastrin and histamine.

HCl is also stimulated by Ach.
Explain how parietal cells produce HCl.
1. carbonic anhydrase facilitates the production of carbonic acid.
2. ATPase mediated pumping of proton out of the cell.
3. ATP based carrier proteins pump Cl out of the cell.
4. H+ and Cl- combine extracellularly in the canaliculi and then into the lumen of the stomach the HCl goes.
What are the three mechanisms that the stomach lining uses to protect itself from HCl?
1. Mucous secretions from surface/neck cells.
2. Trapping of bicarb in the mucous.
3. Prostaglandin medicated rich blood flow in the lamina propria.
What do chief cells do?
They synthesize enzymes and thus the cells contain zymogen granules.

The zymogen granules are released on the apical surface. The basal surface contains abundant RER, which is necessary to synthesize the zymogens.

These are called chief cells because they are the most commonly found cells in the stomach.
What does a stomach mucous cell do? What type of cell is this?
Stomach mucous cells are simple columnar epithelium. They have mucous granules in the apical portion of the cell cytoplasm.
What are enteroendrocrine cells? What do they produce? Give two examples. What are some other names for these cells.
Enteroendocrine cells (in addition to paracrine cells) are plentiful in the GI tube. They in general secrete peptide and amino acid HORMONES.

Examples: Gastrin and histamine.

These called are also called Diffuse Neuroendocrine system.