Esophagus and Stomach Flashcards
What are the four layers of the digestive tract from inward to outward?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa / Adventitia (Fibrosa)
What are the layers of the mucosa and their properties?
- Epithelium - SSNK or simple columnar
- Lamina propria. LCT + diffuse or nodular lymphatic tissue called GALT, maybe containing mucosl glands
- Muscularis mucosae - Thin layer of smooth muscle, with inner circular and outer longitudinal components.
What is the submucosa of the digestive tract? Where does it contain glands?
Dense irregular connective tissue with blood vessels, lymphatics, and nerves. Contains ganglion cells of the submucosal or Meissner’s plexus.
It contains glands in the esophagus and duodenum only.
What is the muscularis externa? What type and arrangement of muscles is it?
Two muscle layers normally: inner circular and outer longitudinal. Smooth muscle except in beginning of esophagus and end of anal canal
3 layers in stomach - inner oblique added
Contains Ganglia of myenteric (Auerbach’s) plexus
What is the myenteric / Auerbach’s plexus?
Plexus found between layers of muscularis externa. The ganglia are found here and are a component of the intrinsic enteric autonomic nervous system
- Regulate peristalsis and secretory functions of mucosa and submucosal glands
What is the serosa / adventitia layer of the digestive tract?
Serosa (peritoneal) - outer layer of CT covered by a simple squamous mesothelium
Adventitia (fibrosa) (retroperitoneal) - no mesothelial covering when retroperitoneal, just CT
What is definitive about the lining of the oropharynx?
- SSNK epithelium
- Prominent elastic layer in lamina propria that sends fibers to anchor mucosa into muscle layer
- Submucosa typically not present
- Has an adventitia (not peritoneal)
What is definitive about the mucosa of the esophagus?
- SSNK epithelium
- Mucosal or cardiac glands near ends of esophagus in lamina propria
- Muscularis mucosae is a single, well-developed layer of longitudinally oriented smooth msucle
What is distinctive about the submucosa of the esophagus?
Has esophageal glands proper - submucosal glands.
They are compound tubuloalveolar glands, which are mostly mucous, but are some serous cells that produce LYSOZYME
How does the muscularis externa of the esophagus change travelling downward?
Upper third is skeleton, transitions to smooth muscle by lower third. (Voluntary to involuntary swallowing)
What happens at the esophagogastric junction in terms of the epithelium?
There is an abrupt change from stratified squamous nonkeratinized to simple columnar
What are the three histological regions of the stomach?
- Cardiac stomach - contains cardiac glands
- Fundic stomach - gastric or funduic glands
- Pyloric stomach - pyloric glands
What are rugae?
TEMPORARY longitudinal folds of the SUBMUCOSA present in stomach, for expansion / filling
What are mammillated or gastric areas of the stomach?
Small, bulging areas of the stomach which represent thickened mucosa, for increased surface area for secretion.
What are gastric pits?
Indentations or holes in mucosa which mucosal glands of the stomach empty into.
What characterizes the surface epithelium of the stomach and what is its function?
Simple columnar epithelium which covers surface and gastric pits with surface mucous cells. They produce a thick, cloudy mucus which has a high bicarbonate content to protect the epithelium from acidic damage
Where do the mucosal glands of the stomach lie?
In the lamina propria of the mucous layer. includes cardiac, gastric, and pyloric.
What characterizes the muscularis mucosae of the esophagus / stomach?
It is deep to the glands, but has smooth muscle projections between the glands to contract and empty the glands
What are the layers of the muscularis externa of the stomach and its general function? Where is the myenteric plexus found here?
Inner oblique, middle circular, outer longitudinal. They function to contract and homogenize food as the gastric secretions are added, creating chyme.
Myenteric plexus: between circle and longitudinal layers
What are the two staining areas of gastric glands and what accounts for this?
Upper portion: eosinophilic - parietal cells
Lower portion: basophilic - chief cells
What cells are found primary in the neck area of gastric glands + their function?
Mucous neck cells - produce a soluble mucinogen which is different than surface mucous cells
Parietal cells - Acidophilic cells which secrete HCl and produce gastric intrinsic factor
What is the appearance of parietal cells and why?
They contain intracellular canaliculi which are deep plasma membrane invaginations. Increases SA for secretion of HCL. They also have abundant mitochondria to make them look eosinophilic.
How do parietal cells produce HCl? This is convoluted
Through carbonic anhydrase, which converts water and CO2 into H+ and HCO3-. Active cells have tubulovesicular membranes which contain H+,K+ ATPase that fuse with plasma membrane to increase intracellular canaliculi.
Anion exchanger pumps out bicarbonate and brings in Cl-. Cl- is channeled out by passive transport.
K+ is brought into the cell by Na+ / K+ ATPase, allowed to diffuse into lumen to be used in H+ / K+ ATPase exchanger, to bring K+ back in and pump out H+.
The H+ and Cl- are ultimately released into the gland, while NaHCO3 is in the lamina propria.
What happens to inactive parietal cells?
An increase in cytoplasmic tubulovesicular membrane system, with canaliculi retracted back into the cytoplasm
What stimulates HCl secretion by parietal cells?
Gastrin, acetylcholine, and histamine
What is gastric intrinsic factor?
Glycoprotein produced by parietal cells which complexes with vitamin B12, which is necessary for small intestinal absoprtion
How is heartburn treated?
Histamine receptor antagonists, which competitively inhibit histamine receptors which stimulate parietal cells
What would happen if gastric intrinsic factor was not produced?
Lack of B12 uptake and subsequent anemia
Why are chief cells basophilic?
Because they have lots of rough ER and prominent golgi complexes for the production of pepsinogen granules
What are pepsinogen granules?
Granules concentrated apically in the chief cells, which contain pepsinogen. It is the zymogen form of pepsin which is activated by acidic gastric juice to form pepsin, which aids in protein digestion.
Where are enteroendocrine cells found? What is open vs closed?
Singly distributed through the gland. All put together, they would be the largest of the endocrine glands
All cells rest on basal lamina, but not all contact the lumen.
Open: contact lumen
Closed: do not contact lumen
Where are enteroendocrine secretions released and what is their mode of action?
At the basal surface to be released towards the lamina propria. They have a paracrine or true endocrine function.
What do enteroendocrine cells respond to and how do they stain?
Respond to pressure, luminal content, or neuroendocrine stimulation
Stain argyrophilically
How are enteroendocrine cells classified and what is the main one of the stomach?
Classified by secretory product and granule morphology
Primary: Gastrin cells
What is location, function, and inhibition of gastrin cells?
Gastrin cells - located in pyloric region
Function - stimulate HCl production by parietal cells - they detect when pH is too high
Inhibited by: Somatostatin, which also inhibits other GI hormones. It is produced by somatostatin cells in duodenum
What other endocrine products are secreted in small intestine but function in the stomach?
Secretin (this is weird) and gastric inhibitory peptide - inhibit gastric acid secretion.
Motilin - increases GI motility
Where are undifferentiated stem cells of gastric glands? What is their function?
In the base of pits and the neck of glands.
Function: Renew surface epithelium every 3-5 days
Cells in gland - every 180 days (much less frequent)
What is the location and function of cardiac glands?
Location: cardiac region of stomach, they empty into short gastric pits in a thin mucosa
Function: Mucous cells secrete mucus to help protect esophageal epithelium from gastric reflux
What other cells are in cardiac glands?
enteroendocrine, mucous neck cells, and undifferentiated stem cells
What is the appearance and location of pyloric glands?
Appearance: Have long gastric pits, much deeper than cardiac or gastric glands
Location: Pyloric region of stomach
What is the function of pyloric glands?
Primarily mucous cells which secrete mucus to protect pyloric mucosa
Also secrete lysozyme as an antibacterial
Pyloric glands also have the gastrin-produing enteroendocrine cells
What is the lamina propria of the pyloric glands like?
Contains more lymphatic tissue than seen in lamina propria of other stomach regions.
Where does Helicobacter pylori reside and what is its action + its consequence?
Resides in pyloric region of stomach, producing ammonia via urease to neutralize acid locally and let bacteria survive. The bacteria survive and cause destruction of surface epithelium, causing gastric ulcers + bleeding.
How does H. pylori perturb the pH of the stomach?
They inhibit somatostatin-producing cells, which causes an increase in gastrin release via gastrin cells. Gastrin stimulates gastric juice release via parietal cells.
