Histology of GI Flashcards
What are the 4 main layers of the GI tract?
- Mucosa (innermost) 2. Submucosa 3. Muscular propria 4. Adventitia/serosa (outermost)
Where does the oesophagus sit?
Behind the trachea
What is the epithelium in the oesophagus?
Squamous –> protective mechanism (due to abrasion from food)
Labelled cross-section of oesophagus
What do oesophageal submucosal glands secrete? Where are they?
In the submucosa
Secrete mucous to lubricate the oesophageal wall
What does the muscosa layer of the oesophagus consist of?
Consists of the epithelium, the lamia propria and the muscularis mucosa
What is the muscularis mucosa?
A thin layer of smooth muscle. This layer becomes more pronounced in the distal aspects of the oesophagus.
Describe the submucosa in the oesophagus
The submucosa lies external to the muscularis mucosa and is highly vascular. This layer is formed from loose connective tissue and also contains oesophageal submucosal glands
Describe the muscularis propria in the oesophagus
This is a more substantial quantity of muscle than the muscularis mucosa. At the proximal end of the oesophagus, this layer is formed from skeletal muscle which gradually transitions to smooth muscle in the distal third.
Describe the adventitia of the oesophagus?
The adventitia of the oesophagus is formed from mesothelium and connective tissue
the pale area between the epithelium and the submucosa.
What does the lamina propria contain?
Lymphatic vessels and tissue, capillaries, oesophageal cardiac glands and loose connective tissue
What do the oesophageal cardiac glands secrete?
pH neutral mucous to protect from stomach acid
Where are oesophageal cardiac glands found?
Found within the mucosa of the oesophageal wall. These glands are predominantly found in the distal part of the oesophagus
What do longitudinal mucosal folds in the oesophagus allow?
Expansion to accommodate fod
What is the stomach lined by?
Simple columnar epithelium
What do the cells of the stomach epithelium act as?
Surface mucous cells –> their secretion protects the stomach lining from the harshness of the acidic stomach contents
Describe the musculature in the oesophagus compared to the stomach
Stomach thinner musculature than oesophagus
Describe the difference in mucosa from the oesophagus to the stomach
Oesophagus –> squamous mucosa
Stomach –> glandular mucosa
What effect can excess acid have on oesophagus?
Reflux can cause glandular metaplasia at base of oesophgus (where you wouldn’t normally see glandular epithelium) –> Barrett’s metaplasia/oesophagus
Can cause cancer
What is the epithelium in the cardiac region of the stomach?
Glandular
What is the epithelium in the fundus/body region of the stomach?
Glandular, straight / tubular glands
What is the epithelium in the pylorus region of the stomach?
Glandular, branched/coiled
What glands are present in the cardiac region of the stomach? What are the secretions?
- Cardiac glands
- Mucous based secretions that contribute to the protection of the oesophagus
What glands are present in the fundus/body region of the stomach? What are the secretions?
- Gastric glands
- Gastric juice
What glands are present in the pylorus region of the stomach? What are the secretions?
- Pyloric
- Mucous based secretions
What is the composition of gastric juice?
Water, electrolytes, hydrochloric acid, pepsin, mucous and intrinsic factor
What is intrinsic factor important for?
Vitamin B12 absorption
Describe appearance of surface mucous cells
Columnar cells, pale staining, nuclei oval
Describe location of surface mucous cells
Luminal surface of stomach, partly line gastric pits
What do surface mucous cells secrete?
Protective bicarbonate ions
Describe appearance of parietal cells
Large cells that may appear triangular depending on the section. Spherical nucleus with eosinophilic cytoplasm
Describe location of parietal cells
Along the length of the gland but most in isthmus
What do parietal cells secrete?
Hydrochloric acid
Describe appearance of chief cells
Basally located condensed nucleus and basophilic granular cytoplasm
Describe location of chief cells
Fundus of the gastric gland
What do chief cells secrete?
Pepsinogen (converted to pepsin when it is activated by the low pH of the gastric juices)
How to distinguish the duodenum?
- By the Brunner’s glands – if they are present then you are looking at the duodenum
- If they are absent the best you can say is that you are looking at an area of small bowel
- Villi are present to increase the surface area of the duodenum to increase absorption. They look quite dark because there are scattered chronic inflammatory cells within the lamina propria
What is the effect of coeliac disease on the villi?
Destroys villi so they’re flat –> cannot absorb nutrients
Structure of ileum
- No Brunner’s glands
- Villi
What is the lumen of the SI characterised by?
Folds in the mucosal surface and the presence of villi. These features result in an increased surface area for nutrient absorption and are therefore more numerous in the proximal regions of the small intestine
As the small intestine approaches the terminal ileum, the features associated with nutrient absorption decrease as function prepares to transition to that of the large intestine.
What are the variety of cell types in the intestinal villi?
- Enterocytes
- Goblet Cells
- Paneth Cells
- Neuroendocrine Cells
- Stem cells
- Intraepithelial lymphocytes
What lies at the base of the villi?
The intestinal glands (Crypts of Lieberkühn). The Crypts of Lieberkühn extend from the muscularis mucosae to the luminal surface of the intestine.
What do the Crypts of Lieberkühn consist of?
Enterocytes: absorptive cells
Goblet Cells: Mucin production for lubrication and protection
Paneth Cells: defensive function
Enteroendocrine Cells:
M Cells (microfold cells)
Why is the appendix dark?
Lots of lymphoid cells
Describe the colon
- There are lots of lymphoid aggregates in the large and small bowel
- The colon has a regular crypt architecture with straight tubular glands – the crypts do not branch
- The crypts appear pale because of their mucus content
- The lamina propria looks dark because of the chronic inflammatory cells in it (again normal)
- No villi
Describe the rectum
- No villi
- Thick muscularis propria
Describe the transition from rectum to anus
Glandular (rectum) to squamous (anus)
Stratified squamous epithelium because underlying cells need to be protected more
