Case 1 Histology Flashcards
what are the 4 layers of the wall of the GI tract? what is in each?
• Mucosa = innermost layer which consists of an epithelium, an underlying lamina propria and a layer of smooth muscle (muscularis mucosa)
- epithelium (protective, secretive and/or absorptive)
- lamina propria = connective tissue containing vessels, glands & lymphoid tissue
- muscularis mucosa smooth muscle (inner circular, outer longitudinal), moves the mucosa – this muscular layer is only for local movements
• Submucosa = a (dense irregular) connective tissue layer that contains blood vessels, lymphatics and Meissner’s plexus (submucosal plexus)
- supports mucosa
- glands in some regions
• Muscularis externa = a smooth muscle layer, whose inner fibres (squeezes gut) are arranged circularly and outer ones longitudinally (shortens gut) – contains the myenteric plexus
- responsible for GI movements (peristalsis, segmentation)
• Adventitia = outer, connective tissue layer which contains blood vessels and lymphatics – it’s referred to as a serosa if it is covered by a mesothelial layer
- Serosa is a serous membrane that covers those structures within the peritoneal cavity (if it is intraperitoneal, it is classed as serosal as the serous membrane is visceral peritoneum)
- Extraperitoneal structures are attached to surrounding structures by connective tissue fibres that form the adventitia (if it is extraperitoneal, then it has an adventitia and the extraperitoneal structures are attached to surrounding structures by connective tissue fibres that form the adventitia)
what is the epithelium stained like?
stained dark purple due to the high proportion cellular material
what is the epithelium of the oesophagus?
non-keratinised stratified squamous
what does the submucosa of the oesophagus contain? what staining like? what is muscularis externa layer like? what about outer layer?
- many elastic fibres which allows the oesophagus to distend during swallowing
- seromucous glands whose secretions aid lubrication
- they are particularly numerous at the distal end of the oesophagus as the mucous that they secrete protects the oesophageal mucosa from gastric acid reflux
- blood vessels, lymphatics, nerves
- pale staining
- muscularis externa - layer in the top third of the oesophagus contains skeletal muscle, in the middle, it is a mixture of smooth and skeletal muscle and in the bottom third it is entirely smooth
- adventitia but the last part is serosa
what is the mucosa of the stomach packed with?
branched tubular glands which penetrate through the lamina propria
what extends form the luminal surface to the gastric glands? what is at the base of the gastric glands? what type of epithelium present? what cells are present in the gastric gland?
- gastric pits
- thin muscularis mucosa
- (mucous columnar cells), simple columnar epithelium
Cells present:
- Surface lining
- Mucous neck
- Parietal
- Chief
- Neuroendocrine
what’s in the submucosa of the stomach?
loose connective tissue and contains numerous blood vessels
what is the arrangement of the fibres of the muscularis mucosa in the stomach?
arranged in three layers; inner oblique, middle circular and outer longitudinal = more muscle for churning
what can be seen between the muscle layers in the stomach?
blood vessels and nerves (myenteric plexus)
what forms the outer layer of the stomach wall?
thin serosa
how can the pyloric end of the stomach be distinguished?
presence of the gastric glands and the thick muscle of the pyloric sphincter
describe the mucosa of the duodenum
- the villi projection into the lumen are covered with simple columnar epithelium
- with goblet cells
- crypts of Lieberkhuhn are short tubular gland that are continuous with the base of the villi
when the crypts of Lieberkhuhn are cut in cross section, what do they look like?
circular spaces that are surrounded by tall columnar epithelial cells
what separates the mucosa from the submucosa?
muscularis mucosa
what’s in the submuscosa of the duodenum?
- in the area close to the gastric junction, numerous Brunner’s glands are present
- these glands project into the mucosa
- they secrete mucous and HCO3- for protection against acid and to increase pH
- they are only found in duodenum
- (they secrete an alkaline fluid composed of mucin, which exerts a physiologic anti-acid function by coating the duodenum epithelium, therefore protecting it from the acid chyme of the stomach)
how many layers in the muscularis externa of the duodenum?
2 - circular and longitudinal
what is the outer layer of the duodenum? what does it contain?
- the first part of the duodenum is covered by a serosa
- in this case it is quite thick and contains numerous blood vessels and fatty tissue
- the rest is covered by adventitia
(In the abdomen, whether an organ is covered in adventitia or serosa depends upon whether it is intraperitoneal (serosa – a layer of mesothelium, the visceral peritoneum) or retroperitoneal (adventitia))
describe the mucosa of the jejunum
- Plicae circulares – circular folds in the mucosa and submucosa
- Mucosal villi project from the plicae into the lumen and crypts of Lieberkuhn extend from the villi to the muscularis mucosa
- Simple columnar epithelium covers the villi
- The brushborder effect on the surface of the epithelial cells is formed by microvilli
- The lamina propria containing blood vessels and nerves projects into each villus
- The lamina propria of each villus also contains a blind-ended lymphatic capillary, termed a lacteal
describe the submucosa of the jejunum
- no specific features
- very thin
describe the muscularis externa of the jejunum
between the inner circular and outer longitudinal layers there is the myenteric plexus
describe the outer layer of the jejunum
thin serosa forming the outer layer of the jejunum (consists of simple squamous epithelium and a connective tissue layer underneath (lamina propria serosae)?)
how can the ileum be distinguished?
- by the presence of Peyer’s patches
- large lymphoid nodules that are located in the mucosa
what is the wall of the ileum like? outer layer?
- structure similar to that seen in the other parts of the small intestine
- similar to jejunum with less plicae circulares and villi
- serosa
describe the mucosa of the large intestine
- There are no villi present (as don’t need to increase surface area for absorption of water) but numerous straight, tubular glands (crypts) extend from the luminal surface down to the muscularis mucosa
- The epithelial cells are simple columnar with short blunt microvilli
- Many GOBLET CELLS (appear as empty spaces on H&E stained specimens - pale stain) are present throughout the epithelium (they are a secretory epithelial cell lineage found in both the small and large intestines – they produce mucus, which is composed chiefly of mucins and inorganic salts suspended in water – important component of mucosal barrier which serves as a lubricant and aids in the preservation of the epithelium)
- The dark stained nuclei of many LYMPHOCYTES can be seen throughout the mucosa and submucosa
describe the submucosa of the large intestine
many lymphocytes (dark stain)
describe the muscularis externa layer of the large intestine
- The muscularis externa looks different here compared to the small intestine
- The inner circular fibres appear similar to elsewhere in the tract but the external longitudinal layer is incomplete
- It does not surround the whole of the gut tube, instead it is arranged as three distinct bands termed teniae coli
- most of it is only one layer of inner circular muscle
- however, in some parts it is 2 layers and the second part is longitudinal muscle but it is seen in 3 bands called teniae coli – this ruffles the large intestine
describe the four layers of the appendix
- Appendix is a blind evagination of the caecum and therefore presents the same four layers as the large intestine
- However, the lumen is small and there are fewer glands in the mucosa
- There are no teniae coli and the muscularis mucosa is composed of two complete layers
- Numerous lymphocytes are present on the mucosa and submucosa
- It’s surrounded by a serosa
describe the four layers of the appendix
- Appendix is a blind evagination of the caecum and therefore presents the same four layers as the large intestine
- Mucosa
- simple columnar epithelium
- small lumen
- many lymphocytes
- fewer glands in mucosa
- Numerous lymphocytes are present on the mucosa and submucosa
- There are no teniae coli and the muscularis mucosa is composed of two complete layers
- It’s surrounded by a serosa - note the mesoappendix which attaches the caecum to the appendix
what are the modifications of the small intestine to increase surface area?
- Plicae circulares (especially lower part of duodenum and jejunum)
- Villi
- Microvilli
describe the gastro-oesophageal junction
- epithelium
- submucosa
- muscle
- Epithelium is non-keratinised stratified squamous
- Seromucous glands are located in the submucosa
- Smooth muscle
in the stomach, where are veins located?
submucosa
what is the function of the rugae in the stomach?
enable the expansion of the stomach
