GI histology Flashcards
What are the two predominant epithelial types of the GI tube?
Stratified squamous non-keratinised epithelium (for the anal canal and the mouth) and simple columnar epithelium.
What is the epithelium in the mouth?
Difference in these papillae?
Circumvallate are named because they have the boundary wall around them (shown in red).
The circumvallate also contain some glands which aid in the taste sensation.
Filiform papillae are spiny and contain keratin which means that they are friction generating.
What are acini?
Other parts of a gland?
Acinar=secretory=the circled bit which is resonsible for the secretions.
Multiple acinar will end up near a small duct which join to form a bigger and bigger duct which eventually makes the big parotid duct to the outside world.
The glands need some connective tissue so that everything is kept in place (otherwise they will be like grapes being thrown around).
From the capsule there is connective tissue partitions (septa and trabeculae) coming inside the gland separating the glands into small parts which gives rise to the lobes and lobules.
These septa will connect the blood vessels and nerves to the inside of the gland.
Connective tissue is not uniformly thick, the parotid gland is very thick, this is why when parotid is infected it is very painful.
Difference in these glands? Where would they come from in the mouth?
Parotid almost always serous: circular acinar.
Sublingual mucous: much more pale because mucous is pale, big acinar with individual cells visible.
Submandibular: mixed, dark and light colour. Both serous and mucous acinar.
There are also minor glands in the mouth also.
Explain the difference in a serous vs mucous secreting gland?
What type of gland is this?
What is this?
What cells are ducts made from?
Cuboidal or short columnar.
Heaps of mitochondria this is because they contribute by altering pH. Mitochondria are normally stacked at the bottom of the cell within basal infoldings. This pushes the nucleus to the middle of the cell. On the other side are more mitochondria. All the mitochondria actually make the cell a darkish colour.
How can ducts transmit fluid antigravity?
Travel against gravity both parotid and sublingual.
To enhance this travel there are a special smooth muscle like cells (they are actually epithelial cells but have contractile units). Myoepithelial cells. They can squeeze the acinar which push the saliva into the duct, the myoepithelial cells also sit a long side the ducts which can push it along.
Explain the walls of a gut tube (and what is in each layer, including plexus?)
5th ‘layer’ is the serosa which is nothing but the peritoneum. Not apart of the gut tube however. It is not always present around the gut (think about the colon as it is retroperitoneal.
Explain the gut wall in the oesophagus?
The little blue things are the mucous secreting cells which sit in the submucosal layer.
There are only two places where you will find submucosal glands and the oesophagus is one of them, this makes it easy to tell if you are looking at the oesophagus.
Inbetween the circular and longitudinal muscle you find the myenteric plexus.
There is no serosa in the oesophagus.
If you want to distinguish the lamina propria from the submucosa then….
look for the muscularis mucosa which is brown.
What is the purpose of the stomach rugae?
Stomach can only expand toward the left hand side because the liver is on the the lesser curvature. This is why there is a lot of rugae on the greater curvature, they are folds.
There are lines down the lesser curvature which aid liquids to the sphincter.
Explain the gastric mucosa?
What occurs with the muscularis mucosa?
Lots of very deep pits in the stomach. These are pores.
The depth of the pore is called a pit.
Lots of branches at the bottom of the pit called the glands.
These glands are within the lamina propria.
Inside the glands are many types of cells but on the surface there is one type of cell, gastric cells simple columnar cells (this is where the epithelium changes, it will only change back to stratified squamous when we get to rectum).
What are the 4 exocrine cells in the stomach?
Where are these cells normally found?
Surface cells produce mucous: protection from acid. The pit is also lined with these cells for protection, lots of RER to secrete these mucous.
Glands contain:
Neck which has a lot of mucous neck cells (likely to be thicker mucous for protection).
Chief cells and parietal cells are digestive cells which are at the bottom of the gland.
Chief cells secrete digestive enzymes, columnar cells, protein secreting therefore RER and mitochondria.
Parietal cell (oxyntic cells) more toward the lumen than the chief cells.
Two more types of cells, the neuroendocrine cells which are all the way through the gut.
stem cells found everywhere (often at the bottom) always right at the bottom for protection.
Some stem cells are also found at the neck exclusively in the stomach. This is because the cells are sheading often and need to be replaced at the top of the pits and covering the surface.
What cell type is this and what does it secrete?
Parietal cell/oxyntic cell
What are all of the foldings of the small intestine?
What are the names of the invaginations of the small intestine?
Glands/crypts.
Open as small apetures between villi.
What are the cells of the intestine?
What is the layer on top of the microvilli in the intestine?
Its function?
On top of the microvilli is a protective layer (in yellow) called the glycocalyx coat.
It has several functions 1. protection from infection 2. protection of acid, 3. contains some digestive enzymes which break down the end products of carbs and proteins (final stage of digestion aka disaccharides to monosaccharides).
What are the cells in the crypts of the small intestine?
What is the major striking feature of the duodenum? Explain the function?
Major striking feature in the duodenum is the submucosal glands. Look at the epithelial layer and if you see villus then it is the duodenum for diagnostics. If it is flat then it is the oesophagus. Acid chyme you need more alkaline mucous secreted by these glands.
In the jejunum and ileum there are no submucosal glands.
Where would you find peyers patches?
What is diagnostic of the large colon?
Haustra and appendices epiploicae.
Explain the epithelia and structure of the colon?
Large intestine is more simple.
There are no villous, but there are still glands but these glands are a lot more simple (called tubular glands).
Histology of the appendix?
