Intestinal microanatomy Flashcards
What are the three main ways the small intestine is adapted for absorption?
Plicae circularis - big transverse folds (like the rings of the trachea)
Villi - finger like projections that come off the plica circularis consisting of simple columnar epithelium (most prominent in the jejunum section of the small intestine)
Microvili - creates a brush border on top of the enterocytes that form the villi. (simple columnar epithelium)
what are the three main structures inside of a villi and what is there function?
Capillary vessels - absorbs glucose and amino acids and drains them down into the submucosa where there are tributaries of the hepatic portal vein which can take the nutrients away
Lacteals - tiny vessels which transport lipids and glycerol into the lymphatics (also located in the submucosa)
Smooth muscle - has two functions. It contracts in order to cause rhythmic beating of the villi which increases during digestion. It also contracts to help squeeze/milk the lacteals.
What is the film formed on top of microvilli called and what is its function?
The glycocalyx. This is the “sugar coat” which is found on top of the microvilli which acts as a selective barrier by attracting desirable molecules and blocking unwanted molecules.
What is the signigficance of the actin contained in the microvilli?
The actin is embedded in the cytoskeleton of the smooth muscle which means when the muscle contracts it is transmitted into the microvilli and makes them beat.
Where are brunners glands found and what is their function?
Brunners glands are only found in the submucosa of the duodenum and are responsible for producing an alkaline mucous. This mucous helps to change the pH from the acidic 1-2 pH in the stomach to the alkaline 7-8 pH needed in the small intestine as its epithelium is not designed to survive in acidic environments.
Where does the majority of food absorption occur in the small intestine?
In the jejunum.
Are the different parts of the small intestine surrounded by serosa or adventitia?
Duodenum (prox half) = serosa (intraperitoneal)
Duodenum (dist half) = adventitia (retroperitoneal)
Jejunum and ilieum = serosa (intraperitoneal)
Where are peyers patches found and what is their function?
Peyers patches are aggregates of lymphatic tissue found in the submucosa of the ileum. This lymphatic tissue is required as the ilieum is interfacing/passing into the colon where there is a lot of bacteria.
These are macroscopically visible (with the naked eye) and are big purple splotches because lymphocytes stain dark purple.
What are the two main cell types present in the mucosa of the large intestine (colon)?
Columnar absoprtive cells - absorb water from the chyme so it becomes harder/ more compact
Goblet cells - secrete mucus to lubricate the chyme/faeces
What are the three distinguishing features of the large intestine?
Teniae coli - three distinct strips/bands of muscle running along the colon that allow each segment of the colon to contract independently
Haustra - pocketlike sacs created when the teniae coli contract
Epiploic appendices - fat filled pouches of visceral peritoneum
Describe the pattern or cell renewal and differentiation in the digestive tract? Relate this to chemotherapy and why it cause nausea/diarrhoea
The surface cells are very mitotocially active and renew every few days whereas the deeper cells renew only every couple of months.
Chemotherapy targets the mitotic-ally active cells (surface cells) which means they shed and cause diarhhoea.
