the lower GI tract Flashcards
what is the structure of the small intestine?
long, coiled, hollow tube. consists of the duodenum (which extends from the pylorus), the jejenum (where majority of nutrient absorption occurs) and the ileum which joins the colon of the large intestine.
how does the small intestine have such a large surface area?
it is very long and has many folds (pilcae circulares) these folds are covered in villi, which are also covered in microvilli.
what is the brush border?
the villi on the mucosal surface of the small intestine + enzymes.
what are the crypts of Lieberkhun?
they are glands found between villi in the small intestine. they house secretory cells.
what is the function of secretory cells in the crypts of Lieberkhun?
to secrete bicarbonate rich intestinal juices
what are the functions of the small intestine?
secretions and chemical digestion
what is secreted by the small intestine?
alkaline intestinal juice, enzymes produced by absorbative cells lining the villi. also intestinal glands contain endocrine cells which secrete hormones.
what are the endocrine cells that secrete hormones in the small intestine and what do these hormones do?
K cells- secrete gastric inhibitory peptide (inhibits HCl and stimulates insulin production)
S cells- secrete secretin, involved in osmoregulation and bicarbonate production regulation.
CCK cells- secrete cholecystokinin which stimulates bile release to digest fats and proteins.
what takes place in the duodenum?
chyme is mixed with pancretic juice and bile. enzymes break down nutrients in the chyme.
what happens when the nutrients have been broken down?
the end products are absorbed by mucosal epithlial cells–> transported to interstitial space and then absorbed into capillaries where they enter the bloodstream
what is the structure of the large intestine?
made up of the caecum, colon and the rectum. it has Teniae coli which are bands of smooth muscle these bands result in Haustra (pockets) that give the L intestine a segmented look. It has no folds.
what is the function of the large intestine?
motility (contracts in segments to move bolus via peristalsis) mucus secretion (lubricates bolus and faeces) no role in digestion but absorbs leftover ions, minerals and vitamins in bolus.
what is the structure of the colon of the large intestine?
ascending colon, transverse colon, descending colon and signoid colon which empties into rectum.
what are the functions of the
colon?
faeces production
water absorption
faeces storage
absorption of vitamins produced by bacteria
what is the role of bacterial colonies in the colon?
ferment carbohydrates and release gases.
synthesise vitamin B and K
breakdown bilirubin into pigments.
how does defecation occur?
both the external and internal anal sphicters need to relax.
