gastroenterology- small bowel Flashcards
function of small bowel?
absorb nutrients, salts and water
What is function of mesentery?
anchors small and large bowel from abdonminal wall, allowing movement
and provides conduit for vessles and nerves
What makes up small bowel and is exclusive to it?
villi
characteristics of villi?
what cells make up villi?
enteroctyes - absportive
secretory - scattered goblet and enteroendocrine cells
what cells make up up crypts of lieberkuhn?
Paneth and stem cells
What are characteristics and function of enterocytes?
tall columnar cells with micro villi and basal nucleus
specialsited for absoprtion and trasnport of substnaces
life span 1-6 days
LARGE SA
what is another word for brush border?
microvilli
what is the surface of microvilli covered in?
glycoclayx
Which membrance is glycocalyx found?
What is its function?
apical
protection from digestional lumen
produces ‘unstirred layer’ - that regulates rate of absoprtion from intestinal lumen
What is the unstirred layer?
layer of water and mucous
What do goblet cells contain?
mucous containnig granules at apical end of cell
What is the function of mucous of the goblet cell?
faclitates passage of material through bowel
distribution of goblet cells?
as you go down bowel more goblet cells,
more in colon
not a lot in duodenum
where are enternedocrine found?
scattered among enterocytes
in lower parts of crypts
What is function of enteroendorine cells?.
hormone secreting - affect gut motility
where are pnaeth cells?
bases of crypts
what do paneth contain?
large acidophlic granules
what do paneth granules contain?
lysozyme, protects stem cell
glyocopritnets and zinc
(zinc can be used as essential trace metal for no of enzs)
what are other functions of paneth cells?
engulf bacteria and protoza
regulating intestinal flora
What is purpose of stem cells in GI tract?
continaully replenish surface of epithelium
migrate to top of villus replace cells at top of villus
can divide to many cell types - pluripotent
why do enterocytes and goblet cells have short life span?
only 36 hours
can be affected bt toxic substances in diet and lesions are short lived - important as they are first line of defense against GI pathongens
How are entercytes replenished?
escalator like transit
if impaired by e.g radiation severe intestinal dysfunction
is there a sudden transition between duodenum,jejunum,ileum?
NO
How is duodenum distingushed?
they have brunners glands
submucosal coiled tubular mucous glands secrete alkaline fluid, open into base of crypts
what is purpose of alkaline secretions of brunner’s gland?
neutralizes acidic chyme from stomach
optimise pH for action of pancreatic enzymes
difference between jejunum and ileum?
jejunum - thick waller than illem as it has more plicae circualres
differnet attachment to aorta - jejunum above and left, ilem below and right
jeje- few arcades and long terminals, iluem - more arcades and shorter terminals
iluem only has peyers patch
functions of small intestine motility?
what are 3 movement parts of motility?
segmentations
peristalis
migrating motor complex
What is segmentation?
mixing
stationary contraction of circular muscless
more freq in duodenum
pix pancratic enzyme and bine to mix chyme
what is peristalisi?
sequestial contraction of adjacment rings of smooth muscles
propels chyme towards colon
what is migrating motor complex?
cycles of smooth muscles contraction sweeping through cut
prevents migration of coloinc bacteria in ileum
how do pancreatic enzymes and bile enter duodenum?
from common bile duct and main pancreatic duct
where else are enzymes produced apart from pancrase?
duodenal epitherlium
where does digestion of carbs being + by which enzyme?
mouth
salivary a amylase - destroyed in stomach by low pH
Where does pancreatic a amylase have it effects?
secreted into duodenum in response to meal
continues digestion in small bowel
what does a amylase need to work optimunally?
Cl- and neutral/slightly alkaline pH
where exactly in small bowel does it have it effect?
- mainly lumen and adsorbs brush border then after the products
digestion of amylase products occurs at bursh border
How is glucose and galactose absorpted?
by secondary active tranposrt
SGLT-1 apical membrane
How is fructose absoprted?
facilitated diffusion, GLUT-5 apical membrane
what does GLUT 2 do?
facilitates exit at basolateral membrane into intersistial space
where does digestion of protien begins?
stomach by pepsin
but it is inactivated in alakine of duodenum
how are the proteases activated?
enterokinase (enz located on duodenal brush border) activates trypsin from trypsinogen
trypsin acitavtes other protients
How does digestion of different AA length work?
AAn progessively hydrolysed at brush border to AA
some AAn are direclty absobred via action of H+ and PepT1
digested to AAs by peptidases in enterocytes
what is first step of lipid digestion?
secretion of bile salts and pancreatic lipases
what is 2nd step of digestion of lipids?
emulisification, increase surface area for digestion
what is 3rd step of lipases
enyzmatic hydrolosysis of ester linkages
colipase complexes with lipase - prevent bile salts displacing lipase from fat droplet
what is the last step of lipid digestion?
solublity of lipoytic products in
bile salt MICELLES
What happens to FA after mielles?
leave it and enter enterocytes
FA and MG resynthesized intro triglyverides by monogltceride acylation (major) or phosphatidic acid pathway (minor)
Forms chylomicrons- liportien, mainly TGs in golgi appartus
and released by exosytsosi into lacteal, lymph capillary transports away from bowel
how is ilewum sperated from colon?
by ileocaecal valve
What is function of ileocaecal valve?
relax and contract control passage of material into colon
prevents backflow of bacteria into ileum
