Malabsorption Clinical Cases Flashcards
how much dietary fluid does the average person take in per day
and how many received by the small intestine due to secretions
1-2 litres dietary
6-7 litres from secretions
describe the absorption by enterocytes of the small intestine on the apical surface
1) on apical lumen side
HCO3- / Cl- antiport = chloride into the cell and HCO3 out into lumen
Na+/H+ antiport = Na into the cell and H+ into the lumen
Na+/glucose symport both into the cell from the lumen
describe the absorption by enterocytes on the basal side
cl- / K+ freely leak out from cell into the interstitial space
Na+/K+ ATPase pumping Na out the cell and K init the cell
glucose freely moves out from cell into interstitium
describe how ORT works
glucose and sodium enter cell via symport which means water follows it into the cell (water potential in the cell becomes more negative which is the driving force)
Na/K atpase of basal aspect sodium out and K into cell
k leaks back out and glucose leaks out followed by water
what are the two processes that pull water into the cell from the lumen
increase in luminal osmotic pressure resting from influx of ions
crypt cells secrete electrolytes which contain the CFTR gene
cystic fibrosis transmembrane conductance regulator
describe the structure of vilis with crypts
villi stick out with microvilli which absorb
crypts of liberkuhn secrete
how long does cell migration to the villus tip take
3-4 days and then they apoptosis
describe how water is secreted in crypt cells
Na/K on basal membrane make na into intersitium and k into cell
K leaks out on basal to intersistium
symporter on basal aspect transports 2 cL into the cell and 1 Na and 1 K
(secondary active transport)
elevated cAMP active CFTR chloride channel which allows Cl into the lumen
this draws sodium paracellularly into the lumen
cl and Na increase in the lumen brings water with it
what is impaired digestion
pancreatic insufficiency (CF, chronic pancreatitis) lack of bile (liver disease, biliary obstruction) lack of intestinal enzymes (lactose intolerance)
what is impaired absorption
damage to absorptive surface (coeliac disease, crohns disease)
decrease to absorptive ares (intestinal resection )
inherited defects such as SLT1 mutation
what are the 4 mechanisms for causing diahorrea
secretory
osmotic
inflammatory
abnormal motility
what is borbygmi
loud bowel sounds
how can you diagnose for lactose intolerance
consume dairy products and no increase in blood glucose with flatulance and abdominal pain
why do you get the symptoms of lactose intolerance
lactose build up and bacterial fermentation
water moves into lumen via osmosis
where is the CFTR gene located
chromosome 7
how does CFTR mutation affect a baby
the secretary mechanism is inadequate due to absence of CFTR so water absorption is dominant
meconium is too thick to pass through intestine and leads to meconium ileus
how does CFTR affect a child/adult
thicker ucus blocks pancreatic duct leading to lack of digestive enzymes
poor digestion of food (mainly fats) increases osmotic potential of gut lumen and leads to osmotic diarrhoea
what are the major symptoms and signs of cystic fibrosis
salty skin
male infertility
progressive lung infection
persistent cough
why does cholera produce secretory diarrhoea
cholera toxin irreversibly raises intracellular cAMP
cAMP opens CFTR allowing Cl- ions to enter the lumen
Na/K ions following to maintain electrical neutrality
water follows
secretory diarrhoea as driven by Cl-
what does the cholera toxin bind to
Gs protein stimulating adenylate cyclase and making cAMP from ATP
describe the glucose galactose intolerance, which tissues are affected and what it is associated with
mutations and reductions in channel expression
affects small intestine
produces osmotic diarrhoea
describe genetic basis of cholera, which tissues are affected and what it is associated with
no genetic basis
toxin infection via gram negative vibrio cholera
affects small intestine
produces secretory diarrhoea
describe genetic basis of CF, which tissues are affected and what it is associated with
CFTR mutation (stop working)
affects pancreas and lungs (any epithelial tissue)
produces osmotic diarrhoea
describe genetic basis of coeliac disease, which tissues are affected and what it is associated with
DQ2 and DQ8 leucocyte antigens MHC which target villi in small intestine
affects small intestine
produces osmotic diarrhoea
