Malabsorption Clinical Cases

Question 1

how much dietary fluid does the average person take in per day
and how many received by the small intestine due to secretions

Answer 1

1-2 litres dietary

6-7 litres from secretions

Question 2

describe the absorption by enterocytes of the small intestine on the apical surface

Answer 2

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

Question 3

describe the absorption by enterocytes on the basal side

Answer 3

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

Question 4

describe how ORT works

Answer 4

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

Question 5

what are the two processes that pull water into the cell from the lumen

Answer 5

increase in luminal osmotic pressure resting from influx of ions
crypt cells secrete electrolytes which contain the CFTR gene
cystic fibrosis transmembrane conductance regulator

Question 6

describe the structure of vilis with crypts

Answer 6

villi stick out with microvilli which absorb

crypts of liberkuhn secrete

Question 7

how long does cell migration to the villus tip take

Answer 7

3-4 days and then they apoptosis

Question 8

describe how water is secreted in crypt cells

Answer 8

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

Question 9

what is impaired digestion

Answer 9

pancreatic insufficiency (CF, chronic pancreatitis) 
lack of bile (liver disease, biliary obstruction) 
lack of intestinal enzymes (lactose intolerance)

Question 10

what is impaired absorption

Answer 10

damage to absorptive surface (coeliac disease, crohns disease)
decrease to absorptive ares (intestinal resection )
inherited defects such as SLT1 mutation

Question 11

what are the 4 mechanisms for causing diahorrea

Answer 11

secretory
osmotic
inflammatory
abnormal motility

Question 12

what is borbygmi

Answer 12

loud bowel sounds

Question 13

how can you diagnose for lactose intolerance

Answer 13

consume dairy products and no increase in blood glucose with flatulance and abdominal pain

Question 14

why do you get the symptoms of lactose intolerance

Answer 14

lactose build up and bacterial fermentation

water moves into lumen via osmosis

Question 15

where is the CFTR gene located

Answer 15

chromosome 7

Question 16

how does CFTR mutation affect a baby

Answer 16

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

Question 17

how does CFTR affect a child/adult

Answer 17

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

Question 18

what are the major symptoms and signs of cystic fibrosis

Answer 18

salty skin
male infertility
progressive lung infection
persistent cough

Question 19

why does cholera produce secretory diarrhoea

Answer 19

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-

Question 20

what does the cholera toxin bind to

Answer 20

Gs protein stimulating adenylate cyclase and making cAMP from ATP

Question 21

describe the glucose galactose intolerance, which tissues are affected and what it is associated with

Answer 21

mutations and reductions in channel expression
affects small intestine
produces osmotic diarrhoea

Question 22

describe genetic basis of cholera, which tissues are affected and what it is associated with

Answer 22

no genetic basis
toxin infection via gram negative vibrio cholera
affects small intestine
produces secretory diarrhoea

Question 23

describe genetic basis of CF, which tissues are affected and what it is associated with

Answer 23

CFTR mutation (stop working)
affects pancreas and lungs (any epithelial tissue)
produces osmotic diarrhoea

Question 24

describe genetic basis of coeliac disease, which tissues are affected and what it is associated with

Answer 24

DQ2 and DQ8 leucocyte antigens MHC which target villi in small intestine
affects small intestine
produces osmotic diarrhoea

Question 25

what does coeliac disease do

Answer 25

triggered by gliadin (breakdown of gluten)

atrophy of villi and crypt hyperplasia

Question 26

what are the signs and symptoms of coeliac disease

Answer 26

bloating, diarrhoea, abdominal pain, tingling hands
(osmotic diarrhoea, parasthesia - caused by malabsorption of calcium, anaemia caused by malabsorption of iron and folate)

Question 27

how do you investigate for coeliac

Answer 27

blood test for anti-tissue trasnglutaminase antibodies or anti-endomysial antibodies
upper GI endoscopy and biopsy - show atrophy

Question 28

what is the treatment for coeliac

Answer 28

life long removal of gluten products