Physiology of digestion Flashcards
which organ produces acid
stomach
produces 2.5l of secretions per day
oesophageal and duodenal sphincters to prevent acid from going either way
mucus barrier to protect ells from acid
which cells produce acid
parietal cells produce HCL
what do other cells in the stomach produce
enterochromaffin produce histamine
g cells produce gastrin
d cells produce somatostatin
mucus cells produce mucus
chief cells produce pepsinogen (inactive form of pepsin)
what does amylase do
breaks down carbohydrates
found in the mouth and pancreas
glucose is absorbed in stomach and small intestine (with help of insulin)
what do proteases do
breakdown down proteins
pepsinogen goes to pepsin
trypsinogen goes to trypsin (pancreas) activated by enteropeptidase
chymotrypsinogen goes to chymotrypsin (pancreas) activated by trypsin
absorption in small intestine
what does lipase do
breaks down fats
pancreatic lipase and pancreatic lipase-related protein 2
bile salts emulsify fats and allow lipases to act
how is b12 absorbed
liberated from protein binding by acid and pepsin in stomach
binds to r factors
pancreatic proetases release this complex in duodenum where it then binds to intrinsic factor
IF-B12 complex absorbed in terminal ileum
what is b12 deficiency caused by
poor dietary intake - alcoholics, elderly
gastric causes - antibodies to parietal cells (pernicious anaemia)
small bowel - coeliac disease, bacterial overgrowth, surgical resection
medication
role of folate
dna synthesis and repair
found in animal products and leafy green veg in polyglutamate form
cleaved into monoglutamate form in jejunem
increased use in pregnancy
causes of folate deficiency
poor dietary intake
small bowel diseases - coeliac, crohns, resection
drugs - methotrexate, trimethoprim, phenytoin
causes of folate deficiency
poor dietary intake
small bowel diseases - coeliac, crohns, resection
drugs - methotrexate, trimethoprim, phenytoin
types of iron in food
heme iron - found in meats, complexed to heme, in ferrous 2+ form, well absorbed
non-heme - veg, cereals etc, in ferric 3+ form, not well absorbed
iron supplementation
oral iron is poorly absorbed (10-15%)
unabsorbed iron causes side effects
why is absorption so inefficient
hepcidin
high circulating iron is toxic so the body limits increase in plasma iron
high plasma iron causes high hepcidin which impairs further iron absorption (up to 48h)
how does gastric acid play an important role in iron absorption
gastric acid reduces fe3+ to fe2+ form and promotes formation of chelates
vitamin c can also do this and promote absorption
people with achlorhydria do not absorb fe3+
