nutrient digestion Flashcards
what are monosaccharides
breakdown products of complex carbs that are absorbed in small int
what are disaccharides
lactose - glc + galactose
sucrose - glc + fruct
maltose - glc + glc
how are polysaccharides digested (starch, glycogen)
hydrolysed by a-amylase
how are monosaccharides absorbed across intestinal epithelium cells
Villi and microvilli on apical membrane and tight junctions
Glc need transporter - SGLT1 and Na+, water passes through tight junctions, conformational change, GLUT-2 transporter on basolateral side
what are the 2 membranes in the small intestine cells
- apical - brush border w microvilli (go through this first)
- basolateral
what transporters does glucose need in SI
SGLT1
GLUT-2
what transporters does fructose need in SI
GLUT-5
what is blood glucose maintained at?
5 mlmol
how are proteins broken down into small peptides + AA
enzymes hydrolyse peptide bonds = proteases or peptidases
what does AA absorption require
SAAT1 and Na+
water through
what does peptide absorption require
PepT1 and Hion transport
Na and K pump
what is the microclimate at the brush border in SI
acidic, pH < 6, lower than the lumen
how is insoluble fat in form of triaglycerol digested in SI
digested by pancreatic lipase - water-soluble enzyme, can only digest surface of fat droplet
emulsification
micelles
what is ingested fat in the form of
triaglycerol
what does emulsification require from the body
mechanical disruption and smooth muscle contraction
what is absorption of fat enhanced by
micelles
what do micelles do in absorption of fat
keep molecules separated from each other
Micelle breakdown
- release small amount of FA + monogylcerides into solution, diffuse across cell membrane
- micelle not absorbed
why do you need emulsifiers for fat absorption
prevents small droplet reforming to large
what are some amphiphatic molecules, what do they do
bile salt and phospholipids in bile, production of emulsifiers and micelles for solubilising fats - into FA and monoglycerides
what happens to digested fats once they enter SI cell
enter smooth endoplasmic reticulum (sER)
reformed into triacylglycerols
through golgi apparatus and exocytosed into ECF
chylomicrons
pass into lacteals between endothelial cells into lymphatic system
how are fat soluble vitamins absorbed into SI
A, D, E, K
same as fat
broken down by pancreatic lipase
emulsified and micelles
how are water soluble vitamins absorbed into SI
B, C, folic acid
passive diffusion or carrier-mediated transport
how is vitamin B12 absorbed
binds to intrinsic factor in stomach, absorbed in distal ileum
what is the result of B12 deficiency
pernicious anaemia (rbc dont mature)
how is iron absorbed
across brush border membrane - DMT1 into duodenal enterocytes (cell of intestinal lining)
incorporated into ferritin (intracellular iron store, bound form)
unbound iron across membrane into blood stream
what does iron in blood bind to?
transferrin
what happens in hyperaemia
too much iron in body. -> inc ferritin levels -> more iron bound in enterocytes
what happens in anaemia
not enough iron in body -> dec ferritin levels -> more iron released in blood
what is ferrittin
protein-iron, intracellular iron store
