[Physiology] Nutrient Digestion and Absorption 2 Flashcards
what form is almost all ingested fat in
triacylglycerol
where does all fat digestion take place
small intestine
what causes fat digestion to take place in the small intestine
pancreatic lipase
how do triacylglycerols appear
large lipid droplets that are insoluble in water
what is lipase
water soluble enzyme
what is problematic with pancreatic lipase
digestion can only take place at surface of droplet ⇒ very slow
what does lipase break triacylglyceride down into
monoglyceride + 2 fatty acids
what is emulsification
dividing large lipid droplets into smaller droplets (~1 mm diameter)
what is the benefit of emulsification
⇒ increased surface area and accessibility to lipase action.
what does emulsification require
Mechanical disruption
Emulsifying agent
what causes mechanical disruption
smooth muscle contraction within the muscularis externa of the stomach - grinds and mixes lumenal contents
what is an emulsifying agent
Bile salts + phospholipids secreted in bile
amphiphatic molecules with polar and non polar portions
what do non polar portions associate with
non-polar interior of lipid droplet
leaves polar portions exposed at the surface
what do polar portions do to other small lipid droplets
prevent reforming into large droplets
is emulsification alone enough to enhance absorption of lipase digestion
no it is still very slow
what enhances this absorption further
formation of micelles
what are micelles
similar to emulsion droplets but much smaller (4-7 µm diameter)
Micelle = bile salt + monoglycerides + fatty acids + phospholipids
Micelle =
bile salt + monoglycerides + fatty acids + phospholipids
where are polar portions located on a micelle
the surface
where are non polar portions located
micelle core
what happens as soon as a micelle touches the lipid membrane
they are absorped they are fat
micelle breakdown
release of small amounts of free fatty acids (FFA) and monoglycerides into solution ⇒ diffusion across plasma membrane of absorbing cells
what happens once the micelle enters the acid microclimate
acids within take on that hydrogen ion, and they lose their charge and that releases them from the micelle fatty acids and monoglycerides being absorbed and they go into the microclimate region.
anything that doesn’t get absorbed gets taken up into micelle.
keeps moving around until ultimately all of the fatty acids and monoglycerides have eventually be taken up across the apical membrane.
having no charge they will then cross the lipid membrane much more readily.
what happens after the fatty acids and monoglycerides enter the SER
they are reformed into triacylglycerols (by enzymes located within the sER)
what are the reformed triacylglycerol droplets coated with
amphiphatic protein (emulsification)
How are Triacylglycerol droplets transported through cell
vesciles formed from the SER membrane processed through Golgi apparatus until reaching the basolateral membrane where they are exocytosed into extracellular fluid at serosal membrane
what are extrecellular fat droplets known as
Chylomicrons
chylomicrons
(also contain phospholipids, cholesterol & fat-soluble vitamins) ~1 µm diameter
what can chylomicrons not do
can’t get through the tight junctions at the end of the endotherlial cells that make up the capillaries there -cant go into your blood, which is good because you don’t want fat going into your circulatory system. Instead they pass into lacteals - branch of your lymphatic system.
once chylomicrons are in the lymphatic system where do they end up
thoracic duct
what do chylomicrons pass into instead of blood
lacteals
what are the two classes of vitamins
Fat-soluble vitamins
Water-soluble vitamins
what are the fat soluble vitamins
A, D, E, K
what are the Water-soluble vitamins
B group, C and folic acid
what is vitamin B12
large charged molecule
Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum.
what is pernicious anaemia
B12 deficiency (failure of red blood cell maturation)
how much of daily ingested iron is absorbed across intestine into blood
10%
how is iron transported across brush border enzymes
(via DMT1) into duodenal enterocytes
why do divalent metals require a transporter
These are extremely toxic and corrosive if unbound.
where does the vast majority of iron go
protein complex known as ferratin
if the iron does not get incorporated into ferritin what happens
it goes to the basolateral membrane, and then it gets transported across the basolateral membrane via a protein called IREG 1
Once it goes into blood it binds to another protein called transferrin
what is ferritin expression regulated by
the bodys iron status
hyperaemia results in
increased ferritin levels in the duodenal enterocytes ⇒ more iron bound in enterocytes
anaemia results in
decreased ferritin levels ⇒ more iron released to blood
