Lipids and Vitamins Flashcards
Secreted lipids
found in bile (phospholipids)
sloughed intestinal cells and bacterial membranes
Gastric Lipase
only active and stable at pH 4
located near oil-water border
Secreted by chief cells
resistant to Pepsin degradation
inactivated by pancreatic proteases in SI
cleaves FAs from TAGs ( Some of which can be absorbed in the stomach —>1FFA+1 DAG
Pancreatic lipase
*Major lipolytic enzyme: secreted in large amts
released from acinar cells
dependent of colipase, alkaline pH, Ca, Bile salts FA substrates
function of pancreatic lipase
associate with colipase, which allows it to get close to micelle
hydrolyze TAGs —>2 FFA+ 1MAG
pancreatic lipase inhibitors
Pancreatic lipase inhibitor
results in higher concentration of TAGs in stool
phospholipase A2
pancreatic, needs bile salts and alk pH
cleaves glycerophospholipid–>1 FFA (MAG)
Carboxyl ester hydrolase
non substrate specific
hydrolyzes all esters (b/w all ester linkages)
—>free cholesterol and free glycerol
same action as Bile salt stimulated milk lipase (due to lack of infant pancreatic lipase activity)
CCK
stimulated by FFA in the duo
stimulates bile into duo
stimulates secretion of pancreatic lipase and esterase
Micelle
lipid MONOlayer with tails facing into the hydrophobic core
creates a shorter distance for enzymes to reach substrates located in the core
Bulk water phase of the lumen
where hydrolysis and micelle formation take place
Unstirred water layer
just next to the cell membrane, allows short and medium FA directly into enterocytes due to favorable protonated environment (High Na/H exchanger activity)
large FA chains are brought back into micelles
re-esterification
occurs in the enterocyte w/in the sER
Long chain FAs are assembled into TAGs and phospholipids
Chylomicrons
Apolipoproteins+TAGs + phospholipids + cholesterol esters are brought together in the sER
largest lipoproteins made of TAGs
surface coated with apos , lecithin and PLs
Water soluble vitamins
abs in SI
have specific carriers and or brush border and luminal enzymes for deconjugation or phosphorylation
many Na dependent
utilize GPCR and cAMP
Fat soluble vitamins
called so bc of chemical structure and storage in fat deposits
rely on lipid absorption
Folate
deficiency can cause neural tube defects in developing fetus (spina bifida and anecephaly)
water soluble
Tetrahydroafolate (THF)
biologically active form of folate
cofactor for synth of thymine and purines (NEED FOR DNA SYNTH)
deficiency—>inhibited DNA synth—>megaloblastic anemia (extra large cell due to inhibited RNA synthesis)
tx= pteroylmonoglutamate
pteroylmonoglutamate
Helps transport Folate conjugase into enterocytes
in the liver it is changed to THF
tx for THF deficiency
Vitamin B12 (Cobalamin)
only synthesized by microbes (found in animal products)
coenzyme
also causes megaloblastic anemia
- Need IF, which binds B12 in the SI
Intrinsic factor
binds B12 in the SI, once it is released from haptocorrin
IF has receptor with enterocyte cell membrane, causes B12 to be brought into the cell
B12 is recycled, by being added to bile which is reabsorbed in the ilium
Vitamin B12 deficiency
vegetarian diet pernicious anemia (loss of parietal cells) megaloblastic anemia Crohns disease Ileal resection
can cause decreased methionine, which can cause a lack of Folate
Pernicious anemia
caused by lack of parietal cells
to to atrophy or AI attack against the cells
due to molecular mimicy against H. Pylori
medium chain FAs
absorbed independently of micelles
once inside the enterocytes they can be directly transferred into the blood
fat substitute for pt with related malabsorption
Emulsion droplet
contains MAGs, chol, lipases, bile salts and soaps on surface, DAGs, TAGS, and chol esters are at the core
MAGs are hydrolyzed first and FFAs are released
DAGs and TAGs replace the surface MAGS
droplet decreases in size, and SA increases which promotes more digestion of surface lipases until it becomes a micelle
