Digestion and transport of dietary lipids

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Packet 1

38%

American diet intake of fat

Less than 30%

recommended intake of fat

Lingual and gastric lipases

back of tongue digests short& medium chains, less than 12C (active in infants for cow's milk)

Cholecystokinin

a gut hormone that stimulates the secretion of pancreatic enzymes

Bile salt

binds to globules of dietary fat made my peristalsis to increase the surface area, come from cholesterol, lack doubt bond and has more -OH which means that its more soluble

Bile salt fate

5% leave via feces 95%reabsorbed at ileum, go to liver then are stored in the gallbladder

Pancreatic lipase

digests dietary TAG, works on FA of all lengths from position 1 & 3 (secreted with co lipase and bicarb-stimulated by secretin to raise pH to 6)

Esterase

remove FA's from compounds an example is cholesterol esterase

Phospholipase A2

digests phospholipids making a free FA and a lysophospholipid

Micelles

tiny microdrolets emulsified by bile salts after digestion, they travel through a layer of water to the microvilli where lipids are absorbed and bile salts are left behind

Short and medium chains of FA

don't need bile salts for absorption, go into blood bound to albumin and not lymph

Synthesis of TAG

in the epithelial cells, FAs are activated to fatty acyl CoA+ 2-monoacylgrylcerol diacylglycerol reacts with fatty acyl CoA then  TAG

2-monocaylglycerol

intermediate of TAG synthesis in intestinal cells

Phosphatidic acid

intermediate of TAG synthesis in tissues that is not intestinal cells

Synthesis of chylomicrons

- phospholipids come with other proteins and contain cholesterol, fat soluble vitamins, and apoproteins

RNA editing

a gene makes Apo-B in mRNA the "C" is switched to "U" which results in a stop codon so result is not ApoB-100 (for VLDL) but ApoB-48 for Chylomicrons

How are chylomicrons released?

Exocytosis into the chyle of the lymphatic system then enter blood via the thoracic duct

How long does it take for chylomicrons (dietary fat) to enter blood?

1-2 hours after the start of meal and continues for many hours

Nascent chylomicrons

accept proteins from HDL in the lymph and blood result in a mature chylomicron

HDL

transport apoE and apoCII

ApoE

recognized by the receptors in the liver and enter by endycytosis and then is digested by lysosomes

ApoCII

activates LPL (lipoprotein lipase) which is on the capillaries endothelial cells (proteoglycans in the basement membrane) of muscle and adipocytes and cells of lactating mammary glands

LPL isozyme in adipose tissue

has a high Km then muscle (think heart) because you only want it to be most active after a meal when TAG is abundant

LPL (lipoprotein lipase)

digest TAG of the chylomicrons and VLDL

Olestra

an artificial fat substitute, taste without calories it's a sucrose molecule with FA that are esterifies, can't be hydrolyzed by the pancreatic lipase and pass through the intestinal tract

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