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MONOGASTRIC GI > 6.2b – Lipid Digestion and Absorption > Flashcards

6.2b – Lipid Digestion and Absorption Flashcards

1
Q

What are the phases of lipid digestion in the SI?

A

-emulsification
-hydrolysis
-absorption
-re-esterification
-packaged into chylomicrons

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2
Q

Emulsification:

A

-TAG: hydrophobic
-enzymes: hydrophilic
*reduces TG from large fat globules to tiny droplets=greater SA for enzyme

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3
Q

Gastric lipases show stereospecificity for:

A

-sn-3

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4
Q

Pancreatic lipases can hydrolyze the bonds at:

A

-sn-1
-sn-3

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5
Q

Pancreatic and gastric lipases CANNOT hydrolyze bonds at:

A

-sn-2

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6
Q

Pancreatic and lipoprotein lipase require a:

A

-cofactor for lipolysis

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7
Q

Gastric lipase:

A

-acid lipase gene family
-does NOT require a cofactor for lipolysis
-may contribute up to 25% of dietary lipid lipolysis

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8
Q

What is the optimal pH of gastric lipase:

A

-3-6

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9
Q

Where/how is gastric lipase secreted in humans?

A

-with pepsinogen by chief cells in fundus

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10
Q

Where is gastric lipase secreted in dogs?

A

-through gastric mucosa
>decreasing concentrations from cardia to pylorus

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11
Q

Where is gastric lipase secreted in cats?

A

-throughout stomach
>uniform concentration

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12
Q

What stimulates the secretion of gastric lipase?

A

-gastric motility
-cholinergic stimuli
-gastrin

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13
Q

What does DAG and FAs produced as a result of gastric lipase promote?

A

-emulsification of dietary fat
>grinding and mixing

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14
Q

What size is fat that enters the SI?

A

-droplets (less than 0.5mm)

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15
Q

Fat digestion and the SI:

A

-majority of lipid digestion
-catalyzed by pancreatic enzymes

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16
Q

What facilitates fat digestion in the SI?

A

-hepatic secretion of bile acids for emulsification
>partition into emulsified lipid droplets
-increased pH from bicarbonate secretion (Brunner’s glands)

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17
Q

What does acidic chyme from the stomach into the duodenum trigger?

A

-secretion of CCK by endocrine cells of SI
>CCK triggers release of bile from gallbladder

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18
Q

Where and how is bile reabsorbed?

A

-95% in the ileum
>utilizes a Na co-transport system (enterohepatic circulation)

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19
Q

Where is the absorption of lipid digestion products the most efficient?

A

-proximal duodenum

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20
Q

What is the role of bile acid micelles in the absorption of lipid digestion products?

A

-helps to overcome the diffusion barrier associated with the unstirred water layer
>absence: limited number of lipid molecules
>presence: lipid molecules delivered to brush border membrane by the micelles

21
Q

What else might be incorporated into the micelles with bile acids to cross the unstirred water layer? (mixed micelles)

A

-digestion products
>mononacylglycerols
>FAs
>lysopholipids
>cholesterol
>Vit A, D, E, K

22
Q

What does the exocrine pancreas secrete?

A

-pancreatic lipase
-procolipase
-pancreas lipase related polypeptide 2 (PLRP2)
-carboxy ester lipase
-prophospholipase A2

23
Q

Pancreatic lipase:

A

-secreted in active form
-optimal pH ~8
-works at liquid-aqueous interface of emulsified lipid particle

24
Q

What does pancreatic lipases catalyze and then form?

A

-catalyze FA from sn-1 and sn-3 of TAGs and DAGs
-form 2-monoacylglycerols and FAs
>carboxyl ester lipase and PLRP2 involved to a lesser extent

25
Q

Colipase:

A

-secreted from pancreas as procolipase
-activated by trypsin
*necessary for interaction of pancreatic lipase with bile acid emulsified droplets

26
Q

Phospholipase A2:

A

-catalyzes the hydrolysis of FA at sn-2 to form lysophospholipids and FAs

27
Q

Passive diffusion absorption of lipids:

A

-driven by concentration gradient
-maintained by intracellular reesterification
-products ‘dissolve’ in lipids of the brush border membrane
Ex. short chain FAs

28
Q

Carrier facilitated absorption of lipids:

A

-carrier proteins to transport them
>except MAG

29
Q

Lipid metabolism within the enterocyte:

A

-FA binding proteins transport FA and MAGs to ER for processing
>forms TAG and cholesterol esters
-esterified products are incorporated into apolipoprotein B48 containing chylomicrons
-transported to Golgi for final processing
>attachment of ApoB-48
-enter lymphatic circulation and eventually systemic circulation

30
Q

Chylomicron vs. VLDL proteins:

A

-ApoB-48for chylomicron
-ApoB-100 for VLDL synthesized by liver

31
Q

What are 2 pathways of lipid metabolism in the enterocyte?

A

-MAG pathway
-glycerol 3-phosphate pathway

32
Q

MAG pathway:

A

-MAG transferase (MAGT) adds 1st FA
-DAG transferase (DAGT) adds 2nd FA
*get a TAG (goes to ER/Golgi and released as chylomicron into lymph)

33
Q

Chylomicrons released into lymphatic system:

A

-by reverse pinocytosis (too large to enter directly)
-runs into thoracic duct that drains the fat into bloodstream at L. subclavian valve
*similar to VLDL secretion by hepatic cells

34
Q

Short and medium chain FAs and glycerol can be absorbed into:

A

-blood via capillary
>can bypass many of the steps due to being more soluble

35
Q

High vs. low density lipoproteins:

A

-based on density of the PROTEIN
>lowest in chylomicrons (largest in size)
>highest in HDL (smallest in size)

36
Q

Chylomicron origin and function:

A

-ileum
-transport ingested fat and fat-soluble vitamins
>usually disappear rapidly in blood (<1hr)
*not in interstitial fluid

37
Q

VLDL origin and function:

A

-liver
-transport synthesized glycerides
*not in interstitial fluid

38
Q

LDL origin and function:

A

-lipolysis of VLDL
-deliver cholesterol to cells
*9% in plasma

39
Q

HDL origin and function:

A

-liver and ileum
-reverse cholesterol transport
*20 in plasma

40
Q

FAs from CM are primarily delivered to:

A

-80%: adipose tissue, heart and muscle
-20%: liver

41
Q

TAGs from CM are hydrolyzed by:

A

-lipoprotein lipase found on capillary walls

42
Q

What are TAGs hydrolysed to?

A

-DAG, MAG then FFA’s and glycerol
>most FFA enter tissues
*CM remnant is delivered to liver

43
Q

Lipid low inclusion levels:

A

-extrapolation to 100% required
>use graded levels and regression analysis

44
Q

What are lipids interactions with other nutrients?

A

-synergism b/w unsaturated FA and saturated FA on FA digestibility
-high levels of soluble non-starch polysaccharides (NSP) reduce lipid digestibility
-high levels of some minerals (ie. Ca)

45
Q

High levels of soluble NSP reduce lipid digestibility:

A

-increased digesta viscosity (poultry)
-inconsistent effect in swine

46
Q

What does high levels of Ca cause in terms of lipid digestibility?

A

-soap formation=reduces digestibility

47
Q

Only 48% of endogenous losses were FA, where did the rest come from?

A

-bile acids
-cholesterol
-pigments
-lipid soluble intermediates
-phospholipids

48
Q

Steatorrhea:

A

-abnormal amounts of fat in the feces
>due to pancreatic insufficiency

MONOGASTRIC GI (24 decks)

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