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Digestion and Renal Sciences > Digestion and Absorption of Fat > Flashcards

Digestion and Absorption of Fat Flashcards

1
Q

when is fat an energy source?

A

in the fasted state

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2
Q

What makes lipids good storage molecules?

A

non-polar and can be stored in the anhydrous state

2x amount of energy per gram compared to other sources

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3
Q

What does Beta-oxidation produce?

A

acetyl-CoA which can go into the TCA cycle

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4
Q

Why are fats important for some vitamins?

A

vitamins A, D, E and K are fat-soluble and depend on solubilisation within bile micelles for intestinal absorption

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5
Q

What diseases can vitamin D deficiency lead to?

A
  • impaired bone mineralisation so rickets and osteomalacia

- also can be linked to osteoporosis and cancer

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6
Q

What are some ways you can get vit D?

A

sunlight

egg yolk

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7
Q

Ways to get vit E?

A

veg oils
palm oil
olive oil

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8
Q

What is vit E important for?

A

antioxidant protecting against cardiovascular disease and cancer

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9
Q

What are the symptoms of vit E deficiency?

A

neurological problems due to poor nerve conduction

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10
Q

What is vit K important for?

A

blood coagulation
bone metabolism
vascular biology or deposition of insoluble calcium stars in the arterial vessel walls

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11
Q

What are some symptoms of essential fatty acid deficiency?

A 
skin atrophy 
dry skin
impaired vision
mood swings
impaired growth
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12
Q

What form of fat is 90% of dietary fat?

A

triglycerides

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13
Q

Why is not all fat derived from the diet?

A

-endogenous lipids in the GI lumen are predominately from bile which contains: phospholipids, unesterified cholesterol, membrane lipids from desquamated cells, lipids derived from dead colonic bacteria

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14
Q

extra

A

!!!

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15
Q

What are the ways that emulsification can take place

A
  1. chewing and gastric churning allows mixing of lingual and gastric juices
  2. squirting of gastric contents in the duodenum
  3. food prep
  4. intestinal peristalsis mixes luminal contents with pancreatic and biliary secretions
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16
Q

Why is emulsification required?

A

to reduce the size of the lipid droplets and increase their surface area to ratio volume

17
Q

What prevents lipid particles from coalescing?

A
  • coating of emulsification droplets with membrane lipids, denatured protein, dietary polysaccharides etc
  • polar groups of phospholipid project into the water
  • core of emulsion parcel composed of triglyceride which contains cholesteryl esters and other non-polar lipids
18
Q

Give a summary of lipid digestion

A
  1. lipid digestion begins in the mouth mediated by lingual lipase
  2. in the stomach, both lingual lipase and gastric lipase digest large amounts of lipid
  3. lingual and gastric lipase release a single fatty acid from triglycerides, leaving behind intact diglycerides
19
Q

What happens to the released long chain fatty acids?

A

they are not absorbed in the stomach as they re insoluble at acidic PH and so remain in the core of the triglyceride droplets

20
Q

What happens to the medium and short chain fatty acids?

A

mainly ionised at the acidic gastric PH, remain in solution and are passively absorbed across the gastric mucosa into portal blood

21
Q

What happens once the fatty acids reach the duodenum?

A

they trigger the release of CCK from I cells in the duodenum mucosa

22
Q

What does CCK stimulate?

A
  1. the flow of bile into the duodenum by gall bladder contraction and relaxation of the sphincter of Oddi
  2. The secretion of pancreatic enzymes including lipase and esterases
  3. stimulate production of zymogen
23
Q

What is the major lipolytic enzyme?

A

pancreatic lipase (digests all dietary triglycerides not hydrolysed in the stomach)

24
Q

What is required for full lipolytic activity of pancreatic lipase?

A
  1. colipase (for ligand binding conformation)
  2. alkaline PH
  3. bile salts
  4. fatty acids
25
Q

What is colipase important for?

A
  1. acting as the anchor for the binding of the lipase

2. and or by first forming a colipase-pancreatic-lipase complex that can then bind to the lipid interface

26
Q

What is the product to pancreatic lipase?

A
  • fatty acids

- 2-monoacylglyceride

27
Q

How does lipid absorption occur?

A
  • as surface triglycerides are hydrolysed they re replaces by triglycerides from the core of the emulsion particle resulting in an ever decreasing emulsion droplet
  • this leads to the budding off from the main droplet to form multi-lamellar vesicle (several lipid bilayers). This occurs due to fatty acids, monoglycerides, bile salts etc building up on the surface of the emulsion particle
  • addition of more bile salts to the multilamellar vesicles thins out the lips coating and coverts it to unilamellar vesicles, which are then converted into mixed micelles composed of bile salts and mixed lipids
28
Q

What happens as the fatty acid chain length gets longer?

A

solubility decreases and partitioning into micelles increases

29
Q

What are the barriers that lipolytic products need to overcome to get into the enterocytes?

A
  • mucus gel layer lining the intestinal epithelial surface
  • the unstirred water layer
  • the apical membrane
30
Q

Describe short/medium chain fatty acid absorption ease into the enterocyte

A

-readily soluble in water, so diffusion through unstirred layer into the enterocyte is efficient

31
Q

What happens when the fatty acid/bile mixed micelles reach the enterocyte surface?

A

-they encounter a low-PH generated by the Na-H exchange at the brush border membrane
-fatty acids are protonated and leave the mixed micelle to enter the enterocyte by: non-ionic diffusion, collision and incorporation of the fatty acid into the cell membrane or an active carrier mediated process
into the lymphatic system

32
Q

What happens to bile salts after entry?

A

absorbed at the terminal ileum and colon where they are redirected to the liver and portal blood (enterohepatic circulation)

33
Q

What happens when the long chain fatty acids reach the enterocyte?

A
  1. long chain fatty acids and other products of lipid digestion are converted back into triglycerides, phospholipids and esters of cholesterol in the ER
  2. Fat droplets form cisternae of the SER
  3. Apoproteins are synthesised in the RER and then transferred to the SER where apoproteins associate with lipid dropletes
  4. Nascent chylomicrons arrive at the cis face of the Golgi apparatus. Here, apoproteins are glycosylated
  5. Vesicles carrying chylomicrons or VLDLs bud off from the trans golgi apparatus and move to the basolateral membrane in the transport vesicles
  6. transport vesicles fuse with the basolateral membrane, releasing chylomicrons or VLDRs
  7. Chylomicrons and VLDLs pass through large internclothelial channels of lymphatic capillaries and enter the lymph
  8. Glycerol, short chain and medium chain fatty acids pass through the enterocyte and enter the blood capillary

Digestion and Renal Sciences (13 decks)

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