Lecture 16: Lipids Flashcards Preview

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Flashcards in Lecture 16: Lipids Deck (42):
1

Define lipids

Organic molecules that dissolve readily in organic solvents but are much less soluble in water

2

What are main lipid classes in body and diet

Triglycerides

Phospholipids

Sterols

Others: vitamins ADEK, sphingolipids, saccharolipids

3

What are the functions of lipids?

Energy source + reserve

Major membrane constituents

Regulation of physiologic processes

4

What are triglycerides?

Glycerol + 3 fatty acids

5

What are the functions of triglycerides?

Energy transport and storage, insulation, cushioning

6

Which unsaturated fatty acid bonds lead to straight chains and bent chains?

Where do trans-fatty acids occur?

Cis = bent

Trans = straight

Meats + dairy products
=> inc. risk of heart disease, diabetes and breast cancer because of food processing that involves addition of hydrogens to double bonds

7

Which fatty acid double bonds are essential, which humans cannot make?

Omega 3 and omega 6

Omega 3 = alpha linolenic acid

Omega 6 = linoleic

8

Differentiate between omega-6 and omega-3 fatty acids

Omega-6 = precursors of arachidonic acid (pro-inflammatory)
Found in: seeds, nuts, meat

Omega-3 = precursors of EPA (anti-inflammatory) and DHA
Found in: fish, soybeans, walnuts

9

What determines inflammatory and vascular tone?

Balance of arachidonic acid and EPA/DHA-derived lipid mediators = eicosanoids

10

Describe short-chain fatty acids (SCFA)

Produced from fiber

Absorbed by epithelial cells and used for energy generation, allowing energy extraction from non-digestible food

11

Describe medium-chain fatty acids (MCFA)

Found in dairy products and certain vegetable oils (coconut, palm)

More readily absorbed and metabolized than long-chain fatty acids

12

Describe phospholipids

Diglycerides with a phosphate-linked organic group

13

Describe sterols

Multiple ring lipids derived from steroid alcohols

Contain no fatty acids

14

Describe cholesterol

Cell membranes
Bile acid precursor

NOT energy source

Non-essential in diet

Made by liver

15

Where is bile acid excreted into?

Where is it taken up again for recirculation?

Intestinal lumen via bile duct in duodenum

Terminal ileum

16

Describe bile acid structure and function

Hydrophobic + hydrophilic elements

Acts as detergent to emulsify lipids and make them easier to absorb

17

What is the only excretion pathway for cholesterol in the body?

Fecal loss of bile acids (since synthesized from cholesterol)

18

Describe the steps of lipid absorption

Emulsified in intestinal lumen

Broken down into more water-soluble molecules

Uptake into epithelium

Resynthesized in epithelial cells and exported to circulation

19

What helps emulsify large lipid droplets into smaller ones?

Peristalsis in the stomach and small intestine

Bile acid as detergents

20

How are triglycerides digested?

Hydrolyzed to free fatty acids and monoglycerides or glycerol by lipases

21

What three lipases help with triglyceride digestion?

Lingual lipase

Gastric lipase

Pancreatic lipase

22

What is lingual lipase secreted by ?

"Von Ebner" serous glands on tongue

23

Which lipase is important for infant nutrition and adults with pancreatic insufficiency?

Lingual lipase

24

What is gastric lipase secreted by?

Chief cells in gastric glands

25

What is gastric lipase inhibited by?

Bile acids in small intestine

26

What is pancreatic lipase secreted by?

Pancreatic acinar cells, released in pancreatic juice into duodenum

27

At what pH is gastric lipase activity optimal?

Acidic pH

28

At what pH is pancreatic lipase activity optimal?

Alkaline pH

29

Do gastric lipase and pancreatic lipase require cofactors for activity?

Gastric lipase = no

Pancreatic lipase = pancreatic co-lipase (to anchor)

30

What is the product of phospholipase A2 (PLA2) activity?

Lysophospholipid

31

What is PLA2 secreted by?

Pancreatic acinar cells as a zymogen

Proteolytically activated in intestinal lumen

32

Describe the digestion of cholesterol that must take place before dietary cholesterol can be absorbed in intestine.

How efficient is this process?

Hydrolyzed to remove ester, resulting in cholesterol + fatty acid

Moderately efficient

33

What are potential pathways for fatty acid uptake into intestinal epithelial cells?

Passive

Transporter-mediated

34

Passive intestinal uptake of fatty acids -

Differentiate between paracellular and transcellular uptake and which is the more difficult of the two

Paracellular uptake through tight junctions

**Transcellular uptake across epithelial cell

**more difficult because would require "flipping" of lipids in order to integrate into apical sheet of lipid belayer

35

What are cytoplasmic fatty acid-binding proteins?

Sequester fatty acids as soon as they cross membrane

Important for transport of fatty acids to specific target within the cell

Act as lipid sensors

36

What is NPC1L1?

Protein that acts as a cholesterol receptor to mediate uptake by endocytosis

37

Describe epithelial lipid processing.

Cholesterol is re-sterilized

Phospholipids are resynthesized

Monoglycerides/fatty acids converted back to TG's

38

How are re-synthesized lipids exported?

Assembled with apolipoproteins to form chylomicrons

Chylomicrons are too big for capillaries, so they exit through lympathic vessels

39

How does the exit route differ for medium chain and long chain fatty acids?

Medium = portal vein

Long = lymphatic

40

Distinguish efficiencies of intestinal uptake for monoglycerides, fatty acids, glycerol, and sterols

Very efficient = monoglycerides, FA's, glycerol

Less efficient = sterols

41

Why are bile acids critical for lipid emulsification?

They associate with TG's to form micelles

Micelles allow greater access of pancreatic lipases to free the FA's

FA's, once freed, are then able to be actively taken up by epithelial cells

42

Name six major mediators of lipolysis and indicate which require bile acids and which require activation from pro-form

Gastric lipase
Pancreatic lipase = requires BA
Colipase = require activation
Phospholipase A2 = require activation
Cholesterol esterase = requires BA
Breast milk lipase