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Flashcards in Lipid Metabolism Deck (38)
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1

Types of lipids

- triglycerides (main one)
- phosopholipids
- cholesterol

2

Fatty acids

Basic moiety of all lipids
- long chain hydrocarbon organic acids

3

Lipid functions

Triglycerides are used primarily for energy production (similar to CHO)
- composition: 3 fatty acids and 1 glycerol
- cholesterol and phospholipids used to make cell membranes

4

Lipoproteins

Carrier service for lipids in the plasma
- transport lipids to and from liver
- transport lipids to other tissues for use/storage
- made of cholesterol, triglycerides, phospholipids, and protein

5

Types of lipoproteins

- chylomicrons: carry digested fat from intestines to lymphatics (most relevant)
- low density lipoproteins: contains higher cholesterol
- very low density lipoproteins: high triglycerides/moderate cholesterol
- high density lipoproteins: contains lower cholesterol

6

Bile formation

Bile is made by hepatocytes at rate of 1/2 - 1 liter/day
- stored in gallbladder
Functions
- fat digestion
- excretion of wastes, including cholesterol and bilirubin

7

Bile composition

Bile salts make up 50% of composition
- bile salts made from cholesterol --> cholic acid or chenodeoxycholic acid --> conjugation with taurine or glycine --> conjugated bile acids

8

Role of bile salts

Bile released from gallbladder when fat reaches duodenum
- contraction stimulated by cholecystokinin
- bile salts emulsify fat globules and then form micelles that allow further digestion/absorption of fats
- bile salts are left behind in GIT lumen and recycled back to liver for repeat use

9

Cholecystokinin via blood stream causes

- gallbladder contraction
- relaxation of sphincter of Oddi

10

Where is bile stored?

Gallbladder
- concentrated up to 15 times

11

What does secretin in the bloodstream do?

Stimulates liver ductal secretion
- Na and HCO3 added via secretin hormone to prevent bile from being too acidic

12

Step 1 of lipid digestion

Bile salts break down fat globules (mostly TG) into smaller sizes (emulsification) so lipase enzymes can act on them

13

Step 2 of lipid digestion

Bile salts form micelles
- micelles allow water soluble enzymes to act further on fat for digestion
- shuttle broken down fats (free fatty acids) to the intestinal brush border and release them into the intestinal cells
- free fatty acids shuttled to smooth ER of cell and new TG are packaged into chylomicrons --> released from base of cell into thoracic duct OR FFA are absorbed directly into blood from GIT

14

What is the biggest component of a chylomicron?

Triglycerides

15

Chylomicrons

Type of lipoprotein, mostly triglycerides
- increase in serum after a meal, causing turbidiy or whitish color, while they carry TG in the bloodstream
- are cleared within 30 minutes in normal animals

16

Primary hypertriglyceridemia in dogs

Breed predisposition
- schnauzers
- shetland sheepdogs
Diagnosis
- elevated FASTING triglycerides
Consequences
- pancreatitis
- poor glucose regulation in diabetics
- ocular problems

17

Fate of triglycerides in the blood: option 1

Taken up by liver
- TG split into free FA --> oxidation of FA to supply ATP for body functions OR synthesis of cholesterol, phospholipids, and most lipoproteins

18

_____ of cholesterol made in liver is converted to bile salts

80%
- remainder is transported in lipoproteins in the blood to needy tissues

19

Phospholipids made in liver

Transported by lipoproteins
- cell membrane formation
- intracellular structure formation/reactions
- second messenger systems

20

Fate of TG in the blood: option 2

Used by other tissues for energy or storage
- especially adipose, heart, and muscle
- taken up via lipoprotein lipase (LPL) found in walls of capillaries
- chylomicron --> LPL --> TG and phospholipids --> free FA + glycerol (lipolysis)
- left over chylomicron is cholesterol rich and gets cleared by liver

21

Free FA is used for

- energy via beta oxidation, Kreb's cycle, and oxidative phosphorylation
- storage of fat
- production of new TG or other lipids

22

Lipolysis

TG hydrolyzed to FA + glycerol
- glycerol enters cells --> glycolysis
- FA goes to needy tissues --> further processing

23

Lipolysis step 2

Fatty acids shuttled to mitochondria
- FA moved to mitochondria for degradation and oxidation
- amino acid carnitine acts as an enzyme to assist in this movement

24

Lipolysis step 3

Beta oxidation of fatty acids yields acetyl CoA
- yields 4 H+

25

Lipolysis step 4

Acetyl CoA enters TCA cycle
- products (per acetyl CoA): 2 CO2, 8 H+, 1 ATP

26

Lipolysis step 5

Oxidative phosphorylation of >100 H+ atoms from previous steps
- yields more than >100 ATP

27

When would the body make more fatty acids?

- if body can't use carbs (diabetes)
- in starvation
- to store excess carbs and protein

28

Synthesis of fatty acids from excess carbs and protein

Necessary if CHO or protein are in excess and no more glycogen can be formed
- storage of fat provides a log of energy back up
- fat is more energy dense than carbs
- 1st step is conversion of glucose or AA to acetyl CoA

29

Synthesis of fat from proteins and CHO occurs in the ____

Liver

30

Lipid storage

Adipose tissue's major function is storage of TG until needed by liver or other tissues
- adipocytes are 80-90% stored fat
- TG stored inside cell in liquid form
- lipases are activated once this stored fat is needed by the rest of the body