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Flashcards in Lipid Metabolism Deck (38)
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Types of lipids

- triglycerides (main one)
- phosopholipids
- cholesterol


Fatty acids

Basic moiety of all lipids
- long chain hydrocarbon organic acids


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



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


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


Bile formation

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


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


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


Cholecystokinin via blood stream causes

- gallbladder contraction
- relaxation of sphincter of Oddi


Where is bile stored?

- concentrated up to 15 times


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


Step 1 of lipid digestion

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


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


What is the biggest component of a chylomicron?




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


Primary hypertriglyceridemia in dogs

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


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


_____ of cholesterol made in liver is converted to bile salts

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


Phospholipids made in liver

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


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


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



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


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


Lipolysis step 3

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


Lipolysis step 4

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


Lipolysis step 5

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


When would the body make more fatty acids?

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


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


Synthesis of fat from proteins and CHO occurs in the ____



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