Lipid Metabolism Flashcards
Steps of Lipid Metabolism
Lipid digestion Lipid absorption Lipid transport Lipid catabolism Lipid biosynthesis
Functions of Lipids
Energy Cell membranes Cell signalling Facillate absorption of fat-soluble vitamins Biosynthetic precursors Protection and Insulation
Lipid Digestion
Lipase enzymes - triglyceride -> monoglycerides
MOUTH
Ligual Lipase = chemical digestion
STOMACH
Gastric Lipase = chemical&mechanical digestion
SMALL INTESTINE
Pancreatic Lipase + Bile Salt = from pancreas to small intestine + bile salt emulsifies lipids
Cholecystokinin
Digestive hormone
Stimulate release of pancreatic lipase from pacreas + release stored bile salts from gall bladder into intestine
Bile salts
Amphiphatic compound that emulsifies fat to form micelles
Pancreatic Lipase
hydrolyse triglycerides into monoglycerides - FA and glycerol
Lipid absorption
1) FA and monoglycerides are emulsified by bile salts to form micelles
2) FA enter epithelial cells and form triglycerides
3) Combine with proiteins inside golgi body = CHYLOMICRONS
4) Enter lacteal ( lymphatic capillary that absorbs dietary fats in villi of small intestine) and transported away from intestine
Chylomicrons
Amphipathic vesicles that package lipids into larger particles
Made up of apolipoprotiens/triglycerides/cholestrol/phospholipids
Chylomicrons transport DIETARY triglycerides through bloodstream to liver/adipose/muscle etc
Source = intestine
Lowest density - highest density of TGs
Feasting
Excess energy is consumed - stored in adipose tissue as triglycerides
Fasting
No food
Triglycerides from adipose tissue are broken down releasing FAs as an energy source
Lipid Transport
Hydrophobic lipids require special transport proteins - lipoproteins 4 types of lipoproteins - chylomicrons - VLDL - LDL - HDL
VLDL
High %TG
Source = Liver
Transport ENDOGENOUS triglycerides to body tissues
LDL
Highest %cholestrol ‘BAD CHOLESTROL’
Source = liver
Transport CHOLESTROL to body tissues
HDLS
Highest %protein - highest density ‘GOOD’
Source: Liver and Intestine
Transports CHOLESTROL from tissues TO LIVER for breakdown
LIpid Transport
Exogenous pathway - DIET - Chylomicrons
Endogenous pathway
Reverse Transport pathway - HDL
Stages of Lipid Transport
1) Chylomicrons carry triglycerides from small intestine to body cells
2) Chylomicron remant travels to liver for disassembly
3) VLDL produced by liver brings triglycerides to body cells
4) VLDL becomes IDL and LDL as triglycerides are removed
5) LDL delivers cholestrol to body cells
6) HDL picks up excess cholestrol and delivers to liver for disposal
Liver cells in lipid transport
Store fats - triglycerides and glycerol
Produce bile from cholesterol
Produce VLDL to deliver triglycerides
Lipid Catabolism
Chylomicrons are broken down to Lipoprotein Lipase LPL in capillaries of skeletal/cardiac/muscle/adipose tissues
Lipolysis - TG -> FA + Glycerol
Glycerol = Glyceraldehyde 3 Phosphate - Acetly CoA - enter TCA cycle to produce ATP
FA = Acetyl CoA
Ketone/Ketone body production
produced by liver during starvation when glycogen is depleted (24h)
body uses fat as source of energy
DKA
Diabetic ketoacidosis
- diabetics/ starvation use ketones as fuel as they can’t use glucose + liver breaks down fat too fast
Excess Acetyl CoA
Created from beta oxidation and TCA cycle is overloaded = creation of ketones
HMG CoA
precursor of cholestrol and converted to beta hydroxybutyrate = primary ketone body in blood
Synthesis of ketone bodies
Acetoacetate - transported to tissues outside liver converted to acetyl CoA and oxidation in TCA cycle = generate energy
Brain adapts to using acetoacetatae or Beta hydroxybutyrate in starvation instead of glucose as fuel
Cholestrol
Role = Bile acids + Streoid hormones = adrenal/sex
Made from Acetyl CoA
