W3 - Fat metabolism Flashcards
What is LDL associated with?
⬆️ risk of heart disease
What are each ends of the FA called?
Omega
Carboxyl
How might adipose tissue turnover decline?
If health status declines
i.e athletes have a very high turnover rate
What cytokines does adipose tissue secrete?
Inflammatory cytokines
When are lipids insoluble?
In aqueous solutions
i.e blood
How is fat transported in the blood?
In chylomicrons or lipoproteins
FAs oxidised in the mitochondria of skeletal muscle during exercise are derived from 2 main sources. What are these?
Adipose tissue
Muscle TAG (delivered in chylomicrons + VLDL).
(Plasma TAG may also be used).
TAG in adipose tissue is split into FA + glycerol. What happens to these?
Glycerol is released into circulation w/ some of the FAs,
Small & of FAs are NOT released into circulation but used to form new TAF in the adipose tissue = Reesterification.
What happens to the FAs that have been released from adipose tissue?
Transported to other tissues + can be uptake by skeletal muscle during exercise.
What happens to the glycerol released from the adipose tissue?
Transported to liver
- Acts as a gluconeogenic substrate to form glucose.
What can circulating TAG i.e VLDL do temporarily?
Bind to LPL to allow FAs to be split off so that they can be taken up by muscle.
What are IMTG split by?
HSL
What are the steps that could limit fat oxidation
Lipolysis
Removal of FA from fat cell
Transport of fat by bloodstream
Transport of FAs into muscle cell
Transport of FAs into mitochondria
Oxidation of FAs in b-oxidation pathway + TCA cycle
Where are most FAs stores as?
TAG in subcutaneous adipose tissue.
These must be mobilised + transported to the site of oxidation.
What do adipocytes contain?
Lipases that breaks down TAG
What does the SNN stimulate HSL to do?
Split TAG into FAs + glycerol.
What does the conversion of the inactive form of HSL to the active form depend on?
SNN + circulating epinephrine.
Where is norepinephrine release from in the SNN?
It’s nerve endings
What is often used as a measure of lipolysis?
Measurement of glycerol in the blood
What % of FAs are reesterified in lipolysis at rest?
~70%
What happens to reesterification during exercise?
Suppressed to incr availability of FAs in adipocyte.
What stimulates lipolysis during exercise?
Catecholamines released from the adrenal gland
What does reesterification depend on?
Rate at which FA are removed from the adipocyte by the blood
Rate of G-3-P prod
Activity of TAG synthesising enzymes
What does the removal of FAs from adipocyte into the bloodstream depend on?
Blood flow to adipose tissue
Albumin conc in blood
No. of free binding sites for FAs on albumin
What is the most abundant protein in plasma?
Albumin
- Acts as a carrier protein transporting FAs
What happens when albumin arrives at target tissue?
Binds to specific ABPs
Binding to this aids the release of FAs from albumin + their uptake.
What does LPL in the vascular wall do?
Hydrolyses some TAG in circulating lipoproteins passing through the capillary bed.
== FA are released, muscle takes them up to use for oxidation.
FA uptake from plasma lipoprotein TAG
Happens slowly
Accounts for less than 3% of the energy expenditure during prolonged exercise.
What transport proteins are found in the sarcolemma/
FABPpm protein
FAT/CD36 protein
What does muscle contraction do to plasma membrane FAT/CD36?
Increases it = incr. FA transport into cells.
What are FAs bound to in the sarcoplasm?
FA-binding protein (FABPc).
– Thought to be responsible for the transport of FAs from sarcolemma to mitochondria.
Which muscle fibres have a higher content of IMTG?
Type 1
Muscle contains HSL
What is it activated by
b-adrenergic stimulation
Muscle contains HSL
What is it inhibited by
Insulin
What can happen with the FAs liberated from IMTG?
Can be released into blood
Reesterified
Oxidised w/in muscle
What are FAs bound to until transported into mitochondria?
FABPc
What can FAs in the cytoplasm be activated by?
ACoA synthetase or thiokinase
What is formed once the ACoA synthetase or thiokinase meets with the FAs in the cytoplasm?
Forms ACoA complex
FAs in cytoplasm can be activated by ACoA synthetase or thiokinase to form ACoA complex.
What happens next with this complex?
Used for synthesis of IMTGs
OR
Is bound to carnitine under the influence of the CPT1 enzyme.
What is the 1st step in transport of FA into the mitochondria?
Bonding of carnitine + activated FA
What is released when carnitine binds to FA?
CoA
CHO + fat are always oxidised as a mixture
What does the prominent fuel used depend on?
Intensity
Duration
Level of aerobic fitness
Diet
CHO intake before or during exercise
What does the rate of lipolysis in adipose tissue depend on?
Circulating conc of hormones (epinephrine stimulates lipolysis + insulin inhibits lipolysis).
When does fat oxidation peak ?
~50-60% vo2 max
What does training do to fat oxidation?
Enhances
What are the adaptations contributing to stimulation of fat oxidation in trained athletes?
⬆️ mit density + ⬆️ no, of oxidative enzymes in trained muscle
⬆️ capillary density = enhances FA delivery to muscle
⬆️ FABP conc which may facilitate uptake of FAs across sarcolemma
⬆️ CPT conc which facilitates transport of FAs into mitochondria
