Feed Fast Cycle

8/11/2019 Feed Fast Cycle

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FEED FAST CYCLE

ABSORPTIVE STATE

(FED STATE)

Two to four hours after ingestion of normal

meal glucose, Amino acids and TAG(incorporated

with chylomicrons)

insulin - glucagon. substrate availability - insulin/glucagon

ratio Anabolic state.


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Enzyme changes in absorptive state

Flow of intermediates through metabolicpathway is controlled by 4 mechanisms.

1. Availability of substrates( Minutes)

2. Allosteric regulation ( Minutes)( At rate limiting steps)

3. Covalent modification of enzymes ( minutes to

hours)Mostly dephosphoryted enzymes are Active

4. Induction repression of enzyme synthesis

(hours to Days)


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LIVER


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Carbohydrate Metabolism

Net consumer of glucose retains 60% of glucosefrom portal system.

1. Phosphorylation of glucose

Glucokinase , high km for glucose. High km is inabsorptive state.

2. Glycogen synthesis

glycogen synthase activity by dephosphorylation

and G.6.Po4 levels3. Activity of HMP shunt

5-10. % glucose metabolized by liver

G.6.Po4- NADPH use in fat synthesis


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4. Glycolysis - Activity of regulated

enzymes.

5. gluconeogenesis. Pyruvate carboxylase

inactive due to level of acetyl CoA which is

allosteric effector.


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FAT METABOLISM

fatty acid Synthesis

Availability of substrate( Acetyl CoA + NADPH

from CHO metabolism)

Activation of Acetyl COA carboxylase by

dephosphorylation and availability of

Allosteric Activator (Citrate)

Acetyl coA Melonyl CoA

Rate limiting step/ inhibitor of fatty acid

oxidation.

carboxylase


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TAG SYNTHESIS

Aceyl CoA De novo synthesis from acetyl coA

+ Hydrolysis of TAG component of

chylomicron remanant.

Glycerol.3.Po4 (Provided by glycolytic metabolism

of glucose)

TAG (VLDL)


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Amino Acid Metabolism A.A Degradation

Amino acid level than liver can use in synthesisof proteins & other nitrogen containingcompounds.

No storage for surplus A.A

Released in Blood for tissues to use in proteinsynthesis. OR

Deaminated & Carbon skeletons are degraded topyruvate, acetyl coA and intermediates of TCAcycle oxidized for energy production for F Asynthesis.

Limited capacity for branched chains. A.Adegradation( metabolized in muscle).


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Protein synthesis

No storage of proteins in liver.

Transient increase in the synthesis of hepatic

proteins for replacement of protein degraded

in previous post absorptive period.


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Adipose tissues

Energy storage depot.

70kg male -14 kg adipose tissue or half of

muscle mass.

In obesity 70% of Body weight (entire volume

of each adipocyte is occupied by a droplet of

TAG).


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Carbohydrate Metabolism

glucose transport (GLUT-4). Insulin level.

glycolysis for Glycerol Po4 synthesis.

HMP shunt for NADPH Production.


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FAT METABOLISM

Synthesis of Fatty Acids

From acetyl CoA is low except when refeeding afterprolonged fast.

Mostly dietary fat(chylomicrons)and VLDL from Liver.

TAG synthesis

Fatty Acids are provided by hydrolysis of TAG ofchylomicrons and VLDL.

FA released from lipoproteins by LPL in capillaryendothelium of muscle & adipose tissues. Glycerol Po4

for TAG synthesis comes from glycolysis (No GK).TAG Degradation:

insulin dephosphorylation of hormone sensitivelipase.


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Resting Skeletal Muscle

Able to respond to substantial changes indemand for ATP with muscle contraction.

At rest 30% of oxygen consumption of body.

During vigorous exercise 90% of total o2

consumption.

Oxidative tissue (potential for transient periods ofanaerobic glycolysis).


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HEART MUSCLE SKELETAL MUSCLE

Continuously active Contracts intermittently

Completely Aerobic Both Aerobic & Anaerobic

Negligible energy stores like

glycogen & lipids.

Considerable stores of glycogen


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Major metabolic pathways in skeletal

muscles during absorptive state.


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Carbohydrate metabolism

transport of glucose

Glycogen synthesis

Fat Metabolism

F.A are of secondary importance as fuel for muscles(FED state). Only glucose is the source of energy.

Amino Acid Metabolism

Protein synthesis

uptake of branched chain amino acids &degradation( branched chain amino acid

transferase).


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BRAIN

2% of adult weight/ receives 15% of cardiac output.

20% of basal oxygen consumption at rest and consumes 25%

of total Glucose.

Glucose uptake is by GLUT 3,4

Glycogen stores are minimal so continuous supply of glucose

is essential.

In hypoglycemia severe and irreversible damage can occur.

Feed Fast Cycle

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