the fed state

Question 1

what is the fed state?

Answer 1

The ‘well fed’ state, is the 2-4 hour period after a normal meal.
These fuels are oxidized for the bodys energy needs
- Excess is transported to storage sites
- Readily available substrates
 Therefore an ‘anabolic’ state
 Increased triacylglycerol and glycogen synthesis
Oxidation or storage is determined by the insulin/glucagon ratio

Question 2

carbohydrate metabolism

Answer 2

digestion, absorption and transportation, to convert carbohydrates into a format which can be used for energy.
- Most commonly consumed as polysaccharides [e.g. starch, fibre or cellulose] or disaccharides [e.g. lactose, sucrose, galactose], these need to be broken down to monosaccharides

Question 3

digestion of carbohydrates

Answer 3

• begins in the mouth- alpha-amylase

- continues in small intestine- pancreatic amylase

Question 4

absorption and transportation of carbohydrates:

Answer 4

• monosaccharides absorbed by intestinal epithelial cells.

- transported to the liver through the hepatic portal vien

Question 5

glucose oxidation for energy and enters biosynthetic pathways

Answer 5

• Glucose transported via the blood stream to the peripheral tissues- forms the carbon skeleton of most compounds
• Surplus glucose is initially stored as glycogen in the liver or muscles, before longer term storage [triacylglycerols].

Question 6

protein metabolism

Answer 6

proteins cleaved by pepsin in the stomach. proteolytic enzymes in the small intestine: trypsin, chymotrypsin, elastase, carboxypeptidase A and.

Question 7

amino acid absorption and storage

Answer 7

• absorbed into intestinal epithelial cells, released into hepatic portal vein.

no AA storage- free AAs absorbed from blood used for protein synthesis and biosynthesis e.g. neurotransmitters and heme. carbon skeleton may be oxidised

Question 8

fats metabolism

Answer 8

TAGs are the major lipids of the diet. fats are not soluble.
- emulsified by bile salts (synthesised in the liver, stored in gall bladder)
- pancreatic lipase converts TAGs to fatty acids & 2-monoacylglycerols
- form micelles contacting with bile salts
Fatty acids absorbed into intestinal epithelial cells and then reformed into TAGs
TAGs combined with proteins, phospholipids, cholesterol into ‘chylomicrons’
- Secreted into the lymphatic system
- Enter bloodstream via thoracic duct to be utilized by different tissues

Question 9

the liver and metabolism

Answer 9

Uniquely situated in metabolism with connection to digestive tract and circulatory system
The first major organ that nutrients meet after they are absorbed from the intestine- hepatic portal vein earlier
- Acts to regulate fluctuations in substrate supplies for cells
- Takes up carbohydrates, lipids, and amino acids- metabolized, stored,

Question 10

hepatocytes and GLUT 2

Answer 10

in carb metabolism, increased glucose uptake by hepatocytes, which have GLUT2 in their membrane. this has a high Km* meaning you need quite a lot of glucose around before the liver starts to take it up- allows ‘priority access’ to glucose e.g. brain.

Question 11

increased phosphorylation of glucose:

Answer 11

Glucokinase creates glucose-6-phosphate, which can be converted to glycogen [glycogenesis]
- It can go via the pentose phosphate pathway [HMP- hexose monophosphate shunt]
- A metabolic pathway parallel to glycolysis,
- Generates NADPH and pentoses and ribose-5-phosphate [a precursor for the synthesis of nucleotides]
The pyruvate produced by glycolysis [break down of glucose] can be converted by acetyl CoA and used to synthesise fatty acids.
Excess glucose is converted to TAG
- Packed into very-low density lipoproteins [VLDL]

Question 12

increased glycogenesis

Answer 12

• glycogen synthase is activated and converts glucose-6-phosphate to glycogen.
• the amount of glycogen that the liver can synthesise/store will vary- maximum of ~300g

Question 13

increased glycolysis

Answer 13

more [glucose->pyruvate]
increased insulin-to-glucagon results in increased glycolytic enzymes:
- glucokinase, PFK-1 and pyruvate kinase
- pyruvate dehydrogenase [converting pyruvate to acetyl CoA] is dephosphorylated and active as pyruvate inhibits PDH kinase- increased acetyl CoA

Question 14

the liver being the site of fatty acid synthesis

Answer 14

• increased during the absorptive state due to acetyl CoA and NADPH availability [from pentose phosphate pathway]. also activation of acetyl CoA Carboxylase:
• > allosteric activator present, citrate
• > activated by dephosphorylation

Question 15

increased acetyl CoA

Answer 15

• pyruvate from glycolysis enters mitochondria
• citrate leaves due to isocitrate dehydrogenase inhibition
• cleaved by ATP-citrate lyase [enzyme that catalyses the conversion of citrate to acetyl CoA and oxaloacetate

Question 16

increased triacylglycerol synthesis:

Answer 16

• Increased acetyl CoA presence and also due to hydrolysis of TAG component from chylomicrons

Question 17

TAG storage

Answer 17

• Packaged in VLDLs and transported to adipose tissues and muscle tissue
• • for energy use and storage

Question 18

amino acid metabolism

Answer 18

If AAs are not used for protein synthesis in the liver [which is increased], then they are exported to other tissues for use, or degraded

• Degradation will involve deamination- urea formed- the urea cycle converts highly toxic ammonia to urea for excretion
• Carbon skeleton will be degraded to pyruvate, acetyl CoA, or TCA cycle intermediates

Question 19

adipose tissue

Answer 19

• second only to liver in its ability to distribute fuel molecules.
• increased carbohydrate metabolism.
• glucose is phosphorylated to glucose 6-P- enters the pentose phosphate pathway, or glycolysis
• FA and glycerol released from TAGs y lipoprotein lipase [LPL]- an enzyme in capillary walls

Question 20

skeletal muscle

Answer 20

• glucose is used to replenish glycogen stores depleted by exercise
• AAs taken up for restorative synthesis.

carb metabolism:
- increased insulin-to-glucagon ratio and availability of glucose 6-P favours glycogen synthesis.

Fat metabolism:
- FAs are of secondary importance compared to glucose.

AA metabolism:
- increased uptake of branched chain AAs: leucine, isoleucine, valine, contains transaminase

Question 21

brain tissue

Answer 21

Very dependent on glucose, under normal conditions the nervous system requires about 150g per day

• • If levels drop below 40 mg/100 ml: dizzy/light headed
• • Glucose needed as an energy source & precursor for neurotransmitters

• Substrates must be able to pass through blood brain barrier

• No significant glycogen stores
• No significant TAG stores
• Dependent on blood glucose

Question 22

refeeding syndrome

Answer 22

occurs about 4 days after refeeding begins. symptoms:
- fluid and electrolyte disorders [hypophosphatemia].
- neurologic, pulmonary, cardiac complications. can lead to death.
patients are at risk if they’ve not fed for 7 days.
during starvation, hormonal and metabolic changes prevent protein/muscle breakdown:
- low insulin, increased glucagon
- adipose tissue release fatty acids and glycerol
- glycogen breakdown and gluconeogenesis, lipid and protein breakdown commence

• ketone bodies and FAs become the major fuel source.
• intercellular minerals become depleted
• during refeeding, shift back to carb metabolism- insulin stimulates glycogen, fat, protein synthesis. sudden demand for minerals and cofactors for glycolytic enzymes.
• uptake of minerals from extracellular fluid leads to electrolyte/ osmotic disturbances- can lead to cardiac and neurological problems
• consult experts: monitor vital functions, fluid balance, and plasma electrolytes