Integration of metabolism

17 important questions on Integration of metabolism

What does cholecystokinin (CCK) do?

Cholecystokinin is a family of peptide hormones of various lengths secreted into the blood by cells in the duodenum and jejunum regions of the small intestine as a postprandial satiation signal. The CCK binds to the CCK receptor, a G-protein-coupled receptor located in various peripheral neurons, that relay signals to the brain. This binding initiates a signal-transduction pathway in the brain that generates a feeling of satiety. CCK also stimulates the secretion of pancreatic enzymes and bile salts from the gallbladder.

What does glucagon-like peptide 1 (GLP-1) do?

GLP-1 is secreted by intestinal L-cells  and induces feelings of satiety that inhibit further eating. GLP-1 also potentiates glucose-induced insulin secretion by the pancreatic B cells while inhibiting glucagon secretion.

What is the key regulator of leptin and adiponectin?

AMP-activated protein kinase (AMPK). This enzyme is active when AMP levels are elevated and ATP levels are diminished. This activation leads to a decrease in anabolism and an increase in catabolism, most notably an increase in fatty acid oxidation.
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What is type 1 diabetes mellitus?

Type 1 diabetes is caused by the autoimmune destruction of the insulin-secreting B cells in the pancreas and usually begins before age 20.

* Insulin-dependent diabetes

What is type 2 diabetes mellitus?

With type 2 diabetes the patients have a normal of even higher level of insulin in their blood, but they are unresponsive to the hormone (insulin resistance).

Which pathways contribute to insulin resistance?

Diacylglycerols and ceramide activate stress-induces pathways that interfere with insulin signaling.

Mitochondria are not capable of processing all of the fatty acids by B oxidation; fatty acids accumulate in the mitochondria and eventually spill over into the cytoplasm. They reincorporate into triacylglycerols.

How does ATP depended insulin release work?

Glucose gets transported into the pancreatic B cell by GLUT 2 (only when sufficient glucose present). Glycolysis and cellular respiration result in ATP and the ATP activates the K+ pump which pumps the K+ out of the cell. Ca+ goes into the cell, which trigger the transport of insulin filled vesicles resulting in insulin release.

What is the molecular mechanism behind type 1 diabetes?


Insulin is deficient, so the entry of glucose in adipose and muscle cells is impaired.
The liver becomes stuck in a gluconeogenic and ketogenic state.
The excessive level of glucagon relative to that of insulin leads to a decrease in the amount of fructose 2,6-bisphosphate, which stimulates glycolysis and inhibits gluconeogenesis.
An excessive amount of glucose is produced by the liver and released into the blood.
Water accompanies the excreted glucose (through urine) so the patient is hungry and thirsty. Because of the ketone body production, the pH also drops.

Why is there ketone production in diabetes?

A lack of insulin leads to uncontrolled breakdown of lipids and proteins, resulting in the ketogenic state.
Large amounts of acetyl CoA are then produced by B oxidation. However, much of acetyl CoA cannot enter the citric acid cycle because there is insufficient oxaloacetate for the condensation step. So the cells generate ketone bodies.

How does muscular activity help to prevent diabetes?

Regular exercise enhances the production of proteins required for fatty acid metabolism, such as enzymes of beta oxidation.
The increase in fatty acid oxidizing capability and additional mitochondria allow for the efficient metabolism of fatty acids. Because an excess of fatty acids results in insulin resistance, efficient metabolism of fatty acids results in an increase in insulin sensitivity.

How is an optimal mix of fuels achieved during a marathon?

- A low blood-sugar level leads to a high glucagon/insulin ratio, which in turn mobilizes fatty acids from adipose tissue.
- Fatty acids enter muscle, where they are degraded by B oxidation to acetyl CoA and then to CO2.
- The elevated acetyl CoA level decreases the activity of pyruvate dehydrogenase complex to block the conversion of pyruvate into acetyl CoA.
- Fatty acid oxidation decreases the funneling of glucose into the citric acid cycle and oxidative phosphorylation.
- Glucose is spared so that just enough remains available at the end of the marathon.

How is the blood-glucose concentration kept at or above 4.4 mM during fasting?

1. The mobilization of glycogen and the release of glucose by the liver
2. The release of fatty acids by adipose tissue
3. The shift in the fuel used from glucose to fatty acids by muscle

Describe what happens in the refed state

- Fat is processed exactly in the same way as in the normal fed state
- The liver does not initially absorb glucose from the blood, but leaves it to other tissues instead. The liver even remains in a gluconeogenic mode. The newly synthesized glucose is used to replenish the liver's glycogen stores. As the blood-glucose concentration continues to rise, the liver completes the replenishment of its glycogen stores and begins to process the remaining glucose for fatty acid synthesis.

What are the dominant metabolic processes during starvation?

- Mobilization of triacylglycerols in adipose tissue
- Gluconeogenesis by the liver

How do organs yield energy from ketone bodies?

Acetoacetate is activated by the transfer of CoA from succinyl CoA to give acetoacetyl CoA. Cleavage by thiolase then yield 2 molecules of acetyl CoA, which enter the citric acid cycle.

What happens after the depletion of the triacylglycerol stores?

The ketone body contribution disappears, and the only source of fuel that remains is protein.

Describe the metabolism of ethanol and what happens to the body after excessive drinking.

1. Alcohol dehydrogenase (cytosol)
Ethanol + NAD+ --> Acetaldehyde + NADH + H+

2. Aldehyde adehydrogenase
Acetaldehyde + NAD+ + H2O --> Acetate + NADH  + H+

Ethanol consumption leads to an accumulation of NADH.
- High concentration of NADH inhibits gluconeogenesis by preventing the oxidation of lactate to pyruvate > lactate accumulates > hypoglycemia and lactic acidosis.

- High concentration of NADH inhibits fatty acid oxidation. The excess of NADH signals that conditions are right for fatty acid synthesis > triacyglycerols accumulate in liver > fatty live

- NADH inhibits citric acid regulatory enzymes > accumulation Acetyl CoA > prododuction ketone bodies > acidosis. Buildup acetaldehyde (insufficient processing)

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