Q.Explain Cori's cycle.

The Cori cycle recycles the lactic acid produced during strenuous muscle activity back into usable glucose, via the liver.

During vigorous or prolonged muscular activity, the demand for ATP can exceed the rate at which oxygen can be delivered to the muscle fibres. Under such anaerobic (oxygen-deficient) conditions, muscle cells continue to break down glucose through glycolysis, but instead of the pyruvic acid entering the oxygen-requiring Krebs cycle, it is reduced to lactic acid (lactate) by the enzyme lactate dehydrogenase. This process regenerates NAD⁺ so glycolysis can continue, but it is far less efficient (produces only 2 ATP per glucose) and leads to lactic acid build-up, contributing to muscle fatigue and cramps.

Steps of the Cori cycle:

1. In the muscle, glucose → pyruvic acid (glycolysis) → lactic acid (under anaerobic conditions).
2. Lactic acid diffuses out of the muscle cells into the blood and is carried to the liver.
3. In liver cells, lactic acid is reconverted to pyruvic acid and then, using oxygen and ATP energy (this is where the "oxygen debt" incurred by the muscle is repaid), it is converted back into glucose by the process of gluconeogenesis. …

The Cori cycle recycles lactic acid: muscles make lactate anaerobically, the liver turns it back into glucose, and that glucose returns to the muscles.

During strenuous exercise the oxygen supply to skeletal muscles becomes insufficient. The muscles then respire anaerobically:

1. In the muscle, glucose is broken down by glycolysis to pyruvic acid, which, in the absence of enough oxygen, is reduced to lactic acid. This lactic acid accumulates and causes muscle fatigue.

2. The lactic acid diffuses out of the muscle into the blood and is carried to the liver.

3. In the liver, lactic acid is first oxidised back to pyruvic acid, which is then converted into glucose by the process of gluconeogenesis.

4. This newly formed glucose is released into the blood and transported back to the muscles, where it can again be used as fuel (or stored as glycogen).

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Cori's cycle recycles the lactic acid made by fatigued muscle back into usable glucose via the liver.

During vigorous or prolonged muscular activity, the oxygen supply to muscle fibres may become insufficient to sustain aerobic respiration. Under these low-oxygen conditions, muscle cells shift to anaerobic glycolysis: glucose is broken down to pyruvic acid, which is then reduced to lactic acid (instead of being fully oxidised via the Krebs cycle), regenerating NAD+ so glycolysis can continue and ATP can still be produced, albeit far less efficiently.

The cycle itself:

1. Lactic acid accumulates in the working muscle, causing muscle fatigue/cramps, and diffuses into the bloodstream.
2. Blood carries the lactic acid to the liver.
3. In the liver, lactic acid is reconverted to pyruvic acid and then, via gluconeogenesis, back to glucose (this step consumes ATP, effectively "paying back" some of the energy debt using the liver's aerobic capacity).
4. This newly formed glucose is released into the blood and can be transported back to the muscle to be used again as fuel, or stored as liver glycogen. …

In Cori's cycle, muscle lactic acid travels to the liver, is turned back into glucose, and the glucose returns to the muscle - recycling lactate between muscle and liver.

During vigorous muscular activity, the oxygen supply becomes insufficient, so the muscles respire anaerobically. In this anaerobic glycolysis, glucose is broken down to pyruvic acid and then to lactic acid, which accumulates in the muscle and causes muscle fatigue.

The Cori's cycle (named after Carl and Gerty Cori), also called the lactic acid cycle, is the process by which this lactic acid is dealt with:

1. In the muscle: glucose -> (glycolysis, anaerobic) -> lactic acid, releasing some ATP for muscle contraction.
2. The lactic acid diffuses out of the muscle into the blood and is carried to the liver.
3. In the liver: the lactic acid is oxidised back to pyruvic acid and then reconverted into glucose by the energy-requiring process of gluconeogenesis. Some of this glucose is stored as glycogen; some is released into the blood. …