What Is the Cori Cycle?

The Cori cycle is a natural, metabolic pathway that was named after its discoverers, Carl Ferdinand Cori and Gerty Cori in 1929. It is sometimes referred to as the lactic acid cycle because it involves the production of lactate. The Cori cycle occurs when the muscles need energy.

Lactate is a substance produced by the cells. The Cori cycle involves turning lactate into glucose because the body cannot use lactate for energy. This is a way to bring energy to the muscles during intense workouts and other times of lower oxygen levels in the body.

This article discusses how the Cori cycle works, why it's important, where it occurs, its steps, limitations, and more.

What Is the Cori Cycle?

Our muscles require glucose (sugar) for energy during exercise. However, when a person is exercising strenuously, oxygen may not reach the muscles fast enough to keep up with the workout. This is known as anaerobic exercise, any exercise that occurs in the absence of oxygen. This need for quick energy triggers the Cori cycle.

The Cori cycle involves an exchange between the muscles and the liver to allow the body to use carbohydrates for energy. This is because our cells cannot use lactate for energy.

To sustain energy while exercising, lactate must leave the muscle cells and be transported through the circulation to the liver, where it is converted back to glucose so the muscle cells can use it. Once glucose is returned to the muscles, the cells can use it for energy, and glucose is either turned back to lactate or stored.

Why Is the Cori Cycle Important?

During physical activity, the muscles need constant energy. But they cannot use lactate unless it is sent through the circulation to the liver. The Cori cycle transports the lactate byproduct to the liver where it is processed and recycled to glucose through a process called gluconeogenesis.

Once this process takes place, the muscles can then use glucose for energy. Gluconeogenesis is the pathway in which glucose is produced in the body.

When lactate builds up in the muscles, it can decrease exercise performance. When it is not removed, it can cause the muscles to become acidotic. The Cori cycle is the body's natural mechanism for removing lactate and prevents lactate from building up in the muscles.

Where Does the Cori Cycle Occur?

The Cori cycle occurs between the muscles and the liver in the cytoplasm of the cells. It also occurs in red blood cells, in immune cells in the lymph, in cells in the bone marrow, and in cells in the skin. The renal (kidney) tubules are also involved in the process.

Steps of the Cori Cycle

These are the steps of the Cori cycle during exercise, prolonged fasting, and injury:

1. Lactate is transported to the liver through the blood.
2. Lactate is processed by lactate dehydrogenase (LDH) to become a substance called pyruvate.
3. Pyruvate goes through the process of gluconeogenesis to produce glucose.
4. Finally, glucose is exported into the blood and taken up by the muscles.

Limitations of the Cori Cycle

The Cori cycle is not meant to be used long-term and is not as efficient as the body's usual energy process called the Krebs cycle. When the muscles do not have enough oxygen to sustain activity, lactate can build up.

The problem is that after prolonged periods of time, lactate accumulation occurs and muscles may begin to fatigue. In addition, the Cori cycle's recycling of glucose cannot be sustained indefinitely because it costs more energy than it creates.

Glycogen Storage Disease Type III (Cori Disease)

Glycogen Storage Disease Type III (GSD-III), also known as Cori Disease, AGL deficiency, and Forbes disease, is a genetic disorder in which glycogen cannot be adequately produced or broken down. It is characterized by a deficiency of the debrancher enzyme, amylo-1, 6-glucosidase.

GSD-III is inherited as an autosomal recessive trait and has an incidence of about 1 in 100,000 in the United States. The inability to produce or break down glycogen can cause low blood sugar (hypoglycemia), enlarged liver (hepatomegaly), failure to thrive, and recurrent illness or infections. Treatment includes dietary changes that focus on protein-rich foods and monitoring blood sugar and ketones.

Summary

The Cori cycle is a natural metabolic pathway that helps the body by providing continuous energy to the muscles. During this process, the muscles and liver work together to remove lactate and recycle it as glucose.

A Word From Verywell

The Cori cycle is an important way for your body to utilize energy while exercising. If you have ever experienced muscle fatigue or soreness during an intense workout, you have likely felt the effects of lactic acid. Work with your healthcare provider to develop the right physical activity plan for you.