The cori cycle refers to the metabolic pathway where lactate produced from anaerobic glycolysis in muscles is transported via blood to the liver, where it is converted back to glucose and glycogen. It was discovered by Carl and Gerty Cori. During intense exercise, oxygen demand exceeds supply and muscles rely on glycolysis, producing lactate. Lactate enters the bloodstream and is taken up by the liver, where it is oxidized to pyruvate and then glucose through gluconeogenesis. Glucose is returned to muscles, allowing continued glycolysis. This cycling of lactate and glucose between muscles and liver during exercise is known as the cori cycle.

1. CORI CYCLE.

2. Introduction.
• The cori cycle refers to the metabolic pathway in which
lactate produced by anaerobic glycolysis in the muscles move
via the blood stream to the liver where it is converted into
blood glucose and glycogen
• First discovered by carl and gerty cori.
• It is a cycle in which …
glycogen in the muscle is degraded to produce lactic acid →
blood→ liver → where it is changed back into glycogen.
• When needed the glycogen is broken down into glucose and
the blood carries the glucose to the muscle.

4. Cori cycle.
• During the muscle activity require moderate amount of
glucose.
• Which can be supplied by the blood glucose or breakdown of
glycogen reservoir present in the muscle tissue.
• During time of great excertion ,muscle tissue uses oxygen
faster than it can be supplied by the blood stream so the
muscle must operate anaerobically.
• Under these condition the glucose breakdown stopes at the
3 carbon acid lactate.

5. • Lactate enters into bloodstream and picked up by the liver.
• Liver convert lactate back into the glucose .
• Glucose further returned to the muscle for further glycolysis.
• The cycling of glucose and lactate between skeletal muscle
and liver known as the cori cycle.

7. • Vigorous exercise can lead to oxygen shortage (anaerobic
conditions), and energy requirements must be met by
increased levels of glycolysis.
• Under such conditions, glycolysis converts NAD to NADH, yet
O2 is unavailable for regeneration of NAD via cellular
respiration.
• Instead, large amounts of NADH are reoxidized by the
reduction of pyruvate to lactate.
• The lactate thus produced can be transported to the liver,
where it is reoxidized by liver lactate dehydrogenase to yield
pyruvate, which is converted eventually to glucose.

8. • In this way, the liver shares in the metabolic stress created by
vigorous exercise.
• It exports glucose to muscle, which produces lactate, and lactate
from muscle can be processed by the liver into new glucose.
• Liver, with a typically high NAD/NADH ratio , readily produces more
glucose than it can use.
• Muscle that is vigorously exercising will enter anaerobiosis and show
a decreasing NAD/NADH ratio, which favors reduction of pyruvate to
lactate.

10. Significance.
• Prevent lactic acidosis in the muscle under anaerobic
conditions.
• The cycle is important in producing ATP,an energy source
during muscle activity.
• Cori cycle functions ,more sufficiently when the muscle
activity has ceased thus allowing the oxygen debt to be
repaid.

11. • The drug metformin can precipitate lactic acidosis in patients
with renal failure because metformin inhibits cori cycle.
• Normally the excess lactate would be cleared by kidney but in
patients with kidney failure the kidney cannot handle the excess
lactic acid.

12. Summary.
• The cori cycle refers to the metabolic pathway in which
lactate produced by anaerobic glycolysis in the muscles move
via the blood stream to the liver where it s converted into
blood glucose and glycogen.
• First discovered by carl and gerty cori.
• Vigorous exercise can lead to oxygen shortage, and energy
requirements must be met by increased levels of glycolysis.
• Under these condition the glucose breakdown into lactate.

13. • The plasma membrane is freely permeable to lactate.
• Lactate is carried from the skeletal muscle through blood and
handed over to liver, where it is oxidized to pyruvate.
• Pyruvate, so produced, is converted to glucose by
gluconeogenesis, which is then transported to the skeletal
muscle.
• The cycle is important in producing ATP,an energy source
during muscle activity.

14. Reference.
• Devlin. M .Thomas,Testbook of Biochemistry with clinical
correlation .6th edition, A John wiley and Sons . Inc.
publication. Page no. 609-610.
• Nelson David L, Cox Michael M, Lehningers principle of
Biochemistry , Fourth edition ,M.H freeman and company
,New York , page no.539.
• Berg M Jeremy, Tymoczko john L, Stryer Lubert,
Biochemistry, sixth edition, M.H freeman and company
,New York, page no. 468.
• Voet Donald, Voet Judith G and Pratt, Fundamentals of
biochemistry, 2nd edition, A John wiley and Sons . Inc.
publication. Page no. 751