Under anaerobic conditions, pyruvate is converted to lactate. Where is lactate primarily transported for further metabolism?

• A. Transported to the liver where it can be converted back to glucose
• B. Quickly metabolized in muscle to produce energy without liver involvement
• C. Stored as fat in adipose tissue
• D. Exits the body via breath

Answer: (A)

When oxygen is scarce, muscles rely on anaerobic glycolysis and convert pyruvate to lactate to regenerate NAD+, allowing glycolysis to continue and produce a small amount of ATP. The lactate then leaves the working muscle and travels through the bloodstream to the liver, where it is converted back to glucose via gluconeogenesis as part of the Cori cycle. This liver-based reconversion supplies glucose to the blood and to muscles for later energy use. While some lactate can be oxidized in other tissues, the liver is the primary site for turning lactate into glucose, rather than being stored as fat or expelled by breath.