Glukoosivarannot

Glukoosivarannot are the body's reserves of glucose, stored primarily as glycogen in the liver and in skeletal muscles. In humans these stores serve two main purposes: to sustain blood glucose levels during fasting and to supply immediate energy for muscle contraction during exercise. The liver acts as the central regulator, able to release glucose into the bloodstream, whereas muscle glycogen serves locally for muscle activity and cannot directly replenish blood glucose.

Glucose storage occurs through glycogenesis, promoted by insulin after carbohydrate intake. When glucose is needed, glycogenolysis breaks glycogen down to glucose-6-phosphate; in the liver this is converted to free glucose and released into blood, but muscles lack glucose-6-phosphatase and thus export glucose to blood is not possible. Hormonal control involves glucagon and epinephrine raising glucose availability during fasting or stress; cortisol also supports gluconeogenesis during longer-term fasting.

Quantitatively, the liver stores about 100 grams of glycogen, while skeletal muscle stores around 300–400 grams, totaling roughly half a kilogram of readily mobilizable carbohydrate in a typical adult. Hepatic glycogen can be depleted within 12–24 hours of fasting, after which gluconeogenesis maintains blood glucose. Muscle glycogen depletion relates to activity level and may occur within hours of sustained exertion; recovery parallels dietary carbohydrate intake and training status.

Disorders affecting glukoosivarannot include glycogen storage diseases, which disrupt glycogen synthesis or breakdown. Clinically, the concept helps explain energy nutrition, exercise physiology, and metabolic regulation.