Which hormone is responsible for activating glycogen phosphorylase?

Glycogen phosphorylase is the enzyme responsible for the breakdown of glycogen into glucose, which is crucial for regulating blood sugar levels, especially during periods of fasting or increased energy demand. Glucagon plays a key role in this process. It is a hormone produced by the alpha cells of the pancreas and its primary function is to raise blood glucose levels when they fall too low.

When blood glucose levels decrease, glucagon is released into the bloodstream. It binds to receptors on liver cells, activating a signaling cascade that leads to the phosphorylation of glycogen phosphorylase. This phosphorylation activates the enzyme, prompting it to break down glycogen into glucose-1-phosphate. The glucose-1-phosphate can then be converted into glucose-6-phosphate and ultimately released as free glucose into the bloodstream, thus increasing blood glucose levels.

In contrast, hormones like insulin work to decrease blood glucose levels by promoting the storage of glucose as glycogen, suppressing glycogen breakdown. Cortisol, while it can influence glucose metabolism, serves more as a stress hormone with a complex role in promoting gluconeogenesis and overall metabolic effects rather than directly activating glycogen phosphorylase. Somatostatin primarily functions to inhibit the secretion of other hormones, including