Stress Response Counterregulatory Hormones

Insulin is the dominant storage hormone. When glucose falls or severe illness threatens perfusion, the body shifts from storing fuel to making fuel available. This response preserves glucose for the brain and other organs that cannot rapidly switch to fat metabolism. The first defense against falling glucose is reduced endogenous insulin secretion. If glucose continues to fall, glucagon rises and signals the liver to release stored glycogen and make new glucose. Catecholamines follow, stimulating glycogen breakdown, lipolysis, tachycardia, and vasoconstriction. Cortisol and growth hormone are slower defenses; they support gluconeogenesis, protein breakdown, lipolysis, and peripheral insulin resistance over hours rather than minutes. During trauma, burns, surgery, sepsis, or other critical illness, the hypothalamic-pituitary-adrenal axis and sympathoadrenal system raise ACTH, cortisol, epinephrine, norepinephrine, glucagon, and growth hormone. The result is increased circulating glucose, free fatty acids, and amino acids. In the short term, this is adaptive: the body is redirecting fuel toward survival. Inflammatory cytokines intensify the effect. The liver produces more glucose through glycogenolysis and gluconeogenesis, while skeletal muscle and adipose tissue become less responsive to insulin. Stress hyperglycemia can...