7.5 Integration of hormonal control of metabolism

Hormones play a crucial role in regulating metabolism. Insulin and glucagon, produced by the pancreas, are the primary players. Insulin promotes glucose uptake and storage, while glucagon mobilizes energy reserves. These hormones work together to maintain blood sugar balance.

Other hormones like epinephrine, cortisol, and thyroid hormones also influence metabolism. They affect energy production, storage, and use throughout the body. Understanding how these hormones interact is key to grasping metabolic regulation and its impact on overall health.

Hormonal Regulation of Metabolism

Insulin and Glucagon: Primary Metabolic Regulators

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• Insulin functions as anabolic hormone produced by pancreatic β-cells
  • Promotes glucose uptake, glycogen synthesis, and lipogenesis
  • Inhibits gluconeogenesis and lipolysis
  • Activates insulin receptors leading to GLUT4 transporter translocation for glucose uptake
• Glucagon acts as catabolic hormone secreted by pancreatic α-cells
  • Stimulates glycogenolysis, gluconeogenesis, and lipolysis
  • Increases blood glucose levels during fasting or stress
  • Activates adenylyl cyclase, increasing cAMP levels and protein kinase A activation
• Insulin and glucagon exert opposing effects on glycogen metabolism
  • Insulin promotes glycogen synthesis
  • Glucagon stimulates glycogen breakdown

Other Key Hormones in Metabolic Regulation

• Epinephrine and cortisol function as stress hormones
  • Work synergistically with glucagon to mobilize energy stores
  • Increase blood glucose levels
• Thyroid hormones (T3 and T4) regulate basal metabolic processes
  • Control basal metabolic rate
  • Influence heat production
  • Affect overall energy expenditure in the body
• Growth hormone promotes anabolic processes
  • Enhances protein synthesis and lipolysis
  • Stimulates glucose sparing
  • Promotes bone and muscle growth
• Leptin and ghrelin regulate appetite and energy balance
  • Leptin suppresses hunger (produced by adipose tissue)
  • Ghrelin stimulates hunger (produced by stomach cells)

Interplay of Hormones and Metabolism

Signaling Pathways and Glucose Metabolism

• Insulin signaling pathway activates glucose uptake
  • Involves insulin receptor activation
  • Leads to GLUT4 transporter translocation to cell membranes
• Glucagon signaling promotes glucose production
  • Activates adenylyl cyclase
  • Increases cAMP levels
  • Activates protein kinase A
• Insulin and glucagon regulate hepatic glucose production
  • Insulin suppresses gluconeogenesis and glycogenolysis
  • Glucagon promotes these processes

Lipid and Protein Metabolism Regulation

• Insulin suppresses hormone-sensitive lipase activity
  • Inhibits lipolysis (breakdown of fat)
• Glucagon and catecholamines activate hormone-sensitive lipase
  • Promote fat breakdown
• mTOR pathway plays central role in protein metabolism
  • Activated by insulin and amino acids
  • Regulates protein synthesis and cell growth
• Cortisol and growth hormone induce insulin resistance
  • Leads to increased glucose production
  • Decreases glucose uptake in peripheral tissues

Hormonal Imbalances and Disorders

Diabetes and Insulin-Related Disorders

• Insulin deficiency leads to type 1 diabetes mellitus
  • Results in hyperglycemia and impaired glucose utilization
• Insulin resistance causes type 2 diabetes mellitus
  • Also leads to hyperglycemia and impaired glucose utilization
• Metabolic syndrome involves complex hormonal and metabolic dysregulation
  • Characterized by insulin resistance, hypertension, dyslipidemia, and central obesity

Other Hormonal Imbalances and Their Effects

• Excess cortisol production (Cushing's syndrome) disrupts metabolism
  • Causes insulin resistance and hyperglycemia
  • Increases protein catabolism
• Thyroid hormone imbalances affect basal metabolic rate
  • Hypothyroidism slows metabolism
  • Hyperthyroidism accelerates metabolism
• Growth hormone abnormalities impact body composition
  • Growth hormone deficiency decreases muscle mass and increases adiposity
  • Excess growth hormone leads to acromegaly and insulin resistance
• Leptin and ghrelin imbalances affect appetite regulation
  • Leptin resistance or deficiency contributes to obesity
  • Ghrelin imbalances can lead to eating disorders or obesity

Hormonal Coordination of Nutritional Response

Fed State Metabolic Regulation

• Increased insulin secretion characterizes the fed state
  • Promotes glucose uptake and glycogen synthesis
  • Enhances lipogenesis
  • Inhibits gluconeogenesis and lipolysis
• Leptin levels increase after eating
  • Suppresses appetite
  • Promotes energy expenditure

Fasting and Exercise Metabolic Adaptations

• Fasting state triggers hormonal changes
  • Decreased insulin and increased glucagon levels
  • Stimulates glycogenolysis, gluconeogenesis, and lipolysis
  • Maintains blood glucose levels
• Prolonged fasting induces additional hormonal responses
  • Triggers release of cortisol and growth hormone
  • Promotes protein catabolism
  • Enhances gluconeogenesis and lipolysis
• Exercise stimulates catabolic hormone release
  • Induces catecholamine and glucagon secretion
  • Mobilizes energy stores
  • Increases glucose production to meet energy demands

Appetite Regulation and Stress Response

• Ghrelin levels fluctuate to regulate meal patterns
  • Increase before meals (stimulates hunger)
  • Decrease after eating (promotes satiety)
• Hypothalamic-pituitary-adrenal (HPA) axis coordinates stress response
  • Releases cortisol to mobilize energy resources
  • Maintains glucose homeostasis during stress
• Leptin levels decrease during fasting
  • Reduces appetite-suppressing effects
  • Promotes food-seeking behavior