Lecture Notes on Endocrine System and Exercise Metabolism

Key Glands Involved in Exercise Metabolism

• Anterior Pituitary Gland

  • Secretes hormones based on hypothalamic stimulating and inhibitory hormones.
  • Increases secretion of all anterior pituitary hormones during exercise.
  • Growth Hormone
    • Promotes muscle hypertrophy and tissue building.
    • Increases fat metabolism and blood free fatty acid levels.
    • Helps in sparing glucose by increasing fat utilization.
    • Release proportional to exercise intensity.

• Thyroid Gland

  • Releases Triiodothyronine (T3) and Thyroxine (T4) both at rest and during exercise.
  • Increases metabolic rate, protein synthesis, glucose uptake and utilization.
  • Enhances fatty acid availability and aerobic metabolism.
  • Increases number and size of mitochondria over time.

• Adrenal Glands

  • Adrenal Medulla
    • Releases norepinephrine and epinephrine, mostly epinephrine (80%).
    • Stimulates sympathetic nervous system during exercise.
    • Prolonged action due to circulation in the bloodstream.
    • Increases heart rate, contractility, blood pressure, respiration, metabolism, and glycogenolysis.
    • Facilitates blood flow redistribution to active skeletal muscles through vasoconstriction.
  • Adrenal Cortex
    • Releases corticosteroids: glucocorticoids, mineralocorticoids, and gonadocorticoids.
    • Cortisol (main glucocorticoid)
      • Increases gluconeogenesis and free fatty acid availability.
      • Enhances protein catabolism and decreases glycolysis.
      • Acts as anti-inflammatory, sparing glucose for the brain.
      • Released after ~30 mins of moderate-intensity exercise.

• Pancreas

  • Primary organ controlling blood glucose at rest and during exercise.
  • Releases Insulin when blood glucose is high.
    • Facilitates glucose transport into cells, decreasing blood glucose.
    • Promotes glycogen, protein, and fat synthesis; decreases lipolysis and gluconeogenesis.
  • Releases Glucagon when blood glucose is low.
    • Increases glucose release from liver and skeletal muscle, enhancing glycogenolysis and gluconeogenesis.

Importance of Blood Glucose

• Blood glucose is crucial for body functions during exercise.
• Insulin secretion decreases during exercise to manage glucose use.
• A follow-up discussion on glucose entry into muscle cells will be addressed in another video.