The Role of Circulating and Local Hormones

Circulating Hormones

Circulating hormones are chemical messengers that travel through the bloodstream to reach their target tissues. Let's break down the key players and their roles:

1. Insulin

• Produced by: Beta cells in the pancreas
• Primary function: Blood glucose regulation
• Key actions:
  • Promotes glucose uptake by cells
  • Stimulates glycogen storage in liver and muscles
  • Increases protein synthesis
  • Promotes fat storage

Think of insulin as the "storage hormone" - it helps pack away nutrients for later use!

2. Glucagon

• Produced by: Alpha cells in the pancreas
• Primary function: Raises blood glucose levels
• Key actions:
  • Stimulates glycogen breakdown
  • Promotes gluconeogenesis (making new glucose)
  • Increases fat breakdown

Insulin and glucagon work as antagonistic pairs - when one goes up, the other typically goes down.

3. Adrenaline (Epinephrine)

• Produced by: Adrenal medulla
• Primary functions during exercise:
  • Increases heart rate
  • Dilates airways
  • Mobilizes energy stores
  • Redirects blood flow to working muscles

During a 100m sprint, adrenaline helps prepare your body by:

• Increasing heart rate for better oxygen delivery
• Breaking down glycogen for quick energy
• Dilating airways for better breathing

Local Hormones

Local hormones (also called paracrine hormones) act near their site of release. They're crucial for exercise adaptation and performance.

1. Prostaglandins

• Produced by: Most tissues
• Key roles:
  • Inflammation regulation
  • Blood flow control
  • Pain sensation
  • Temperature regulation

2. Growth Factors

• Types include:
  • Insulin-like Growth Factor (IGF)
  • Vascular Endothelial Growth Factor (VEGF)
• Functions:
  • Promote muscle growth and repair
  • Stimulate new blood vessel formation
  • Aid in tissue recovery after exercise

Don't confuse local hormones with circulating hormones - local hormones work right where they're produced, while circulating hormones travel through the bloodstream to reach their targets.

Exercise Response

During exercise, both circulating and local hormones work together:

1. Immediate Response:
   • Adrenaline increases
   • Insulin decreases
   • Local growth factors activate
2. Recovery Phase:
   • Prostaglandins aid inflammation and repair
   • Growth factors promote adaptation
   • Insulin levels normalize

When studying hormone responses to exercise, remember that timing matters:

• Some responses are immediate (like adrenaline)
• Others take hours or days (like growth factors)