Homeostasis Lecture Notes

Key Concept: Homeostasis

• The body's internal balance, especially regarding calcium levels.

Importance of Calcium

• Essential for:
  • Nerve contractions
  • Muscle contractions
  • Blood clotting
• Not just for strong bones and teeth.

Calcium Regulation

• Osteoblasts: Build bone
• Osteoclasts: Break down bone
• Bone acts as a reservoir for calcium, adjusting based on dietary intake.

Hormonal Regulation of Calcium

• Calcitonin:
  • Lowers blood calcium levels.
  • Comes from the thyroid gland.
  • Stores excess calcium in bones.
• Parathyroid Hormone (PTH):
  • Raises blood calcium levels.
  • Comes from the parathyroid glands.
  • Stimulates bone resorption, kidney reabsorption, and increased intestinal absorption.

Adrenal Glands

• Located above the kidneys, resemble "party hats".
• Two parts:
  • Cortex: Outer layer
  • Medulla: Inner layer

Hormones from the Adrenal Medulla

• Catecholamines (Epinephrine/Norepinephrine):
  • Response to acute stress
  • Fight or flight response
  • Effects include increased heart rate, blood pressure, respiratory rate, and glycogenolysis.

Hormones from the Adrenal Cortex

• Over 30 steroid-based hormones:
  1. Mineral Corticoids: Regulate electrolytes (e.g., aldosterone for sodium reabsorption)
  2. Glucocorticoids: Regulate metabolism, stress response (e.g., cortisol)
  3. Gonadocorticoids: Supplementary sex hormones (e.g., androgens)

Mineral Corticoids

• Aldosterone:
  • Increases sodium reabsorption
  • Affects blood pressure and water retention

Glucocorticoids

• Cortisol:
  • Stress hormone
  • Affects fat and protein metabolism
  • Anti-inflammatory properties
  • Stabilizes blood sugar between meals

Gonadocorticoids

• Androgens (e.g., testosterone) influence sex drive and bone strength.

Adrenal Gland Disorders

• Addison’s Disease:
  • Insufficient hormone production by the cortex
  • Symptoms: Fatigue, weight loss, salt craving, etc.
• Cushing’s Disease:
  • Excessive hormone production
  • Symptoms: Obesity, thin limbs, bruising, etc.

Additional Notes

• Electrolyte balance is crucial for muscle and nerve function.
• Homeostasis may be temporarily overridden by stress responses for survival.