Regulation of Blood Calcium Levels

Optimal Calcium Levels

• Normal Range: 9 to 11 milligrams per deciliter.
• Feedback Mechanism: Activated when calcium levels approach these limits.

Components of the Feedback Cycle

1. Stimulus

   • Disruption in blood calcium levels.

2. Sensory Receptor: Thyroid Gland

   • Specific cells: Parafollicular cells or C cells.
   • Function: Detect high blood calcium levels.

3. Control Center

   • Same as sensory receptors (C cells).
   • Activated gene triggers response.

4. Output

   • Release of calcitonin (CT) when blood calcium is high.
   • Function of Calcitonin: Lowers blood calcium levels.
     • Mnemonic: "Calcitonin tones down calcium" or "Calcitranin cuts it out."

Effector Response

• Effector Organs and Cells
  • Osteoclasts
    • Normally break down bone increasing blood calcium.
    • Calcitonin inhibits their activity (stops bone breakdown).
  • Kidneys
    • Filter and excrete excess calcium into urine.
    • Reduce calcium reabsorption to increase calcium excretion.

Additional Response: Osteoblasts

• Osteoblasts
  • Build new bone using calcium from blood.
  • Indirectly influenced by osteoclast activity.
  • Increase activity to incorporate calcium into new bone.

Feedback Type

• Negative Feedback
  • Goal: Decrease blood calcium to normal levels (9-11 mg/dL).
  • Process:
    • High blood calcium detected by C cells.
    • Calcitonin released to decrease calcium levels.
    • Kidney and bone cells function to lower calcium.

Summary

• Blood calcium regulation is a critical homeostatic process.
• The thyroid gland's C cells detect and respond to changes by releasing calcitonin.
• Osteoclast activity is decreased while kidney excretion of calcium is increased.
• Osteoblasts help incorporate calcium into bone.
• Overall, this process exemplifies a negative feedback mechanism to maintain calcium balance.