Lecture on Endocrine System and Negative Feedback

Introduction

• Importance of homeostasis and endocrine hormones.
• Key anatomical structures: Hypothalamus, Anterior Lobe of Pituitary Gland, Thyroid Gland.

Negative Feedback Mechanism

• Purpose: Maintain optimal hormone levels in the blood.
• Components:
  • Hypothalamus: Initiates hormone release.
  • Pituitary Gland: Releases stimulating hormones.
  • Target Glands (e.g., Thyroid): Produce end hormones.

Example: Thyroid Hormone Regulation

• Thyroid Hormone Functions:
  • Regulates metabolism.
  • Essential for growth and development.
  • Critical for nervous system development.

Hormone Release Process

1. Low Thyroid Hormone Levels:
   • Hypothalamus releases Thyrotropin Releasing Hormone (TRH).
2. Pituitary Gland Reaction:
   • Stimulated by TRH to release Thyroid Stimulating Hormone (TSH).
3. Thyroid Gland Stimulation:
   • TSH prompts thyroid to produce T3 (triiodothyronine) and T4 (thyroxine).
4. Increased Thyroid Hormone Levels:
   • Blood levels of thyroid hormone rise.

Negative Feedback to Maintain Balance

• High levels of thyroid hormone inhibit further release of TRH from hypothalamus.
• Decrease in TRH leads to less TSH, reducing thyroid hormone production.
• Balance is restored as excess hormone levels drop.

Other Endocrine Pathways

• Cortisol Regulation:
  • Process Similar to Thyroid:
    • Hypothalamus releases Corticotropin Releasing Hormone (CRH).
    • Pituitary releases Adrenocorticotropic Hormone (ACTH).
    • Adrenal cortex produces cortisol.
  • Negative Feedback:
    • High cortisol levels inhibit CRH and ACTH production.

Disorders Related to Hormone Imbalance

• Cortisol Imbalance:
  • Cushing's Disease: Excess cortisol (hypercortisolism).
  • Addison's Disease: Insufficient cortisol production.
• Thyroid Hormone Imbalance:
  • Thyrotoxicosis: Excessive thyroid hormones.
  • Hypothyroidism: Insufficient thyroid hormones.

Conclusion

• Hormone regulation via negative feedback is crucial for maintaining physiological balance.
• Disruption in feedback can lead to significant health issues.