Endocrine System and the HPT Axis

Key Concepts

• The endocrine system uses negative feedback loops to regulate hormones.
• Focus on the Hypothalamus-Pituitary-Thyroid (HPT) axis.
• Discuss conditions: Hyperthyroidism and Hypothyroidism.

HPT Axis Overview

• Organs Involved:
  • Hypothalamus
  • Pituitary gland
  • Thyroid gland

Function of the HPT Axis

• Hypothalamus:

  • Acts as a controller, always "on" unless inhibited.
  • Releases Thyrotropin Releasing Hormone (TRH).

• Pituitary Gland:

  • Receives TRH, which stimulates it to release Thyroid Stimulating Hormone (TSH).
  • TSH targets the thyroid gland.

• Thyroid Gland:

  • Stimulated by TSH to release T3 (Triiodothyronine) and T4 (Thyroxine).
  • Regulates metabolism by converting food into energy.

Hormones and Their Functions

• TRH (Thyrotropin Releasing Hormone):

  • Excitatory effect on the pituitary gland.

• TSH (Thyroid Stimulating Hormone):

  • Stimulates the thyroid to produce its hormones.

• T3 and T4:

  • Increase metabolic rate by enhancing breakdown of food into energy.
  • Inhibit the hypothalamus and pituitary to regulate hormone levels.

Conditions

• Hyperthyroidism:

  • Caused by excess T3 and T4.
  • Symptoms: Fast heart rate, jitteriness, overactive mind.

• Hypothyroidism:

  • Caused by insufficient T3 and T4.
  • Symptoms: Weight gain, low energy, lethargy.

Regulatory Mechanism

• Negative Feedback Loop:
  • T3/T4 inhibit TRH and TSH production when levels are high.
  • Low T3/T4 levels cause hypothalamus to produce more TRH, restarting the cycle.

Summary

• The HPT axis involves a dynamic equilibrium of hormone levels.
• Negative feedback ensures hormone levels remain within a normal range.

Additional Considerations

• Possible causes of thyroid disorders include tumors and autoimmune diseases affecting the pituitary or thyroid glands.

Next Steps

• Watch further videos on tumors and autoimmune diseases affecting the HPT axis for deeper understanding.