Hypothalamic–Pituitary–Thyroid (HPT) axis

The Hypothalamic–Pituitary–Thyroid (HPT) axis is a tightly regulated feedback system involving:

1. Hypothalamus
2. Anterior Pituitary Gland
3. Thyroid Gland

Together, they control the production of thyroid hormones (T3 and T4), which affect almost every cell in your body.

🔄 How the HPT Axis Works (Step-by-Step)

1. Hypothalamus Releases TRH

• The hypothalamus detects the need for more thyroid hormones (e.g. low metabolism, cold, stress).
• It releases TRH (Thyrotropin-Releasing Hormone).

2. TRH Stimulates Anterior Pituitary to Release TSH

• TRH travels via the hypophyseal portal system to the anterior pituitary.
• The anterior pituitary responds by secreting TSH (Thyroid-Stimulating Hormone).

3. TSH Stimulates the Thyroid Gland

• TSH travels through the bloodstream to the thyroid gland (located in the neck).
• It stimulates the thyroid to absorb iodine and produce the hormones:
  • T3 (Triiodothyronine) – the more active form
  • T4 (Thyroxine) – the more abundant form, converted into T3 in tissues

4. T3 and T4 Affect the Body

• These hormones:
  • Increase metabolic rate
  • Regulate body temperature
  • Support brain development
  • Influence heart rate, muscle tone, and energy production

5. Negative Feedback Loop

• When T3 and T4 levels are sufficient or high, they inhibit:
  • Further TRH release from the hypothalamus
  • Further TSH release from the pituitary
• This prevents overproduction and maintains hormonal balance.

🔍 Why the HPT Axis Matters

This axis helps the body adapt to:

• Cold (by increasing metabolism and heat production)
• Growth and development (especially in infants/children)
• Daily energy needs

Disruption of this axis can lead to:

📊 Hormone Flow Summary:

🧠 Summary Table: