Negative Feedback

1⃣ Adrenaline

  • Produced by: Adrenal glands (on top of kidneys).

  • Released during: Fear or stress → “fight or flight” response.

  • Effects:

    • Increases heart rate → more oxygen & glucose delivered to brain & muscles.

    • Prepares body for rapid action (running or fighting).

2⃣ Thyroxine

  • Produced by: Thyroid gland (base of the neck).

  • Main functions:

    1. Stimulates basal metabolic rate → speeds up chemical reactions in the body.

    2. Supports growth and development.

3⃣ Negative Feedback & Thyroxine Regulation

  • Concept: The body maintains stable levels of hormones via negative feedback.

  • How it works for thyroxine:

    1. Low thyroxine → brain signals pituitary gland to release TSH (thyroid-stimulating hormone).

    2. TSH triggers thyroid → releases more thyroxine.

    3. High thyroxine → brain detects increase → pituitary reduces TSH → thyroid releases less thyroxine.

  • Result: Thyroxine levels stay balanced.

🔑 Key idea: If a hormone level falls, the body acts to increase it; if it rises too high, the body acts to decrease it. This keeps conditions in the body stable.

4⃣ Examples of Negative Feedback in the Body

  • Thyroxine regulation

  • Blood glucose control

  • Menstrual cycle hormones