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Endocrine system – glands, hormones and feedback loops

BiologyHuman & Animal PhysiologyAges 16–17

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An endocrine map: tap the hypothalamus, pituitary, thyroid, adrenal glands, pancreas, ovaries or testes to see their hormones, target organs and effects, and compare nervous and hormonal control with a reflex and an adrenaline "fight or flight" response. A feedback screen models blood glucose (insulin, glucagon, type 1 and type 2 diabetes), the TRH → TSH → thyroxine axis (iodine deficiency and goitre), the stress axis CRH → ACTH → cortisol (acute and chronic stress) and the positive feedback of oxytocin during birth.

Lesson: The endocrine system: hormones, negative and positive feedback, homeostasis

What it shows

Endocrine glands secrete hormones directly into the blood, which carries them to target organs with matching receptors. Hormonal control is slower than nervous control but lasts longer. The pituitary, controlled by the hypothalamus, is a "master gland" whose hormones make other glands release theirs. Most hormone levels are kept steady by negative feedback: a rise in thyroxine, cortisol or blood glucose triggers responses that bring it back down. Positive feedback amplifies a change instead, as when oxytocin strengthens contractions during birth. Diabetes shows what happens when blood glucose control fails.

How to use

In Endocrine map, tap a gland to read its hormones and watch them travel to their targets; switch Body to compare female and male. Press Hand touches a hot object (reflex) and Sudden fright (adrenaline) to compare their timelines. In Feedback loops, choose a Loop and a condition, set the slider, untick Feedback working to see its role, and press the blue button to run again; each run is recorded in the table.

Parameters you can change

  • Screen Endocrine map, Feedback loops
  • Body Female, Male
  • Control loop Blood glucose: insulin, glucagon, Thyroid: TRH → TSH → thyroxine, Stress: CRH → ACTH → cortisol, Oxytocin in birth (positive feedback)
  • Person (blood glucose) Healthy, Type 1 diabetes (untreated), Type 2 diabetes
  • Type of stress Acute stress (once), Chronic stress (daily, 2 weeks)
  • Size of the change 0–100 %

Questions to explore

  1. Why does blood glucose rise only a little after a meal in a healthy person but stay high in untreated type 1 diabetes?
  2. Why does a lack of iodine make the thyroid gland grow larger?
  3. How does the positive feedback of oxytocin differ from the negative feedback that controls thyroxine?

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