The diagram shows feedback mechanisms associated with the thyroid gland.

A and D are the same it  is releasing the thyrotropin releasing hormone from the Hypothalmus

B and E are the same it is releasing the thyroid stimulating hormone from the anterior Pituitary

C and F are the same  it is releasing the Thyroxine Hormone from the Thyroid


I believe this is a Complex, multilevel POSITIVE feedback


This causes Thyroxine to to increase


My understanding is the blood level of thyroxine gets too low, thus sending signal to the hypothalmus that makes it send thyrotopin releasing hormone to the Anterior pituitary, then the anterior pituitary rleases thyroid stimulating hormone so that the thyroid will release thyroxine....


Hope it helps and I think I am correct if I am wrong please let me know