Endocrine organs and the presence of feedback controls. Both positive and negative feedback controls exist for each endocrine gland having a regulating (R) and stimulating (S) hormone. Those acting through hypothalamic-pituitary axis include: thyroid hormones on TRHTSH axis, cortisol on CRH-ACTH axis, gonadal steroids on GnRH-LH/FSH axis and insulin-like GH on GHRH-GH axis. Those independent of pituitary control (shown by interrupted arrows) have also feedback controls by calcium on PTH, and hypoglycaemia on insulin release by pancreatic islets.