Fig. 8.8 
The involvement of ACTH and cortisol in the hypothalamic-pituitary-adrenal axis. 
Cortisol produced in the adrenals or by an adrenal tumour has a negative feedback effect on ACTH production. Oral steroids have the same effect. Conversely, ACTH stimulates cortisol production and secretion, as do pituitary or ectopic tumours and intramuscular injections of ACTH.