Elevation of blood glucose concentration stimulates endocrine cells in the pancreas to release insulin. Insulin has the major effect of facilitating entry of glucose into many cells of the body - as a result, blood glucose levels fall.
Therefore, the level of ACTH will be low. Alternatively, Cushing's syndrome might result because of hypersecretion of ACTH. In fact, Cushing's syndrome is more commonly caused by a pituitary adenoma (a pituitary tumor than by an adrenal tumor.
When the level of blood glucose falls sufficiently, the stimulus for insulin release disappears and insulin is no longer secreted. Numerous other examples of specific endocrine feedback circuits are presented in the sections on specific hormones or endocrine organs.
The release from negative feedback inhibition means that more CRH and ACTH will be secreted. More ACTH will stimulate the remaining adrenal tissue to grow and to secrete more cortisol. This will have the effect of bringing cortisol back up towards its normal daily level of secretion.
Cushing's syndrome caused by a pituitary adenoma is known as Cushing's disease. In Cushing's disease, both ACTH and cortisol levels will be high. Hyposecretion of cortisol is known as adrenal insufficiency.
(The following is the previous answer, which I think is incorrect, but I include it because of the very real possibility that there may be some confusion between behavior and physiology?
Secondary adrenal insufficiency (or hypopituitary adrenal insufficiency ) describes the situation where abnormally low ACTH levels lead to hyposecretion of cortisol. Interestingly, this can occur after the end of high dose glucocorticoid therapy ( glucocorticoid is the name for a molecule that is a glucocorticoid receptor agonist; the glucocorticoid receptor is the receptor for cortisol).
The behavioural response is the sensation of thirst, which is especially enhanced when it is not quenched. Also, the ADH Regulation is trying to maintain stability since there is an imbalance in the blood osmotic pressure, making this system a negative feedback loop.
) The thirst sensation is a positive feedback control system. Any increase in the osmotic blood pressure stimulates the osmoreceptors, neurons that are located in the hypothalamus that monitor blood osmotic pressure.
Consider a case where one adrenal gland is damaged. This will cause decreased secretion of cortisol, and there will be a decrease in the degree of negative feedback inhibition on the hypothalamus and anterior pituitary.
Adrenal insufficiency involving hyposecretion of both cortisol and aldosterone is known as Addison's disease. In primary adrenal insufficiency, there is a release of the pituitary from negative feedback inhibition, and consequently, ACTH levels are high.
Another type of feedback is seen in endocrine systems that regulate concentrations of blood components such as glucose. Drink a glass of milk or eat a candy bar and the following (simplified) series of events will occur: Glucose from the ingested lactose or sucrose is absorbed in the intestine and the level of glucose in.
This is illustrated in the table for disorders of cortisol secretion. Cushing's syndrome is the name given to hypersecretion of cortisol (or hypercortisolism ). Cushing's syndrome frequently causes a very characteristic type of central obesity.