When cortisol levels in the blood are low, a group of cells in the hypothalamus release a hormone called corticotrophin-releasing hormone (CRH) which stimulates the pituitary gland to secrete adrenocorticotropic hormone into the bloodstream. This is called the hypothalamic–pituitary–adrenal (HPA) axis. Secretion of adrenocorticotropic hormone is controlled by three inter-communicating regions of the body, the hypothalamus, the pituitary gland and the adrenal glands. How is adrenocorticotropic hormone controlled? It also increases production of the chemical compounds that trigger an increase in other hormones such as adrenaline and noradrenaline. Once adrenocorticotropic hormone reaches the adrenal glands, it binds on to receptors causing the adrenal glands to secrete more cortisol, resulting in higher levels of cortisol in the blood. This is called a diurnal (circadian) rhythm. Like cortisol, levels of adrenocorticotropic hormone are generally high in the morning when we wake up and fall throughout the day and lowest during sleep. It is secreted in several intermittent pulses during the day into the bloodstream and transported around the body. Cortisol from the adrenal then feeds back to the hypothalamus to shut down the cycle.Īdrenocorticotropic hormone is made in the corticotroph cells of the anterior pituitary gland. ACTH travels to the adrenal glands via the bloodstream (arrow). Corticotrophin-releasing hormone from the hypothalamus acts on the pituitary (inset), which secretes ACTH.
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