Control of Cortisol Hormone Production

ACTH stimulates both the production and subsequent release of cortisol from the zona fasciculata of the adrenal cortex into the bloodstream.

Cortisol circulates to almost every tissue, organ and cell in the body. It prepares the body to defend itself against danger, spiking to higher levels as needed for flight or for fight. The threat may be internal such as from infection, illness, or injury, or external such as from an environment threat (perceived or real).

Cortisol: increases blood pressure, heart rate and respiratory rate; stimulates the liver to make glucose (a simple sugar for energy); converts proteins and carbohydrates into muscle energy.

ACTH release not only stimulates cortisol production but also aldosterone production and release from a separate zone of the outer cortex of the adrenal glands.  Aldosterone is an essential hormone that alerts the kidneys to reabsorb sodium and water, increase the volume of circulating blood and blood pressure to deliver essential supplies to cells for energy and cell repair. This may be needed to add in the event of blood loss or injury or the need for ‘flight or fight’.

Adrenaline (epinephrine) and norepinephrine are known as catecholamines. Manufactured in the adrenal medulla or ‘centre portion’ catecholamines serve as the body’s alert system. Activated by the ACTH as a response to stress, these hormones also increase cortisol levels, constrict blood vessels, increasing blood pressure, heart rate and glucose levels to assist the body to adapt to or escape from a stressor.

The low or basal amount of CRH, ACTH and cortisol is produced by the body over each 24-hour period to keep the body in a stable or homeostatic state.  At the onset of sleep cortisol levels reach their lowest in the early hours of the morning.  This signals the hypothalamus to release CRH, stimulates ACTH to rises and turns on the production of cortisol. This is known as a positive feedback mechanism (+ve). (Figure 1). Although during the day demand for cortisol varies with different stressors, cortisol levels slowly decline until the low levels allowing the onset of sleep. This daily cycle is known as a circadian rhythm. (Figure 2).

After cortisol receptors are full, cortisol circulating in the blood reaches a threshold level which provides a negative feedback (-ve) signal the hypothalamus and pituitary to scale back production of CRH and ACTH completing the circadian cycle.

Figure 1 Feedback mechanism of cortisol, CRH and ACTH production:

Figure 2:  https://slideplayer.com/slide/8073009/:

24 hour circadian rhythm typical of cortisol and ACTH production with late night low concentrations and early morning high concentrations.