This exerts a negative feedback effect high serum cortisol levels inhibit further production of cortisol. Cortisol inhibits both release of CRH from the hypothalamus and of ACTH from the adenohypophysis.

Cortisol then initiates a series of metabolic activities which help to relieve the physiologic effects of stress. In response to the presence of CRH, the adenohypophysis secretes adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex to release cortisol. Initially, the hypothalamus reacts to physical or psychogenic stress by secreting corticotropin-releasing hormone (CRH), which is carried to the anterior pituitary gland (adenohypophysis) via the hypothalamic-hypophyseal portal system. The regulation of cortisol secretion involves a complex closed-loop negative feedback system. The net effect of these actions is to make these noncarbohydrate nutritive elements readily available for energy. Cortisol increases the rate of gluconeogenesis by the liver, decreases the utilization of glucose by the cells, reduces cellular protein and enhances utilization of amino acids by the liver, and promotes mobilization of fatty acids from adipose tissue into the plasma. The physiologic effects of the glucocorticoids promote the metabolic breakdown or anabolism of carbohydrates, proteins, and fats. The remainder of the hormonal activity is provided by corticosterone and cortisone. The principal glucocorticoid is cortisol (also known as hydrocortisone), which is responsible for more than 95 per cent of all glucocorticoid activity. Epinephrine is important in initiating the physiological changes in the “fight or flight” response (see alarm reaction) and has a more prolonged effect than norepinephrine because of being removed more slowly from the blood.

Epinephrine and norepinephrine both constrict blood vessels (except in muscle tissue) and are released in anticipatory states and other times of increased emotion, causing such changes as elevated blood pressure release of glucagon, insulin, and fatty acids into the blood and increases in heart rate, sweating, metabolic rate, and peristaltic activity.

In this way, the adrenal medulla and the sympathetic nerves support each other and can act as substitutes for each other. Their production and distribution by the blood usually occur at the same time that the organs are being stimulated by the sympathetic nerves. These hormones enter the blood stream and are carried throughout the body where they indirectly act as stimulants to the various organs. It releases the hormones epinephrine and norepinephrine in response to stimulation of the sympathetic nervous system. This is actually a glandular extension of sympathetic effector fibers or postganglionic neurons.

Meaning of adrenal gland