These are synthesized in the same cells. However, once secreted they interact with four adrenergic receptors such as 1, 2, 1, 2, and 3 that mediate the cellular effects of the hormones. Stress the predominant stimulus that leads to secretion of these hormones. More accurately stimuli such as injury, anger, pain, cold, strenuous exercise, and hypoglycemia as a result of stress response generate sympathetic impulses in the cholinergic preganglionic fibers that provides the neural impetus to the chromaffin cells, and this ultimately culminates into the release of catecholamines. Biochemically, however, catecholamines stimulate glucose production in the liver, lipolysis in the adipose tissue, and promotes anaerobic metabolism in the muscles leading to lactate production. Whereas, the adrenal medulla responds to predominantly neural stimuli, the outer adrenal cortex that literally encapsulates the medulla and forms the bulk of the gland, responds only to endocrine stimulation and releases a number of hormones which have steroid structures chemically. These hormones are glucocorticoids, aldosterone, and adrenal androgens. The cells of the three zones secrete different steroid hormones: the cells of the zona glomerulosa secrete the mineralocorticoids; those of the zona fasciculata secrete glucocorticoids, while the cells of the zona reticularis secrete sex steroids or androgens (Brook, C., and Marshall, N. 2001).
Figure 1: Adrenal Cortex and Medulla
Adrenal Cortex: Glucocorticoids act to counteract many effects of stress throughout the body. Stress is difficult to define, but it is known that it includes physical trauma, intense heat or cold, infections, mental or emotional trauma. The effects of glucocorticoids at the tissue level in order to neutralize the effects of stress include cardiovascular, neurological, and anti-inflammatory effects as well as effects on the immune system. Cortisol level responds within minutes to stress, whether it is physical such as trauma, surgery, or exercise; psychological such as anxiety and depression, or physiological hypoglycaemia or fever. The protective effect that glucocorticoids confer at the time of stress would be evident in the observed fact that such stresses may cause hypotension, shock, and death when there is glucocorticoid deficiency. The overall actions of glucocorticoids are directed at enhancing the production of glucose that can be readily utilised in the body to produce energy and at the same time they reduce all other metabolic activities not directly involved in that process. Physiologic effects of glucocorticoids include regulation of protein, carbohydrate, lipid, and nucleic acid metabolism. These antagonize the secretion and action of insulin and raise blood sugar levels. At the same time, these also inhibit peripheral glucose uptake. This promotes hepatic glycogen content through hepatic glucose synthesis or gluconeogenesis (Berg, J.M., Tymoczko, J.L., and Stryer, L., 2002). Taking the example of exercise as a stress initiating event, as the epinephrine and nor epinephrine are released as a sympathetic response, the concomitant glucocorticoid release makes sure that the increased metabolic rate of exercise can