What is the nature of the relationship between the two different parts of the adrenal glands? What are the hormones and targets of the hormones secreted by each part of the adrenals?
The two adrenals, which lie very near the surface of the kidneys, play multifaceted roles effecting a wide variety of responses in the body. Each adrenal is actually made up of two glands that arise from different embryonic material and remain functionally separate: the inner adrenal medulla and the outer adrenal cortex. The adrenal medulla releases adrenaline and noradrenaline which cause the "fight-or-flight" responses typified by a rise in blood pressure, an acceleration of heart beat, an increased conversion of glycogen to glucose and release of glucose into the blood by the liver, a vasoconstriction of blood vessels serving the skin and digestive tract, and a vasodilatation of blood vessels serving the skeletal and heart muscles. Adrenaline also acts as an inhibitor to insulin. Adrenaline elevates blood-sugar levels by stimulating liver cells to break down glycogen into glucose and by stimulating muscle cells to turn stored glycogen into lactic acid which, released into the blood by the muscle cells, is converted into glucose by the liver. The adrenal cortex secretes three types of hormones all of which are steroidal. Glucocorticoids stimulate carbohydrate formation from protein and fat and, thus, elevate glycogen stores and help to maintain
