Hear This Illustration: the Adrenal (Suprarenal) Glands

Hear This Illustration: The adrenal (suprarenal) glands

The adrenal glands, like the pituitary, are actually glands derived from two different embryonic structures and producing two different classes of hormones. They are called the adrenals or suprarenals because of their anatomic position above the kidneys.

At the center of the gland we find the adrenal medulla. This part of the gland developed from the same embryonic tissue that gave rise to the sympathetic ganglia and other nervous tissue structures. The hormones produced here are norepinephrine and epinephrine, also known as adrenaline. This is chemically very similar to the neurotransmitter norepinephrine, which we find commonly at work in the sympathetic nervous system. When stimulated, the adrenal medulla releases more of these adrenaline- like chemicals that reinforce the sympathetic nervous system response.

On the other hand, the adrenal cortex produces an entirely different class of hormones. These are steroids which are structurally and functionally quite different from the epinephrine-like substances produced in the medulla. The three histologically distinct regions of the cortex each produce its own hormone. The inner most layer, the zona reticularis secretes steroidal substances that are androgenic in nature. That means they tend to stimulate masculinizing features of the body similar to what testosterone might do. Excessive facial hair in women is sometimes caused by over activity in the zona reticularis of the adrenals.

The zona fasiculata is the thickest layer of the adrenal cortex and produces a class of steroids collectively referred to as glucocorticoids. They are called glucocorticoids because they affect glucose metabolism, are produced in the cortex and are steroidal in structure. The most familiar of these glucocorticoids is cortisone. A form of this hormone, prednisone, is used clinically as a steroidal anti-inflammatory drug.

Finally, the outermost layer, the zona glomerulosa produces mineralcorticoids. Again these are called mineralcorticoids because they affect the body’s ability to manage electrolytic minerals such as potassium and sodium and are steroids produced by the adrenal cortex. Mineralcorticoids affect urine output by regulating blood electrolyte concentrations