The adrenal cortex, as part of the adrenal gland, represents an important hormonal gland. Its hormones significantly control mineral metabolism, the body’s stress response, and sexual function. Diseases of the adrenal cortex can lead to severe hormonal dysfunction.
What is the adrenal cortex?
The adrenal cortex, together with the adrenal medulla, forms a paired hormonal gland called the adrenal gland. Each person has two adrenal glands. They are located on the upper poles of both kidneys, respectively. Functionally, the adrenal glands represent two distinct organs. While the adrenal cortex produces steroid hormones and is involved in mineral, water and sugar balance, the adrenal medulla exerts a decisive influence on the sympathetic nervous system with the help of the hormones adrenaline and noradrenaline. The adrenal cortex, which is also called the cortex glandulae suprarenalis, looks yellowish due to its lipid content. As a cortex, it forms the outer part of the adrenal gland. It produces over 40 different steroid hormones called corticosteroids. Phylogenetically, the cortex and medulla still represent two separate organs in fish. In amphibians and reptiles, both organs were already attached to each other. Only in mammals and birds are the adrenal cortex and medulla so closely related that they can be considered externally as a unit despite their different functions.
Anatomy and structure
As mentioned earlier, the adrenal cortex surrounds the adrenal medulla and, together with it, forms the adrenal gland. Both adrenal glands are arranged in pairs and each occupies the upper poles of the kidneys. They are surrounded by a fine connective tissue capsule. The adrenal cortex can be divided into three layers. The outer layer, also called the zona glomerulosa, is arranged in a tangle in humans. It produces the hormone aldosterone for mineral metabolism and has a total share of 15 percent of the adrenal cortex. The middle layer, the zona fasciculata, has the largest share of approximately 78 percent. It is responsible for the production of glucocorticoids such as cortisol. With a comparatively small share of about 7 percent, the lower section of the adrenal cortex, the zona reticularis, controls the production of sex hormones. However, all three zones are dynamic. Their expression changes constantly in the course of life. For example, their size ratio shifts after puberty in favor of the zona glomerulosa and zona reticularis. The differentiation of the two functional parts of the adrenal glands is also already expressed by its different origin. Whereas the adrenal cortex is of mesodermal origin, the adrenal medulla originally forms from neurons.
Function and tasks
The adrenal cortex controls both mineral metabolism and sugar balance, secretes so-called stress hormones during stress, and is involved in the formation of sex hormones. Despite seemingly different functions, they all have in common that they are dependent on steroid hormones (corticosteroids). The synthesis of all hormones of the adrenal cortex occurs via cholesterol, also called cholesterol. The hormone aldosterone is produced in the zona glomerulosa. This hormone maintains the balance between the sodium and potassium levels in the blood. In the middle zone, the zona fasciculata, the synthesis of the so-called glucocorticoids, including cortisol, takes place. Cortisol is a stress hormone and has a great influence on blood glucose levels. A stress reaction requires an increased release of energy, which can only be guaranteed by a rapid supply of glucose from the body’s own proteins. So as cortisol is released, blood glucose levels also rise. The third zone, the so-called zona reticularis produces mainly androgens, which act as precursors of sex hormones. The formation of steroid hormones is embedded in the overall regulatory mechanism of the endocrine system. For example, the pituitary gland produces an adrenocortical function regulating hormone also known as ACTH. Disturbances in this regulatory mechanism sometimes lead to severe hormonally related diseases. The causes of these disorders may be primary to the adrenal cortex or secondary to the pituitary gland.
Diseases and disorders
Because of the many hormones produced in the adrenal cortex, a variety of medical conditions can occur.Known hormone disorders manifest themselves, for example, as Conn’s syndrome, Cushing’s syndrome or Addison’s disease. Conn syndrome is based on the overproduction of the hormone aldosterone and is also called primary hyperaldosteronism. It is characterized by potassium deficiency and is a rare cause of hypertension. Symptoms of this condition include hypertension, angina pectoris, headaches, shortness of breath, and cardiac arrhythmias. Increased production of aldosterone can be caused by genetic causes, an adrenocortical adenoma, or enlargement of the adrenal cortex. In Cushing’s syndrome, too much cortisol is secreted. This results in an increase in blood sugar levels and suppression of the immune system. Characteristic symptoms include full moon face, truncal obesity, diabetes, elevated blood pressure, edema, and increased susceptibility to infection. Increased cortisol production may be caused primarily by an adenoma on the adrenal cortex or secondarily by diseases of the pituitary gland. Treatment depends on the underlying disease. Underproduction of cortisol leads to a condition called Addison’s disease. Addison’s disease is characterized by general weakness, susceptibility to infection, low blood pressure, digestive disturbances, weight loss, and brownish discoloration of the skin. Low production of cortisol can be caused primarily by diseases of the adrenal cortex, secondarily by disorders at the pituitary gland, and tertiarily by regulatory disorders during treatment with corticosteroids. If, for example, cortisone treatment is abruptly discontinued, the so-called Addison crisis often occurs because the control mechanism of the body’s own cortisol synthesis does not function again until after a delay. Primary parathyroid dysfunction is often caused by infections, autoimmune diseases, or tumors and is sometimes genetic.
