Did you know that the adrenal glands are only called that because they are located next to the kidneys? Otherwise, the two organs have little to do with each other: The kidneys produce our urine and regulate blood pressure and acid-base balance; the adrenal glands, on the other hand, make hormones.
What do the adrenal glands look like and where exactly are they located?
The Latin name of the adrenal gland, glandula suprarenalis, literally means “gland above the kidney.” In humans, the two adrenal glands sit like small caps on top of the kidneys. They weigh about five to ten grams each and are about the size of two matchboxes. Together with the kidneys, they are embedded in a fatty capsule (capsula adiposa renis) and connective tissue (fascis renis).
The adrenal glands consist of cortex (cortex glandulae suprarenalis) and medulla (medulla glandulae suprarenalis), which perform different functions. The adrenal cortex accounts for about four-fifths of the total weight of the adrenal glands and can be divided into three layers according to their appearance:
- On the very outside is the zona glomerulosa, in which the individual cells are arranged in clusters.
- This is followed by the zona fasciculata, in which the cells form strands or parallel bundles.
- The innermost layer, zona reticularis, is structured like a network.
The adrenal cortex surrounds the adrenal medulla (medulla glandulae suprarenalis). The medulla belongs to the sympathetic nervous system and contains hormone-producing cells as well as nerve cells.
What are the functions of the adrenal glands?
The Roman anatomist Bartholomeus Eustachius discovered and named the adrenal glands as early as 1564, but it was not until more than three centuries later that all their functions were also known: The four different zones of the adrenal glands are specialized in the production of different hormones.
Multi-talented adrenal cortex
The adrenal cortex alone produces over 40 different hormones. The three most important are aldosterone, cortisol and the androgens. The adrenal cortex is controlled by hormonal regulatory circuits, first and foremost by the hypothalamus and pituitary gland (pituitary gland) in the brain.
On the very outside, in the zona glomerulosa, the building block cholesterol is converted into aldosterone. This mineral corticoid, along with the renin-angiotensin system, regulates our body’s sodium and potassium levels and is important for fluid and salt balance. Aldosterone causes the kidneys to retain more sodium and thus also water. As a result, it affects blood pressure (simplified: the more water and sodium retained in the body, the higher the blood pressure).
The zona fasciculata produces glucocorticoids such as the versatile cortisol: it increases the new formation of sugar, breaks down fats and proteins. This gives the body more energy. In addition, cortisol inhibits inflammation by suppressing the immune system‘s reactions. Cortisol is closely related to cortisone, which is used as a medication for allergic or inflammatory reactions, for example.
Androgens come from the zona reticularis. In the body, androgens are converted into the sex hormone testosterone, which in men promotes the function and growth of the penis and testicles and regulates sperm production. Unlike aldosterone and cortisol, however, only five percent of androgens are produced in the adrenal cortex; the testes produce the rest.
Stress organ adrenal medulla
The adrenal medulla is part of the sympathetic nervous system. Here, the catecholamines epinephrine (= epinephrine), norepinephrine (= norepinephrine), and dopamine are produced from the amino acid L-tyrosine. Catecholamines are also called stress hormones because they are active in the body primarily in stressful situations: Blood pressure and heart rate rise, blood sugar levels and sweat secretion are increased, intestinal activity is slowed down and the airways are dilated. This is useful in the event of an attack by wild animals or muggers, but rather counterproductive in everyday life, for example before an exam or a speech.
