The Adrenal Gland – Function and Diseases
The adrenal glands, lat. Glandula Suprarenalis, are endocrine glands which are located above our kidneys, separated by a thin fat layer. This is the reason for the Latin name, „supra“ meaning „over“ and „renal“ meaning „kidney”. The term ”endocrine“ describes specific gland cells, which secrete their products, hormones, into our blood circulation. To understand this process, we have to take a closer look at the anatomical structure of the adrenal glands.
The adrenal glands can be divided into two parts, an outer part called adrenal cortex which itself can be subdivided into 3 layers (Zona Fasciculata, Zona Reticularis, and Zona Glomerulosa) and an inner part called adrenal medulla.
To sum up at this point, one can say that there are two different types of glands systems, producing different kinds of hormones.
The adrenal cortex mainly produces steroid hormones, which are produced in the 3 layers, already mentioned above.
The outer layer, Zona Glomerulosa, produces mineral corticoids, especially aldosterone, which is obligatory to resorb water back from our kidney, so that it is not lost with our urine. The more water we get back, the more blood volume we have and therefore aldosterone has a big influence on regulating our blood pressure and electrolyte balance.
The Zona Fasciculata, situated between Zona Reticularis and Glomerulosa, mainly produces glucocorticoids such as cortisol and cortisone. Cortisol is an essential hormone as it influences our metabolism by increasing our glucose concentration in our blood circulation as the name glucocorticoid already suggests. It also takes part in bone formation and our fat- and protein metabolism. Especially for medical treatments it is well known in its role as a suppressor of the immune system and therefore for its anti-inflammatory effect.
In the inner layer called Zona Reticularis, especially androgens are produced such as dehydroepiandrosterone, DHEA, and androstenedione which are then converted to testosterone in our liver.
Within the adrenal medulla, our second adrenal gland system, we find modified nerve cells, called A- and N-cells. As soon as there is a higher stress level in our body or in other words an increased level of activity, those 2 cell types get activated. Being activated A-cells start producing adrenalin whereas the N- cells produce noradrenalin. Both secreted hormones will quickly increase our heart activity in terms of increasing the blood pressure or heart rate just to give a few examples.
In general diseases associated with the adrenal gland are either classified into a hyper or hypo function. Hereafter, the most common diseases are listed and shortly explained:
Cushing’s disease is characterised by an excessive production of cortisol. No matter what kind of origin, a tumour or the pathological growth of both adrenal glands systems for example, led to this condition, the clinical picture is always termed „Cushing’s disease“. Affected patients will for example suffer from a disturbed sugar metabolism. Besides treating that disturbed sugar metabolism, it’s important to remove the tumour by surgery.
In case of Conn syndrome or hyperaldosteronism the adrenal cells produce too much aldosterone, which then leads to an increased blood pressure and a disputed amount of minerals in our body. Reasons leading to that syndrome are divers. They can be linked to a tumour or to hyperplasia, meaning a pathological increase in cell number.
When suffering from hyperplasia, also known as idiopathic aldosteronism, it is common to treat these patients with an aldosterone antagonist, which works against the hormone. In case of a tumour, surgery is recommended.
Besides hyper function, patients can also develop a hypo function of the adrenal which is generally called adrenocortical insufficiency. In case of primary adrenocortical insufficiency, called Addison’s Disease, the reason for the disorder may be due to an impairment of the adrenal gland itself as patients for example suffer from autoimmune diseases.
The secondary form of hypo function develops from an impairment outside the adrenal gland, mostly located in the Hypothalamus (the inter brain) which is not able to release adrenal gland stimulating hormones (e. g. ACTH) anymore due to a tumour or circulatory disorders. With those missing stimulating hormones the adrenal gland cannot produce enough hormones, which especially is the case for cortisol.
In terms of therapy, it is important to substitute with the missing hormone.
A pheochromocytoma is a tumour located in the adrenal medulla, which consists of modified nerve cells that have a major influence on for example the blood pressure or the heart rate.
Patients with that kind of tumour have logically a disrupted blood pressure regulation and it requires surgery to remove the tumour.
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Illustrationen: © Yve Köhler