Anatomy & Organs

Adrenal medulla – structure, function & diseases

Adrenal medulla

The adrenal gland is divided functionally and topographically into the adrenal cortex (Cortex glandulae suprarenalis) and the adrenal medulla (Medulla glandulae suprarenalis). The adrenal medulla forms the smaller part of the adrenal gland. Adrenaline and noradrenaline are produced in the medulla of the adrenal gland .

What is the adrenal medulla?

The adrenal gland is a hormonal gland that sits on top of the kidney poles. Two organs are combined in the adrenal gland, which weighs around five grams. On the one hand, the adrenal cortex, in which hormones are produced, and on the other hand, the adrenal medulla, which is part of the sympathetic nervous system . The adrenal medulla is not actually a hormonal gland, but an extension of the autonomic nervous system .

From a developmental point of view, the adrenal medulla is a sympathetic ganglion , that is, an accumulation of nerve cells that belong to the sphere of activity of the sympathetic nerve. The sympathetic nervous system is also known as the fight and flight nerve. It puts the body on the alert and ready to perform. With increased sympathetic activity, for example, the heart beats faster and the bronchi are expanded.

Anatomy & Structure

The adrenal medulla is inside the adrenal gland, surrounded by the adrenal cortex. Embryologically, the adrenal medulla comes from the so-called neural crest. During embryonic development, structures of the peripheral nervous system in particular arise from this structure . So the adrenal medulla arises from a part of the nervous system .This is why there are highly specialized nerve cells, the chromaffin cells, of the sympathetic nervous system in the adrenal medulla. A distinction is made between chromaffin A cells (type I) and chromaffin N cells (type II). The cells are called chromaffin because they stain well with chromium salts. 80% of the cells of the adrenal medulla are A-cells, 20% are N-cells. The cells are arranged in groups or strands around the finest blood vessels (capillaries and venules).

Function & Tasks

Looking at the function of the adrenal medulla, and specifically the chromaffin cells, it quickly becomes clear why the cells are named A-cells and N-cells. The catecholamine adrenaline is formed in the A cells of the adrenal medulla, and the hormone or neurotransmitter noradrenaline is formed in the N cells. Adrenaline, also known as epinephrine, is known as the stress hormone and is synthesized from the amino acids L-phenylalanine and L-tyrosine.

Adrenaline increases heart rate, blood pressure rises, the bronchial tubes expand and deep breathing is made possible. Energy is also provided through the breakdown of fat (lipolysis) and through the release and production of glucose. The blood circulation is centralized, so that the vital organs and the muscles of the legs and arms are supplied with more blood. Gastrointestinal activity , on the other hand, is inhibited.

Adrenaline is released by nerve stimuli or by other hormones, for example by an increased cortisol level . Triggers can be stress , injury, inflammation or low blood sugar levels . If the concentration of adrenaline in the blood is too high , production is physiologically inhibited again by a negative feedback mechanism. Noradrenaline, also known as norepinephrine, is produced from dopamine using the enzyme dopamine hydroxylase . vitamin Cplays an important role here as a cofactor. Norepinephrine is related to adrenaline, but due to the lack of a methyl group in its chemical structure, its effects are sometimes different from those of adrenaline.

The main site of action of norepinephrine are the arterioles , ie the small arteries in the bloodstream . The norepinephrine leads to a narrowing (vasoconstriction) of these vessels. This leads to an increase in blood pressure. However, the function of noradrenaline as a neurotransmitter is more important than this hormonal effect . In the sympathetic nervous system, noradrenaline acts as a transmitter substance at the synapses. With the help of a neurotransmitter, stimuli can be transmitted from one nerve cell to other (nerve) cells. Besides acetylcholine, noradrenaline is the most important neurotransmitter in the autonomic nervous system. Norepinephrine is released from the adrenal medulla during stress.

Diseases

Pheochromocytoma is a tumor that is predominantly found in the adrenal medulla and is also the most common disease of the adrenal medulla. In most cases, the pheochromocytoma is hormonally active, i.e. it produces adrenaline, noradrenaline and, in rare cases, dopamine. The cardinal symptom of pheochromocytoma is high blood pressure , since both adrenaline and noradrenaline cause an increase in blood pressure by narrowing the blood vessels.The tumor does not always produce the hormones evenly. If he repeatedly spurts adrenaline or noradrenaline into the blood in large quantities, this leads to paroxysmal blood pressure crises. These are accompanied by feelings of anxiety , sweating and tachycardia . The attacks can be triggered, for example, by activating the abdominal pressure during a bowel movement or by nicotine consumption .

In both forms of pheochromocytoma, headaches , nausea , vomiting and an accelerated pulse ( tachycardia ) also occur. The diagnosis of pheochromocytoma is made by determining the breakdown products of hormones in the urine . Therapy consists of surgical removal of the tumor tissue. Various diseases such as diabetes mellitus , amyloidosis , porphyria or long-term alcohol abuse can result in hypofunction of the adrenal medulla. Constant stress over a long period of time is also discussed as a triggering factor for adrenal fatigue.

Hypofunction of the adrenal medulla manifests itself in symptoms such as chronic fatigue , lack of energy and depression . Those affected suffer from recurring infections , allergies and disorders of the immune system . They have very poor concentration and have a rather short attention span. Digestion is irregular and dizziness occurs, especially when standing up quickly . A characteristic of adrenal fatigue is that symptoms improve when the stress subsides. For example, the symptoms are much milder on vacation.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.