Adrenal Medulla - Function & Diseases

The adrenal medulla is a part of the adrenal gland that secretes important hormones which regulate the fight or flight response in the body. These hormones mainly include adrenaline, known as epinephrine, and noradrenaline, which is also called norepinephrine, playing a very significant role in many stress responses. In this article, the adrenal medulla, anatomy of adrenal glands, the structure of the adrenal medulla, functions of the adrenal medulla, disorders of the adrenal medulla, diagnosis and treatment of disorders of the adrenal medulla, and role in stress response are discussed. Adrenal Medulla is a topic of the chapter Chemical Coordination and Integration chapter of Biology.

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This Story also Contains

1. What is the Adrenal Medulla?
2. Anatomy of Adrenal Glands
3. Structure of Adrenal Medulla
4. Adrenal Medulla Hormones
5. Functions of the Adrenal Medulla
6. Disorders of the Adrenal Medulla
7. Diagnosis and Treatment of Disorders of Adrenal Medulla
8. Role in Stress Response

What is the Adrenal Medulla?

The adrenal medulla represents a small triangular structure topping each kidney and forming the inner portion of adrenal glands. It accounts for 10% of the weight of the gland and is covered by the adrenal cortex. The medulla produces those hormones essential for the body's response to stressful conditions, thus maintaining physiological balance.

Anatomy of Adrenal Glands

There are two main divisions of the adrenal glands:

• The outer region, or adrenal cortex, is the largest part of the gland. It has three subdivisions that produce different hormones; zona glomerulosa, zona fasciculata, and zona reticularis.
• The section situated inside the cortex is the adrenal medulla. It is responsible for producing adrenaline, which is also known as the stress hormone.

Both regions are surrounded by an adipose capsule, which serves as a protective covering for the adrenal gland.

There are some specific cellular features of the adrenal medulla. They are:

• In order to regulate adrenal medulla hormones, a specific blood supply is required.

• The system of nerves known as the "greater splanchnic nerve" supports medullary communication with other parts of the body.

• The chromaffin cells possess tiny granules that are released when the splanchnic nerve cells activate a response to stress. This signal leads to the circulation of adrenaline and noradrenaline in the blood.

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Structure of Adrenal Medulla

The adrenal medulla is centrally located within the adrenal glands and is characterized by:

Chromaffin Cells

Such cells are rather crucial in producing hormones. They will be irregularly shaped and located near blood vessels, thus allowing for the secretion of hormones into the bloodstream.

Cell Organisation

These chromaffin cells lie anatomic ally and functionally fine near blood vessels so that their release from the body takes place efficiently. They also connect with the autonomic nervous system which aids in regulating their activity.

Adrenal Medulla Hormones

There are several important hormones produced in the adrenal medulla:

Epinephrine (Adrenaline)

This is released during stressful conditions. This peptide hormone increases heart rate, shifts blood flow to the muscles and the brain, and increases blood sugar to raise quick response.

Roles of Adrenaline

Adrenaline is released by the medulla as a response to low blood sugar levels or while the body is in work or exercise mode. It shows a reaction to stress by body mechanisms such as:

• It helps by sending oxygen to muscles at high levels.
  
  
• It controls the rise in blood pressure and the required heart rate.
  
  
• It widens the small arteries for easy blood circulation.

Norepinephrine (Noradrenaline)

Vasoconstriction is a reduced diameter of the blood vessels caused due to norepinephrine. Along with epinephrine, it increases blood pressure. The activities involve the body's 'fight or flight' response, usually including the maintenance of cardiac function.

Role of Noradrenaline

Noradrenaline causes the body to respond to stress by causing the following changes:

• It causes an increase in blood sugar levels.

• The blood vessels are narrowed down as required.

• It causes a rise in blood pressure levels.

• It also takes part in the brain’s function of storing memories.

• It supports us in waking up.

• It supports emotional abilities and health.

• It gives us the strength to pay attention and be focused.

Dopamine

This catecholamine is produced in smaller amounts and represents the precursor to norepinephrine. It has an action on neurotransmission, mood, and regulation of motor control.

Functions of the Adrenal Medulla

The major functions of the adrenal medulla are

Fight or Flight Response

It makes hormones like epinephrine and norepinephrine following the receipt of the 'stress' signal from the sympathetic nervous system. With its stimulation, it readies the body for immediate action with a racing heartbeat, blood supply to the muscles, and loads of energy.

Hormone Conversion

The medulla is concerned with the conversion of the amino acid tyrosine to epinephrine and norepinephrine. This function is vital in keeping up the 'preparedness' of the body to meet stress.

Disorders of the Adrenal Medulla

The disorders of Adrenal Medulla include:

Pheochromocytoma

This is the most common disorder directly related to the adrenal medulla. The literal meaning is a tumour of chromaffin cells causing excess production of epinephrine and norepinephrine. Common symptoms include high blood pressure, tachycardia and sweating.

Diagnosis and Treatment of Disorders of Adrenal Medulla

Pheochromocytoma and such related disorders are diagnosed based on the measurements of hormone levels from blood and urine, imaging studies like CT scans or MRIs, and biopsy if necessary.

Treatment

This is mostly done through surgical removal of the tumour. At times medication is given before surgery which would lessen symptoms due to the controlled amount of hormones.

Role in Stress Response

It is because of the adrenal medulla that, during instances of acute stress, the human body gets its share of catecholamines, responsible for adjustments to be made in a range of physiological functions so that the organism receives properly set for an impending challenge.

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