Adrenal gland: Structure, Hormones, Disorders, Differences Between Adrenal Cortex And Adrenal Medulla, Practice Problems and FAQs

You all like superheroes like spiderman, ironman, batman etc. You all might have dreamt of becoming a superhero one day. Tell me, what will happen if you have a super power? It will be really amazing. Right? You can help others with superpowers. An interesting fact is that, there is a hormone in your body which can make you a superhero. Yes, it is not a joke.

Have you ever heard about adrenaline rush? This can make your body prepare for an incident which happens suddenly and help you to fight with the odd situations. This hormone releases in situations like when you see a person in trouble, when a dog chases you or when you are anxious. This helps you to react to the situation wisely and courageously. This hormone is called adrenaline which is released from the adrenal gland. Adrenal gland is a part of the human endocrine system. Let’s discuss more about it in this article.

Fig: Adrenal glands

Table of contents

• Adrenal gland
• Structure of the adrenal gland
• Hormones of the adrenal gland
• Disorders of the adrenal gland
• Differences between adrenal cortex and adrenal medulla
• Practice Problems
• FAQs

Adrenal gland

Adrenal glands are also called glands of emergency. Our body has one pair of adrenal glands, situated on top of the kidneys. These glands are thus called supra-renal glands. They are yellowish and conical in shape. In an adult, each adrenal gland is 3 – 5 cm in height, 2 – 3 cm in width, and a little less than 1 cm in thickness, with a mass of 4 – 5g normally. A thick capsule made up of connective tissue normally surrounds the adrenal gland.

Fig: Adrenal glands

Structure of the adrenal gland

The adrenal gland consists of two parts. They are the adrenal cortex and adrenal medulla.

Adrenal cortex

It is the yellowish region located outside and is formed from the mesoderm. This region is highly vascularised and rich in vitamin C and cholesterol.

Fig: Adrenal cortex

Zones of the adrenal cortex

The adrenal cortex can be divided into three zones such as zona glomerulosa, zona fasciculata and zona reticularis. The zona in the name means belt.

Fig: Zones of adrenal cortex

Zona glomerulosa

It is the outer zone that lies below the capsule. This zone possesses closely packed cells arranged in spherical clusters. This zone secrets a group of hormones called mineralocorticoids.

Zona fasciculata

It is the middle zone. Fascicul means bundles. So the cells in this layer are arranged in long straight columns or bundles. This zone secrets a group of hormones called glucocorticoids.

Zona reticularis

It is the inner zone. Reticuli means network. The cells of this zone are arranged in branched cords. This zone secrets a group of hormones called gonadocorticoids.

Fig: Zones of adrenal cortex

Adrenal medulla

It is a centrally located and soft reddish brown region.

Fig: Adrenal medulla

Hormones of the adrenal gland

The following are the hormones secreted by the adrenal gland:

• Corticosteroids - Secreted by the adrenal cortex.
• Catecholamines - Secreted by the adrenal medulla.

Adrenal cortex hormones

All the hormones of the adrenal cortex have a corticoid as their suffix because they are synthesised from cholesterol, and they are collectively called corticoids or corticosteroids. As we saw previously, the hormones secreted by the adrenal cortex are of three types such as mineralocorticoids, glucocorticoids, and gonadocorticoids.

Fig: Hormones of the adrenal cortex

Glucocorticoids

As the name suggests, these hormones primarily regulate carbohydrate metabolism. It is also involved in the metabolism of fats and proteins. In our body, cortisol is the main glucocorticoid. There are other two corticoids present, namely, cortisone and corticosterone. Cortisol is released when our body is in stress, that is why this is also called the stress hormone. This hormone acts on cells of the liver (hepatocytes) mainly. Let us learn about the role of glucocorticoids now.

Functions of glucocorticoids

The following are the major functions of glucocorticoids:

Gluconeogenesis

Glucocorticoids stimulate conversion of non - carbohydrates (like glycerol or amino acids) to carbohydrates. This process is termed as gluconeogenesis. The result of this process is an increase in the glucose levels in the blood.

Fig: Gluconeogenesis

Proteolysis

Glucocorticoids also stimulates proteolysis, that is, it stimulates the breakdown of proteins in cells and thus it increases the amino acid levels of blood.

Fig: Proteolysis

Lipolysis

A third effect of glucocorticoids is lipolysis in adipose tissue. It is the breakdown of fats in adipose tissue and release of the fatty acids into the bloodstream.

Fig: Lipolysis

Slowing down the wound healing

These hormones slow wound healing through retarding the tissue repair process.

For treatment of rheumatoid arthritis

Glucocorticoids are very useful in the treatment of rheumatoid arthritis and other chronic inflammatory disorders.

Functions of cortisol

The following are the major functions of cortisol:

Anti-inflammatory and immunosuppressive functions:

Cortisol is an anti-inflammatory and immunosuppressive hormone. It reduces the number of immune cells by inhibiting the white blood cells participating in it and suppresses the production of antibodies to suppress the overall immune responses.

Fig: Immune response by glucocorticoids

Maintenance of cardiovascular system

Cortisol is also involved in maintaining the cardiovascular system as well as the kidney functions. Cortisol stimulates RBC production.

Fig: Organs controlled by glucocorticoids

Mineralocorticoids

These hormones are responsible for the regulation of mineral metabolism and control the sodium and potassium ratio in the extracellular and intracellular fluids. These hormones regulate electrolyte and water balance in the body. The secretion of these hormones are stimulated by a fall in the sodium concentration, rise in the potassium concentration or a fall in the volume of blood. The common mineralocorticoids are aldosterone and deoxycorticosterone.

Aldosterone

It is the principal and the most abundant mineralocorticoid. It acts on the cells of the kidneys.

Functions of aldosterone

The functions of mineralocorticoids include the following:

• It helps in the reabsorption of sodium, chlorine and water from the kidney tubules, saliva, bile and sweat.
• It helps in the expulsion of potassium and phosphate ions from the body.
• It also helps in the maintenance of electrolytes, body fluid volume, osmotic pressure and blood pressure.

Deoxycorticosterone

A steroid hormone synthesised in the zona fasciculata and zona glomerulosa of the adrenal gland is called deoxycorticosterone. It acts as a precursor for synthesising cortisol and aldosterone. This hormone plays an important role in stress related changes in seizure control. It is also an agonist of the receptors of mineralocorticoid and an antagonist of the receptors of glucocorticoids. Agonist is a substance that normally binds to a receptor present inside a cell or outside the cell and results in the same action as the substance that normally binds to the receptor.

Gonadocorticoids

Gonadocorticoids are also called the sex hormones of adrenal glands. Male sex hormones are produced in large quantities, while female ones are produced in small quantities. The male sexcorticoids are called androgens and the female sexcorticoids are termed as oestrogens.

Androgens

These hormones act on the cells of testes. They play a role in the growth of axial hair, pubic hair and facial hair during puberty in males.

Fig: Activity of androgens

Estrogens

These are the female sex corticoids and act mainly on the ovaries. It stimulates the development of secondary sexual characters in females such as enlargement of breasts, onset of menstrual cycle etc. These also play a role in the growth of axial hair, pubic hair and facial hair during puberty in females.

Fig: Activity of estrogens

Adrenal medulla

The adrenal medulla is the inner reddish part of the adrenal gland consisting of large cells. These are the modified cells of the sympathetic nervous system (SNS). These cells are formed from the neuroectoderm. These represent the sympathetico-adrenal system which is an integrated system of adrenal medulla and SNS. 

The modified cells of the SNS have lost their normal processes and are now glandular in function. The adrenal medulla is thus an extension of the sympathetic nervous system and therefore they are collectively termed as the Sympathetic-adrenal system.

Fig: Sympathetic-adrenal system

Catecholamines

The hormones of adrenal medulla are synthesised from tyrosine and all the hormones are collectively called catecholamines. The adrenal medulla secretes two hormones called adrenaline or epinephrine and noradrenaline or norepinephrine.

Fig: Hormones of adrenal medulla

Adrenaline and noradrenaline are rapidly secreted in response to stress of any kind and during emergency situations and are called emergency hormones. Adrenaline is released in situations like fight, fright or flight and hence called the 3F hormone. Hence the adrenal gland is called the 3F gland. They also stimulate the breakdown of glycogen resulting in an increase of blood sugar levels and also stimulate the breakdown of lipids and proteins. They act on cells of skeletal, cardiac and smooth muscles, blood vessels and fat cells.

Flight or fight response

The fight or flight response is an automatic reaction to stressful or frightening situations. The perception of threat activates the sympathetic-adrenal system that releases the adrenaline and noradrenaline hormones which prepares the body to fight or flee. These hormones increase alertness, pupillary dilation, piloerection (raising of hairs), sweating etc. It also inhibits the functions of the gastrointestinal tract. It helps in the dilation of bronchi in low doses. It decreases peristalsis also.  Both the hormones increase the heart beat, the strength of heart contraction and the rate of respiration.

Fig: Fight or flight response

Disorders of adrenal gland

The disorders of the adrenal gland can be caused by the damage in one or both of the adrenal glands. It can also be caused by any problems with the pituitary glands too. Such disorders can develop when there is an overproduction or underproduction of hormones secreted by the adrenal glands. This can also happen when more hormones are introduced from an outside source. Some of the disorders of the adrenal glands are as follows:

• Addison's disease
• Cushing's syndrome
• Conn's syndrome
• Adrenal virilism
• Gynecomastia

Let’s discuss more about these disorders.

Addison's disease

It is also known as hypocorticism. This disorder was first described by the father of Endocrinology, Thomas Addison. The deficiency of mineralocorticoids and glucocorticoids results in Addison's disease. There will be low blood sugar level and less concentration of Na⁺ and high concentration of K⁺ in the plasma in this condition. Loss of Na⁺ and water through urine also happens.

Common symptoms of Addison's disease

• Bronze like pigmentation of skin (Hyperpigmentation)
• Vomiting
• Nausea
• Diarrhoea
• Fatigue
• Weakness

Fig: Common symptoms of Addison’s disease

Cushing's syndrome

Due to the tumour in the adrenal cortex there will be excess cortisol formation, which will lead to a disorder called cushing’s syndrome. High blood sugar level and elimination of sugar through urine are characteristics of cushing’s syndrome. Low concentration of K⁺ and high concentration of Na⁺ in plasma are also caused by this syndrome.

Common symptoms of Cushing's syndrome

• High blood pressure and blood volume
• Obesity
• Neck has fat pads
• Red cheek
• Poor wound healing
• Moon face
• Wasting of thigh muscles

Conn's syndrome

Conn’s syndrome is also known as aldosteronism. Excess secretion of aldosterone causes this disorder. High concentration of Na⁺ and low concentration of K⁺ in the plasma are the characteristics of this disorder.

Common symptoms of Conn's syndrome

• High blood pressure and blood volume
• Fatigue
• Headache
• Anxiety
• Memory loss

Fig: Common symptoms of Conn's syndrome

Adrenal virilism

The excess secretion of androgens, which is the male sex corticoids in the female is called adrenal virilism.

Common symptoms of adrenal virilism

• Development of external male characters like beard, moustaches
• Development of male voice

Gynecomastia

The excess secretion of estrogens, which is the female sex corticoids is known as gynecomastia.

Common symptoms of gynecomastia

• Enlargement of mammary glands
• Sparse body hair
• Atrophy of testes
• Feminie distribution of fats

Differences between adrenal cortex and adrenal medulla

The following are the major differences between adrenal cortex and adrenal medulla:

Practice Problems

1. Select the incorrect option with respect to the location of the gland.

1. Pituitary gland - Sella turcica in skull
2. Adrenal gland - Below stomach
3. Parathyroid gland - Back side of the thyroid
4. Thymus - Behind the sternum bone

Solution: Our body has a pair of adrenal glands, one at the top of each kidney. Pituitary gland is located in a bony cavity called sella turcica in the skull. There are four parathyroid glands in our body which are present on the back side of the thyroid gland. Thymus gland is located between lungs behind the sternum bone on the ventral side of the aorta. Hence the correct option is b.

2. On feeling the tremor of an earthquake, there was a sudden panic. The heartbeat of a man who was trying to escape from the building suddenly increased. Which hormone is responsible for this sudden increase in heart rate during an emergency situation?

1. Thyroxine
2. Adrenaline
3. Parathyroid hormone
4. Thymus hormone

Solution: On feeling the tremor of an earthquake the man was in stress and perceived it as an emergency. As a result adrenaline and noradrenaline are rapidly secreted by adrenal medulla. Adrenaline and noradrenaline are secreted in response to stressful and emergency situations and are called emergency hormones. Adrenaline is also called the 3F hormone, as it is secreted in situations like fight, fright or flight. These hormones increase the heart beat, the strength of heart contraction and the rate of respiration. This helps to get more oxygen to the muscles. Hence the correct option is b.

3. Which of the following is incorrect about the adrenal gland?

1. Located on the posterior part of the kidney
2. Located on the anterior part of the kidney
3. A pair of adrenal glands are present in the human body
4. It is composed of two types of tissues

Solution: The adrenal gland is located on the anterior part or top of each kidney. Thus a pair of adrenal glands are present in the human body. It is composed of two parts. The part located in the outer region of the adrenal gland is called the adrenal cortex and the part located in the inner region is called adrenal medulla. Hence the correct option is a.

4. Which one of the following secretions is not likely to get affected if there would be injury to the adrenal cortex?

1. Aldosterone
2. Cortisol
3. Adrenaline
4. Both adrenaline and cortisol

Solution: Adrenal glands are composed of two parts, the adrenal cortex and adrenal medulla.

Aldosterone (mineralocorticoid) and cortisol (glucocorticoid) are corticoids which are secreted by the adrenal cortex. The adrenal medulla secretes two hormones called adrenaline or epinephrine and noradrenaline or norepinephrine. The hormones of the adrenal medulla are called catecholamines. Hence injury to the adrenal cortex will not affect secretion of adrenaline hormone as it is secreted by adrenal medulla. So the correct option is c.

5. Which are the three zones of the adrenal cortex. Explain?

Answer: The adrenal cortex can be divided into three zones such as zona glomerulosa, zona fasciculata and zona reticularis. The zona in the name means belt.

• Zona glomerulosa - It is the outer zone that lies below the capsule. This zone possesses closely packed cells arranged in spherical clusters. This zone secrets a group of hormones called mineralocorticoids.
• Zona fasciculata - It is the middle zone. Fascicul means bundles. So the cells in this layer are arranged in long straight columns or bundles. This zone secrets a group of hormones called glucocorticoids.
• Zona reticularis - It is the inner zone. Reticuli means network. The cells of this zone are arranged in branched cords. This zone secrets a group of hormones called gonadocorticoids.

Fig: Zones of adrenal cortex

6. Explain about the sex hormones of adrenal gland?

Answer: Gonadocorticoids are also called the sex hormones of adrenal glands. Male sex hormones are produced in large quantities, while female hormones are produced in small quantities. The male sexcorticoids are called androgens and the female sexcorticoids are termed as oestrogens.

• Androgens - These hormones act on the cells of testes. They play a role in the growth of axial hair, pubic hair and facial hair during puberty in males.
• Estrogens - These are the female sex corticoids and act mainly on the ovaries. It stimulates the development of secondary sexual characters in females such as enlargement of breasts, onset of menstrual cycle etc. These also play a role in the growth of axial hair, pubic hair and facial hair during puberty in females.

7. What are flight, fright or fight hormones?

Answer: The adrenal medulla secrete a hormone called adrenaline or epinephrine. Adrenaline is rapidly secreted in response to stress of any kind and during emergency situations like fight, fright or flight and hence called the 3F hormone. So the adrenal gland is called the 3F gland. These hormones also stimulate the breakdown of glycogen resulting in an increase of blood sugar levels and also stimulate the breakdown of lipids and proteins. These act on cells of skeletal, cardiac and smooth muscles, blood vessels and fat cells. These hormones increase alertness, pupillary dilation, piloerection (raising of hairs), sweating etc. It inhibits the gastrointestinal tract. It helps in the dilation of bronchi in low doses. It decreases peristalsis also.

8. What are mineralocorticoids?

Answer: Mineralocorticoids are responsible for the regulation of mineral metabolism. Aldosterone is the principal and the most abundant mineralocorticoid. It acts on the cells of the kidneys. The major functions of mineralocorticoids include reabsorption of sodium and water and expulsion of potassium and phosphate ions from the body. Thus, aldosterone helps in the maintenance of electrolytes, body fluid volume, osmotic pressure and blood pressure.

FAQs

1. What is the common test used for adrenal?

Answer: The ACTH (adrenocorticotropic hormone) stimulation test is the common test used to diagnose insufficient production of adrenal hormones. In this test, the person will be given an intravenous injection (IV) of the man-made ACTH.

2. What causes tumours in the adrenal gland?

Answer: The pheochromocytoma is the tumour in the adrenal gland. This causes the adrenal gland to make more hormones like norepinephrine and epinephrine. This tumour can occur in the 30s to 50s and happens in both men and women.

3. What part of the brain normally controls the adrenal glands?

Answer: Adrenal glands produce hormones in response to signals from the anterior part of the pituitary gland in the brain called ACTH (adrenocorticotropic hormone). ACTH is produced in response to the hormone produced by the hypothalamus called corticotropin-releasing hormone (CRH). This is referred to as the hypothalamic pituitary adrenal axis.

4. What are the common signs of adrenal gland problems?

Answer: The following are the common signs shown by the human body when there is a problem associated with the adrenal gland:

• Extreme fatigue
• Darkening of the skin or hyperpigmentation
• Weight loss and decreased appetite
• Cravings for salts
• Low blood pressure
• Fainting
• Nausea
• Diarrhoea
• Vomiting
• Hypoglycemia or low blood sugar
• Joint pains or muscle pains
• Abdominal pain
• Irritability
• Body hair loss
• Depression
• Behavioural disorders
• Sexual dysfunction in women

Fig: Common signs of adrenal gland problems

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