Human body performs multiple functions like growth, development and metabolism by various hormones and glands that constitute an endocrine system. This system coordinates with the nervous system to ensure appropriate body functions. Adrenal gland is one among various glands of endocrine system.
What is Adrenal Gland?
Adrenal gland is an endocrine gland which secretes a number of hormones that assists in the proper functioning of the bodily functions. Adrenal gland plays a major role by regulating the immune system, blood pressure control, stress balance and gonadal activities in the human body. Our body consists of a pair of adrenal glands that are located bilaterally in lower abdomen. Each gland is situated superio-medially to the kidneys in retroperitoneal cavity, below the diaphragm. The glands are separated from the diaphragm above by tendinous structure called Crura of the Diaphragm.
Both the glands are covered by rich connective tissue layer called renal facia and adipose tissue (fatty tissue) capsule that protect the glands. The glands are also supplied by rich renal arterial capillary network for nutrition and are drained by superior veins.
Function of Adrenal Gland: What Does the Adrenal Gland Do?
The shape of the right adrenal gland is pyramidal whereas the left adrenal gland is more crescentic or semi-lunar. Adrenal gland produces various hormones that help in maintaining multiple body functions. Let us now see the function of each of the parts and sub-parts of the adrenal glands.
Each adrenal gland consists of two parts:
The cortex constitutes the outer part of the gland and sheaths the Inner medulla. The adrenal cortex further consists of 3 layers:
- Zona Glomerulosa: It is the outer most layer of the adrenal cortex. It releases a mineralocorticoid steroid hormone “Aldosterone”. The function includes:
- Regulating the blood pressure by maintaining balance between salt and water intake.
- Majorly helping in reabsorbing the plasma Sodium (Na+) levels in the Kidneys at the distal tubular and collecting duct level during glomerular filtration. It also helps in conserving the Sodium levels in the colon, Salivary and sweat glands.
- Promoting the excretion of Potassium (K+) to help maintain the electrolyte balance of the body.
- Enhancing water retention for homeostatic blood pressure control and blood volume maintenance.
- Regulating the Na-K pump across the cell membranes and ensures endothelial functions.
- Zona Fasciculate: It lies below Zona glomerulosa and above Zona reticularis. It releases glucocorticoids namely Cortisol. Cortisol can also be released in response to ACTH (Adrenocorticotrophic hormone) from pituitary glands.
- Cortisols help in maintaining the stress and psychological balance and are produced during stressful conditions.
- Maintains the blood sugar levels by the processing gluconeogenesis during hypoglycemic conditions.
- It metabolizes fat, proteins and carbohydrates in the liver during low sugar concentration.
- Regulates the immune system of the body and suppresses inflammation by preventing antibody response.
- Successful treatment for allergies.
- Plays an important role in wound healing.
- Interferes with bone growth.
- Maintains the body electrolyte balance.
- Functions with neurotransmitter in creating short term memories.
- Zona Reticularis: Lies below Zonafasciculata and adjacent to the inner medulla. It releases 3 types of androgens namely Dehydroepiandrosterone (DHEA), Dehydroepiandrosterone sulfate (DHEA-S), Androstenedione. Dehydroepiandrosterone (DHEA) gets converted to Estrogen and Androstenedione, which is a precursor of Testosterone. Androgens are produced from the cholesterol and are basically the precursors of human sex hormones namely Testosterone and Estrogen/Oestrogen. Androgens are released inblood stream and get converted into Testosterone and Estrogens in Testes and Ovaries respectively.
- Testosterone is primarily a male sex hormone that performs anabolic and androgenic activities. The anabolic activities include muscle mass growth and bone density whereas androgenic activities include gonadal maturation, puberty and development of secondary sexual characters like sperm production, descending testes, voice hoarsening, hair growth (facial, axillary, pubic), sweat gland secretion, Adam’s apple development in larynx, bone growth, etc. Small amount of testosterone is also produced in female body by ovaries and adrenal system.
- Estrogens or Oestrogen are primarily the female sex hormone. These hormones cause the development of female reproductive system and its maturation. These are responsible for developing the female secondary sexual characters like breast development, menstrual cycle, puberty. Estrogens are also present in males and perform the function of sperm maturation. It also helps in libido (sexual desire) to maintain a sexual life. There are 3 kinds of Estrogen namely Estradiol, Estriol, and Estrone.
Inner Medulla of Adrenal Gland
This constitutes the inner part of the gland. Also called as the type of Sympathetic ganglion as it has preganglionic nerve innervations. The inner medulla releases Catecholamines namely Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine). Medulla produces 80% of Adrenaline and 20% of Noradrenaline under sympathetic nervous system stimulation and secretes the hormones directly in the blood circulation.
- Adrenaline (Epinephrine): The adrenaline hormone:
- Released during vigorous exercise by adrenal medulla in the blood.
- Released during fearful conditions and emotional stress. Prevents emotional trauma.
- Degrades the long term memory enhancing a positive life style. Prevents psychological trauma.
- Released during cardiovascular conditions like cardiogenic shock, myocardial infarction, myocardial arrest.
- Released during hypoglycemic conditions.
- Helps control hypoxia (low oxygen levels).
- Noradrenaline (Norepinephrine)
- Is released during stress.
- Acts as a neurotransmitter.
- Initiates the glucose release from the stored areas.
- More active during wakefulness and are released the least during sleep.
- Increases the blood supply to the heart.
- Constricts the blood vessels to maintain the blood pressure and volume.
- Dilates the pupils of the eye.
- Helps in fat metabolism on liver.
- Helps in muscle activity by triggering glucose uptake by the cells.
What Happens in Case of Adrenal Gland Hormone Imbalance?
The hormones secreted by the adrenal gland perform a number of functions which requires the hormones to be secreted in the correct amount. A slight imbalance, either over or under production can lead to various dysfunctions in the body. The hormonal imbalance for each of the hormone secreted by the adrenal gland is as follows:
- Aldosterone Deficiency can be caused due to various reasons like adrenal insufficiency disorders, congenital adrenal hyperplasia, pituitary disorder etc. Lack of Aldosterone may lead to:
- Hyperkalemia (excessive potassium ions release in blood) causing renal tubular acidosis
- Loss of body electrolytes
- Low blood pressure
- Decreased blood volume.
- Increased Aldosterone Secretion: On the other hand, increased production of Aldosterone leads to hypokalemia (loss of potassium ions in blood stream) causing renal alkalosis. Associated symptoms include fatigue, excessive urination, muscle weakness and cramps, increased thirst, increased Sodium levels in the blood causing elevated blood pressure.
Androgen Hormone Imbalance:
The adrenal glands can either over or under secrete the androgen hormones. The symptoms are different for males and females.
Over-production of Androgens
In Females it leads to:
- Excessive production of androgens in woman can lead to the breast cancer.
- Increased ovarian testosterone production in women can mitigate the risk of polycystic ovarian disorder and postmenopausal cancer.
- It affects the menstrual cycle and cause dysmenorrhea.
- Over release of free testosterone in plasma cause hirsutism (excessive facial hair growth).
In Males it leads to:
- Excessive Testosterone in men tends to change the life style pattern like more inclination towards alcohol, smoking and more of aggressive behavior.
- More prone to injuries.
Under-production of Androgens
In Females it leads to
- Lowering of blood pressure (hypotension)
- Decreased HDL (high density lipids/good cholesterol) levels and increased LDL (low density lipids/ bad cholesterol) levels.
- Increased risk of cardiovascular disorders.
- Risk of diabetes.
- Hair loss
- Dryness in skin
- Weight gain
- Joint pain and inflammation
- Depressive behavior and slight amnesia
- Vaginal problems
- Frequent body aches
In Males it can lead to
- Lack of sexual desire and sexual life disturbance.
- Development of breast (Gynaecomastia)
- Hair loss (Alopecia)
- Increased in abdominal fat (belly fat)
- Decreased bone density leading to bone weakness and bone disorders
- Depressive psychological behavior.
- Over secretion of Cortisol
- Excessive release of Glucocorticoids may lead to Cushing’s syndrome characterized by muscle weakness, obesity, thinning of skin.
- Prolonged Cortisol release in the blood stream might lead to progressive bone disorders like Osteoporosis as it restricts bone formation. It inhibits calcium absorption at small intestine (duodenum and jejunum).
- It excretes Potassium from the cells causing decreased blood calcium levels and the condition is termed as Hypokalemia. Hypokalemia may lead to shock and can aggravate cardiovascular risks.
- Inhibits the collagen synthesis and interferes with wound healing. Too much stress causes release of more of cortisols that prolongs the wound healing time.
- Inhibits the protein synthesis leading to increase in amino acids in blood stream.
- Increases the susceptibility to infections as it decreases the body immunity.
- Prolonged Cortisol release effect the brain cells and interferes with the memory and cause depression.
- Excessive Cortisol consumed during pregnancy may lead to developmental changes in the fetal growth.
Under secretion of Cortisol
- Failure of adrenal glands to function and produce steroid hormones (Cortisol and androgen) is termed as Addison’s disease. It is characterized by excessive weight loss, skin darkening and hyperpigmentation, abdominal pain, dehydration, vomiting, hypoglycemia causing weakness, loss of electrolytes causing fall in blood pressure and convulsions.
- Adrenal insufficiency and hypocortisolism may occur due to various reasons like renal surgery, adrenal gland removal etc.
- Sometimes, adrenal hormonal production is also inhibited during Adrenal crisis in circumstances like emotional stress, hypotension, surgical procedure, chronic infections, nervous injury and unconsciousness.
Imbalances of Adrenaline and Noradrenaline Hormones
Excessive Noradrenaline/ Norepinephrine leads to
- Injury to the brain
- Increased cardiovascular risks.
- Decreased blood pressure
- Increased motility of digestive tract
- Weight loss
Excessive Adrenaline/Epinephrine leads to
- Extreme stress and psychological imbalance like ADD (attention deficit disorder)
- Short tempered behavior
- Premature aging
- Irregular sleep pattern
- Talkative personality.
Hence, it can clearly be understood that adrenal glands play an important role in maintaining the metabolism of human body by releasing various hormones and is a crucial endocrine gland. If the symptoms of hormonal imbalance are noted over a period of time one should take it very seriously and must consult with an Endocrinologist at the earliest.