Adrenal Glands – Production Control, List The Actions And Major Disorders

Adrenal glands are a pair of yellowish flat pyramid like glands which lie at the upper end of the kidneys. They look like a cap on the kidney and each gland has an outer yello adrenal cortex and inner reddish-brown adrenal medulla. Adrenal medulla secretes two harmones called adrenaline or epinephrine and non adrenaline or non epinephrine. These are commonly known as catecholamines in conditions of physical and mental stress such as fall in blood sugar levels or when a person is injured or exposed to cold conditions or suffering with pain. It is also secreted during anger, fear or grief. It helps the body to face these conditions it is therefore called emergency hormone or fight hormone. These hormones increase alertness, pupilary dilation, raising of hair, sweating etc.

The hormone increases blood supply to heart and skeletal muscles. It constricts arterioles and blood supply to skin and gastrointestinal tract. The bronchioles dilate. There is increased rate of breathing, oxygenation and heartbeat to meet any emergency. Catecholamines stimulate the breakdown of glycogen resulting in increased concentration of glucose in blood, they also stimulate the breakdown of lipids and proteins.

Adrenal cortex can be divided into three layers call zona reticularis (inner layer) zona fasciculata (middle layer) zona glomerulosa (outer layer). Adrenal cortex secretes many hormones called corticoids such as

• Glucocorticoids: involved in carbohydrate metabolism, for example: cortisol
• Mineralo corticoids: corticoids which regulate the balance of water and electrolytes in our body, for example: aldosterone.

Glucocorticoids stimulate gluconeogenesis, lipolysis and proteolysis and inhibit cellular uptake and utilization of amino acids.

Cortisol is also involved in maintaining the cardiovascular system and kidney functions, it also produces anti-inflammatory reactions and suppresses the immune response. Cortisol stimulates RBC production. Aldosterone acts at renal tubules and stimulates reabsorption of Na+ and water and excretion of k+ and Po 4. Thus aldosterone helps in the maintenance of electrolytes, body fluid volume, osmotic pressure and BP. Small amount of androgenic steroids are also secreted by adrenal cortex which play a role in the growth of axial hair, pubic hair and facial hair during puberty.

The table below is to understand the hormones of the adrenal glands in brief.

Hormones of the Adrenal Glands

Hormones of The Adrenal Medulla

The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline), two closely related hormones that have very similar actions on target cells. Epinephrine forms about 80% of the secretions.

The sympathetic division of the autonomic nervous system regulates the secretion of adrenal medullary hormones. They are secreted whenever the body is under stress, and they duplicate the action of the sympathetic division on a bodywide scale. The medullary hormones have a stronger and longer-lasting effect in preparing the body for “fight or flight.” The effects of epinephrine and norepinephrine include (1) a decrease in blood flow to the viscera and skin; (2) an increase in blood flow to the skeletal muscles, lungs, and nervous system; (3) conversion of glycogen to glucose to raise the glucose level in the blood; and (4) an increase in the rate of cellular respiration. Epinephrine and norepinephrine are particularly important in short-term stress situations. In times of chronic stress the adrenal cortex makes further adjustment.

Parathyroid Hormone

Hormones of The Adrenal Cortex

Several different steroid hormones are produced by the adrenal cortex, but the most important ones are aldosterone, cortisol, and the sex hormones.

Aldosterone (al-do-ster’-on) is the most important mineralocorticoid secreted by the adrenal cortex. Mineralocorticoids regulate the concentration of electrolytes (mineral ions) in body fluids. Aldosterone stimulates the kidneys to retain sodium ions (Na+) and to excrete potassium ions (K+). This action not only maintains the normal balance of Na+ and K+ in body fluids but also maintains blood volume and blood pressure. The reabsorption of Na⁺ into the blood causes anions, such as chloride (Cl^–) and bicarbonate (HCO₃^–), to be reabsorbed due to their opposing charges. And it causes water to be reabsorbed by osmosis, which maintains blood volume and blood pressure. Aldosterone secretion is stimulated by several factors, including (1) a decrease in blood level of Na⁺, (2) an increase in blood level of K⁺, or (3) a decrease in blood pressure, which leads to angiotensin II production.

Glucocorticoids are so named because they affect glucose metabolism. There are three major actions of glucocorticoids. (1) In response to chronic stress, glucocorticoids ensure a constant fuel supply by promoting the conversion of noncarbohydrate nutrients into glucose. This is important because carbohydrate sources, such as glycogen, may be exhausted after several hours without food or strenuous exercise. (2) They facilitate the utilization of glucose by cells. (3) They reduce inflammation.

Cortisol is the most important of several glucocorticoids that are secreted by the adrenal cortex under the stimulation of ACTH. The blood levels of glucocorticoids are kept in balance because they exert a negative-feedback control on the secretion of CRH and ACTH.

The adrenal cortex also secretes small amounts of androgens (male sex hormones) and estrogens in response to ACTH from the anterior lobe of the pituitary gland. The estrogens have little significant function. The androgens promote the early development of male reproductive organs, but in adult males their effects are masked by sex hormones produced by testes. In females, adrenal androgens contribute to the female sex drive. In both sexes, excessive production results in exaggerated male characteristics.

Disorders Cushing syndrome results from hypersecretion by the adrenal cortex. It may be caused by an adrenal tumor or by excessive production of ACTH by the anterior lobe of the pituitary gland. This syndrome is characterized by high blood pressure, an abnormally high blood glucose level, protein loss, osteoporosis, fat accumulation on the trunk, fatigue, edema, and decreased immunity. A person with this condition tends to have a full, round face and an enlarged abdomen.

Addison disease results from a severe hyposecre- tion by the adrenal cortex. It is characterized by low blood pressure, low blood glucose and sodium levels, an increase in the blood potassium level, dehydration, muscle weakness, and increased skin pigmentation. Without treatment to control blood electrolytes, death may occur in a few days.