The adrenal gland is one kind of endocrine gland, which is also known as a suprarenal gland. It is two in number that is placed on the upper pole of each kidney at the level of 1st lumbar vertebra. The right adrenal gland of humans is pyramidal in shape, while the left adrenal gland is crescent-shaped and slightly larger than the right adrenal.
Each gland measures about 3 cm in width, 5 cm in length and about 1 cm in thickness, which is surrounded by the fibrous capsule. It surrounds the kidney. In the adult human body, the combined weight of the two glands ranges from 7-10 grams. It is yellowish in color. The adrenal gland consists of two parts, the outer cortex and inner medulla.
It is the outermost layer of the adrenal gland. This gland produces some essential hormones such as aldosterone, cortisol and androgens. The cortex consists of polyhedral epithelioid cells which are arranged in three layers:
1. Zona Glomerulosa: It is the outermost zones which are located just under the fibrous capsule of the gland. This outer layer produces a mineralocorticoid hormone, such as aldosterone. Generally, it is secreted by the activity of the aldosterone synthetase enzyme. This hormone helps to regulate long term blood pressure.
2. Zona Fasiculata: It is the middle layer which is located between the zona reticularis and the zona glomerulosa. This layer is the largest layer among three layers, which accounts for about 80% of the cortex. Cells in this layer are arranged in columns and contain lots of lipid droplets, smooth endoplasmic reticulum (ER) and mitochondria. Glucocorticoids such as cortisol hormones are produced from this layer.
3. Zona Reticularis: It is the inner irregular network rows of the cell layer. It is placed directly adjacent to the madula. This layer contains small cells with a small amount of cytoplasm and lipid droplets. It also contains some lipofusion pigment. It produces hormones like androgens.
Hormones of Adrenal Cortex
A number of cortical hormones are secreted from the cortex. They are grouped into three types:
Glucocorticoids: These groups of hormones are mainly secreted from zona fasiculata. They include cortisol, cortisone, corticosterone.
Minerelocorticoids: This group of hormones is secreted mainly from the zona glomerulosa. They include aldosterone and deoxycorticosterone (DOC).
Sex steroids: This group of hormones is secreted mainly from zona reticularies. They include androgen, estrogen, progesterone, etc.
The Functions of Adrenal Cortex
Effect on Carbohydrate Metabolism: Glucocorticoids help for the metabolism of carbohydrates as follows:
Effect on Minerals and Water Metabolism: Mineralocorticoids increase reabsorption of NaCl, bicarbonates, and water. It depresses of potassium and phosphate reabsorption by the renal tubules.
Effect on Protein Metabolism: Glucocorticoids break down tissue protein into amino acids; thus, body proteins are lost, and nitrogen excretion increases.
Effect on Fat Metabolism: Glucocorticoids increase the fat absorption from the intestine. They also increase lipid and cholesterol levels in the blood and decrease the synthesis of lipids from carbohydrates.
Effect on different System: Glucocorticoids decrease the number of eosinophils and lymphocytes in the blood. They regulate the composition of blood, blood volume, blood pressure, etc. It also controls bone formation, muscular activities, the function of the nervous system and the digestion system.
The vital part of the adrenal gland is known as the medulla, which is surrounded by the adrenal cortex. It consists of densely packed polyhedral cells that are surrounded by blood tissue. These cells are known as chromaffin cells. The adrenal medulla produces catecholamine adrenaline and noradrenaline hormones.
This organ can produce about 80% adrenaline or epinephrine and 20% noradrenaline or norepinephrine. These are protein hormones. Epinephrine (adrenaline) and nor-epinephrine together called catecholamines that are produced from the adrenal medulla and nerve endings such as sympathetic and parasympathetic nerves.
Functions of Epinephrine
Functions of Nor-epinephrine
Nor-epinephrine is also known as noradrenaline. Chemically, it is catecholamine and phenethylamine. It acts as a chemical messenger and transmits signals across nerve endings. It releases higher levels during the situation of stress or danger. Generally, it secretes the lowest amount during sleep and increases during wakefulness.
Disorders and Diseases of the Adrenal Glands
There are multiple disorders and diseases caused by the adrenal glands when it does not work precisely. The following most common disorders and diseases of the adrenal glands are:
It is caused due to hyposecretion or insufficient secretion of cortisol hormone.
Over production or hyper-functions of adrenal cortex causes the following diseases:
It is caused by over secretion of cortisol hormone. There are the following many symptoms of cushing`s syndrome:
It is caused due to the excessive secretion of adrenal androgen. It shows the following symptoms: