Adrenal gland,Suprarenal glands,Disease,AcuTreatment,Cure Without Medicine,Cure,Acu,Medicine,Acupressure points,Treatment,Adrenal cortex,Blood supply,Adrenaline and noradrenaline,Androgens,Adrenal insufficiency,Secondary adrenal insufficiency,Congenital adrenal hyperplasia,Adrenal tumors

The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which produces steroid hormones and an inner medulla. The adrenal cortex itself is divided into three zones: zona glomerulosa, the zona fasciculata and the zona reticularis.

The adrenal cortex produces three main types of steroid hormones: mineralocorticoids, glucocorticoids, and androgens.Mineralocorticoids (such as aldosterone) produced in the zona glomerulosa help in the regulation of blood pressure and electrolyte balance. The glucocorticoids cortisol and corticosterone are synthesized in the zona fasciculata; their functions include the regulation of metabolism and immune system suppression. The innermost layer of the cortex, the zona reticularis, produces androgens that are converted to fully functional sex hormones in the gonads and other target organs. The production of steroid hormones is calledsteroidogenesis, and involves a number of reactions and processes that take place in cortical cells. The medulla produces thecatecholamines adrenaline and noradrenaline, which function to produce a rapid response throughout the body in stress situations.

Adrenal gland

Adrenal gland & Kidney

A number of endocrine diseases involve dysfunctions of the adrenal gland. Overproduction of cortisol leads to Cushing’s syndrome, whereas insufficient production is associated with Addison’s disease. Congenital adrenal hyperplasia is a genetic disease produced by dysregulation of endocrine control mechanisms. A variety of tumors can arise from adrenal tissue and are commonly found inmedical imaging when searching for other diseases.

 

Structure

The adrenal glands are located on both sides of the body in the retroperitoneum, above and slightly medial to the kidneys. In humans, the right adrenal gland is pyramidal in shape, whereas the left is semilunar and somewhat larger. The glands are usually about 5 x 3cm in size, and their combined weight in an adult human ranges from 7 to 10 grams. The glands are yellowish in colour.

The adrenal glands are surrounded by a fatty capsule and lie within the renal fascia, which also surrounds the kidneys. A weak wall of connective tissue separates the glands from the kidneys. The adrenal glands are directly below the diaphragm, and are attached to the crura of the diaphragm by the renal fascia.

Each adrenal gland has two distinct parts, each with a unique function, the outer adrenal cortex and the inner medulla, both of which produce hormones.

Cortex

The adrenal cortex is the outermost layer of the adrenal gland. Within the cortex are three layers, called “zones”. When viewed under a microscope each layer has a distinct appearance, and each has a different function. The adrenal cortex is devoted to production ofhormones, namely aldosterone, cortisol, and androgens.

Zona glomerulosa

The outermost layer of the adrenal cortex is the zona glomerulosa. It lies immediately under the fibrous capsule of the gland. Cells in this layer form oval groups, separated by thin strands of connective tissue from the fibrous capsule of the gland and carry wide capillaries.

This layer is the main site for production of aldosterone, a mineralocorticoid, by the action of the enzyme aldosterone synthase.Aldosterone plays an important role in the long-term regulation of blood pressure.

Zona fasciculata

The zona fasciculata is situated between the zona glomerulosa and zona reticularis. Cells in this layer are responsible for producingglucocorticoids such as cortisol. It is the largest of the three layers, accounting for nearly 80% of the volume of the cortex. In the zona fasciculata, cells are arranged in columns radially oriented towards the medulla. Cells contain numerous lipid droplets, abundantmitochondria and a complex smooth endoplasmic reticulum.

Zona reticularis

The innermost cortical layer, the zona reticularis, lies directly adjacent to the medulla. It produces androgens, mainly dehydroepiandrosterone (DHEA), DHEA sulfate (DHEA-S), and androstenedione (the precursor to testosterone) in humans. Its small cells form irregular cords and clusters, separated by capillaries and connective tissue. The cells contain relatively small quantities of cytoplasm and lipid droplets, and sometimes display brown lipofuscin pigment.

Medulla

The adrenal medulla is at the centre of each adrenal gland, and is surrounded by the adrenal cortex. The chromaffin cells of the medulla are the body’s main source of thecatecholamines adrenaline and noradrenaline, released by the medulla. Approximately 20% noradrenaline (norepinephrine) and 80% adrenaline (epinephrine) are secreted here.

The adrenal medulla is driven by the sympathetic nervous system via preganglionic fibers originating in the thoracic spinal cord, from vertebrae T5–T11. Because it is innervated by preganglionic nerve fibers, the adrenal medulla can be considered as a specialized sympathetic ganglion. Unlike other sympathetic ganglia, however, the adrenal medulla lacks distinct synapses and releases its secretions directly into the blood.

Blood supply

The adrenal glands have one of the greatest blood supply rates per gram of tissue of any organ: up to 60 small arteries may enter each gland. Three arteries usually supply each adrenal gland:

  • The superior suprarenal artery, a branch of the inferior phrenic artery
  • The middle suprarenal artery, a direct branch of the abdominal aorta
  • The inferior suprarenal artery, a branch of the renal artery

These blood vessels supply a network of small arteries within the capsule of the adrenal glands. Thin strands of the capsule enter the glands, carrying blood to them.

Venous blood is drained from the glands by the suprarenal veins, usually one for each gland:

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