adrenal gland

adrenal gland

adrenal gland or suprarenal gland, endocrine gland (see endocrine system) about 2 in. (5.1 cm) long situated atop each kidney. The outer yellowish layer (cortex) of the adrenal gland secretes about 30 steroid hormones, the most important of which are aldosterone and cortisol. Cortisol regulates carbohydrate, protein, and fat metabolism, and its secretion is controlled by the output of adrenocorticotropic hormone (ACTH) from the pituitary gland. Aldosterone regulates water and salt balance in the body; its secretion is only slightly influenced by the pituitary. Steroid hormones also counteract inflammation and allergies and influence the secondary sex characteristics to a limited degree. The adrenal cortex controls metabolic processes that are essential to life and if it ceases to function death ensues within a few days. Artificial synthesis of the steroid hormones has made it possible to treat many conditions related to underactivity of the adrenal cortex, e.g., Addison's disease. The inner reddish portion (medulla) of the adrenal gland, which is not functionally related to the adrenal cortex, secretes epinephrine (adrenaline) and norepinephrine. The release of these hormones is stimulated when an animal is excited or frightened, causing increased heart rate, increased blood flow to the muscles, elevated blood sugar, dilation of the pupils of the eyes, and other changes that increase the body's ability to meet sudden emergencies.

In mammals, the adrenal glands (also known as suprarenal glands) are the triangle-shaped endocrine glands that sit on top of the kidneys; their name indicates that position (ad-, "near" or "at" + -renes, "kidneys"; and as concerns supra-, meaning "above"). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline.

Anatomy and function

Anatomically, the adrenal glands are located in the thoracic abdomen situated atop the kidneys, specifically on their anterosuperior aspect. They are also surrounded by the adipose capsule and the renal fascia. In humans, the adrenal glands are found at the level of the 12th thoracic vertebra and receive their blood supply from the adrenal arteries.

The adrenal gland is separated into two distinct structures, both of which receive regulatory input from the nervous system:

Arteries and veins

Although variations of the blood supply to the adrenal glands (and indeed the kidneys themselves) are common, there are usually three arteries that supply each adrenal gland:

Venous drainage of the adrenal glands is achieved via the suprarenal veins:

The suprarenal veins receive(ing?) blood may form anastomoses with the inferior phrenic veins.

The adrenal glands and the thyroid gland are the organs that have the greatest blood supply per gram of tissue. Up to 60 arterioles may enter each adrenal gland.

See also

References

Notes

General references

  • - "Adrenal Gland"
  • - "Posterior Abdominal Wall: The Retroperitoneal Fat and Suprarenal Glands"
  • Adrenal Gland, from Colorado State University

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