Anatomy, Abdomen and Pelvis, Adrenal Glands (Suprarenal Glands)

Article Author:
Rishi Megha
Article Editor:
Stephen Leslie
Updated:
9/19/2018 3:56:30 PM
PubMed Link:
Anatomy, Abdomen and Pelvis, Adrenal Glands (Suprarenal Glands)

Introduction

The suprarenal glands are also called the adrenal glands and are a significant part of the endocrine system. The paired suprarenal glands are triangular in shape and measure approximately 5 cm by 2 cm and are located on a superior portion of each kidney, and weigh 4 to 5 grams.

The suprarenal glands secrete several vital hormones that play a role in the regulation of the immune system, metabolism, salt and water balance, and aid the body during periods of stress.

Structure and Function

The adrenal glands lie close to very important vessels and organs. The right gland is close to the right hemidiaphragm, liver, and inferior vena cava. The left gland lies proximal to the aorta, spleen, and tail of the pancreas. 

The suprarenal gland is composed of 2 distinct tissues, the cortex, and medulla. The adrenal cortex is the outer layer, and the adrenal medulla is the inner layer of the suprarenal gland. A thick capsule consisting of connective tissue surrounds the whole adrenal gland. The adrenal cortex tends to be fattier and thus has a more yellow hue. The adrenal medulla is noted to be a more reddish-brown color in nature.

The suprarenal cortex is much larger than the medulla, as the medulla only accounts for approximately 15% of the gland. It is composed of three distinct zones: "GFR."

Zona glomerulosa (outer layer)

  • The zona glomerulosa is responsible for the synthesis of mineralocorticoids, of which, the most important is aldosterone. This hormone plays a role in electrolyte balance and regulation of blood pressure.

Zona fasciculata (middle layer)

  • The zona fasciculata produces glucocorticoids of which the predominant hormone is cortisol. This hormone plays a role in the regulation of blood sugar via gluconeogenesis. Cortisol also modulates the immune system and plays a role in the metabolism of fat, protein, and carbohydrates. The secretion of cortisol is regulated by the adrenocorticotropic hormone which is released from the pituitary gland.

Zona reticularis (inner zone)

  • The zona reticularis produces androgens and play a role in the development of secondary sexual characteristics. The primary androgen produced in the zona reticularis is dehydroepiandrosterone (DHEA), which is the most abundant hormone in the body. It serves as a precursor for the synthesis of many other hormones produced by the suprarenal gland, such as progesterone, estrogen, cortisol, and testosterone.

The function of these 3 zones can be remembered by the mnemonic "Salt, Sugar, Sex," as they correlate to the function of the hormones produced in each layer of the adrenal cortex.

The adrenal medulla synthesizes catecholamines. Catecholamines are made from the precursor of dopamine and combined with tyrosine, thus resulting in Norepinephrine. Once norepinephrine has been created, it is then methylated via Phenylethanolamine N-methyltransferase (PNMT). PNMT is only found in the adrenal medulla.

Blood Supply and Lymphatics

Since the suprarenal glands make a significant amount of important hormones, these glands require a large blood supply. Thus, these glands are extremely well vascularized.

The 3 chief sources of blood to the suprarenal glands include:

  1. The superior adrenal arteries are small branches coming off the inferior phrenic artery
  2. The middle adrenal artery comes directly off of the abdominal aorta
  3. The inferior adrenal artery originates from the renal artery bilaterally

The venous drainage from the adrenal glands is dependent on the side of the gland. The left adrenal gland is anatomically further away from the inferior vena cava, and therefore the left adrenal vein drains into the inferior vena cava. The right adrenal vein is much closer to the Inferior vena cava and drains directly into this large vessel.

Surgical Considerations

When removing a pheochromocytoma, a neuroendocrine tumor based on the chromaffin cells of the adrenal medulla that produces large amounts of catecholamines, it is crucial to ligate the vein before manipulation of the organ. If the adrenal vein is not ligated before manipulation of the organ, large amounts of catecholamines will spill out into systemic circulation. This results in a catecholamine rush, resulting in an overtly exacerbated "flight or fight," response. Interestingly, these tumors tend to occur most frequently in 40 to 50-year-old Americans.

For standardized test purposes, remember that MEN-II is associated with pheochromocytoma and medullary thyroid cancer.

Clinical Significance

The adrenal cortex is noteworthy in its use of cholesterol as a significant precursor for its hormones.

Pathological events of the cortex zones result in the following:

Zona Glomerulosa: Conn syndrome manifested by hyperaldosteronism, which excites the response of the renin-aldosterone-angiotensin system (RAA). This results in a patient that is typically on 3 anti-hypertensives, with persistent hypertension, with a chemical analysis that demonstrates hypokalemia and mild hypernatremia.

Zona Fasiculata: Cushing disease manifested by elevated levels of cortisol resulting in abdominal striae with significant central obesity, buffalo hump of the nape of the neck, and hyperglycemia. Other attributes include poor wound healing.

Zona Reticularis: Precocious puberty manifested by early puberty in males or virtualization of young females with androgenic characteristics.

The suprarenal medulla is made of specialized cells known as chromaffin cells. These cells aggregate in small clusters around blood vessels. The chromaffin cells in the medulla synthesize epinephrine and norepinephrine. These sympathetic hormones have many physiological activities including playing a role in the "fight or flight" response, increasing heart rate, increasing force of contraction of the heart, metabolic rate, and heightened cognitive awareness.

Other Issues

Adrenal Incidentaloma

  • These happen more frequently than expected, and can approach up to 4% of CT scans.
  • If a patient has a history of prior cancer, this is an indication for biopsy.
  • If this patient is known to have no primary cancer, it is then imperative to rule out a functional adrenal overgrowth.

An algorithm for adrenal incidentaloma includes addressing if the tumor is functional.

Perform appropriate tests, for example, low dose-dexamethasone suppression test, plasma metanephrines, plasma aldosterone. If these are positive, the patient will likely need adrenalectomy.

If the tests are negative, consider metastasis. Is there a history of former primary cancer? If the answer is yes, can a biopsy confirm metastatic disease? Do not biopsy an adrenal incidentaloma unless there is a known history of cancer. Breast and lung cancer are most common. This can lead to seeding a primary adrenal cancer from the biopsy into the surrounding tissues. 

If there is no history of cancer and the adrenal incidentaloma is less than 4 cm repeat CT in 4 to 6 months. If it is larger than 4 to 6 cm, evaluate for functional workup and adrenalectomy.

Non-functional masses are created in the biochemical work-up.

Typically, these masses are less than 4 cm.

A functional mass that produces functional hormones requires intervention, whether medical or surgical. These include:

  • (G) Elevated aldosterone: Conn syndrome
  • (F) Elevated cortisol: Cushing syndrome
  • (R) Elevated androgens: Precocious Puberty


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