Suprarenal glands

Anatomy

The suprarenal glands are located in the retroperitoneal space of the abdomen above the superior poles of the kidneys. These golden yellow organs are enveloped with renal fascia, which loosely connects them to the crura of the diaphragm. The two glands are asymmetrical; the right suprarenal gland is shaped like a pyramid while the left is semilunar in appearance.

Anteriorly, the right suprarenal gland is adjacent to the inferior vena cava and the right lobe of the liver, while posteriorly it is adjacent to the right crus the diaphragm. The lower part of the posterior surface is associated with the superior pole of the kidney. On the other hand, anterior to the left suprarenal gland is the stomach, spleen and pancreas. Similar to the right, the left suprarenal gland is related posteriorly to the left crus of the diaphragm and the superior pole of the kidney.

The medial borders of the right and left suprarenal glands are related to the right and left celiac ganglia respectively. Each suprarenal gland has a hilum, located more superiorly on the right than the left, through which veins and lymphatic vessels leave the gland.

Arterial supply

Arterial branches enter the suprarenal glands at multiple locations (not just at the hilum). The main arteries supplying the suprarenal glands are the:

1. Superior suprarenal arteries: around 6-8 in number, which are usually branches of the right and left inferior phrenic arteries.
2. Middle suprarenal arteries: one on each side, typically originating from the lateral aspects of the abdominal aorta.
3. Inferior suprarenal arteries: one on each side, typically emerging from the stem of the renal arteries.

Venous drainage

A single central vein emerges from the hilum of each suprarenal gland.

1. The right suprarenal vein is short and travels horizontally to drain into the inferior vena cava.
2. The left suprarenal vein is relatively longer and travels vertically to drain into the left renal vein.

Lymphatic drainage

The lymphatic vessels draining the parenchyma of the suprarenal gland also emerge from the hilum and drain into the lumbar lymph nodes of the lateral para-aortic group of lymph nodes.

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Nerve supply

The suprarenal glands are supplied by a large network of autonomic nerves. These nerves can regulate blood flow and hormone secretion. Hormone secretion by the suprarenal gland is regulated by neural and endocrine mechanisms. While the cortex is primarily regulated by hypothalamic-pituitary-adrenal axis, the medulla forms a part of the sympathetic nervous system.

The glands are mostly supplied by the greater thoracic splanchnic nerve in two ways:

• Some preganglionic fibers synapse in the celiac ganglion. The postganglionic sympathetic fibers form the suprarenal plexus supplying blood vessels of the gland.
• Some preganglionic sympathetic fibers directly innervate the medulla of the suprarenal gland, which is considered to be a modified sympathetic ganglion.

Structure

Each suprarenal gland is surrounded by a thick connective tissue capsule and can be divided into two important regions:

1. Outer cortex
2. Inner medulla

Functions

Both the cortex and medulla of the suprarenal glands are necessary for hormone secretion. Each layer predominantly synthesizes and secretes a different type of hormone.

1. Zona glomerulosa: secretes mineralocorticoids (Aldosterone), essential for maintaining water and electrolyte balance.
2. Zona fasciculata: secretes glucocorticoids (Cortisol), which play an important role in carbohydrate, fat and protein metabolism.
3. Zona reticularis: synthesizes weak androgens also known as gonadocorticoids (dehydroepiandrosterone - DHEA), which serve as precursors for testosterone.
4. Medulla of suprarenal gland: secretes catecholamines like epinephrine and norepinephrine. These hormones are secreted in response to stress, playing an important role in the “fight-or-flight” response.

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Variations

• Adrenal rests are suprarenal cortical tissue located elsewhere. This ectopic tissue can be seen in the areolar tissue around the suprarenal gland itself or at more distant locations, such as the spermatic cord, epididymis, ovary or broad ligament.
• At birth the suprarenal glands are large, nearly a third of the size of the kidney. They shrink postnatally and start regrowing again by 2 years of age, reaching their maximum size at puberty.

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