Structure
The suprarenal (or adrenal) glands are a set of small, golden-brown organs which lie on top of the kidneys. The right suprarenal gland is pyramidal in shape, while the left gland has a crescentic shape with a sharp superior border and a rounded inferior border.
The suprarenal glands are composed of two embryologically distinct tissues, the cortex and medulla. The outer cortex has a pale yellowish appearance and arises from embryonic mesoderm. The inner medulla is a darker reddish color and arises from neuroectoderm. The glands are responsible for synthesizing and secreting a variety of steroid hormones and catecholamines.
Despite their small size, the suprarenal glands are one of the most extensively vascularized organs. They have a well-established arterial supply via the superior, middle, and inferior suprarenal arteries, which emerge from the inferior phrenic artery, directly from the abdominal aorta, and the renal artery, respectively. They form a subcapsular arterial plexus, which supplies the cortical and medullary tissue.
The medullary veins merge to form the suprarenal veins that exit the hilum. The right suprarenal vein is short vein and joins the inferior vena cava directly. The left suprarenal vein, on the other hand, travels inferomedially to join the left renal vein.
The suprarenal glands are innervated via a suprarenal plexus. It contains mainly preganglionic sympathetic fibers that synapse deep with the medullary chromaffin cells, stimulating catecholamine release. Some postganglionic sympathetic fibers travel with the blood vessel, regulating blood flow, while others terminate in the cortex and are believed to be involved in modulating steroid hormone release. The cell bodies of afferent nerve fibers, arising from the suprarenal medulla, are more commonly located in the spinal (or dorsal root) ganglia.
Related parts of the anatomy
Anatomical Relations
The suprarenal glands are situated on the anterior superomedial aspect of the upper poles of both kidneys. Each gland is enveloped by a fibrous capsule and has a perinephric fatty layer outside it. Together, they’re enclosed by renal fascia.
The anterior surface of the right suprarenal gland has narrow medial and lateral aspects. These are posterior to the inferior vena cava and bare area of the liver, respectively. The lower aspect of the posterior surface lies in contact the superior aspect of the upper pole of the kidney, while the upper aspect of the posterior surface rests on the right crus of the diaphragm. The inferior surface of the gland is in contact with the anterior superomedial aspect of upper poles of kidneys.
The anterior surface of the left suprarenal gland faces the posterior aspect of the lesser sac; thus, a large portion of the upper surface is covered by peritoneum. The lower aspect of the anterior surface is in contact with the splenic artery and the body of the pancreas. The medial aspect of the posterior surface is in contact with the left crus of the diaphragm, while the lateral posterior surface is adjacent to the kidney.
Function
The suprarenal glands are endocrine organs involved in hormone production. These hormones are produced by the tissues within the glands and are subsequently released into the bloodstream to reach their target organs.
The different components of the gland possess distinct functions. The cortex is regulated hormonally, via the hypothalamic-pituitary-axis, and by neural regulation, via diurnal secretion of hormones (Dijkstra, Binnekade and Tilders, 1996).
The medulla responds to sympathetic preganglionic neuron stimulation, and so is regulated by the same mechanisms governing the sympathetic nervous system.
The cortices are responsible for the production of mineralocorticoids, glucocorticoids, and androgens, while the medulla produces catecholamines in response to sympathetic stimulation (Pocock, Richards and Richards, 2013).
List of Clinical Correlates
- Suprarenal hyperplasia
- Cushing’s syndrome
- Pheochromocytoma
References
Dijkstra, I., Binnekade, R. & Tilders, F. J. (1996) Diurnal variation in resting levels of corticosterone is not mediated by variation in adrenal responsiveness to adrenocorticotropin but involves splanchnic nerve integrity. Endocrinology, 137(2), 540-7.
Pocock, G., Richards, C. D. & Richards, D. A. (2013) Human Physiology, 4 edition. OUP Oxford.
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Adrenal gland histology: Video, Anatomy & Definition
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Adrenal Gland
The adrenal glands are paired organs adjacent to the kidneys which are comprised of a cortex and a medulla.
