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Other Terms: Suprarenal gland, Glandula suprarenalis, Glande surrénale, Nebenniere, Glándula suprarrenal
The adrenal glands are two small flattened bodies of a yellowish color. They are situated at the back part of the abdomen, behind the peritoneum and above and in front of the upper end of each kidney. The right one is somewhat triangular in shape. They are considered retroperitoneal. The left is more semilunar, usually larger, and placed at a higher level than the right. They vary in size in different individuals. Their usual size is from 3-5 centimeters in length and 4-6 millimeters in thickness. Their average weight is from 1.5-2.5 grams.
The relations of the two adrenal glands differ on the two sides of the body. The right adrenal gland is situated posterior to the inferior vena cava and right lobe of the liver. It is anterior to the diaphragm and upper end of the right kidney. It is slightly triangular in shape. Its base is directed downward and is in contact with the medial and anterior aspects of the upper end of the right kidney. It presents two surfaces: an anterior and a posterior. The anterior surface looks forward and laterally and has two areas: a medial, nonperitoneal area and a lateral, triangular area. The medial area lies behind the inferior vena cava. The lateral area is in contact with the liver. The upper part of the lateral area is devoid of peritoneum and is in relation with the bare area of the liver near its lower and medial angle. Its inferior portion is covered by peritoneum, reflected onto it from the inferior layer of the coronary ligament; occasionally the duodenum overlaps the inferior portion. The hilum is located a little below the apex. The suprarenal vein emerges from the hilum to join the inferior vena cava. The posterior surface of the adrenal gland is divided into upper and lower parts by a curved ridge. The upper part rests upon the diaphragm. The lower part is in contact with the upper end and the adjacent part of the anterior surface of the kidney. The left adrenal gland is slightly larger than the right. It is crescent in shape and its concavity is adapted to the medial border of the upper part of the left kidney. It presents a medial border, which is convex and a lateral border which is concave. Its upper end is narrow and its lower end is rounded. Its anterior surface has two areas: an upper and a lower. The upper area is covered by peritoneum of the omental bursa which separates it from the cardiac end of the stomach. The lower area is in contact with the pancreas and splenic artery and is not covered by peritoneum. On the anterior surface is a hilum from which the suprarenal vein emerges. Its posterior surface presents a vertical ridge which divides it into two areas: the lateral and medial. The lateral area rests on the kidney. The medial is small and is on the left crus of the diaphragm.
The surface of the adrenal gland is surrounded by an adipose capsule and renal fascia. It is closely invested by a thin fibrous capsule. The adrenal gland consists of two portions a cortex and medulla. The cortex constitutes the chief part of the organ and is a deep yellow color. It Is involved in the synthesis of corticosteroid hormone from cholesterol. It consists of a fine connective tissue network, in which is imbedded the glandular epithelium. The epithelial cells are polyhedral in shape and possess rounded nuclei. Many of the cells contain coarse granules, others lipoid globules. Three distinct zones can be made out owing to the differences in the arrangement of the cells: the zona glomerulosa, zona fasciculata, and the zona reticularis. The zona glomerulosa is situated beneath the capsule. It is the outermost layer. It contains cells arranged in rounded groups. The cells of this zone are very granular. The zona glomerulosa is the main site of mineralcorticoid production, chiefly aldosterone. The zona fasciculata is continuous with the zona glomerulosa. It is located between the zona glomerulosa and the zona reticularis and is composed of columns of cells arranged in a radial manner. These cells contain finer granules and in many instances globules of lipoid material. The zona fasciculata functions in glucocorticoid production, chiefly cortisol. The zona reticularis is in contact with the medulla and is the innermost layer. It consists of cylindrical masses of irregularly arranged cells. These cells often contain pigment granules which give this zone a darker appearance than the rest of the cortex. It produces androgens, chiefly dehydroepiandrosterone and dehydroepiandrosterone sulfate. The medulla is soft, pulpy and dark red or brown. It is extremely vascular and consists of large chromaffin cells arranged in a network. The irregular polyhedral cells have a finely granular cytoplasm that secretes epinephrine and norepinephrine. In the meshes of the cellular network are large anastomosing venous sinusoids which are in close relationship with the chromaffin cells. There is a loose meshwork of supporting connective tissue containing non-striated muscle fibers. This portion of the gland is richly supplied with non medullated nerve fibers.
The nerves are exceedingly numerous and are derived from the sympathetic trunks. It receives innervation from the greater, lesser, and least splanchnic nerves.
The arteries supplying the adrenal glands are numerous and are large. They are the superior suprarenal, inferior suprarenal, and the middle suprarenal arteries. The superior suprarenal arises from the inferior phrenic. The inferior suprarenal arises from the renal artery. The middle suprarenal artery arises directly from the abdominal aorta. They subdivide into minute branches previous to entering the cortex, where they break up into capillaries which end in the venous plexus of the medulla.
The suprarenal vein returns the blood from the medullary venous plexus and receives branch from the cortex. It emerges from the hilum and on the right side opens into the inferior vena cava, and on the left into the renal vein.