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Suprarenals

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					Suprarenal Gland
The suprarenal glands are associated with the superior pole of each kidney. They consist of an outer cortex and an inner medulla. The right gland is shaped like a pyramid, while the left gland is semilunar in shape and the larger of the two. The suprarenal glands are surrounded by the perinephric fat and enclosed in the renal fascia, though a thin septum separates each gland from its associated kidney. The glands are enclosed by renal fascia by which they are attached to the crura of the diaphragm. The gland is made up of a superficial layer the cortex, and a deeper part called the medulla. The suprarenal cortex derives from mesoderm and secretes corticosteroids and androgens. These hormones cause the kidneys to retain sodium and water in response to stress, increasing blood volume and blood pressure. The outermost layer of cortex is called the zona glomerulosa. Here the cells are arranged in the form of inverted Ushaped structures, or acinus like groups. The cells of the the zona glomerulosa produce the hormone aldosterone. The next zone is called the Zona fasciculata, here the cells are arranged in straight columns. The cells of the zona fasciculata produce hydrocortisone. The innermost layer of the cortex is called the zona reticularis as the cords of cells branch and anastamose with each other forming a kind of reticulum. The cells o the zona reticularis produce sex hormones, including progesterone, oestrogens and androgens. The suprarenal medulla is a mass of nervous tissue. The adrenal medulla derives from neural crest cells.These cells secrete catecholamines (mostly epinephrine) into the bloodstream. The powerful medullary hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) activate the body to a flight-or-fight status in response to traumatic stress. They also increase heart rate and blood pressure, dilate the bronchioles, and change blood flow patterns, preparing for physical exertion. The medulla is made up of a group of cells, some of which may be arranged in columns. The cell groups or columns are seperated by wide sinusoids. Nerve fibres and neurons are also present. When the suprarenal is fixed in a solution containing a salt of chromium (e.g. potassium dichromate) the cells of the medulla show yellow granules in their cytoplasm. This is called chromaffin reaction and the cells that give a positive reaction are called chromaffin cells.The cells of the cortex do not give this reaction. A similar reaction is given by cells of sympathetic ganglia. The cells of the duprarenal medulla are considered to be modified postganglionic sympathetic neurons. Like typical postganglionic sympathetic neurons, they secrete noradrenalin and adrenalin into the blood. Relations of Suprarenal glands (a) Relations common to both glands The posterior surface of each suprarenal gland rests (in its upper part) on the diaphragm, and (in its lower part) on the superomedial part of the corresponding kidney. Medial to each gland there is the corresponding crus of the diaphragm on which there is the corresponding coeliacganglion, and the corresponding inferior phrenic artery (a branch of the abdominal aorta).

(b) Additional relations of the right suprarenal gland The anterior surface of the right suprarenal gland can be divided into medial and lateral parts by a vertical line. The medial part is overlapped by the inferior vena cava. The lateral part conies into contact with the liver. The upper half of the lateral part is in contact with the bare area of the liver, while its lower part is separated from the visceral surface by peritoneum.

(c) Additional relations of the left suprarenal gland The upper part of the anterior surface is covered by the peritoneum forming the posterior wall of the lesser sac. It forms part of the stomach bed. The lower part of the anterior surface is overlapped by splenic artery and the body of the pancreas: this part is not covered by peritoneum. The left gastric artery lies medial to the left suprarenal gland. Suprarenal vasculature The arterial supply to the suprarenal glands is extensive and arises from three primary sources:
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as the bilateral inferior phrenic arteries pass upward from the abdominal aorta to the diaphragm, they give off multiple branches (superior suprarenal arteries) to the suprarenal glands; a middle branch (middle suprarenal artery) to the suprarenal glands usually arises directly from the abdominal aorta; inferior branches (inferior suprarenal arteries) from the renal arteries pass upward to the suprarenal glands.

In contrast to this multiple arterial supply is the venous drainage, which usually consists of a single vein leaving the hilum of each gland. On the right side, the right suprarenal vein is short and almost immediately enters the inferior vena cava; while on the left side, the left suprarenal vein passes inferiorly to enter the left renal vein.

Lymphatic Drainage The lymph drains into the lateral aortic nodes. Nerve Supply Preganglionic sympathetic fibres from the splanchnic nerves supply the glands. Most of the nerves end in the medulla of the gland. Clinical Significance Cushing’s syndrome Sprarenal cortical hyperplasia is the most common cause of Cushing’s syndrome, the clinical manifestations include moon-shaped face, truncal obesity, abnormal hairiness (hirsuitism) and hypertension. If the syndrome occurs later in life, it may result from an adenoma or carcinoma of the cortex. Addison’s disease Adrenocortical insufficiency (addison’s isease) is characterized clinically by increased pigmentation, muscular weakness, weight loss and hypotension. Pheochromocytoma Pheochromocytoma, a tumor of the medulla, produces a paroxysmal or sustained hypertension. The symptoms and signs result from the production of a large amount of catecholamines, which are then poured into the blood stram. Surgical significance The suprarenal glands together with the kidneys are enclosed within the renal fascia; the suprarenal glands however, lie in a separate compartment, which allows the two organs to be seperated easily during surgery.


				
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