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The vasa recta of the kidney, (vasa recta renis) are the straight arterioles, and the straight venules of the kidney, – a series of blood vessels in the blood supply of the kidney that enter the medulla as the straight arterioles, and leave the medulla to ascend to the cortex as the straight venules.
The vasa recta have a similar loop shape so that the gradient does not dissipate into the plasma. [citation needed] The mechanism of counter current multiplication works together with the vasa recta's counter current exchange to prevent the wash out of salts and maintain a high osmolarity at the inner medulla. [citation needed]
Vasa recta are straight arteries arising from arterial arcades (anastomoses of the jejunal and ileal arteries, branches of superior mesenteric artery) in the mesentery of the jejunum and ileum that supply the jejunum and ileum. [1] The vasa recta of the jejunum are long and few, compared to the ileum where they are numerous and short.
The descending vasa recta, ascending vasa recta vessels, and the loop of Henle together form the countercurrent system of the kidney. In the afferent arteriole, blood is supplied at high pressure, which promotes filtration, and in the efferent arteriole, it is at low pressure, which promotes reabsorption .
As well, blood in the vasa recta still has large proteins and ions which were not filtered through the glomerulus. This provides an oncotic pressure for ions to enter the vasa recta from the interstitium. [citation needed] The main function of the loop of Henle is to set up a concentration gradient. [citation needed]
Peritubular capillaries surround the cortical parts of the proximal and distal tubules, while the vasa recta go into the medulla to approach the loop of Henle. [1] [2] About one-fifth of the blood plasma is filtered into Bowman's capsule as the blood passes through the glomerular capillaries; four-fifths continues into the peritubular capillaries.
The blood exiting the efferent arterioles of these nephrons enter the vasa recta, which are straight capillary branches that deliver blood to the renal medulla. These vasa recta run adjacent to the descending and ascending loop of Henle and participate in the maintenance of the medullary countercurrent exchange system.
When renal blood flow is reduced (indicating hypotension) or there is a decrease in sodium or chloride ion concentration, the macula densa of the distal tubule releases prostaglandins (mainly PGI2 and PGE2) and nitric oxide, which cause the juxtaglomerular cells lining the afferent arterioles to release renin, activating the renin–angiotensin–aldosterone system, to increase blood pressure ...