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The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
The collecting duct system begins in the renal cortex and extends deep into the medulla. As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system. [1]: 67
To achieve such balance between water and ions, the loop of Henle coordinates its function with the collecting duct to regulate the amount of water to reabsorb or to excrete. While the loop of Henle makes the medulla of the kidney salty, the collecting duct regulates the permeability of water that could be reabsorbed to such salty environment.
The medullary rays of the cortex contain the proximal straight tubules, the cortical part of the thick ascending limb of the loops of Henle, and the cortical part of the collecting ducts. [72] The cortex is divided into lobules, each of which is a medullary ray in conjunction with connected to it nephrons, and interlobular arteries that pass ...
The thick ascending limb is found in the medulla of the kidney, and the thick ascending limb can be divided into a part that is in the renal medulla and a part that is in the renal cortex. The ascending limb is much thicker than the descending limb.
The initial filtering portion of a nephron is the renal corpuscle, which is located in the cortex. This is followed by a renal tubule that passes from the cortex deep into the medullary pyramids. Part of the renal cortex, a medullary ray is a collection of renal tubules that drain into a single collecting duct. [citation needed]
A cortical lobule (or renal lobule) is a part of a renal lobe. It consists of the nephrons grouped around a single medullary ray, and draining into a single collecting duct. Its near identical parallel is the rectal lobe [citation needed], which is present in the majority of mammals.
The point where DCT contacts the cortical thick ascending limb of the loop of Henle is called macula densa. It has tightly packed columnar cells which display reversed polarity and may monitor the osmolarity of blood. Histologically, cells of the DCT can be differentiated from cells of the proximal convoluted tubule: