URINARY SYSTEM III

Histology 2016-2017
Department of Anatomy &Histology: Dr.Rajaa Ali
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URINARY SYSTEM III
Kidney: Cortex.
Presence of:
• Malpighian or renal corpuscles;
• Proximal convoluted tubules with brush border (darkly stained);
• Distal convoluted tubules without brush border (lightly stained).
Distal Convoluted Tubule
The distal convoluted tubule (DCT) is shorter and less convoluted than the PCT and is found in the cortex.
It is lined by simple cuboidal epithelium (no brush border; Fig.).
It actively reabsorbs sodium ions from the tubular fl uid. This reabsorptive activity is directly coupled with the secretion of hydrogen or potassium ions into the tubular fl uid. (One hydrogen ion or one potassium ion is secreted for every sodium ion reabsorbed.) This process of reabsorption and secretion is controlled by the hormone aldosterone secreted by the adrenal cortex.
Thus, DCT is involved in maintenance of acid-base balance in body fl uids.
Collecting Tubule and Collecting Duct (Fig.)
The collecting tubule begins in the medullary ray as the continuation of DCT. As it enters the medulla it is joined by several other collecting tubules to form a larger duct, the duct of Bellini or the papillary duct which opens on the apex of the pyramid (renal papilla).
The collecting tubules are lined by simple cuboidal epithelium with distinct cell boundaries and clear pale cytoplasm.
The papillary ducts are larger, wider and lined by tall columnar cells with pale-staining cytoplasm.
The collecting tubules and ducts are not normally permeable to water. However, in the presence of antidiuretic hormone (ADH) secreted by the neurohypophysis, they become permeable to water. As a result, water is drawn out of the collecting ducts because of the hypertonic tissue fl uid in the medullary interstitium.