The collecting ducts span the renal cortex and medulla and concentrate the urine. The collecting duct is composed of simple cuboidal epithelium. There are two distinct cell types present in the collecting tubules: intercalated cells and principal cells. The principal cells are the predominant cell type with short sparse microvilli and contain Na+/K+ ATPase pump and aquaporin, which is an anti-diuretic hormone [ADH]-regulated water channel. The intercalated cells are fewer in number, but they are important for the regulation of blood pH. These cells will adjust bicarbonate or hydrogen ion reabsorption.
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