Papilla - Overview

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The mouse kidney is covered by a thin connective tissue capsule and consists of, from its convex border to its concave border, a cortex, a medulla, and a single papilla that can be very long. The papilla drains into the renal pelvis, the anterior end of the ureter, which joins the kidney on its concave border at the hilus. The functional unit of the kidney is the nephron, which comprises a glomerulus (a capillary bed that is particularly small in the mouse) surrounded by the Bowman’s capsule, a proximal convoluted tubule, descending and ascending portions of the straight loop of Henle, and a distal convoluted tubule. In between the nephrons is delicate, richly vascular connective tissue. Nephrons drain into collecting tubules, which join to form larger collecting ducts (Bellini ducts) that open into the renal pelvis. In mice, particularly adult males, proteinuria is normal.

The papilla of the mouse kidney is formed by collecting ducts (Bellini ducts) and blood vessels. The collecting ducts are lined by cuboidal to low columnar epithelium.

The micrographs are longitudinal sections of the papilla. The 4X micrograph displays the papilla entering the renal pelvis. The 10X micrograph shows that the renal pelvis is lined by urinary epithelium (transitional epithelium or urothelium). The 10X, 20X, and 40X micrographs present, in increasing detail, the collecting ducts. The 40X micrograph exhibits the cuboidal epithelium of a collecting duct and the bulging nuclei of the mural cells of a collecting tubule.