The opening of Bowman’s capsule allowing the entry and exit of glomerular arterioles is oval in shape (Fig. 1). The border of this opening is represented by the reflection of the glomerular visceral epithelium in the glomerular parietal epithelium. The opening contains both arterioles. The afferent arteriole (AA) has already lost its layer of smooth muscle; thus, only an endothelial tube enters the glomerular tuft. The efferent arteriole (EA) has a smaller lumen than the AA but, on the other hand, has a thicker wall that is established by an endothelial layer and at least one additional layer. Between the two arterioles is the waist of the opening. At this site the extraglomerular mesangium (EGM) passes over into the mesangium proper; this transition is established by only a few cells.
KeywordsParietal Cell Glomerular Basement Membrane Smooth Muscle Layer Afferent Arteriole Efferent Arteriole
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