The juxtaglomerular cells (also called granular cells) are specialized cells that form part of the juxtaglomerular apparatus. Their structure is characterized by: Location: They are found in the walls of the afferent arterioles, which are the small arteries that carry blood to* the glomerulus (the filtering unit) in the kidney. Appearance: They are modified smooth muscle cells. Granules: The most distinctive feature is the presence of numerous granules within their cytoplasm. These granules contain the hormone renin*, which is released when needed. Nucleus: They have a large, often centrally located nucleus. Smooth Muscle: Because they are modified smooth muscle cells, they have the ability to contract and relax, which can help regulate blood flow into the glomerulus.