The glomerulus is structure number 3 in the given options. The glomerulus is a tiny network of blood vessels located in the Bowman's capsule of the kidney. It is a part of the renal corpuscle, which is responsible for filtering blood and removing waste products from it. The glomerulus receives blood from an afferent arteriole and blood is drained from it by an efferent arteriole. As blood passes through the glomerulus, wastes, excess water, and other substances are filtered out and passed into the Bowman's capsule, while important substances are retained in the blood. This filtered fluid is then processed further in the kidney to form urine.