The glomerulus is a tuft of small blood vessels called capillaries located within Bowman's capsule within the kidney. Between the capillaries and Bowman's capsule lies mesangium.Blood enters the capillaries of the glomerulus by a single arteriole called an afferent arteriole and leaves by an efferent arteriole. glomerulus is a network (as a tuft) of capillaries located at the beginning of a nephron in the kidney. It serves as the first stage in the filtering process of the blood carried out by the nephron in its formation of urine.