The part labelled as 1 is a structure of glomerulus. Blood that is about to be filtered enters a glomerulus, which is a tuft of blood capillaries (the smallest of blood vessels). The glomerulus is nestled inside a cup-like sac located at the end of each nephron, called a glomerular capsule. Glomerular capillaries have small pores in their walls, just like a very fine mesh sieve. .The glomerulus, on the other hand, is sandwiched between two arterioles - afferent arterioles deliver blood to the glomerulus, while efferent arterioles carry it away.