A Kidney Can Have Up to 1 Million Nephrons, the Functional

Essay

A kidney can have up to 1 million nephrons, the functional unit of the kidneys. The filtrate that is produced by a series of processes, including filtration, reabsorption and secretion eventually empties from many nephrons into a series of ducts, cup-like structures and eventually into a single cavity called the renal pelvis. Which of these structures would be the least abundant but still contain filtrate rather than urine?
a. papillary ducts
b. collecting ducts
c. minor calyxes
d. major calyxes