The portion of the nephron that empties into the collecting duct is the

Distal tubule

Explanation:

A nephron is a functional unit of the Kidney which plays a role in the filtration of the blood by separating the water, small molecules and ions from the blood.

The structure of nephron consists of the

1. Bowman's capsule - is the first part of the neuron

2 Proximal convoluted tubule - is the folded structure which connects loop of Henle to a Bowman's capsule.

3. Loop of Henle - is the tubule which establishes a salt gradient

4 Distal tubule - the portion where reabsorption takes place and connects the loop of Henle to collecting tubule.

5. Collecting tubule - which collects all the unfiltered substance and transports it to the urinary bladder.

Since the distal tubule is the structure which is connected to the collecting tubule physically therefore distal tubule is the correct answer.