Final answer:
Collecting ducts in the kidneys merge to become terminal ducts, which then empty urine into the minor calyces. They have simple squamous epithelium sensitive to ADH, allowing water reabsorption into the bloodstream.
Step-by-step explanation:
The collecting ducts in the kidneys play a crucial role in urine formation and fluid balance within the body. These ducts are responsible for the final modification of filtrate received from several nephrons. As the collecting ducts descend deeper into the medulla, they merge to form about 30 terminal ducts, which ultimately empty at a papilla into the minor calyces of the renal pelvis. The collecting ducts are lined with simple squamous epithelium and are sensitive to antidiuretic hormone (ADH). When ADH is present, aquaporin channel proteins are inserted into the walls of the ducts, allowing water to pass from the filtrate back into the bloodstream, thus concentrating the urine and conserving water in the body.