The diagram below shows the structure of a single mammalian nephron.

Complete the table below by matching the correct letter (WWW, XXX, YYY, or ZZZ) of the nephron to each physiological statement.
| Statement | Letter |
|---|---|
| Selective reabsorption of all filtered glucose and amino acids occurs at this site. | |
| The cells here contain receptor proteins for antidiuretic hormone (ADH) to regulate water reabsorption. | |
| High hydrostatic pressure forces water and small solutes across membranes into the tubule lumen here. |
Describe how the activity of the ascending limb and the properties of the descending limb of the loop of Henle work together to create the concentration gradient in the medulla tissue fluid.