Nephron Structure and Function Review the structure of the nephron by labeling and color-coding the diagram in Figure 25.1. Then use your textbook to determine which substances are absorbed or secreted from each region of the nephron, and enter this information in the blank boxes to the side of the tubules. Place substances secreted into the urine into the boxes whose arrows are pointing toward the tubules. Place substances into the bloodstream into boxes whose arrows are pointing away from the tubbles,