When observing a slide of the renal medulla, it an be seen that most of the medulla consists of

A) renal corpuscles.
B) glomeruli.
C) cross sections of proximal and distal convoluted tubules.
D) longitudinal sections of nephron loops and collecting ducts.
E) a mixture of all of these structures.

When observing a slide of the renal medulla, it can be seen that most of the medulla consists of longitudinal sections of nephron loops and collecting ducts. This is because the medulla is the inner region of the kidney and contains the loops of Henle and collecting ducts, which are responsible for reabsorption and concentration of urine. While the renal corpuscles and glomeruli are located in the renal cortex, and proximal and distal convoluted tubules may also be found in both the cortex and medulla. Therefore, the best choice is D.