Final answer:
The extensions of the renal tissue between the renal pyramids are called renal columns, which are part of the renal cortex extending into the renal medulla.
Step-by-step explanation:
The extensions of the renal tissue in between the renal pyramids are called renal columns. These are extensions of the renal cortex into the renal medulla, serving an important role as they separate the renal pyramids. The renal columns contain blood vessels and connective tissues and are vital in supporting the structure and function of the kidney. The renal cortex is the outer part of the kidney that houses all of the nephrons and the renal medulla consists of the pyramidal tissue masses where the renal columns are located. The renal columns contribute to the functionality of the kidney by providing pathways for blood vessels and a supportive structure for the renal cortex and the medulla.