Final answer:
The kidneys synthesize calcitriol, the active form of vitamin D, crucial for calcium absorption and bone health.
Step-by-step explanation:
The kidneys help to synthesize calcitriol, which is the active form of vitamin D. The process involves the conversion of vitamin D into a biologically active form known as 1,25(OH)D2 or calcitriol. This conversion is vital for the absorption of calcium in the digestive tract, its reabsorption in the kidneys, and for maintaining normal serum concentrations of calcium and phosphate. These processes are crucial for bone health, muscle contraction, hormone secretion, and neurotransmitter release.