What adaptation do newborns exhibit concerning their kidneys?

Newborns exhibit physiological immaturity regarding their kidneys, which are structurally complete but not fully functional. This means that while the kidneys have all the anatomical components necessary for their role, they are not yet fully capable of efficiently regulating fluid balance, electrolyte levels, and waste elimination as they will be in older children and adults.

In the early days and weeks after birth, newborns have a limited ability to concentrate urine and to excrete certain substances, which can put them at risk for imbalances in fluids and electrolytes. This immaturity also affects their response to changes in hydration status, making careful monitoring of their fluid intake and output crucial during this early period.

The other options do not accurately reflect the adaptation of newborns’ kidneys. They are not fully mature or hyperactive in concentration, nor are they incapable of filtering blood entirely—rather, their filtering function is less efficient compared to older individuals. Understanding this physiological aspect is vital for managing care and anticipating issues related to hydration and electrolyte balance in the newborn population.