Which is not a major function of the kidney?

The regulation of blood cell size is not a major function of the kidney. The primary roles of the kidney include filtration of blood, regulation of electrolyte balance, and excretion of waste products.

The kidney performs filtration to remove waste products and excess substances from the blood, helping to maintain homeostasis. The regulation of electrolyte balance is crucial for various bodily functions, as the kidneys control the levels of essential ions such as sodium, potassium, and calcium, ensuring they remain within appropriate ranges. Additionally, the kidneys excrete waste products like urea and creatinine, which are byproducts of protein metabolism and need to be cleared from the body to prevent toxicity.

However, the size of blood cells is determined primarily by their genetic makeup and production in the bone marrow, rather than by kidney function. Therefore, while the kidney plays critical roles in maintaining overall fluid and electrolyte balance and waste removal, it does not influence the actual size of blood cells.