Final answer:
The claim that urine volume is majorly determined by GFR and blood volume is false. GFR does play a critical role in influencing urine volume, but blood volume is not a direct determinant, as urine formation is a complex process involving GFR, tubular reabsorption and secretion, and several other systemic factors.
Step-by-step explanation:
The statement "The two major factors that determine urine volume are glomerular filtration rate (GFR) and blood volume" is false. While GFR is a significant factor affecting urine volume, the blood volume is not considered a direct determinant. Instead, parameters such as systemic blood pressure, autoregulatory mechanisms, sympathetic nervous system activity, paracrine hormones, and the process of tubular reabsorption and secretion play essential roles in urine formation.
Urine volume is influenced by the GFR, which is the volume of filtrate formed by both kidneys per minute. GFR, in turn, is highly influenced by factors including but not limited to hydrostatic pressure and colloid osmotic pressure. The kidneys filter a large volume of blood each day, but due to the reabsorption process, only about 1-2 liters of urine are actually produced daily.
In the nephrons of the kidneys, after glomerular filtration, the filtrate undergoes tubular reabsorption and tubular secretion. These processes are critical in the fine-tuning of the filtrate to form urine. Therefore, when considering the factors that determine urine volume, it's the combination of GFR, reabsorption rates, secretion, and other systemic factors that should be taken into account, rather than simply GFR and blood volume alone.