Proximal tubule balance or glomerulotubular balance predicts that an increase in GFR downstream of an increase in FF will result in:O A. Decreased amounts of sodium absorbed in the peritubuiar capillariesB. Decreased oxygen consumption in the kidneyC. Increased renin production in the JG cellsD. Increased oxygen consumption in the kidney

Kidneys are responsible for blood filtration in the body. The blood reaches the kidney via the renal artery which branches extensively into very fine blood vessels. The blood flows through the thin blood vessels and reaches the nephrons where the blood is filtered. The filtered blood flows out of the kidney via the renal vein and is then circulated back into the system. While the waste material along with water forms urine and reaches the urinary bladder via ureters.Nephrons form the microscopic, fundamental structural, and functional unit of the kidney. There exist millions of nephrons in one kidney. Nephrons consist of two main components, namely glomerulus, and renal tubules which form the actual site of blood filtration. Option D is the correct answer. "Increased oxygen consumption in the kidneys."Peritubular capillaries are tiny blood vessels surrounding the renal tubules of nephrons in the kidneys. The glomerular filtration rate (GFR) is the amount of fluid filtered from the glomerulus into Bowman’s capsule per unit of time. Thus, high GFR is high filtration while low GFR translates to low filtration. Filtration fraction (FF) is the amount of RPF (renal plasma flow) that is filtered through the glomerulus. An increase in the GFR can occur downstream of an increase in the FF. A rise in the FF means more plasma is passing through the glomeruli, leading to increased glomerular filtration pressure which can drive an increase in the GFR.When more plasma is filtered, the concentration of proteins and other solutes in the remaining unfiltered blood increases. This will lead to an elevated concentration of proteins in the peritubular capillaries creating an osmotic gradient around the proximal tubule of the nephron. Since water moves from a low concentration of solutes to a higher concentration of solutes, this higher osmotic pressure drives more reabsorption of water and solutes from the tubular fluid back into the peritubular capillaries. The kidneys consume oxygen to generate energy for tubular reabsorption. Thus, if GFR increases downstream to FF increase, then the reabsorption of water will occur in the proximal tubules, and as a result, the oxygen consumption of the kidney will increase. Options A, B, and C are incorrect. Option A is incorrect because sodium absorption mainly occurs in the nephron's proximal tubule. Peritubular capillaries reabsorb substances like water, glucose, ions, and amino acids passing from the renal tubules. Option B is incorrect because the increase in GFR and FF results in increased oxygen and not a decrease. Option C is incorrect because renin production by the juxtaglomerular (JG) cells is mainly regulated by changes in blood pressure and changes in sodium concentration in the distal tubule. It is not primarily influenced by changes in GFR downstream of changes in FF. Proximal tubule balance or glomerulotubular balance predicts that an increase in GFR downstream of an increase in FF will result in increased oxygen consumption in the kidneys. Thus, option D is the correct answer.