Question 23 A physiologist is studying the effect of food additives on GFR in order to determine the additives that should be avoided in individuals with chronic renal disease. Caffeine was found to increase urine output through an effect on GFR. Using your knowledge of normal physiology identify the likely mechanism for this effect.- Afferent arteriolar vasoconstriction- Efferent arteriolar vasodilation- Afferent arteriolar vasodilation

The urine production is affected by glomerular filtration rate (GFR). GFR is also depends on the diameter of the afferent and efferent arterioles.The caffeine is responsible for increasing urine output by affecting glomerular filtration rate (GFR). Urine output increase indicates increased glomerular filtration rate (GFR) that means more fluids will be entered into the Bowman's capsule from the glomerulus. It can be possible by decreasing the diameter of the efferent arteriole or increasing the diameter of the afferent arteriole that ultimately increases the glomerular filtration pressure and responsible for more urine production by increasing the GFR. Options are: 1. Vasoconstruction of afferent arteriole decreases the diameter of the afferent arteriole that is responsible for decreasing GFR and less urine production. 2. Afferent arteriole vasodilation will decreases urine production because it will decrease GFR. 3. Vasodilation of afferent arteriole will increases the diameter of the afferent arteriole that is responsible for increasing GFR and it also increases the urine production. Hence, option 3 is the right answer.