Recall that urine contains water, urea and salts
1. Brain influences the the functioning of the kidneys
2. Kidneys filter out blood
3. Molecules removed come out the ureter and collect in the bladder as urine
4. Urine contains salt, water and urea --- which affects the composition of the tissue fluid = Osmoregulation
5. Removal of urea = excretion of metabolic waste.