1. Regulation of the volume and composition of internal environment
   1. Regulation of body fluid osmolality and volume
      1. working in an integrated fashion with components of the CV and nervous system - regulates the excretion of water and NaCl
   2. Regulation of electrolyte balance
      1. including but not limited to
         1. Na
         2. K
         3. Cl
         4. HCO3
         5. H
         6. Ca
         7. Phosphate
      2. maintenance/excretion of many intermediates of the Kreb cycle
      3. for many of the electrolytes, kidneys are the sole/primary route for excretion from the body
   3. Regulation of acid-base balance
      1. coordinated action of lungs, kidney, liver
   4. Excretion of metabolic products/foreign substances
      1. urea (from AAs)
      2. uric acids (from purines)
      3. creatinine (from muscle creatine)
      4. end products of haemoglobin metabolism
      5. end products of hormone metabolism
      6. the above are eliminated at a rate that matches their production
      7. drugs/pesticides/chemicals are also excreted
2. Regulation of Blood Pressure
3. Secretes Renin
   1. activates RAAS
4. Secretion of erythropoietin
   1. erythropoietin stimulates RBC formation by bone marrow
5. Activation of Vitamin D
   1. produces 1,25 - dihydroxycalciferol
   2. calcitrol(vit D) necessary for normal reabsorption of Ca by GI tract and its deposition in bone
6. Gluconeogensis