kidney - urine produced from blood coming through renal artery  

• ureter - carries urine to urinary bladder
• split into renal pelvis, renal cortex, renal medulla
• nephron - cells responsible for the filtration, reabsorption, secretion, excretion
  • glomerulus - where blood gets filtered
  • Bowman’s capsule - surrounds glomerulus like a balloon
  • proximal convoluted tubule - extends into medulla, loops back to cortex; water gets reabsorbed
  • loop of Henle - only found in mammals/birds >> ability to concentrate urine
  • things not filtered go to efferent arteriole >> peritubular capillaries
• reabsorption/secretion - water, dissolved solutes must return to blood or else animal urinates to death
  • solid molecules reabsorbed through active transport, cotransport
  • substances get secreted by moving from blood capillaries to filtrate
• excretion - gets rid of harmful substances

transport in nephron - osmotic gradient needed for reabsorption 

• proximal convoluted tubule - active transport of Na+ and Cl- >> reabsorption
  • most of water reabsorbed through wall of collecting duct
  • leaves behind hypertonic urine
• loop of Henle - creates the hypertonic renal medulla that draws water out from nephrons
  • water permeates through descending limb
  • water stays through ascending limb, NaCl leaves
• antidiuretic hormone (ADH) - aka vasopressin
  • produced by hypothalamus, secreted by posterior pituitary gland
  • more ADH >> less water in urine
  • less ADH >> more water in urine
• aldosterone - maintains the Na+ levels (reabsorption), consequently water levels
  • opposed by atrial natriuretic hormone (promotes excretion of salt/water)