production of urine

• glomerular filtration takes place in renal corpuscle when fluid is forced out of blood and collected by glomerular capsule due to a pressure difference
• High pressure forces water and dissolved blood components through semipermeable cell membrane into capsule, this fluid is known as the filtrate
• filtrate contains : water, salts, amino acids, fatty acids, glucose, urea, uric acid, creatinine, hormones, toxins, various ions
• substances reabsorbed : water, glucose, amino acids, ions, urea
• Water reabsorption is regulated depending on body requirements, the permeability of plasma membranes of cells making up tubules can be changed 
• tubular secretion adds materials to filtered blood to be excreted
• substances added : Potassium ions, hydrogen ions, creatinine, urea, drugs (penicillin) 
• tubular secretion can be either passive or active
• two main effects of tubular secretion : 

  • Maintains blood pH - removes excess hydrogen and ammonium ions from acid-producing foods that lower pH
  • Maintains urine pH - hydrogen and ammonium ions makes urine slightly acidic
• Only two cells for filtrate to pass through - capillary wall and capsule wall 
• Large volume of blood passes through each kidney - continual flow maintains concentration gradient
• Each kidney has over a million nephrons - larger surface area for reabsorption and secretion 
• Efferent arteriole has smaller diameter - raising blood pressure so more fluid is filtered out of blood
• nephron is convoluted - increasing surface area for reabsorption and secretion
• substances not reabsorbed is drain into the collecting duct and into the renal pelvis. urine goes down ureter, being pushed by waves of muscle contractions into the bladder. the urethra caries the urine from the bladder to the exterior of the body
• renal corpuscle : filtration of blood from capillaries of glomerulus

  formation of filtrate in glomerular capsule
• proximal convoluted tubule and loop of henle : passive reabsorption of potassium, chloride and bicarbonate ions

  active reabsorption of glucose and sodium

  passive reabsorption of water by osmosis
• distal convoluted tubule : active reabsorption of sodium ions

  active reabsorption of water, depending on the body's water needs

  secretion of hydrogen and potassium ions, creatinine and certain drugs such as penicillin
• collecting duct : active reabsorption of water, depending on the body's water needs