Role of kidney in homeostasis

• Excretory System


  Removes urea, a waste product of metabolism, and regulates the water content of the blood
• Kidney


  • Medulla
  • Ureter
  • Cortex
  • Nephron
  • Renal pelvis
  • Diaphragm
  • Aorta
  • Vena cava
  • Renal artery
  • Renal vein
  • Ureter
  • Bladder
  • Muscle
  • Urethra
• Cleaning the blood


  1. Blood from the aorta moves into the renal artery and into the kidney

  2. The kidney filters the blood and removes some water, urea and excess salts

  3. Cleaned blood returns to the heart in the vena cava

  4. The filtrate called urine leaves the kidneys in the ureters and is stored in the bladder

  5. Urine is passed out of the body through the urethra
• There are about a million nephrons in each kidney. They filter the blood.
• Detecting disease


  • Red blood cells in urine indicates kidney damage or disease
  • Glucose in the urine can indicate diabetes
• Kidney Failure Treatments


  • Dialysis
  • Transplant
• Dialysis


  • Immediately available
  • A long time spent in hospital attached to a dialysis machine every week and diet is restricted
• Transplant


  • Can last 12-15 years with minimal medical intervention
  • Immunosuppressant drugs must be taken to avoid rejection
  • A donor must be found and must have a similar tissue type to the recipient, so a close family living donor is preferable
• How dialysis works


  1. Blood is removed from the body and flows through tubing made from a selectively permeable membrane

  2. Dialysis fluid contains equal concentration of glucose and salts that should not be removed from the blood. It contains no urea and so urea will diffuse from a high concentration in the blood out into the dialysis fluid which is then disposed of

  3. Dialysis fluid and blood will flow counter current to each other to maintain a concentration gradient for diffusion of urea across the whole membrane
• Nephron


  • Afferent arteriole brings blood to the nephron
  • Efferent arteriole, narrower than the afferent, creating pressure in the capillary knot
  • Capillary knot
  • The solution remaining in the tubule, urine, collects in the collecting ducts and this leads to the ureter
  • The collecting duct is under the control of a hormone ADH, this controls how much water can move back into the blood by osmosis
  • Bowman's capsule- filtration under pressure occurs here. Glucose, urea, salts and water are forced out of the blood and into the capsule
  • In the tubule all the glucose and some of the water and salts are reabsorbed into the blood capillaries that wrap around it
• Control of water in the blood by Antidiuretic hormone (ADH)

  1. The brain detects the water content of the blood is too low, more ADH is released into the blood from the pituitary gland, blood takes more ADH to the collecting duct of the kidney, the collecting duct becomes more permeable to water, water in the collecting duct is reabsorbed into the blood by osmosis, a small volume of concentrated urine is released

  2. The brain detects the water content of the blood is too high, less ADH is released into the blood from the pituitary gland, blood takes less ADH to the collecting duct of the kidney, the collecting duct becomes less permeable to water, water is retained in the collecting duct, a large volume of dilute urine is released
• This process operates by negative feedback.