Topic 6 - The Kidney and Homeostasis

• Homeostasis

  Maintaining a constant internal environment
• Things that must be controlled in the body 


  • Body temperature and blood glucose levels
  • Water content of cells and the blood
  • Removal of waste chemicals from the body
• Function of the kidneys

  • Maintain blood water levels
  • Remove waste products such as urea from the blood
  • Removes excess salts from the blood
• Excretion

  Removal of waste products
• The excretory system

  Cleaning the blood -

  • Blood from aorta moves into the renal artery and into the kidney
  • The kidney filters the blood and removes some water, urea, and excess salts
  • Cleaned blood returns to the heart in the vena cava
  • The filtrate called urine leaves the kidneys in the ureters and is stored in the bladder
  • Urine is passed out of the body through urethra
• Detecting disease

  • Red blood cells in urine indicate kidney damage or disease
  • Glucose in urine can indicate diabetes
• Inside the kidney

  Diagram -

  
• Urine is a liquid which consists of salts and urea dissolved in water
• The Nephron (steps 1-5)


  1. Blood entering capillary knot via renal artery contains glucose, protein, urea, salt and water
  2. Ultrafiltration occurs where salt, glucose, urea, water and amino acids are forced into the Bowman's capsule under high pressure due to the capillary knot becoming narrower
  3. These substances are able to diffuse across the membrane as they are small enough
  4. Blood leaving capillary knot contains protein as it is too big of a molecule and hence cannot diffuse into the Bowman's capsule
  5. Useful substances such as urea, glucose, salts, and some water move back into your blood
• The Nephron (steps 6-10)

  1. More water diffuses back into your blood
  2. Blood leaving renal vein contains less urea than blood in renal artery
  3. Liquid goes into the collecting duct and is now called urine
  4. Collecting duct is under the control of a hormone ADH
  5. ADH controls how much water can move back into the blood by osmosis
• The Nephron

  Diagram -

  
• Advantages and disadvantages of kidney failure treatments

  Dialysis -

  Advantage:

  • Immediately available

  Disadvantages:

  • Diet restricted
  • Long time spent in hospital
  • Dialysis machine needs to be used every week

  Transplant -

  Advantage:

  • Can last 12-15 years with minimal medical intervention

  Disadvantages:

  • Immunosuppresant drugs must be taken to avoid rejection
  • Donor with similar tissue type must be found
• Ethical issues of kidney transplants

  • Kidney donor schemes
  • Living donors
  • Xenotransplants
  • Buying and selling of organs
  • Availability of dialysis machines
• Dialysis

  Diagram -

  
• Dialysis key points

  • Dialysis fluid contains equal concentration of glucose and salts that shouldn't be removed from blood
  • Contains no urea so that the urea will diffuse from a high concentration in the blood out into the dialysis fluid which then it is disposed of
  • Dialysis fluid and blood will flow counter current to eachother to maintain a concentration gradient for diffusion of urea across the whole membrane
  • Blood is removed from the body and flows through tubing made from a selectively permeable membrane
• Control of water in the body by ADH

  Low water content

  • Hypothalamus detects low water content
  • More of the anti-diuretic hormone is released into the blood and is secreted by the pituitary gland
  • More ADH is sent to the collecting duct of the kidney
  • Collecting duct becomes more permeable to water
  • Water in duct is reabsorbed into blood by osmosis
  • Small volume of concentrated urine is released
• Control of water in the blood by ADH

  High water content

  • Hypothalamus detects high water content
  • Less of the anti-diuretic hormone is released into the blood from the pituitary gland
  • Blood takes less ADH to the collecting duct of the kidney
  • Collecting duct becomes less permeable to water
  • Water is retained in the collecting duct
  • Large volume of dilute urine is released