Homeostasis & Kidney

• Homeostatic describes the mechanisms by which a constant internal environment is achieved. The stability is known as a dynamic equilibrium in a which a continuous change occurs.
• Positive Feedback is when a high level of something triggers the body to increase it even further. This is rare and can lead to unstable conditions.
• Name 2 types of feedback

  • Positive
  • Negative
• Negative Feedback is when conditions differ from the set point which the body then returns it back to the setpoint/ optimum. It is a continuous cycle.
• Kidneys are supplied with blood at arterial pressure by renal arteries which branch off from the abdominal aorta.

  Blood leaves through the renal vein and into the inferior vena cava.
• What part of the kidney acts as a filter?

  Nephron
• Ultrafiltration is filtration under pressure which separates small molecules from the blood plasma.
• What does ultrafiltration form?

  Glomerular filtrate
• What does glomerular filtrate contain?

  • Water
  • Salts
  • Glucose
  • Urea
• What type of molecules pass out of the capillaries in the glomerulus?

  • Small molecules which have a relative molecular mass of <30000
• What type of molecules remain inside the capillaries?

  • Large molecules which have a relative molecular mass of >68000
• What molecules remain in the capillaries?

  • Proteins
  • Erythrocytes
• How is high hydrostatic pressure maintained in the Bowman's capsule?

  • Contractions from the heart
  • Afferent arteriole has a wider lumen than the efferent arteriole
  • Capillaries in the glomerulus have a large surface area
• Name the 3 structures which make up the Bowman's capsule

  • Capillary walls
  • Basement membrane
  • Layer of endothelium containing podocytes
• What are the pores in capillaries called?

  Fenestrae
• The basement membrane acts as a molecular filters and is an extra-cellular layer as it is made of collagen
• The wall of the Bowman's capsule contains podocytes which have pedicels that extend and wrap around the capillaries.
• Acute kidney failure develops withing hours or days and there is a chance of recovery. It can be caused by trauma to the kidney, intoxication, part of multi organ failure or due to an infection.
• Chronic kidney failure develops over years and is irreversible. It can be caused by high blood pressure, diabetes, inflammation of the kidney, cystic kidneys or an autoimmune disease.
• Treatments of Kidney failure

  1. Controlling protein intake
  2. Controlling blood pressure
  3. Controlling potassium and calcium levels
  4. Antibiotics
  5. Ultrasound and key hole surgery
  6. Dialysis
  7. Kidney transplant
• How does not controlling protein intake reduce kidney function?

  • High protein levels increase urea levels. This can be converted to uric acid which can crystalise to form kidney stones. Kidney stones can damage the tissue causing bleeding. Bleeding can cause small proteins to be excreted, low blood protein causing accumulation of tissue fluid and lower blood pressure.
• How does not controlling blood pressure reduce kidney function?

  • High blood pressure can cause excessive filtration in the glomerulus leading to a loss of nutrients. This can damage the glomerulus allowing proteins to be lost in the urine.
• How does not controlling potassium intake reduce kidney function?

  • Potassium is needed for transmission of nerve impulses and is actively transported into cells. If the concentration of potassium is too high or low, this will affect nerve transmission.
• How does not controlling calcium intake reduce kidney function?

  • Lack of calcium or loss of calcium can lead to brittle bones
  • Too much calcium can cause hormonal production problems and deposition of calcium in issues causing pain eg, retina, muscles and joints.
• Kidney function affected by infections can often be treated by antibiotics
• Ultrasound can be used to break up kidney stones and key hole surgery can be used to remove the fragments.
• 2 types of kidney dialysis

  • Haemodialysis
  • Peritoneal Dialysis
• Haemodialysis uses a machine to remove waste products from the blood.

  It contains a artificial membrane and a fluid called dialysate which is constantly replaced so equilibrium is never reached.

  Dialysate also moved in opposite direction to blood to maintain a concentration gradient
• Peritoneal dialysis which uses membranes in the body to remove waste products.

  Dialysate is pumped into the membrane but is not refreshed so equilibrium is reached.
• Advantages of Haemodialysis

  • Effective removal of waste
  • No equipment to store at home
  • Treatment only occurs 3x a week
• Disadvantages of Haemodialysis

  • Requires vascular access using a large needle
  • Must travel to the hospital
  • Cramping
  • Risk of bacteraemia due to a catheter
• Advantages of Peritoneal dialysis

  • Less risk of cramp
  • No needles
  • Visits to the hospital are only 2x a month
• Disadvantages of Peritoneal dialysis

  • External catheter
  • Risk of peritonitis
  • Risk of weight gain
  • Store equipment
• Kidney transplants can be used when there is complete kidney failure where a kidney from a donor is used. Donors can be dead or alive.
• Advantages of a living donor

  • Shorter waiting time
  • Less risk of rejection
  • Lasts longer
• Disadvantages of a living donor

  • Donor is left with one kidney
  • Complications to both donor and patient during surgery
• Advantages of a deceased donor

  • No need for dialysis
  • Donor is not harmed during surgery
• Disadvantages of a deceased donor

  • Longer waiting times
  • Increase risk of rejection
  • Patient needs to take drugs for the rest of their life
  • Increased risk of infection
  • Only lasts 10-15 years
• Difference in blood group and the antigens on the surface of the cells of the kidney can cause an immune response leading to the donor kidney being attacked and destroyed by the patients immune system.
• A person who has already had a transplant is said to be sensitised which means they are more likely to produce antibodies against the the antigens on the donor organ which increases the chance of rejection.