Kidneys

• Nitrogenous waste

  Ammonia:

  • Very toxic, very soluble
  • aquatic environment
  • since aquatic animals live in water, ammonia can be excreted directly into the water and dissolve making it less toxic - they don't store their nitrogenous waste

  Urea:

  • Less toxic, not as soluble
  • can be diluted and stored
  • less water is needed than if it were ammonia therefore reduces water loss to the environment (dry/land)

  Uric acid:

  • much less toxic and much less soluble
  • can be diluted and stored with less water therefore takes up less space and mass.
  • This can help birds fly with the waste stored in their body
• Ultrafiltration

  High hydrostatic pressure:

  • Contractions of the left ventricle
  • Efferent arteriole has smaller lumen the afferent arteriole - forces fluid out of capillary wall

  1. fenestrations in endothelium/capillary wall
  2. Basement membrane - made of collagen, filters anything below 69000 kDa
  3. Podocytes lining the bowman's capsule - filtrate goes through the gaps between the foot processes
• Selective reabsorption by co-transport

  1. Sodium ions are actively transported from the cytoplasm of the PCT cells into the tissue fluid.
  2. This lowers the concentration of Na+ in the cytoplasm.
  3. The concentration of Na+ in the filtrate is higher than the cytoplasm so Na+ ions move into the PCT cells by facilitated diffusion.
  4. Glucose is co-transport with the Na+ ions.
  5. This increases the concentration of glucose in the cytoplasm of the PCT cells.
  6. Glucose passes from the cytoplasm of the PCT cells into the tissue fluid by facilitated diffusion.
• Kidney anatomy

  ,

  A) Renal artery

  B) Renal vein

  C) Ureter

  D) Cortex

  E) Renal Pelvis

  F) Medulla

  
• Adaptions of proximal convoluted tubule for selective reabsorption

  • The cells lining the proximal convoluted tubule are a type of epithelium
  • Microvilli - increase the surface area for reabsorption.
  • Large numbers of mitochondria to produce the ATP needed for active transport.
  • Basal channels - the concentration of molecules increases in these channels, increasing the concentration gradient.
  • Capillaries in close contact with PCT - short diffusion distance
  • Blood flow in the capillaries removes substances that pass in from the filtrate so maintains the concentration gradient.
• How does the loop of Henle reduce water loss (ascending limb)

  1. The walls of the ascending limb are impermeable to water, while the descending limb is permeable to water.
  2. So, as filtrate flows up the ascending limb, Na+ and Cl- ions pass out of the nephron into the tissue fluid by facilitated diffusion and active transport
  3. The loss of ions from the filtrate means that it is hypotonic to the plasma by the time the filtrate passes into the distal convoluted tubule.
  4. The movement of ions into the tissue fluid in the medulla lowers the low water potential so that it is lower than the filtrate.
• How does the loop of Henle help reduce water loss (descending limb)

  1. The descending limb of the loop of Henle is permeable to water but impermeable to ions.
  2. So water leaves the filtrate of the descending limb by osmosis into the vasa recta where it is removed.
  3. This maintains the lower water potential in the tissues of the medulla.
  4. Since water is being lost from the descending limb, the filtrate becomes increasingly concentrated, at the tip of the loop it is hypertonic to blood plasma.
  5. Water is also reabsorbed in the collecting duct due to the water potential gradient in the medulla.
• Acute Kidney Failure

  Kidney failure develops within hours or days, includes chance of kidney function recovery.

  Possible causes:

  • traumatic - e.g. post surgical
  • acute intoxications
  • Part of multi-organ failure
• Chronic kidney failure

  Kidney failure develops over years, irreversible at the end

  Possible causes:

  • High blood pressure
  • Diabetes
  • bacterial inflammation of the kidney
  • Cystic kidneys
  • various autoimmune diseases
• Osmoregulation and ADH affect on collecting duct

  The control of the water content and solute composition of body fluids

  ADH function:

  • osmoreceptors in the hypothalamus detect a change in water levels
  • posterior pituitary gland secrets antidiuretic hormone
  • ADH makes the plasma membranes of the distal convoluted tubule cells and collecting duct cells more permeable to water
  • This is because it causes aquaporins to become incorporated in the plasma membranes.