Ultrafiltration

• • Occurs in the bowman’s capsule 
  • Small molecules (including amino acids, water, glucose, irea and inorganic ions) are filtered out of the blood capillaries of the glomerular filtrate 
• ultrafiltration diagram

  
• Ultrafiltration process


  1. Arterioles branch off renal artery

  2. Form glomerulus in bowman’s capsule

  3. Capillaries narrow increasing pressure

  4. Smaller molecules forced into bowman’s capsule

  5. Form filtrate
• Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (glomerulus) sitting inside the cup shaped bowman’s capsule
• Capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them
• The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by two cell layers, with a basement membrane in between them
• First cell layer


  • Endothelium of the capillary
  • Perforated by thousands of tiny membrane-lined circular holes
• Next layer


  • Basement membrane
  • Made up of a network of collagen and glycoproteins
• Second cell layer


  • Epithelium of the bowman’s capsule
  • Epithelial cells have many tiny finger-like projections known as podocytes
• As blood passes through the glomerular capillaries, the holes in the capillary endothelial cells and the gaps between the podocytes allows substances dissolved in the blood plasma to pass into the bowman’s capsule
• Fluid that filters through from the blood into bowman’s capsule

  Glomerular filtrate
• Main substances that pass out of capillaries and from the glomerular filtrate

  • Amino acids
  • Water
  • Glucose
  • Urea
  • Inorganic ions (NA+, K+ and Cl-)
• Ultrafiltration diagram

  
• How does ultrafiltration occur 

  • Occurs due to differences in water potential between plasma in the glomerular capillaries and the filtrate in the bowman’s capsule 
  • Water moves down water pot gradient, from a region of higher to lower, water pot is increased by high pressure and decreased by Prescence of solutes 
• factors on WP on ultrafiltration

  
• Overall effect of pressure gradient outweighs the effect of solute gradient 

  • Therefore, water potential of blood plasma in the glomerulus is higher than the water potential of the filtrate from the Bowman’s capsule 
  • Blood flows through the glomerulus, there is an overall movement of water down gradient from blood to bowman’s capsule 
• water movement in ultrafiltration