LEC 26: Nephrons

• Nephron


  Functional unit of the kidney
• Renal Corpuscle


  • Glomerulus
  • Bowman's Capsule
• Glomerulus


  • Tuft of capillaries
  • Blood filtration occurs
• Bowman's Capsule


  • Surrounds glomerulus
  • Collects filtrate
• Renal Tubules


  • Proximal Convoluted Tubule
  • Nephron Loop (Loop of Henle)
  • Distal Convoluted Tubule
  • Collecting Duct
• Proximal Convoluted Tubule


  • Receives filtrate from Bowman's Capsule
  • Reabsorption of water, ions, nutrients
• Nephron Loop (Loop of Henle)


  • Descending limb: permeable to water for water reabsorption
  • Ascending limb: impermeable to water, reabsorbs ions (sodium & chloride)
• Distal Convoluted Tubule


  • Modifies filtrate by selective reabsorption of ions and water
  • Secretes substances into tubular fluid
• Collecting Duct


  • Receives urine from multiple nephrons
  • Adjusts urine concentration by absorbing water with the use of ADH
• Glomerular Capillaries


  Fenestrated = enhance permeability allows the formation of solute-rich but protein-free filtrate
• Glomerular Capsule


  Contains podocytes that facilitate filtrate passage
• Glomerular Filtration


  Movement of fluid (blood plasma) from the glomerulus into the Bowman's Capsule due to higher net filtration pressure in the glomerulus
• Filtration Membrane


  • Allows passage of water and solutes smaller than plasma proteins
  • 3 layers: Fenestrated endothelium, Basement membrane, Slit membrane between Podocyte foot
• Filtration Process

  • Blood plasma squeezed out of the glomerulus into the Bowman's Capsule due to high net filtration inside the glomerulus
  • Hydrostatic pressure in glomerular capillaries pushes water and solutes out of blood across the filtration membrane
• Physical Structures for Glomerular Filtration

  • Glomerular capillaries: fenestrated
  • Glomerular capsule: parietal and visceral layers
  • Podocytes: facilitate filtrate passage
• Forces (Pressures) for Glomerular Filtration


  • Hydrostatic pressure in glomerular capillaries
  • Hydrostatic pressure in the capsular space
  • Colloid osmotic pressure from blood solutes in glomerular capillaries
• Capillary Beds


  • Afferent/efferent arteriole maintains high pressure needed for filtration
  • Peritubular capillaries have low pressure to absorb solutes and water from tubule cells
• Granular cells


  Mechanoreceptors to monitor BP
• Macula Densa Cells


  Chemoreceptors that monitor NaCl of filtrate
• Intercalated cells


  Control pH by secreting/absorbing H+ or bicarbonate
• Hydrostatic pressure in capsular space and colloid osmotic pressure in glomerular capillaries

  Opposes hydrostatic BP inside the glomerulus
• Urine formation


  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion
• Glomerular filtration


  Blood plasma and dissolved substances gets filtered into glomerular capsule
• Tubular reabsorption


  Substances get reabsorbed from renal tubule lumen to peritubular capillaries into the blood
• Tubular secretion


  Wastes get secreted from peritubular capillaries into the renal tubule and then into the urine