Role of the nephron in osmoregulation

• Useful substances such as water and glucose are reabsorbed back into the blood
• What is the primary location of reabsorption in the nephron?

  Proximal convoluted tubule
• What is actively transported out of the epithelial cells in the proximal convoluted tubule?

  Three sodium ions
• What effect does the active transport of sodium ions have on their concentration inside the cells?

  It lowers the concentration of sodium ions
• How does the concentration gradient between glomerular filtrate and epithelial cells affect sodium ion movement?

  Sodium ions diffuse down their concentration gradient
• What type of transport do sodium ions use to enter the epithelial cells?

  Facilitated diffusion through co-transport proteins
• What happens to soluble substances after they enter the epithelial cells?

  They diffuse into the capillaries
• What substances are co-transported with sodium ions into the epithelial cells?

  Glucose, amino acids, chloride ions, vitamins
• How does the diffusion of soluble substances affect water movement?

  It lowers water potential, causing water to move in
• What process allows water to move into the epithelial cells?

  Osmosis
• How do lipid-soluble substances move across the cell-surface membranes?

  By simple diffusion
• What is the overall process of reabsorption in the proximal convoluted tubule?

  • Active transport of sodium ions out of cells
  • Establishment of concentration gradient
  • Diffusion of sodium ions via co-transport proteins
  • Co-transport of glucose, amino acids, etc.
  • Diffusion of soluble substances into capillaries
  • Water movement via osmosis
  • Simple diffusion of lipid-soluble substances
• What structure does the Loop of Henle extend into?

  Medulla of the kidney
• What is the primary function of the Loop of Henle?

  Concentrating urine by absorbing water
• What are the two main parts of the Loop of Henle?

  Ascending limb and descending limb
• How do the walls of the ascending limb compare to the descending limb?

  Ascending limb walls are thicker
• What is the significance of fluid flowing in opposite directions in the Loop of Henle?

  It maintains a concentration gradient
• What effect does a longer Loop of Henle have on water reabsorption?

  It results in more water reabsorption
• What are the characteristics of the descending limb?

  Narrow, thin walls, permeable to water
• How does the ascending limb differ from the descending limb in terms of permeability?

  Ascending limb is impermeable to water
• What is the role of the two limbs of the Loop of Henle?

  They work as a counter-current multiplier
• What happens to the width of the ascending limb as it progresses?

  It starts narrow but then widens
• What ions are the ascending limb permeable to?

  Mineral ions
• Why is the descending limb highly permeable to water?

  Due to its thin walls
• How do the limbs of the Loop of Henle contribute to urine concentration?

  By creating a counter-current flow
• Distal convoluted tubule

  • make final adjustments to water and salts to maintain blood pH
  • cells have microvilli and many mitochondria
  • reabsorbs material via active transport
  • permeability can be affected by various hormones
• Collecting duct

  • found in the medulla
  • connects the nephron with the ureter
  • water moves out by osmosis due to concentration gradient
  • water in the collecting duct leaves it via channel proteins-> aquaporins
  • ADH can alter these to control water loss
• Function of Loop of Henle

  1. Sodium ions actively transported out of the ascending limb
  2. This creates a low water potential in the interstitial region
  3. The walls of the descending limb are very permeable so water passes out by osmosis into the interstitial region
  4. Filtrate progressively loses water, lowering its water potential
  5. At the base of the ascending limb, sodium ions diffuse out of the filtrate then are actively pumped out after, developing a progressively higher water potential