Structure and function of the nephron

• What are nephrons and where are they found?

  Long tubules in the medulla of the kidneys which are surrounded by capillaries.
• Approximately how many nephrons are in each kidney?

  1 Million
• What is the function of the nephron?

  Create urine by filtering the blood to remove waste, then selectively absorb useful substances back into the blood.
• What does urine contain?

  Water, dissolved ions(salts), urea, other small substances e.g hormones, excess vitamins.
• What does urine NOT contain?

  Proteins and blood cells

  Glucose
• Why does urine not contain proteins or blood cells?

  They're to large to be filtered out.
• Why does urine not contain glucose?

  Glucose is reabsorbed back into blood in the proximal convulated tube at the selective reabsorption stage.
• Draw and label the nephron to include:

  Renal capsule

  Proximal convulated tubule(PCT)

  Descending loop of henle

  Ascending loop of henle

  Distal convulated tubule(DCT)

  Collecting duct
• What are the 4 key steps in creating urine in the nephron?

  Ultrafiltration

  Selective reabsorption

  Maintaining sodium ion gradient

  Reabsorption of water
• Where does ultrafiltration occur?

  Renal capsule
• How does ultrafiltration occur?

  Include words: afferent ateriole, capillaries, hydrostatic pressure, glomerulus filtrate.

  Blood enters through the afferent ateriole.

  This splits into lots of smaller capillaries, which causes a high hydrostatic pressure of the blood.

  Water and small molecules, such as glucose and mineral ions are forced out of the capillaries and form the glomerulus filtrate.
• What are the 3 ways these small molecules are filtered out?

  Through small gaps in the capillary endothelium.

  Through the basement membrane.

  Through gaps between podocytes on the membrane.
• What happens to large proteins and blood cells?

  They remain in the blood and leave via the efferent ateriole.
• Where does selective reabsorption occur?

  In the proximal convulated tubule(PCT)
• What happens during selective absorption?

  Reabsorption of glucose.
• How id glucose reabsorbed into the blood?

  1. The concentration of sodim ions in the PCT lining cells is decreased as sodium ions are actively transported out of them into the blood in the capillaries.
  2. Due to the conc gradient, sodium ions diffuse down the gradient from the PCT lumen into the cells lining the PCT. This is cotransport, as the proteins which transport the sodium ions in carry glucose with it.
  3. The glucose can then diffuse from the PCT epithelial cell into the blood stream.
• What are two features of the proximal convulated tubule which make it easier for glucose reabsorption?

  Has walls made of microvilli epithelial cells to provide a large surface area for transporting glucose.

  PCT has lots of mitochondria to provide energy in form of ATP for active transport.
• How is a sodium ion gradient maintained by the loop of henle?

  Sodium ions are actively transported out of the ascending loop of henle into the medulla.
• What does this accumulation of sodium ions in the medulla cause?

  Lowered water potential in the medulla
• What happens as a result of this lowered water potential?

  Water diffuses out of the descending loop of henle by osmosis into the interstitial space and then to the blood in the capillaries.
• What does the loop of henle have in the walls to provide energy for the active transport of sodium ions?

  Mitochondria which provides energy in the form of ATP.
• What is the filtrate like when it reaches the distal convulated tubule?

  Very dilute
• What is the medulla like near the distal convulated tubule?

  Very concentrated
• What happens as a result of this?

  Even more water diffuses out of the DCT and collecting duct, what remains is transported to form urine.