Kidney Reabsorption

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Kidney Reabsorption

• DP Biology - February 2009

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Selective Reabsorption

• Selective reabsorption is the transport of
• molecules from the filtrate back to the blood
• via diffusion, osmosis, or active transport.

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Selective Reabsorption

• Selective reabsorption is the transport of
• molecules from the filtrate back to the blood
• via diffusion, osmosis, or active transport.
• The proximal convoluted tubule is the site of the
• reabsorption of most glucose and minerals,
• some salts, and some water.

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Proximal Convoluted Tubule

• Factors that facilitate reabsorption
• Can you guess?

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Proximal Convoluted Tubule

• Factors that facilitate reabsorption
• Microvilli increase SA

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Proximal Convoluted Tubule

• Factors that facilitate reabsorption
• Microvilli increase SA
• Membrane pumps
• actively transport solutes

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Proximal Convoluted Tubule

• Factors that facilitate reabsorption
• Microvilli increase SA
• Membrane pumps
• actively transport solutes
• Mitochondria supply
• energy

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Proximal Convoluted Tubule

• Factors that facilitate reabsorption
• Microvilli increase SA
• Membrane pumps
• actively transport solutes
• Mitochondria supply
• energy
• Active transport of
• solutes makes solute
• higher outside tubule,
• causing passive diffusion
• reabsorption of water.

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Proximal Convoluted Tubule
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Loop of Henle

• Responsible for most of the water reabsorption
  and
• some Na reabsorption.

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Loop of Henle

• Responsible for most of the water reabsorption
  and
• some Na reabsorption.
• Creates the increasing
• solute in medulla

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Loop of Henle

• Responsible for most of the water reabsorption
  and
• some Na reabsorption.
• Creates the increasing
• solute in medulla
• Length and number of Loops
• of Henle correlate with aridity
• of environment in mammals

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Loop of Henle

• Responsible for most of the water reabsorption
  and
• some Na reabsorption.
• Creates the increasing
• solute in medulla
• Length and number of Loops
• of Henle correlate with aridity
• of environment in mammals
• Uses a countercurrent
• multiplier mechanism

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Loop of Henle

• Descending loop
• Permeable to water /
• impermeable to Na
• Water is reabsorbed into
• vasa recta by osmosis due
• to increasing solute

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Loop of Henle

• Ascending loop
• Impermeable to water /
• Permeable to Na
• Na is passively (lower loop)
• and actively (upper loop)
• transported out of renal
• tubule

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Loop of Henle

• Ascending loop
• Impermeable to water /
• Permeable to Na
• Na is passively (lower loop)
• and actively (upper loop)
• transported out of renal
• tubule
• Na creates high solute in
• medulla
• Some Na reabsorbed into
• vasa recta

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Loop of Henle

• Countercurrent multiplier
• Flow of fluids in opposite
• directions increases
• concentration gradient to
• maximize diffusion.

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Loop of Henle

• Countercurrent multiplier
• Flow of fluids in opposite
• directions increases
• concentration gradient to
• maximize diffusion.
• CCM in both Loop of Henle
• and vasa recta
• Also used by blood vessels
• in extremities to reduce
• heat loss

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Distal Convoluted Tubule

• FYI only
• regulates K, Ca2, Na, pH
• endocrine control

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Osmoregulation in Collecting Duct

• If solute in blood is high
• ADH secreted by pituitary

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Osmoregulation in Collecting Duct

• If solute in blood is high
• ADH secreted by pituitary
• ADH open aquaporins
• (water channels) collecting
• duct, making collecting duct
• permeable to water

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Osmoregulation in Collecting Duct

• If solute in blood is high
• ADH secreted by pituitary
• ADH open aquaporins
• (water channels) collecting
• duct, making collecting duct
• permeable to water
• Water diffuses out by
• osmosis due to high
• solute in medulla

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Osmoregulation in Collecting Duct

• If solute in blood is low
• ADH is NOT secreted
• Aquaporins
• (water channels) are closed,
• making collecting duct
• mostly impermeable to
• water
• Little diffusion of water

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Osmoregulation in Collecting Duct
WITH ADH WITHOUT ADH
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Comparison of Fluid Composition
Can you explain these values? For IB, you need
to know relative concentrations, not actual values
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Diabetes
A diagnostic sign of diabetes is the presence of
glucose in the urine. Why does untreated diabetes
cause glucose to be present in urine?
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Diabetes

• A diagnostic sign of diabetes is the presence of
  glucose in the urine.
• Why does untreated diabetes cause glucose to be
  present in urine?
• Lack of insulin causes high blood glucose
• High glucose in blood leads to high glucose
  in filtrate
• Membrane proteins in proximal convoluted tubule
  transport
• glucose from filtrate to blood but these
  proteins have a
• limited capacity
• Over time, high blood glucose causes
  capillary damage