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URINE FORMATION IN THE NEPHRON

URINE FORMATION IN THE NEPHRON. 9.2. Formation of Urine. 3 main steps: -Filtration, -Reabsorption, -Secretion 1. Filtration Dissolved solutes pass through walls of glomerulus into Bowman’s capsule Plasma proteins, platelets, and blood cells are too large to pass. 2. Reabsorption

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URINE FORMATION IN THE NEPHRON

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  1. URINE FORMATION IN THE NEPHRON 9.2

  2. Formation of Urine • 3 main steps: -Filtration, -Reabsorption, -Secretion 1. Filtration • Dissolved solutes pass through walls of glomerulus into Bowman’s capsule • Plasma proteins, platelets, and blood cells are too large to pass

  3. 2. Reabsorption • 1 mL urine formed / 120 mL fluid filtered  the rest is reabsorbed • Occurs by both active & passive transport • Occurs until the threshold level of a substance is reached  the rest is excreted • Solutes actively transported out of nephron create an osmotic gradient

  4. 3. Secretion • Movement of wastes from blood into nephron • Nitrogen-containing wastes • Histamine • H+ • Drugs (ie: penicillin) • Cells loaded with mitochondria line distal tubule  aid in active transport

  5. 4 PROCESSES IN THE FORMATION OF URINE • Glomerular Filtration • Moves water and solutes from blood plasma into nephron • Creates filtrate • Tubular Reabsorption • Removes useful substances and returns them to blood (eg. sodium) • Tubular Secretion • Moves additional wastes and excess substances from the blood into the filtrate • Water Reabsorption • Removes water from filtrate and returns it to blood

  6. Glomerulus

  7. GLOMERULAR FILTRATION • Factors contributing to filtration: • Permeability of capillaries • Glomerular capillaries have many pores in their walls • Prevent blood cells and proteins from passing through – most other substances can pass • Blood Pressure • 4X greater in glomerulus than in other capillary beds in the body • Provides force for filtration • 180 L / day of filtrate • Very similar to plasma at this point

  8. Proximal Tubule

  9. TUBULAR REABSORBTION: PROXIMAL TUBULE • 65% of filtrate is reabsorbed in the proximal tubule • Involves active and passive transport • Cells of proximal tubule are loaded with mitochondria to aid in transport • Focuses on transporting Na+, glucose • Negative ions follow • Water follows by osmosis

  10. Loop of Henle

  11. TUBULAR REABSORPTION: PROXIMAL TUBULE (CONTINUED) • Loop of Henle • Function: absorb water and ions • Descending loop  very permeable to water, slightly permeable to ions • Medulla is salty  drives movement of water by osmosis • Concentration of Na+ inside Loop of Henle increases • Ascending loop  becomes more permeable to solutes • Thin-walled section: Na+ move along concentration gradients, passing into blood vessels • Thick-walled section: Na+ is now moved out of filtrate by active transport • Helps to maintain salty environment of medulla

  12. Distal Tubule

  13. TUBULAR REABSORPTION: DISTAL TUBULE • Reabsorption of ions decreases the concentration of the filtrate, causing water to be reabsorbed by osmosis • Potassium and hydrogen ions are actively secreted into the distal tubule from the bloodstream • Other substances (eg. Drugs like penicillin) are secreted into the distal tubule

  14. Collecting Duct

  15. REABSORPTION FROM THE COLLECTING DUCT • Passive reabsorption of water in collecting duct • High concentration of ions outside the collecting duct, in the medulla • If blood plasma is too concentrated, permeability to water in the duct will increase • Filtrate is ~4X more concentrated by the time it exits the duct • Filtrate is now called urine • ****TABLE 9.2, Pg 315 – excellent study tool

  16. Summary

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