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Renal Physiology 2, The vertical osmotic gradient provides the mechanism…
Renal Physiology 2
Understand the role of the loop of Henle and how that regulates urine concentration to meet the body’s water requirements.
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Step 1 Glomerulus
Filtrate produced at renal corpuscle has the same composition as blood plasma (minus plasma proteins)
Step 2 Proximal Convoluted Tubule (PCT)
- Active removal of ions and organic substrates.
- Produces osmotic water flow out of tubular fluid
- Reduces volume of filtrate
Step 3 Descending Limb of Henle Loop
Water moves into peritubular fluids, leaving highly concentrated tubular fluid. Reduction in volume occurs by performing water reabsorption.
Step 4 Thick Ascending Limb of Henle Loop
Tubular cells actively transport Na+ and Cl– out of tubule.
Step 5 Distal Convoluted Tubule (DCT) and Collecting Ducts
Osmotic concentration is adjusted through active transport (reabsorption or secretion).
- Final adjustments in volume and osmotic concentration of tubular fluid.
- Exposure to ADH/Vasopressin determines final urine concentration.
Step 6 Vasa Recta
Absorbs solutes and water reabsorbed by nephron loop and the ducts. Maintains concentration gradient of medulla.
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Describe how specific segments of the renal tubule and collecting duct reabsorb water and solutes and secretes solutes into urine.
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- The vertical osmotic gradient provides the mechanism for producing hypertonic urine, by allowing the nephrons to reabsorb water along the entire length of the tubules. The medullary vertical osmotic gradient is established by means of countercurrent multiplication.
- The descending limb of the nephron tubules: (1) is highly permeable to water, and (2) does not reabsorb Na+.
- The ascending limb: (1) actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid, and (2) is completely water impermeable, so salt leaves the tubular fluid without water osmotically following.
- As one moves from the cortex deeper into the medulla, the osmolarity of the interstitial fluid progressively increases to a maximum osmolarity of 1,200 mOsm/L. This is made possible because the ascending and descending limbs are physically close together.
Essentially, system of water/ion exchange as filtrate travels along loop of Henle and DCT.
- Counter current because the blood in the vasa recta moves in different direction of the filtrate
- Interexchange of water and ions as a result
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