2. Renal Physiology 4

Physiology 210 with E.sanders at University of Alberta

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By: Rachel Fung
Created: 2012-02-09
Size: 34 flashcards
Views: 14

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Water regulation on land-animals

Wia = Wd + Wf + Wa - We - Ws

Wia = animal's internal water

Wd = drinking

Wf = food

Wa = absorbed by air

We = evaporation

Ws = secretion/excretion

Sources of water gain

Oxidation of food

Liquid ingested through food

Sources of water loss

Skin , respiratory airways (insensible or unconscious water loss)

Sweat

GI tract (not much unless diarrhea), urinary tract, menstrual flow

How much water is reabsorbed in proximal tubules?

67%

What is the driving force for water reabsorption?

Osmotic gradient set up by sodium - dependent on sodium reabsorption

What hormones regulate water reabsorption in the collecting duct

Vasopressin or antidiuretic hormone (ADH)

Aquaporins

Water channels that are always open in proximal tubule cells and regulated by vasopressin in collecting ducts (regulate how much water needs to be reabsorbed)

Which aquaporins are under physiological control?

Those in the collecting duct

Sodium and water reabsorption

Sodium moves down its gradient into epithelial cell and is actively pumped out - water follows

Concentrated urine

Kidneys save water - hyperosmotic urine

Counter-current mechanism

1. Anatomy and opposing fluid flow through Loop of Henle is in counter direction

2. Reabsorption of NaCl in ascending limb

3. Impermeability of ascending limb to water

4. Trapping of urea in medulla

5. Hairpin loops of vasa recta maintains hyperosmotic interstitium in medulla

6. ADH affecting water reabsorption in collecting duct

Ascending limb permeability

Impermeable to water

Urea

Permeant solute - active solute that can go through membranes of cell

Water reabsorption in Loop of Henle

Reabsorbed through thin descending portion (thin diameter)

Salt reabsorption in Loop of Henle

Reabsorbed through thick ascending portion (thick diameter)

How is urine made hyperosmotic to blood plasma?

Countercurrent multiplication in loop of Henle - single tubule with two sides closely juxtaposed and fluid streams in opposite direction - different transport capabilities on each side of tubule

How is hyperosmolar interstitial fluid generated in renal medulla?

In the loop of Henle the descending limb is isoosmotic, but water leaving raises osmolarity

Ascending limb has active transport of NaCl out and is impermeable to water (hypoosmotic) - interstitial fluid is hyperosmotic (400 mOsm) compared to ascending limb fluid (200 mOsm)

Counter-current multiplier exchange

Multiplication of the gradient down the length of the loop of Henle (always 200 mOsm difference between ascending and descending limbs - greatest at bottom of loop)

Beaver loop of Henle versus humans

Much smaller

Kangaroo rat loop of Henle versus humans

Much larger - goes to 4000 mOsm at the bottom

Fluid concentration in portions of loop of Henle

Becomes concentration in descending limb

Diluted as it climbs up ascending limb and enters distal tubule - very dilute (100mOsm)

How does ADH affect concentration of fluid in distal tubule?

Works on collecting duct - fluid inside becomes isoosmotic with interstitial space

Also stimulates more absorption of water from cortical collecting duct

What is the importance of the high osmolarity gradient established in the interstitial space?

Helps water permeate out of the medullary collecting tubule

Fine tuning entering collecting duct

Water is reabsorbed, some salt is still being reabsorbed

How does vasa recta help counter-current exchange?

1. Blood flow in medulla is low (less than 5% total renal blood flow, prevents solute loss)

2. Blood flow in vasa recta serve as counter-current exchangers (maintains Na and Cl gradient so that its not washed away)

3. Capillaries are freely permeable to ions, urea, and water which move in and out following gradients

Vasa recta effect on medullary hyperosmolarity

Does not create medullary hyperosmolarity, but prevents it from being dissipated (maintains it)

Counter-current exchange in vasa recta

NaCl moves out of ascending limb to enter descending limb

Water diffuses out of the descending limb into the ascending limb

Reinforces counter-current in renal tubules (increase sodium and urea concentration in renal medulla interstitial space)

How much urea is absorbed in proximal tubule?

50%

How much urea is reabsorbed back in the loop of Henle?

50%

How much urea enters distal tubule?

100%

How much urea is reabsorbed from cortical collecting duct?

30%

How much urea is recycled back into tubule?

50%

How does urea aid in maintaining high medulla osmolarity?

Minimal uptake by vasa recta and recycling in interstitial space helps in maintaining high osmolarity in medualla

About this deck

By: Rachel Fung
Created: 2012-02-09
Size: 34 flashcards
Views: 14

About StudyBlue

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy