Renal - Concentration/Dilution of Urine - Lecture 7 Flashcards
Where is the major site that solute and water are separates?
Loop of Henle
- NOT IN PROXIMAL TUBULE because reabsorption of solute & water is proportional
- kidneys must be able to excrete urine of varying osmolality
The plasma osmolality is dependent upon the state of hydration. True or False?
FALSE
- the plasma osmolality is held at 300 mOsm/kgH20 by regulation of the kidney’s output REGARDLESS of the state of hydration
Maintained by:
- Structure/function of renal tubules
- Hormonal Influences
What is antidiuresis? What is found in high concentrations in the plasma during this state?
What type of urine is produced? (volume, osmolality)
- State of DEHYDRATION (severe water deprivation)
- High concentration of ADH in plasma
- -> increased reabsorption of WATER and UREA
(produce low volume, high concentrated urine = dark amber)
What two things are reabsorbed due to the hormonal affects of ADH?
- Urea
2. Water
How is Water Diuresis different from Antidiuresis?
It is the OPPOSITE condition
- State of OVER - hydration (atypical for land dwellers)
- LOW concentration of ADH in plasma
- -> DECREASED reabsorption of WATER and UREA
(produce HIGH volume, LOW concentrated urine = pale yellow)
Of the following, which is most isotonic with plasma, mild hyper osmotic, and STRONGLY hyper osmotic?
- Inner Medulla
- Cortex
- Outer Medulla
Isotonic with plasma = CORTEX (300 mOsm/kg H20)
Mildy Hyperosmotic = OUTER Medulla (300-480 mOsm/kg)
Strongly Hyperosmotic = INNER MEDULLA (480-1200 mOsm/kg)
What 3 major species contribute to the inner medullary hyperosmolality?
Na + ( 1/4) –> 300
Cl - (1/4 or 25%) –>300
Urea (1/2 or 50%) –> 600
total = 1200
What 3 mechanisms regulate medullary hyperosmolality?
- Countercurrent multiplier - establishes initial osmotic gradient
- Urea cycle - Strengthens osmotic gradient
- Countercurrent EXCHANGER - MAINTAINS osmotic gradient
Where in the nephron does ADH act to increase NaCl absorption and water permeability, and urea? (3)
- NaCl - THICK ASCENDING LIMB
- Water - Distal Tubule & COLLECTING DUCT
- Urea - Medulla of the Collecting Duct (along with water)
What is the affect of the Counter Current Multiplier? Where is this affect established?
Generates a HYPEROSMOTIC gradient
- established in the two limbs of Henle’s loop = Vertical Osmotic Gradient
Describe the flow of water & salt in the following parts of the nephron: (be sure to specify what is most permeable in this area, and which areas are under the control of ADH; include Urea where appropriate)
- Thin Descending Loop
- Thin Ascending Loop
- Thick Ascending Loop
- Distal Tubule
- Upper Collecting Duct
- Lower Collecting Duct
- Thin Descending Loop
- passive water reabsorption (high water perm, low salt perm) –> water moves out leaving NaCl behind - Thin Ascending Loop
- Passive NaCl reabsorption (salt leaves, water left behind)
- high salt perm, low water perm. - Thick Ascending Loop (diluting segment)
- MOST active salt pumping in kidney (Na-K-2Cl)
- water-impermeable tubules become hyposmotic - Distal Tubule
- increased H20 permeability and salt transport (reabsorption) - Upper Collecting Duct
- active salt reabsorption
- passive water reabsorption under ADH control - Lower Collecting Duct
- active salt reabsorption
- passive water AND UREA reabsorption under ADH control
What is referred to as the diluting segment of the nephron?
Thick Ascending limb
- active transport of NaCl via Na-K-2Cl cotransport (out of the tubule)
Describe the steps of the Urea Cycle.
- Where is urea concentrated
- Where does urea move out of? (active or passive) What regulates this step?
- Where is urea picked up and by what blood vessels?
- After this, urea diffuses out into which area?
- Where does it again diffuse into?
- Once urea is recycled through the tubular system, where does it return?
- Urea is concentrated in the UPPER collecting duct (impermeable to urea)
- Urea passively moves out of the LOWER collecting duct into the INNER MEDULLA (regulated by ADH)
- Urea in the INNER MEDULLA is picked up by the ascending VASA RECTA
- Urea in the VASA RECTA diffuses out into the OUTER MEDULLA
- Urea in the outer medulla diffuses into the DESCENDING THIN LOOP of hence
- Urea is recycled back to the LOWER COLLECTING DUCT
Where is urea impermeable? What happens here?
Upper Collecting Duct, concentrates the urea in the tubule
What is the purpose of the urea cycle?(2) What does it NOT do?
- PROTECTS VASA RECTA RBC’s against crenation in a hyper osmotic environment
- sets up a gradient for urea to be excreted in low-volume urine
Does NOT set up osmotic gradient for reabsorption of H2O
How does Urea vary with Urinary flow? (V) When flow is greater than 10 mL/min, what happens to Curea?
Varies Directly
Non-linearly
and Passively with flow
- when flow is greater than 10mL/min, Curea plateaus and Curea estimates GFR
Which part of the nephron sits within the highest fluid osmolality?
Fluid surrounding the BEND OF THE LOOP of henle
What is the purpose of the Countercurrent exchanger? What moves passively across vasa recta capillary walls in the renal medulla?
Maintains the hyper osmotic Gradient
- water, salt, and urea
Describe the movement of salt, water, and urea in the following areas:
- Descending Vasa Recta
- Ascending Vasa Recta
- Descending:
- water moves out of the capillary down osmotic gradient
- salt & urea move INTO the capillary - Ascending:
- water moves INTO the capillary
- salt & urea move OUT of the capillary down the concentration gradient
What is the Net Affect of the Counter Current Exchanger (in vasa recta capillaries)?
- Vasa recta exits medulla with slightly MORE SOLUTES than water
- Vasa recta flow is relatively SLOW (medullary gradient maintained)
- WATER SHUNT - excess water is kept out of deep medulla
- SOLUTE TRAPPING - excess solutes are kept in the lower medulla
When does “Washing Out” of the medullary gradient occur?
When Vasa Recta blood flow increases (gradient is washed out, and urine flow is increased)
- takes several days to be re-established
Which part of the medulla is the water shunt? Which is the Salt trap?
Water shunt = OUTER MEDULLA
Salt trap = INNER MEDULLA
Why is the blood exiting the vasa recta capillaries “Hyperosmotic?”
- Osmolarity of ASCENDING blood leads ahead of the interstitial space
( > 300 mOsm/kg H20)
What are the ABSOLUTE requirements for Renal Medullary Hyperosmolarity?
- Unique renal micro-anatomy (long loops of henle)
- Convections of fluids (blood & urine)
- Active Salt pumping (TAL, DT, CD)
- Differential permeabilities to salt and water**
Describe the situations in which the following would be found:
- Uosm/ P osm > 1
- Uosm / Posm < 1
- Uosm/ P osm > 1
- urine very concentrated = ADH AntiDiuresis - Uosm / Posm < 1
- urine very dilute = Water Diuresis
What is Ch2o? What is -CH20?
CH20 = amount of pure (solute free) water the kidney adds to urine
- dilutes urine below osmolality of blood
- Ch20 = amount of pure water SUBTRACTED from urine
- concentrating urine above osmolality of blood
How do negative and positive free water clearance relate to Uosm & Posm?
Negative Free Water clearance (-CH20) Uosm>Posm
- concentrated dark amber urine
ex: ADH Diuresis
Positive Free Water Clearance (CH2O) Uosm<Posm
- diluted pale yellow urine
ex: Water diuresis
What is the tubular conservation of water equal to?
TH20 = -CH20
State examples of Tubular Water Movement Control:
1. Endogenous (1)
- Exogenous (2)
- Endogenous - ADH
- Exogenous: DIURETIC
Furosemide - loop diuretic –> K+ wasting most potent diuretic
Spironolactone - K+ Sparing diuretic –> less potent
