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31 Cards in this Set
- Front
- Back
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What is the Osmolality of the different Nephron Segments?
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How is osmolality affected by High ADH and by lack of ADH?
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*High ADH: Water deprivation, Urinary Concentration.
*Low ADH: Water loading, Urinary Dilution. |
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How permeable to water are the different segments of the nephron?
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![*PCT, PST, tDLH all allow free passage of water (ALL water movement out of the nephron is passive, regardless of where you are).
*Final processing of [water] takes place in the cortical collecting duct.](https://images.cram.com/images/upload-flashcards/67/16/54/2671654_m.png)
*PCT, PST, tDLH all allow free passage of water (ALL water movement out of the nephron is passive, regardless of where you are).
*Final processing of [water] takes place in the cortical collecting duct. |
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What is the Passive Model for "Single Effect" in the thin ascending limb?
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What is the Countercurrent Multiplier Effect?
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*It's the interaction between the single effect of the thick ascending limb of Henle’s loop, creating the medullary concentrating gradient, and hairpin loops of the vesa recta, which help to maintain it.
*The medullary concentrating gradient is maintained b/c loss of water and gain of solute in the tubule as it descends to the papillary tip is OFFSET by plasma gain of solute and loss of water as plasma flows to the cortex from the medulla. |
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Describe the part of the Countercurrent Multiplier Effect that takes place in the vasa recta:
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*As blood flows in from the cortex, it's relatively isotonic.
*As it drops into the medulla, water flows OUT and solute comes IN. The blood is HYPERtonic by the time you're at the bottom of the loop. *As blood ascends back to the cortex, solute moves back OUT and water now moves IN. *All of this is to maintain the [gradient] b/t the cortex and the medulla. |
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What's the role of urea in maintaining the osmotic concentrating gradient?
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*It's an ineffective osmole. It moves freely along with water.
*In the collecting duct out near the cortex, ADH increases permeability to H2O but not urea. *In the collecting duct in the medulla, ADH increases permeability to both H2O and urea. Thus, urea helps maintain the [gradient] b/t the collecting duct and the interstitium. |
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What are the two important concentration gradients?
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1) Cortex/Medulla
2) Collecting Duct/Interstitium |
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What is the [urine] if the collecting duct is impermeable to water?
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*This is a no ADH situation. High volume, dilute urine.
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What is the [urine] if the collecting duct is highly permeable to water?
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*This is a high ADH situation. Low volume, high concentration urine.
*LOTS of aquaporins. |
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What is water cycling like on a typical day for a 70kg male?
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*Homeostasis. What goes in must come out.
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Mr. Aquavit is a 70 year-old man with CHF, peripheral edema, and pulmonary rales. His urine osmolality is 600 mOsm/Kg. He is given 40 mg of furosemide IV and experiences an increased urine flow. What would you anticipate would the urinary findings after furosemide administration?
A) Increased sodium excretion and increased osmolality B) Decreased sodium excretion and decreased osmolality C) Increased sodium excretion and decreased osmolality D) Decreased sodium excretion and increased osmolality E) Increased sodium excretion and unchanged osmolality. |
C) Increased Na excretion and decreased osmolality.
*More sodium goes out, but more water also goes out! |
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What is the Effect of furosemide on free water clearance in patients with CHF?
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Describe the control of ADH release:
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*PVN and SON have receptors that sense tonicity of blood flowing by.
*Feedback: as ADH is released, tonicity is decreased and the osmoreceptors in the hypothalamus turn off ADH. |
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What are the two kinds of ADH receptors?
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*V1 are is located on endothelial cells.
*V2 are found on principal cells in the collecting ducts. Note that ADH, via V2 receptors, also improves clotting via vWF. It is sometimes given to patients with low platelets. |
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What's the pathway that V2 receptors use to increase permeability to water?
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What exactly happens to the aquaporins when ADH is removed?
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They kind of recede!
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Schematics of the Steps in osmoregulation:
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Schematics of the Role of ADH in Urinary Concentration and Dilution:
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A 40 year old woman presents to your office with complaints frequent and large volume urine output. She often must get up at night to pass urine and usually keeps a glass of water at her bedside. She acknowledges that she is always thirsty and drinks at least 2 gallons of water per day.
PMH is notable for bipolar disorder for which she has been taking lithium carbonate therapy. Measured 24 hour urine volume is 12 liters and the serum sodium concentration is 147 mM. Which one of the following is the most likely diagnosis? Psychogenic polydipsia Nephrogenic diabetes insipidus Central (neurogenic) diabetes insipidus Impaired thirst and lack of water intake Salt-wasting nephropathy |
*Nephrogenic diabetes insipidus caused by Lithium.
*The patient’s disorder is due to an impaired nephron response to ADH which is caused by long-term lithium use. |
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Which one of the following tests would you perform to make the diagnosis of nephrogenic DI?
Water load test Water deprivation test with ADH adminsitration Salt loading test Measurement of free water excretion Measurement of urine volume |
Water deprivation test with ADH adminsitration
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How do water deprivation tests with ADH administration work?
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*You deprive people of water and let their plasma osmolality drift up to ~295. At that point, you give ADH (DDAVP).
*If normal, urine osmolality will decrease. In nephrogenic DI, it will not change. *Central DI would respond PARTIALLY. |
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A medical student volunteers to the following experiment. On a normal diet of sodium and water, he ingests 1 liter of water over a twenty minute period. During the next 3 hours urine is collected and measured for volume. On the following day, he undergoes the identical study but substutes 1 liter of normal saline.
Which volume is excreted faster? Water Saline |
Water is excreted faster in a normal person.
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Where is "free water" formed in the nephron?
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What is the Relationship between plasma sodium and osmolality of body fluids?
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How do you calculate plasma osmolality?
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How do you calculate Free Water Clearance? What does the calculation mean?
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*When CH2O is a positive number, it indicates the amount of solute-free water excreted by the kidneys per unit of time.
*If CH2O is a negative number (also known as TCH2O) it indicates the amount of solute-free water absorbed by the kidneys per unit time. |
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Mr. Abercrombie is a 70 year-old with heart failure with the following studies:
*PNa 128, BUN 28, Glucose 90 *Urine flow (V) 1 ml/min, Uosm 542 What is the calculated plasma osmolality? Is there free water clearance or absorption? |
*This patient is hypo-osmolar.
*The pt is holding onto water. |
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What are the osmotic and non-osmotic stimuli that affect ADH?
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*pO2: decreased oxygen tension affects ADH.
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How does ADH release change as volume and osmolality change?
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*As Na is reabsorbed, ADH must increase to retain water.
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Take home points from this lecture:
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*Urinary concentration results from equilabration of collecting duct fluid with the hypertonic medullary interstitium, under the influence of ADH.
*Urinary dilution requires adequate fluid delivery to the “diluting segment” of the nephron and the absence of ADH. *Normal daily variation of urinary concentration and dilution is driven by water intake and resultant osmoregulation. *Under conditions of stress and certain pathologic states, such as HF, non-osmotic stimuli of ADH may take over. |
