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A 22-year-old woman is admitted to the hospital because of a 10-day history of polydipsia and polyuria. She says that the urge to urinate often awakens her at night. She has been taking lithium carbonate for 2 years for bipolar disorder; her dosage was increased 6 months ago because of recurrent severe manic episodes. Her vital signs are within normal limits. Physical examination shows no abnormalities. Over the next 24 hours, urine excretion totals 6.5 L. Laboratory studies at this time show a serum sodium concentration of 148 mEq/L, serum osmolality of 315 mOsmol/kg, and urine osmolality of 75 mOsmol/kg. After administration of desmopressin, urine output and osmolality do not change. Which of the following findings in the nephron best describes the tubular osmolality, compared with serum, in this patient?

Proximal Tubule -- Juxtaglomerular Apparatus -- Medullary Collecting Duct

A) Hypertonic -- hypertonic -- hypertonic
B) Hypertonic -- hypertonic -- hypotonic
C) Hypertonic -- hypotonic -- hypotonic
D) Isotonic -- isotonic -- isotonic
E) Isotonic -- hypotonic -- hypertonic
F) Isotonic -- hypotonic -- hypotonic
G) Hypotonic -- hypertonic -- hypertonic
H) Hypotonic -- hypotonic -- hypertonic
I) Hypotonic -- hypotonic -- hypotonic

I don't know the answer. I just know that E is wrong. Please gine an explanation!
 

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I think B
plasma is hypertonic in this patient and gonna remain hypertonic in PCT
JGA in afferent arteriole receives Hypertonic plasma
due to lithium patient has nephrogenic DI and water is not absorbed in collecting ducts so urine at this level gonna be hypotonic
 

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Im stuck between F and I , but I will go I.(no completely sure)
This case is Nephrogenic DI (because doesnt improve w/ADH) so there is a a lot of water in the lumen (hypotonic)

Normally:
- proximal tubule --> isotonic
-Thin loop --> Hypertonic (because water reabsorption)
-Thick loope --> Hypotonic (water impermeable)
- Distal tubule --> Hypotonic(water impermeable)
-Collecting duct -->Hypertonic (permeable to water -ADH)
 

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I'll go with F. Lithium can cause nephrogenic DI. I think this only affects the late distal tubules and collecting ducts, the rest of the nephron wouldn't be affected. The only answer that fits is F.
 

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A 22-year-old woman is admitted to the hospital because of a 10-day history of polydipsia and polyuria. She says that the urge to urinate often awakens her at night. She has been taking lithium carbonate for 2 years for bipolar disorder; her dosage was increased 6 months ago because of recurrent severe manic episodes. Her vital signs are within normal limits. Physical examination shows no abnormalities. Over the next 24 hours, urine excretion totals 6.5 L. Laboratory studies at this time show a serum sodium concentration of 148 mEq/L, serum osmolality of 315 mOsmol/kg, and urine osmolality of 75 mOsmol/kg. After administration of desmopressin, urine output and osmolality do not change. Which of the following findings in the nephron best describes the tubular osmolality, compared with serum, in this patient?

the reason i chose B is due to fact that she is already hyperosmolar
this hyperosmolar serum is filtered across glomerulus
in PCT the absorption is iso osmotic equal number of water+electrolytes so this is not going to change osmolarity which stays hyperosmolar

JGA in afferent arteriole is receiving hyperosmolar plasma in this particular case

in medullary collecting ducts no concentration occurs from lack of response to ADH in which case urine is diluted most at this level=hypotonic urine
 

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A 22-year-old woman is admitted to the hospital because of a 10-day history of polydipsia and polyuria. She says that the urge to urinate often awakens her at night. She has been taking lithium carbonate for 2 years for bipolar disorder; her dosage was increased 6 months ago because of recurrent severe manic episodes. Her vital signs are within normal limits. Physical examination shows no abnormalities. Over the next 24 hours, urine excretion totals 6.5 L. Laboratory studies at this time show a serum sodium concentration of 148 mEq/L, serum osmolality of 315 mOsmol/kg, and urine osmolality of 75 mOsmol/kg. After administration of desmopressin, urine output and osmolality do not change.Which of the following findings in the nephron best describes the tubular osmolality, compared with serum, in this patient?
I think this is what you missed. It's a comparison of the serum and tubular osmolality. Therefore it'd be isotonic in the proximal tubule, no matter what the serum osmolality is.

Also, JGA is not simply the afferent arteriole. It's an area where the distal tubule (the Macula densa cells) is in close association with the afferent arteriole. It includes the JG cells, plus the MD cells as well as the mesangial cells. Here, I believe it refers to the osmolality of the distal tubule in that area. So basically the early distal tubular osmolality.
 

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I think this is what you missed. It's a comparison of the serum and tubular osmolality. Therefore it'd be isotonic in the proximal tubule, no matter what the serum osmolality is.

Also, JGA is not simply the afferent arteriole. It's an area where the distal tubule (the Macula densa cells) is in close association with the afferent arteriole. It includes the JG cells, plus the MD cells as well as the mesangial cells. Here, I believe it refers to the osmolality of the distal tubule in that area. So basically the early distal tubular osmolality.
that makes sense
 

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I will go with Option B

its the ADH that is concentrating urine in the Collecting ducts,in this pt she is suffering from Nephrogenic DI due to Li use so In the Collecting Duct the urine would be HYPOTONIC w/o ADH's action.

The plasma entering afferent duct is hypertonic, and as we know most water is absorbed in PT, the urine is going to be HYPERTONIC in PT.

JGA around afferent arteriole receives the HYPERTONIC plasma.
 
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