6: Basic Renal Processes for Sodium, Chloride, and Water Flashcards

1
Q

If you give a patient a hypertonic saline bolus, how does this affect its intracellular osmolality?

A

increases

water will shift from IC space to the EC due to the osmotic pull from the hypertonic saline in the IV space

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2
Q

If your patient has hemorrhagic gastroenteritis will large volume of vomiting and diarrhea, how does this affect its intracellular osmolality

A

Increases

vomitus and diarrhea is hypotonic - left-over osmoles increase the IV and interstitial osmolality and pull water from the IC space

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3
Q

If you give your patient a D5W infusion, how does this affect its IC volume?

A

increases - water will distribute evenly through IC and EC space

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4
Q

What percentages of sodium are rabsorbed in the proximal tubule, the loop of Henle and the distal convoluted tubules?

A
  • 65%
  • 25%
  • 10%
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5
Q

compared to the filtered sodium load, what percentage remains in the final urine?

A

less than 1%

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6
Q

What are the major anions absorbed with sodium in the tubules to maintain electroneutrality?

A
  • Chloride
  • Bicarbonate
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7
Q

Where is most bicarbonate reabsorbed?

A

In the proximal tubules (90%)

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8
Q

What are the two sources of body water?

A
  • water intake (drinking/eating)
  • water production during carbohydrate oxidation
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9
Q

What are the 4 ways of bodily water loss?

A
  • urination
  • gastrointestinal losses
  • exhalation
  • skin evaporation
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10
Q

Is the luminal or basolateral membrane of tubular cells more permeable to water?

A

basolateral membrane
high number of aquaporines –> cytosolic osmolality close to that of the interstitium

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11
Q

describe the luminal water permeability of tubular cells in the following nephron segments:
* proximal tubules
* loop of Henle
* distal convoluted tubules
* collecting ducts

A
  • proximal tubules - highly water permeable with aquaporines and permeable tight junctions - reabsorption here is isotonic
  • descending thin loop of Henle early parts still very permeabel to water
  • ascending thick loop of Henle relatively water impermeable - higher Na than water fraction reabsorbed –> tubular fluid leaving here will be hypotonic (osmolality 1/3 of plasma)
  • distal convoluted tubules little to no water reabsorption/very low permeability
  • collecting ducts permeability is highly variable and adjusted depending on body water status
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12
Q

What does obligatory water loss mean?

A

the minimum water needed to excrete sufficient amounts of urea, sulfate, phosphate, and other waste products

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13
Q

Why does starvation decrease one’s ability to survive without water?

A
  • starvation leads to a catabolic state –> releases excess solutes and waste products –> increases the obligatory water loss
  • If no food intake –> no water production from carbohydrate oxidation
  • no protein intake –> not enough urea to achieve sufficient osmolality of the inner medullary interstitium
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14
Q

How is most Na reabsorbed on the apical/tubular side of the poximal tubular cells?

A

via the NHE-3 antiporter
Sodium-hydrogen-exchanger 3

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15
Q

Name 3 solutes that are reabsorbed in the proximal tubules and are sharing a symporter with Na

A
  • Amino acids
  • glucose
  • phosphorous
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16
Q

How does Na exit the cell on the basolateral tubular cell membrane?

A

Na-K-ATPase
Na/HCO3- symporter

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17
Q

Explain how Chloride is reabsorbed in the proximal tubules

A
  • Cl/Base antiporter on luminal membrane and Cl-channel + K-Cl symporters on basolateral membrane
  • paracellular through tight junctions
18
Q

Fill the gaps

A
19
Q

Explain how organic bases and H+ protons are recycled in the poximal tubules

A

Hydrogen ions leave the tubular cells in exchange for Na entering (NHE-3 antiporter)

Base leaves the tubular cell in exchange for a Cl- ion entering (antiporter)

The H+ and base can then unite and are able to diffuse into the cell as Hbase –> will split in the cell and are able to facilitate further Na and Cl absorption

20
Q

What percentage of water and and NaCl are reabsorbed in the loop of Henle?

A

25% of filtered NaCl
10% of filtered water

21
Q

What is the Na concentration of tubular fluid at the end of the loop of Henle?

A

1/3 of plasma –> ~ 50 mEq/L

22
Q

What parts of the Loop of Henle expresses aquaporins?

A

Only the descending limb

23
Q

How are Cl and Na reabsorbed in the THIN ascending loop of Henle?

A

tubular fluid has a higher Na and Cl concentration because of water reabsorption in the descending limb –> creates concentration gradient favoring absorption

Cl is absorbed via Cl channels on both apical and basolateral membranes

Na follows paracellularly through tight junctions

24
Q

How are Cl and Na reabsorbed in the THICK ascending loop of Henle?

A
  • Na-K-ATPase on baselateral side –> creating concentration gradient for Na flux (like everywhere)
  • Na-K-2Cl symporter –> apical membrane –> movement into cell
  • to prevent K depletion in the tubular fluid - K channel moves K down cc gradient out of the cell back into the lumen (K recycling)
  • Cl exits on the basolateral side via Cl channels and K-Cl symporter
  • paracellular Na movement achieves electroneutrality (otherwise too much Cl- would be absorbed alone)
25
Q

Where does the thick ascending limb of the loop of Henle start?

A

at the junction between inner and outer medulla

26
Q

Where does the aldosterone-sensitive part of the nephron start?

A

second half of the distal convoluted tubule

27
Q

How do the distal convoluted tubules further dilute the tubular fluid?

A

NaCl reabsorption with little water absorption
* basolateral Na-K-ATPase
* luminal Na-Cl symporter
* luminnal electrogenic sodium channels
* K and Cl leave on the basolateral side via individual channels + K-Cl symporter

28
Q

What class of diuretics work in the distal convoluted tubules

A

Thiazide diuretics

29
Q

Where in the nephron do the principal and intercalated cells start and what is their proportion?

A

connecting tubule
70% principal cells - rest intercalated

30
Q

What is the main task of principal versus intercalated cells?

A

principal cells - water and Na reabsorption
intercalated cells - Cl, K, acid/base transport

31
Q

What is the tubular and interstitial osmolality in the cortical collecting ducts?

A

interstitium in cortical region always same osmolality as plasma (high blood flow, i.e., ~ 300 mOsm/kg)

tubular osmolality low because of preceeding diluting segments (~ 100 mOsm/kg)

32
Q

What percentage of the filtered water load reaches the collecting ducts?

A

25%

33
Q

Give the primary Na transporter or channel for these segments (give percentage of total Na reabsorption for each)
* proximal tubule
* thick ascending limb of the loop of Henle
* distal convoluted tubule
* collecting duct

A
  • Na-H-antiporter (65%)
  • Na-K-2Cl symporter (25%)
  • Na-Cl symporter (5%)
  • eNaCs (5%)
34
Q

How does ADH increase luminal water permeability?

A

ADH binds to the vasopressin type 2 receptors –> activates adenylate cyclase –> catalyzes intracellular cAMP production –> induces migration of intracellular vesicles containing aquaporin 2 to the luminal membrane

aquaporin 2 will be removed by endocytosis if ADH is absent

35
Q

What solutes achieve the high medullary interstitial osmolality?

A

Na and urea - about half each (Na really just a quarter but accompanied by anion for electroneutraly –> Na x 2 = osmolality contribution)

36
Q

How high does the medullary interstitial osmolality get?

A

As high as 1400 mOsm/kg

37
Q

Explained how the high Na concentration in the medullary interstitium is achieved

A
  • thick ascending loop of Henle absorbs NaCl (NaK2Cl symporter) at higher magnitude than thin descending loop absorbs water –> deposits hyperosmolar fluid in the interstitium
  • vasa recta in medulla - parallel blood vessels with slower blood supply –> don’t remove solutes from medullary interstitium as effectively as in the cortex
  • countercurrent exchange of the vasa recta: ascending vasa recta with fenestrations and ability to diffuse solutes back into the descending vessel –> prevents loss of solutes
38
Q

Other than making the collecting duct more permeable to water, how does ADH affect water reabsorption?

A
  • ADH increase will cause vasoconstriction of the vasa recta (by constricting the pericytes surroung descending vasa recta) –> even slower blood flow –> medullary interstitial osmolality can increase even more
  • ADH raises urea permeability in the inner medullary collecting ducts (ADH-sensitive isoforms of urea uniporters) –> increases medullary osmotic gradient further
39
Q

Explain how the high urea concentration in the medullary interstitium is achieved

A
  • all urea freely filtered
  • proximal tubule: 50% reabsorbed
  • descending thin loop of Henle –> 50% urea gets back into tubular fluid (coming from high medullary interstitial cc) –> restores AMOUNT but cc keeps going up because of almost all water being reabsrobed until reach medullary collecting ducts (50x plasma cc)
  • inner medullary collecting ducts –> half urea absorbed through urea uniporters (driven by high tubular to interstitial cc gradient)
40
Q

Explain the medullary washout

A

overhydration –> less ADH –> less cortical and outer medullary collecting duct water reabsorption –> tubular fluid does not get as concentrated by the time it reached the inner medullary collecting duct —> urea concentration gradient does not cause urea reabsorption or even causes secretion + high internstitial osmolality causes much of the excess water to be reabsorbed –> diluting the interstitium