Body Fluid Osmolality Flashcards
(123 cards)
1
Q
Max osmolality at bottom of LoH
A
1200-1400 mOsm
2
Q
osmolality at top of ascending LoH
A
100 mOsm (HYPOTONIC)
3
Q
Osmolality difference maintained by TAL
A
200 mOsm difference btwn TAL and interstitium
4
Q
causes of the medullary interstitial osmotic gradient
A
- water moves from the descend LoH–>interstitium via aquaporins
- LoH anatomy makes it more concentrated as it dips (bc of Na/K ATPase
5
Q
purpose of the vasa recta
A
dictate the countercurrent multiplier by:
- supplying blood to the medulla
- SLOW blood flow
- increased permeability to solutes and water
6
Q
what is medullary washout
A
when the gradient dissipates bc the blood flows too fast
7
Q
type of osmolality of blood entering the LoH
A
isotonic and 300mOsm
8
Q
Osmolality of descending LoH & interstitium in step 1 or countercurrent multiplier
A
D loH = 300
interstitium =300
9
Q
what moves out of the A LoH
A
salt (no water bc impermeable to water due to tight jcts)
10
Q
How does salt move to the interstitium in the A LoH
A
via the NKCC
11
Q
osmolality of D LoH, interstitium, and A LoH in step 2 of countercurrent multiplier
A
D LoH = 300
interstitium = 400
A LoH = 200
*medullary interstitial fluid is HYPERTONIC
12
Q
osmolality of D LoH, interstitium, and A LoH in step 3 of countercurrent multiplier
A
D LoH = 300 entering, then 400
interstitium = 400
A LoH = 200
*D LoH is at EQUILIBRIUM with interstitium
13
Q
What happens during step 4 of CCM?
osmolality of D LoH, interstitium, and A LoH in step 4 of countercurrent multiplier
A
- more 300 TF pumped in from PCT to D LoH
- bottom of LoH becomes more concentrated
D LoH = 300 - 300 - 400 - 400
interstitium = 300 (top) 400 - 400 - 400
A LoH = 200 top - 200 - 400 - 400
14
Q
What happens during step 5 of CCM?
A
need to dilute the A LoH so solutes dumped from TF to interstitium (so diff is 200mOsm)
D LoH = 300 - 300 - 400 - 400
interstitium = 350 (top) - 500 - 500
A LoH = 150- 150 - 300 - 300
15
Q
What are the final fluid and interstitium concentrations in the final stages of the CCM?
A
D LoH = 300 - 700 - 1000 - 1200
interstitium = 300 -700 - 1000 - 1200
A LoH = 100- 500 - 800 - 1000
16
Q
what parts of the nephron are impermeable to urea
A
- TAL
- DCT
- Cortical CD
17
Q
what creates increased [urea] in the TF
A
- formation of concentrated urine
- increased ADH
- DT water reabsorption
- cortical tube water reabsorption
18
Q
UTA1
A
urea transporter
medullary CD –> TAL
19
Q
UTA3
A
urea transporter
medullary CD –> D LoH
20
Q
UTA3
A
urea transporter
medullary CD –> bottom of LoH
21
Q
percentages of Urea present in PCT, D LoH, TAL, urine
A
PCT = 100%
D LoH= 50%
TAL = 100% (from urea recycling)
urine = 20%
22
Q
where is ADH made
A
supraoptic and paraventricular nerves in the hypothalamus
23
Q
where is ADH released
A
secretory vessels in the posterior pituitary (neurohypophysis)
24
Q
what triggers ADH to be released
A
osmoreceptors detect high plasma osmolality
25
What happens as a result of the osmoreceptors detecting high plasma osmolality?
1. ADH secretion (FAST response) --> Na & water reabsorption via
2. trigger thirst
26
function of aldosterone
"salt-retaining" hormone
27
what triggers aldosterone to be released
1. Angiotensin II
| 2. increased Plasma K+
28
where is aldosterone secreted from
adrenal cortex
29
Where does aldosterone act?
increases ENaC channels in principal cells to increase Na reabsorption
30
effects of aldosterone
1. increase Na absorption (increase plasma Na)
2. increase K secretion (decrease plasma K)
- ----excess K+ in urine
31
how is Na reabsorbed in principal cells
active transport via Na/K ATPase on the basolateral membrane
32
how is K secreted in principal cells
Na/K ATPase AND it diffused down its electrochemical gradient
33
how is Cl- reabsorbed
paracellularly
34
how is water reabsorbed in principal cells
through aquaporins inserted on the apical/luminal membrane by ADH
35
What channel does aldosterone act on?
ENaCs
36
how does ADH affect hydration status
high ADH when hydrated
| low ADH when dehydrated
37
where are aquaporins inserted in the nephron
the collecting duct
38
what does the presence of aquaporins in the CD do to urine
makes urine concentrated bc more water is reabsorbed (pulled into the blood stream instead of staying in the tubular fluid)
39
what part of the collecting duct is permeable to water at all times
the cortical collecting duct
40
hydrated osmolality status
275-295 mOsm
41
dehydrated osmolality status
300mOsm
42
when ADH is "turned off" what is the result
- get dilute urine
- excrete water
- not holding on to salt
* **plasma osmolality INCREASED to normal (bc excreting water in urine)
43
when ADH is "turned on" what is the result
- add aquaporins to the CD
- hold on to water
- get concentrated urine
- excrete solute
- plasma osmolality is DECREASED to normal (bc adding water to blood)
44
what the main problem leading Central diabetes insipidus (DI)
can't make ADH
45
another name for central diabetes insipidus (DI)
"Neurogenic" Diabetes Insipidus
46
causes of central DI
head injury
infection
congenital
47
what will you see in patients with central DI
large volume of dilute urine (>15L/day)
48
how do you Dx central DI
water deprivation test (water restriction)
49
how do you treat central DI
Main: desmopressin (ADH agonist)
water restriction -have to be careful bc it may cause dehydration
50
how does desmopressin work?
its an ADH analog (ADH agonist) that can bind to the V2 receptor and increase water permeability in late DCT and CT
51
causes of nephrogenic DI
kidney can't respond to ADH
52
cause of nephrogenic DI
- there's no countercurrent (LoH impairments due to diuretics can affect concentrating ability)
- DCT/CD don't respond to ADH
- medications such as:
1. lithium (manic depression)
2. tetracycline (antibiotic)
53
what will you see inpatients with nephrogenic DI
- increased volume of dilute urine
- dehydration
- hypernatremia (high plasma Na)
54
how do you treat nephrogenic DI
1. hydration
2. low Na diet
3. Thiazide (for Na excretion)
55
what's the main problem leading to SIADH (Syndrome of Inappropriate ADH)
excess ADH released
56
what causes SIADH
lots of low Na (hypotonic) fluid is in the ECF
57
what will be seen in patients with SIADH (physiological)
Main: Excess water retention
- water will diffuse into the cells (ECF --> ICF)
- cells will swell
* *WATER INTOXICATION
- Dilutional Hyponatremia (decreased plasma osmolality)
58
Clinical Sx for SIADH patients
1. thirst
2. dyspnea
3. vomiting
4. confusion
5. cramps
6. lethargy
59
how does SIADH affect GFR
increased GFR
why? hyponatremia and increasing the GFR will lead to bringing in more Na for reabsorption
60
urinary output in DI
high
61
urinary output in SIADH
low
62
ADH levels in DI
low
63
ADH levels in SIADH
high
64
plasma Na in DI
hypernatremia
65
plasma Na in SIADH
hyponatremia (dilutional hyponatremia)
66
how is central DI distinguished from nephrogenic DI
administer desmopressin
*if the volume output does not decrease AND urine osmolarity does not increase in 2 hours after getting desmopressin, the Dx is NEPHROGENIC DI
67
hydration status for DI
dehydrated
68
hydration status for SIADH
over hydrated
69
fluid status for DI
losing fluid (large urine output)
70
fluid status for SIADH
retaining fluid (water intoxication)
71
thirst status for DI
excessive thirst
72
thirst status for SIADH
excessive thirst
73
how does solute move out of the TF of the TAL into the interstitium
via NKCC
solute moves out
water is stuck inside TF
**this is key to diluting the urine
74
what is hyponatremia
low plasma Na
| excess water in the body
75
what is hypernatremia
high plasma Na
| free water deficit
76
what causes hyponatremia
ADH in kidney (diminish free water excretion)
77
what causes hypernatremia
impaired access and impaired thirst
78
stimuli for hyponatremia
```
Rx
pain
nausea
low arterial vol
strenuous exercise
```
79
role of polydipsia in hyponatremia
NOT a cause!
80
main reasons for hyponatremia
1. true volume depletion
2. effective circulating volume depletion
3. SIADH (water intoxication)
4. low solute intake
81
main reasons for hypernatremia
1. water depletion
2. water + volume depletion
3. osmotic diuresis
4. DI
5. salt intoxication
82
urine osmolality in hyponatremia
>300 mOsm/kg
(vol depletion, eff circ vol depletion, etc)
SIADH ?100-150 mOsm/kg (not maximally dilute)
83
urine osmolality for water depletion in hypernatremia
>600-800
84
urine osmolality for water & volume depletion in hypernatremia
>600-800
85
how does osmotic diuresis affect urine osmolality in hypernatremia
>300
caused by hyperglycemia, manitol
86
how does DI affect urine osmolality
<300
| <100 in complete neprogenic DI bc large volume of dilute urine
87
how does salt intoxication affect urine osmolality and urine sodium
urine osmolality >600-800 mOsm/kg
| urine Na >20 mmol/l (very high!)
88
normal urine output in a healthy person
1-2L/day
89
polyuria
too much urine
>2.5L/day
>40 ml/kg/day
90
causes of polyuria
```
DI
DM
Kidney Ds
Alcohol
Caffeine
Sickle Cell
Anemia
Diuretics
```
91
oliguria
too little urine
| 300-500ml/day
92
causes of oliguria
```
dehydration
blood loss
kidney ds
cardiogenic shock
diarrhea
enlarged prostate
```
93
anuria
no urine
<=50ml/day
94
causes of anuria
kidney failure
obstruction (kidney stone/tumor)
enlarged prostate
95
when would the DCT/CT be impermeable to water
when you drink too MUCH water
- no ADH will be secreted
- no medullary osmotic gradient made
96
what 4 things happen when you drink too much water
1. increase urine flow rate (V)
2. decrease [urea] in inner medulla
3. decrease urea diffusion
4. increase dilute urine
97
when would the DCT/CT be permeable to water
when you drink to LITTLE water
- ADH will be secreted
- aquaporins will be inserted to increase water reabsorption
98
what 2 things happen when you drink too little water
1. decrease urine output (volume)
| 2. increase urine concentration
99
what happens as a result of the interstitium becoming super concentrated
TF will be hypoosmotic compared to the medullary interstitium
water from the TF (D LoH) will move OUT of the tube IN to the interstitium to try to reach osmotic equilibrium
when the water moves out of the TF, the tubular fluid then becomes more concentrated
100
what 4 things cause polyuria
1. increased fluid intake
2. increase GFR
3. increase solute output
4. kidneys DO NOT reabsorb water in late DCT
101
what impacts increased fluid intake in patients w/polyuria
psychogenic causes: stress and anxiety
102
what impacts increased GFR in patients w/polyuria
hypOthyroidism
fever
hypErmatabolic states
103
what impacts increased solute output in patients w/polyuria
DM
hypErthyroidism
hypErparathyroidism
diuretics (increase DCT solutes)
104
what impacts the kidney's inability to reabsorb water in the late DCT in patients w/polyuria
CDI (not making ADH)
NDI (not responding to ADH)
Drugs
Chronic renal failure (CRF)
105
difference between water and solute diuresis
water diuresis: high water excretion and NO salts
solute diuresis: high water excretion WITH salt
106
cause of water diuresis
high water intake
107
cause of solute diuresis
high TF salt
108
Diseases associated with water diuresis
polydipsia (HIGH water intake >6L/day or >100ml/kg/day)
DI
109
Diseases associated with solute diuresis
IV NaCl
hyperglycemia
increased protein intake
AKI recover
110
what is free water clearance
the rate that solute-free water leaves the kidneys
111
what does a positive free water clearance indicate
excess water is EXCRETED in urine
112
what does a negative free water clearance indicate
water is RETAINED/CONSERVED (solutes excreted)
113
if you have a patient with the following things happening, what does it tell you about their free water clearance?
- water retention
- ADH secretion
- Na retention
- K+ secretion
- low plasma K+
urine osmolality > plasma osmolality
NEGATIVE free water clearance
114
equation for free water clearance
V - (Uosm x V)
------------------
Posm
units: ml/min
115
equation for obligatory urine volume
what you excrete
-----------------------------
concentrating ability
116
what is obligatory volume
the minimum volume of urine that you must excrete
117
what urine volumes would cause you to suspect oliguria in infants
<1 ml/kg/hr
118
what urine volumes would cause you to suspect oliguria in children
<0.5 ml/kg/hr
119
what urine volumes would cause you to suspect oliguria in adults
<0.3-0.5 ml/kg/hr
120
what does the ratio of urine osmolality tell you
your ability to concentrate or dilute urine
121
what does a Uosm:Posm >1 mean
concentrated urine
122
what does a Uosm:Posm =1 mean
urine is iso-osmotic with plasma
123
what does a Uosm:Posm <1 mean
dilute urine
