PSL301: Water 5 Flashcards
1
Q
Water balance is mostly regulated by…
A
ADH
2
Q
What are ways of water intake?
A
- food
- drink
- metabolism
3
Q
What are the ways of water loss?
A
- skin
- lungs
- urine
- feces
4
Q
Insensible water loss
A
Water loss through breathing and sweat
5
Q
Why does urine volume not equal water intake?
A
Insensible water loss
6
Q
The body regulates which aspect of water loss?
A
Urine output
7
Q
Net water movement in body:
A
Intake (2.5L) - Outtake (2.5L) = 0
8
Q
Difference between water & sodium regulation
A
Water is tightly regulated
- respond rapidly to changes
- maintain Na concentration
9
Q
Sweating causes rapid reduction in ____
A
urine volume
10
Q
Do we need to drink 8 glasses of water/day?
A
No, the body will just excrete any excess. There is almost no health benefits.
11
Q
How is water balance regulated?
A
- osmoreceptor in hypothalamus detects serum Na concentration
- swell/shrink depending on stimuli -> send info to hypothalamus
- change water excretion using ADH
12
Q
What happens to the osmoreceptor when there is increased intake of water?
A
swell
13
Q
What happens to the osmoreceptor when there is decreased water?
A
shrink
14
Q
When does the osmoreceptor swell?
A
diluted serum Na
15
Q
When does the osmoreceptor shrink?
A
concentrated serum Na
16
Q
What happens when osmoreceptors sense there is concentrated serum Na?
A
Send 2 diff signals to diff parts of hypothalamus
- Increase ADH secretion
- Increase thirst & water drinking
17
Q
2 ways in which vasopressin is secreted
A
- osmotic - osmoreceptor initiated
2. non-osmotic
18
Q
Where is ADH produced?
A
large cell bodies on a few hypothalamic nuclei
- PVN
- SON
19
Q
Where is ADH stored?
A
posterior pituitary
20
Q
How does ADH get from hypothalamus to posterior pituitary?
A
vesicle
21
Q
PVN
A
paraventricular nucleus
22
Q
SON
A
supraoptic nucleus
23
Q
Where is the SON?
A
above the optic chiasm (where optic nerves cross)
24
Q
OR
A
osmoreceptor
25
br
baroreceptor
26
baroreceptors are located at...
carotid sinus
27
baroreceptors react to...
- BP
| - CO
28
baroreceptors are connected to...
| What is the implication of this?
SON
| Circulation also influences ADH secretion
29
Where is the hypothalamic osmoreceptor located?
anterior hypothalamus (OVLT)
30
what happens when osmoreceptors shrink?
1. cation channels open
2. cations enter cell (depolarize)
3. AP lead to increased ADH secretion & thirst
31
OVLT have ___ cation channels
stretch-inhibited
32
When are the ion channels on osmoreceptors open/closed?
closed: diluted Na (stretched)
open: concentrated Na (shrunk)
33
Vasopressin has a threshold. This means....
Below plasma osmolarity of 280 mOsM, there is no effect (no ADH can be found in blood)
34
Relationship between ADH and plasma osmolarity
As plasma osmolarity increases, so does plasma ADH -> LINEAR relationship
35
What happens when plasma osmolarity gets higher than 290?
You start to feel thirsty
36
When vasopressin is signalled to be released, where does it get released to?
venous system
37
secretion of ADH is regulated by...
summation of stimulatory & inhibitory signals to SON and PVN
38
serum sodium ____ stimulates thirst
> 145
39
serum sodium ____ stimulates vasopressin
> 135
40
humans can excrete ___ mL of urine per hour if they wanted to (upper limit). What is the urine osmolality?
>1000
| Low osmolality: 50 - 100 mOsM/L
41
humans can excrete ___ mL of urine per hour if they wanted to (lower limit). What is the urine osmolality?
< 20
| High osmolality: 800 - 1200 mOsM/kg
42
When there is water excess, vasopressin is...
suppressed
43
when there is water depletion, vasopressin is...
high
44
Urine concentration and dilution
1. isotonic in proximal tubule
2. very concentrated in descending limb
3. very dilute in ascending limb (hyposmotic)
4. depends on ADH/hormone action at collecting duct
45
Which transporters are found on the lumenal side of the ascending limb?
Na-K-2Cl cotransporter
| Allow NaCl to be transported without H2O
46
Which face is always permeable to water: apical or basolateral?
basolateral
47
How can permeability to water be blocked at the apical membrane?
Block paracellular pathway
48
How does ADH increase water reabsorption?
1. ADH bind to basolateral membrane receptor V2
2. activate cAMP & secondary messangers
3. cause vesicles w/ aquaporin 2 to move to apical membrane
49
Besides the presence of ADH, what else is needed for water to move out of the lumen? How is this achieved?
- osmotic gradient
| - high solute concentration in ISF because of the solute absorbed out at the ascending limb
50
Which receptor does ADH bind to?
V2 on basolateral membrane
51
Where can V2 receptors be found?
distal convoluted tubule & collecting duct
52
Where are V1 receptors located?
in blood vessels
53
What does V1 receptors do?
Vasopressin binds to them
| Causes constriction of blood vessels
54
What must be functional in order to have urine excretion?
1. thick ascending limb to generate concentrated ISF
| 2. cortical & medullary collecting duct (ADH binding site)
55
How does the CD dilute urine when there is too much water?
- ADH is not secreted
| - Na channels on CD & DCT still pump Na out of lumen
56
How does the CD prevent urine dilution?
countercurrent arrangement of vessels in medulla
57
countercurrent exchange
- arrangement of vasa recta in medulla
- blood becomes progressively concentrated as vessels enter the inner medulla
- prevent disturbing the concentrated ISF
- allow urine to be concentrated
58
Minimum urine osmolality
50 mOsM/kg
59
value: concentrated urine
> 300 mOsM/kg
60
value: dilute urine
< 300 mOsM/kg
61
hyponatremia
too much water
62
hypernatremia
too little water
63
polyuria
high urine flow > 3L/day
64
Is hyper/hyponatremia more common?
hyponatremia
65
hyponatremia is usually caused by...
Too much ADH; failure to suppress ADH
66
What causes reduced circulating volume?
- heart failure
| - volume depletion
67
What might some reasons for too much ADH be?
- decreased circulating volume (baroreceptor stimuli)
- cancer (make ADH)
- drugs
- NOT OSMORECEPTOR
68
hyponatremia is a common symptom of which disease?
heart failure
69
rapid onset of hyponatremia causes...
swelling of brain cells
- increased intercranial pressure
- compression of brain stem in foramen magnum
- seizure, coma, death
70
slow onset of hyponatremia causes...
| why?
no symptoms
| - brain cells adapt by removing solutes (takes water out with it)
71
hypernatremia indicates a problem with...
- thirst/intake of fluid (thirsty, but can't get access to water)
- water loss (less common)
72
consequence of acute hypernatremia
brain cells shrink
- vessels that attach brain to skill breaks -> hemorrhage
- seizure, coma, death
73
consequence of chronic hypernatremia
no symptoms
| - brain cells adapt by adding solutes to hold water in
74
Causes of polyuria
1. not enough ADH (central diabetes insipidus)
2. kidney can't respond to ADH (nephrogenic DI)
3. excess water intake
4. osmotic diuresis / hyperglycemia
75
central diabetes insipidus means...
```
central = problem with hypothalamus or posterior pituitary
diabetes = too much urine
insipidus = dilute urine
```
76
nephrogenic DI vs. central DI
```
nephrogenic = problem at kidney
central = problem at brain
```
77
genetic causes of neprogenic DI
1. abnormal V2 receptor gene (x-linked)
| 2. abnormal aquaporin 2 gene
78
why is polyuria commonly seen in diabetics?
- lots of glucose in blood
- filtered by glomerulus
- not enough SLGT to reabsorb all back to blood
- glucose is a solute, so pulls water into lumen
79
DDAVP
synthetic vasopressin
80
why is hypernatremia so rare?
As long as person is conscious, he/she can drink water to prevent it
81
How do baroreceptors stimulate ADH release?
Connected to SON, which produces ADH
