PSL301: Water 5 Flashcards Preview

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Flashcards in PSL301: Water 5 Deck (81):
1

Water balance is mostly regulated by...

ADH

2

What are ways of water intake?

- food
- drink
- metabolism

3

What are the ways of water loss?

- skin
- lungs
- urine
- feces

4

Insensible water loss

Water loss through breathing and sweat

5

Why does urine volume not equal water intake?

Insensible water loss

6

The body regulates which aspect of water loss?

Urine output

7

Net water movement in body:

Intake (2.5L) - Outtake (2.5L) = 0

8

Difference between water & sodium regulation

Water is tightly regulated
- respond rapidly to changes
- maintain Na concentration

9

Sweating causes rapid reduction in ____

urine volume

10

Do we need to drink 8 glasses of water/day?

No, the body will just excrete any excess. There is almost no health benefits.

11

How is water balance regulated?

- osmoreceptor in hypothalamus detects serum Na concentration
- swell/shrink depending on stimuli -> send info to hypothalamus
- change water excretion using ADH

12

What happens to the osmoreceptor when there is increased intake of water?

swell

13

What happens to the osmoreceptor when there is decreased water?

shrink

14

When does the osmoreceptor swell?

diluted serum Na

15

When does the osmoreceptor shrink?

concentrated serum Na

16

What happens when osmoreceptors sense there is concentrated serum Na?

Send 2 diff signals to diff parts of hypothalamus
1. Increase ADH secretion
2. Increase thirst & water drinking

17

2 ways in which vasopressin is secreted

1. osmotic - osmoreceptor initiated
2. non-osmotic

18

Where is ADH produced?

large cell bodies on a few hypothalamic nuclei
- PVN
- SON

19

Where is ADH stored?

posterior pituitary

20

How does ADH get from hypothalamus to posterior pituitary?

vesicle

21

PVN

paraventricular nucleus

22

SON

supraoptic nucleus

23

Where is the SON?

above the optic chiasm (where optic nerves cross)

24

OR

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