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PHSL 233 > L18 > Flashcards

L18 Flashcards

1
Q

what % of the body is water

A

The body is around 60% water (60% - men; 55% - women)

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2
Q

what is the most important function of the kidney

A

Water homeostasis is therefore one of the most important functions of the kidneys.

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3
Q

what is the kidneys role in water homeostasis

A

Any increases in body water (decreased osmolarity) - need to increase excretion of water by kidneys eg in a high water iet we will urinate a lot more water

Any decreases in body water (increased osmolarity) - need increase reabsorption of water by the kidneys

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4
Q

how is body water/osmolarity monitored (what reflex)

and what detects that change

A

This is monitored by the theist reflex which occurs when the body sensors changes in the body.

This is detected by osmoreceptors and baroreceptors (BP).

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5
Q

where are the osmoreceptors located

A

In the kidney the juxtergolmerior apporatis and the maculardencer cells have osmoreceptor function

Hypothalamus also has osmoreceptors

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6
Q

where are the baroreceptors located

A

Baroreceptors in the the carotid arch and in the aortic sinus

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7
Q

in water homeostasis, water intake = water output. what does this mean in terms of net flow

A

net flow = 0 (normally)

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8
Q

what factors can effect water homeostasis

A

menstruation, vomiting and diarrhea

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9
Q

what is the equation of water excretion in the nephron

A

H2O excreatin = H2O filtered - H2O reabsorbed

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10
Q

Which segments of the nephron ARE permeable to H2O?

A

Proximal Tubule

Thin Descending Limb of Loop of Henle

Late Distal Tubule*

Collecting Duct*

  • Under influence of Vasopressin (AVP)/ Antidiuretic Hormone (ADH)
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11
Q

Which segments of the nephron are NOT

permeable to H2O?

A

Ascending Limb of Loop of Henle (Thin and Thick)

Early Distal Tubule (there is still debate about this)

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12
Q

Which segments of the nephron ARE permeable to H2O under the influence of a hormone (and what hormone is it)

A

Late Distal Tubule*

Collecting Duct*

  • Under influence of Vasopressin (AVP)/ Antidiuretic Hormone (ADH)
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13
Q

Which of the following statements is TRUE?

A. 65% of a male’s body is composed of water.

B. Normally, a person has 4 litres of plasma in their blood.

C. The net water intake and water output of person per day is 0.

D. A person can live without water for 3 months.

A

A. should be 60%

B. should be 3L

C is correct

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14
Q

what is the proximal tubules mechanism for water movement

A

Moves through peri and transcellular pathway

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15
Q

what is the Membrane shuttle hypothesis and freeze fracture technique

(the discovery of how water was reabsorbed)

A

It was assumed that water ‘leaked’ through the cell membrane.
But the very rapid movement of water through some cells was not explained by this theory (too fast to be osmosis)

Membrane shuttle hypothesis – James Wade (1980). he used Freeze fracture microscopy. This is where you froze membranes and then snapped them apart to see what was in them. He found vesicles moving towards a membrane

Presence of water channels (aquaporins) in cells discovered by US
scientist Peter Agre and his team (1988).

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16
Q

what are aquaporins

A

A family of plasma membrane proteins that form channels permitting a high rate of water flow (Higher rate then just by simple diffusion).

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17
Q

where are AQP found

A

Found in organisms as diverse as bacteria, plants and animals.

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18
Q

how do AQP allow for water movement

A

Specific for H2O, single-file movement through pore.

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19
Q

what are AQP impermeable to

how many different types of AQP are there

A

Impermeable to charged species. Therefore some of the 13 different AQ let other uncharged ions through as well

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20
Q

how many liters of water does the proximal tubule receive per day

A

Receives 180 L H2O per day

same as daily filtered load

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21
Q

how many liters of water does the proximal tubule reabsorbe per day

A

Reabsorbs 2/3 of this amount (120 L/day)

67% of the filtered load of H2O

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22
Q

what kind of epithelium is the proximal tubule made up of and what does that allow for

A

Leaky absorptive epithelium

Paracellular and Transcellular movement of H2O

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23
Q

what kind of AQP is located in the proximal tubule

A 
Aquaporin 1 (AQP1)
Transcellular movement of water

Present in both apical and basolateral membranes

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24
Q

how many liters of water does the thin descending limbs of henle receive per day

A

Receives 60 L H2O per day

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25
Q

what kind of epithelium is in the thin descending limb

A

Leaky absorptive epithelial cells

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26
Q

how much water does the thin descending limb reabsorb per day

A

Leaky absorptive epithelial cells of Thin Descending Limbs reabsorb about 30 L of H2O per day
(16% of the filtered load of H2O)

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27
Q

how does reabsorption of water occur in the thin descending limb

A

Reabsorption occurs via AQP1 in both apical

and basolateral membranes

28
Q

how much water does the thin and thick ASCending limbs reabsorbe

A

NONE!! they are impermeable to water

29
Q

what do the thick and thin ascending libs play an important role in

A

the concentration of urine

30
Q

how many liters of water does the late distal tubule receive per day

A

Receives 30 L H2O per day

31
Q

what kind of epithelium is located in the late distal tubule

A

Tight absorptive epithelium

32
Q

how much water does the late distal tubule reabsorbe per day

A

Tight absorptive epithelium of Late Distal Tubule reabsorbs 10 – 20 L H2O each day
(~5-10% of the filtered load of H2O)

33
Q

in the late distal tubule what is water reabsorption regulated by

A

ADH and aquaporin 2,3,4

Reabsorption regulated by vasopressin (AVP) also called antidiuretic hormone (ADH)

The distribution of AQPs is the same as the Collecting Duct (AQP2 in apical membrane and AQP 3 and 4 in basolateral)

34
Q

what AQP are in late distal tubule and collecting duct.

where are they located

A

AQP2 is associated with apical membrane

AQP3 and AQP4 are associated with basolateral membrane

35
Q

how many liters of water does the collecting duct receive per day

A

Receives 10 - 20 L H2O per day

36
Q

what kind of epithelium is located in the collecting duct

A

Tight absorptive epithelial cells

37
Q

how much water does the collecting duct reabsorbe per day

A

Tight absorptive epithelial cells of the Collecting Ducts reabsorb about 15 L per day – ‘fine-tuning’
(~8% of the filtered load of H2O)

38
Q

what is water reabsorption regulated by in the collecting duct

A

Water reabsorption is regulated by vasopressin (AVP) also
called antidiuretic hormone (ADH)*

also AQP 2,3,4

39
Q

what are the 2 major cell types in the collecting duct

A

Principal cells (NaCL and K transport

Intercalated cells is for H+ and K+ balance

40
Q

If you had diabetes you would absorbed very little water in what area of the nephron

A

collecting duct

41
Q

order the AQP from smallest to largest

A

AQP1,2,3,4

42
Q

how many membrane domains do AQP have

A

6

43
Q

where are the different AQP located in the nephron

A

1 = PT and TDL

2 and 3 = LDT and CD

4 = LDT and CD (and PT in mise)

44
Q

what membranes are the AQP located in

A

1= apical and basolateral

2 = apical

3 and 4 = basolateral

45
Q

is AQP 1 regulated by ADH

A

no

46
Q

which APQ does ADH have short and long term effects on

A

2 = short and long term

3 = short term (mRNA) and long term

4 = short term (mRNA) but NOT long term

47
Q

Which of the following statements is TRUE?

A. Aquaporins are only found in animals.

B. AQP2 is located on the apical membrane of Thick Ascending limb cells.

C. AQP3 is located in the basolateral membrane of collecting duct cells.

D. An osmotic gradient is NOT required for water movement

A

A. found in lots of things

B. ascending limbs are NOT permeable to water

C is correct

48
Q

where is ADH produced

A

Produced in hypothalamus

  • paraventricular nuclei
  • supraoptic nuclei
49
Q

what stimulates ADH to be released

A

Increased body osmolarity (osmoreceptors)

Decreased plasma volume (baroreceptor reflex)

50
Q

where is ADH stored and released from

A

Stored and released from the posterior pituitary

51
Q

what kind of hormone is ADH/AVP

A

a peptide hormone therefore it is hydrophilic and will need to bind to a membrane receptor

52
Q

where does ADH act on the nephron

A

• Late Distal Tubule and the Collecting Duct

53
Q

what is the name of and where is the vasopressin receptor located

A

• vasopressin binds to V2 receptor on basolateral membrane

54
Q

once ADH has bound to the V2 receptor what happens intracellularly

A

• activates Adenylate Cyclase which
increases cAMP levels
cAMP activates Protein Kinase A (PKA)

phosphorylation leads to sub-apical AQP2
vesicles moving to membrane via exocytosis

• increased Apical membrane H2O permeability

THEREFORE ONLY AQP2 IS REGULATED BY ADH!!!!!

55
Q

how long does it take to get significantly more AQP into the membrane

A

Within 45 min then you can get more vesicles in the apical membrane

56
Q

what does ADH regulate

A

ONLY AQP2

57
Q

make sure you know the membrane shuttle hypothesis

A

pores are sitting in vesicles under the membrane and when they get phosphorylated they move into it

58
Q

The amount of AQP2 can be correlated with
certain physiological conditions

What would happen to water reabsorption if there were too few AQP2 channels?

A

diabetes

59
Q

when could you get too many AQP2 channels would lead to?

A

Upregulated in congestive heart failure

When you are pregnant you have an increase in weight gain and water inside the body

60
Q

what is Diabetes Insipidus (DI)

A

Disease characterised by excessive urination

20-30L of urine per day

61
Q

there are 2 types of Diabetes Insipidus (DI). what are they

A

Neurogenic (Central) Diabetes Insipidus

Nephrogenic Diabetes Insipidus (Kidney)

62
Q

what is Neurogenic (Central) Diabetes Insipidus

A

Failure to produce or secrete vasopressin

to do with the release from the posterior pituitary. you still make in/is sensed that you need to make it in the hypothalamus but for some reason it is never released

63
Q

what is Nephrogenic Diabetes Insipidus (Kidney)

A

could be because of a …

Mutation of AQP2 channel

Mutation of V2 receptor

64
Q

what is bulk reabsorption of water carried out by

A

AQP1 in the PT

65
Q

fine tuning of water reabsorption is carried out by…

A

AQP2,3,4 in the LDT and CD

PHSL 233 (31 decks)

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