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HUBS192 Melia > Lecture 33: BODY WATER - DISTRIBUTION AND REGULATION > Flashcards

Lecture 33: BODY WATER - DISTRIBUTION AND REGULATION Flashcards

1
Q

What is TBW?

A

55-60% of body weight

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2
Q

What is ECF?

A

1/3 of TBW

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3
Q

What is ICF?

A

2/3 of TBW

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4
Q

What is plasma?

A

1/5 of ECF

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5
Q

What is interstitial fluid?

A

4/5 of ECF

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6
Q

What is osmolarity based on?

A

The number of osmotically active ions or solutes (which attract water)

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7
Q

What is the concentration of NaCl?

A

145mM = 145mM Na+ + 145mM Cl- = 290mosmol/L

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8
Q

What can osmolarity be measure by?

A

Specific gravity

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9
Q

What does iso-osmotic mean?

A

The same osmolarity

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10
Q

What does hypo-osmotic mean?

A

Lower osmolarity

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11
Q

What does hyper-osmotic mean?

A

Higher osmolarity

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12
Q

What is tonicity based on?

A

The effect of a solution on cells

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13
Q

What does an isotonic solution do?

A

Not change the water homeostasis between cells

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14
Q

What is the concentration of sodium in the ECF?

A

145 mmol/L

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15
Q

What is the concentration of sodium in the ICF?

A

15 mmol/L

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16
Q

What is the concentration of potassium in the ECF?

A

4-5 mmol/L

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17
Q

What is the concentration of potassium in the ICF?

A

150 mmol/L

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18
Q

What is the osmolarity of the ECF?

A

275-295 mosmol/L

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19
Q

What is the osmolarity of the ICF?

A

275-295 mosmol/L

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20
Q

What remains relatively constant?

A

Total body water

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21
Q

What must balance?

A

Intake and loss of water

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22
Q

What is adjusted to maintain water balance?

A

Urine output (so the kidneys are the most important in water balance)

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23
Q

Where does reabsorption of sodium occur?

A

PCT, thick ascending limb, DCT and collecting duct

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24
Q

What amount of sodium is absorbed in the PCT?

A

67%

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25
Q

What amount of sodium is absorbed in the thick ascending limb?

A

25%

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26
Q

What amount of sodium is absorbed in the DCT?

A

5%

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27
Q

What amount of sodium is absorbed in the collecting duct?

A

3%

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28
Q

Where does reabsorption of water occur?

A

In the PCT, thin descending limb and collecting duct

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29
Q

What is reabsorption of water in the PCT driven by?

A

Sodium reabsorption in order to make isosmotic solution

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30
Q

What do transporters such as the sodium glucose transporter use?

A

The sodium gradient to reabsorb glucose

31
Q

What does SGLT do?

A

Sodium/glucose - cotransporter from the filtrate to the cell

32
Q

What are aquaporins?

A

Channels for water to get from filtrate into the cell and then into the blood

33
Q

What does a glucose transporter do?

A

Transport glucose from the cell to the blood

34
Q

What does Na+/K+ ATPase do?

A

Transport sodium into the blood from the cell

35
Q

What does the thick ascending limb do?

A

Reabsorbs sodium into the interstitial generating a high osmotic medullary gradient (HOMG)

36
Q

What is the thin descending limb like?

A

Leaky epithelium, facilitating water reabsorption via aquaporins (transcellular) and the paracellular pathway

37
Q

What is the thin descending limb permeable to?

A

Water and impermeable to solutes so it causes the solute concentration to increase (in urine)

38
Q

What is the thick ascending limb permeable to?

A

Impermeable to water and selectively permeable to na+ and cl- so solute concentration decreases (in urine)

39
Q

Where does obligatory reabsorption occur?

A

In the PCT and thin descending limb

40
Q

Is obligatory reabsorption regulated?

A

no

41
Q

What portion of water reabsorption does obligatory reabsorption account for?

A

92%

42
Q

Where does facultative reabsorption occur?

A

In the collecting duct

43
Q

What is the epithelia at facultative reabsorption?

A

Tight (so only transcellular)

44
Q

What is facultative reabsorption regulated by?

A

ADH

45
Q

What portion of water reabsorption does facultative reabsorption account for?

A

2-8%

46
Q

What does changing water content do?

A

Change osmolarity

47
Q

What happens to equalise?

A

Fluid shifts between ECF and ICF

48
Q

What also changes when water content changes?

A

Volume of compartments

49
Q

What happens when volume of compartments change?

A

Cell size changes, cell structure altered and cell functions become impaired

50
Q

What are red blood cells dependent on?

A

An isotonic environment

51
Q

What changes the function of red blood cells?

A

Hypertonic environment (shrivel) or hypotonic environment (burst)

52
Q

What do total body water changes alter?

A

Plasma (ECF) osmolarity

53
Q

What is change in plasma osmolarity detected by?

A

Osmoreceptors in the hypothalamus (brain)

54
Q

What do osmoreceptors stimulate?

A

Pituitary gland to secrete more/less ADH

55
Q

What does ADH do?

A

Alters the permeability of the renal collecting duct so that water is retained/excreted to balance the initial change in TBW

56
Q

What does the effect of ADH mean?

A

Plasma osmolarity and cell volume become stable

57
Q

What happens when dehydration (increased sodium levels) occurs?

A

Increased ADH secretion, thirst and water reabsorption, water into the ECF to decrease Na+ levels

58
Q

What happens when hyper hydration (decreased sodium levels) occurs?

A

Decreased ADH secretion, thirst suppressed and water loss, water decreases in ECF to increase sodium levels

59
Q

What happens without ADH (diuresis)?

A

Small amount of water reabsorption and a large volume of dilute urine is produced

60
Q

What happens with ADH (antidiuresis)?

A

Large amount of water reabsorption and a small volume of concentrated urine is produced

61
Q

What does ADH in the bloodstream do?

A

Finds its receptor in the basolateral side of collecting duct cells

62
Q

What does ADH do once bound to the receptor?

A

Via intracellular signalling cascades increases the number of aquaporins in the apical membrane increasing water permeability of the apical membrane of the collecting duct

63
Q

What can the macula densa cells do?

A

Sense changes in sodium reaching the distal tubule and therefore perfusion of the nephron; if it is too low this leads to a release of renin from juxtaglomerular cells

64
Q

what regulates changes in ECF volume?

A

ANP or aldosterone (renin-All-Aldosterone-System)

65
Q

What is the receptor when increased ECF volume by fluid gain (or fluid and Na+ gain)?

A

cardiac muscle cells

66
Q

What does the receptor stimulate when increased ECF volume by fluid gain (or fluid and Na+ gain)?

A

release of ANP

67
Q

What are the effectors when increased ECF volume by fluid gain (or fluid and Na+ gain)?

A

hypothalamus, kidney and blood vessels

68
Q

What is the response when increased ECF volume by fluid gain (or fluid and Na+ gain)?

A

Increased sodium lossed in urine and increased water lost inurine

69
Q

What is the result when increased ECF volume by fluid gain (or fluid and Na+ gain)?

A

Decreased ECF volume

70
Q

What are the receptors when decreased ECF volume by fluid loss (or fluid and Na+ loss)?

A

baroreceptors and kidneys

71
Q

What do kidneys stimulate when decreased ECF volume by fluid loss (or fluid and Na+ loss)?

A

RAAS - renin release leads to angiotensin ll activation and increased aldosterone release

72
Q

What do baroreceptors stimulate when decreased ECF volume by fluid loss (or fluid and Na+ loss)?

A

sympathetic activation
effectors - hypothalamus, heart and blood vessels
response - increased ADH release

73
Q

What is the response when decreased ECF volume by fluid loss (or fluid and Na+ loss)?

A

Decreased sodium lost in urine and decreased water lost in urine

74
Q

What is the result when decreased ECF volume by fluid loss (or fluid and Na+ loss)?

A

Increased ECF volume

HUBS192 Melia (38 decks)

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