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cardiovascular lectures > water and sodium homeostasis > Flashcards

water and sodium homeostasis Flashcards

1
Q

how is water distributed in body

A

total water body is 60% of body weight
40% of body weight in intracellular fluid
20% of body weight in extra cellular fluid

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2
Q

what is ECF made of

A

intravascular fluid
Interstitial fluid

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3
Q

how does water move

A

from low osmolality to high osmolality to make an isotonic (equal) solution
water is freely permeable through ECF and ICF

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4
Q

what is the main contributor to ECF

A

sodium is main contributor to ECF osmolality and volume

also anions chloride and bicarbonate because sodium is negative so these are positively charged

also glucose and urea contribute to osmolality

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5
Q

what is the main contributor in ICF

A

predominant cation in cells is potassium

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6
Q

what is interstitial fluid

A

surrounds the cells but does not circulate

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7
Q

what is plasma

A

circulates as the fluid component of the blood

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8
Q

how is plasma osmolality determined

A

by sodium and associated anions

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9
Q

how do you estimate plasma osmolality

A

2(Na) + 2(K) + urea + glucose mmol/L

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10
Q

what is end result for osmolality

A

intra and extra cellular osmolality are equal
change in plasma osmolality pulls or pushes water across cell membranes

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11
Q

where do we get water from

A

food and drink
metabolism

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12
Q

where do we lose water

A

skin
lugs
urine
faeces

skin and lungs are insensible water loss - can’t be measured

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13
Q

should water output and Input balance

A

yes

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14
Q

what are IV fluids (intravenous fluids)

A

liquids given to replace water, sugar and salt that you might need if you are ill or having an operation, and can’t eat or drink as you would normally.

given straight into a vein through a drip

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15
Q

why don’t we give water intravenously

A

it is hypo- osmolality/ hypotonic vs cells
water enters blood cells causing them to expand and burst : haemolysis
however this only occurs in the vicinity of the intravenous cannula
if you could achieve instantaneous mixing it wouldn’t occur

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16
Q

describe ECF osmolality

A

it is very tightly regulated
changes in ECF osmolality lead to a rapid response
normal plasma osmolality is 275-295 mmol/kg
water deprivation or loss will lead to a chain of events

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17
Q

how is ECF osmolality resotred

A

1) water deprivation / dehydration
2)

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18
Q

describe ECF volume changes

A

slower response compared to osmolality

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19
Q

Causes of water depletion in body

A

-reduced intake as we get older
- vomiting / diarrhoea / diuresis/ diuretics
- sweating

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20
Q

symptoms of dehydration

A

thirst
dry mouth
in elastic skin
sunken eyes
raised haematocrit
weight loss
confusión - brain cells
hypotension

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21
Q

how does water excess occur

A

when given too many fluids in hospital or just drinking too much water

22
Q

what happens in water excess

A

water goes from ECF to ICF
ECF osmolality decreases
inhibition of ADH from posterior pituitary
no stimulation of thirst centre in hypothalamus
increased urine volume.
risk of cerebral over hydration if acute excessive intake ie water intoxication

23
Q

consequences of excess water

A

hyponatraemia
cerebral overhydration
- headache
- confusion
- conclusions

24
Q

define hydrostatic pressure

A

pressure difference between plasma and interstitial fluid
water moved from plasma into interstitial fluid

25
Q

define oncotic pressure

A

pressure caused by the difference in protein concentration between the plasma and interstitial fluid
water moves from interstitial fluid into plasma

26
Q

what is oedema

A

excess accumulation of fluid in interstitial space
disruption of the filtration and osmotic forces of circulating fluids
obstruction of venous blood or lymphatic return
inflammation increases capillary permeability
loss of plasma protein

27
Q

what is serous effusion

A

excess water in a body cavity

28
Q

pathogenesis of oedema and serous effusion

A

increased fluid leakage into interstitial spaces
OR
impaired reabsorption of fluid

inflammatory
venous
lymphatic
hypoalbuminaemic

29
Q

how much fluid in normal pleural space

A

around 10 ml

30
Q

what are pleural effusions

A

the build-up of excess fluid between the layers of the pleura outside the lungs

31
Q

what are pleura

A

thin membranes that line the lungs and the inside of the chest cavity and act to lubricate and facilitate breathing

32
Q

how much fluid in normal pleural space

A

about 10mL of fluid

33
Q

what causes pleural effusions

A

disruption of balance between

hydrostatoc and oncotic forces in the visceral and parietal pleural vesses
AND
lymphatic drainage

34
Q

what is transudate

A

fluid pushed through the capillary due to high pressure within the capillary

transudates have low protein content

35
Q

what is exudate

A

fluid that leaks around the cells of the capillaries caused by inflammation and increase in permeability of pleural capillaries to proteins

exudates have high protein content

36
Q

why is plural fluid protein measured

A

to differentiate between exudative and transudative effusions

37
Q

what is normal range of plasma sodium

A

135- 145 mmol / L
concentration is a ratio, not a measure of total body content

38
Q

what usually causes high or low sodium

A

gain or loss in water
not sodium

39
Q

what are clinical effects of changes in plasma sodium

A

they are on the brain due to constrained volume ( skull)
rate or change is more important than absolute levels

40
Q

what happens when too much sodium

A

hypernatraemia

water deficit
- poor intake
- osmotic diuresis
- diabetes insípidus

sodium excess
- mineralocorticoid (aldosterone )
salt poisoning

41
Q

what happens when too little sodium

A

hyponatraemia
artefactural

sodium loss
- diuretics
- addison’s disease

excess water
- IV fluids (iatrogenic)
SIADH

excess water and sodium
- oedema

42
Q

effects of too much sodium

A

cerebral intra cellular dehydration
tremors, irritability , confusion

43
Q

effects of too little sodium

A

cerebral intra cellular overhydration
headache, confusion, convulsions

44
Q

what are IV fluids (intravenous fluids)

A

liquids given to replace water, sugar and salt that you might need if you are ill or having an operation, and can’t eat or drink as you would normally.

given straight into a vein through a drip

45
Q

describe steps of water homeostasis

A
  1. osmoreceptors detect water conc
  2. hypothalamus sends signal to posterior pituairy gland
  3. pituairy gland secretes ADH which targets the kidney responsible for maintaining water levels
  4. ADH alters the tubules of kidney to become more/less permeable
  5. if more water required in blood stream –> high conc of ADH make the tubules more permeable
  6. if less water required in blood stream –> low conc of ADH make the tubules less permeable
  7. kidneys conserve water if you are dehydrated and they can make urine more dilute to expel excess water if necessary
46
Q

what is anti diuretic hormone

A

maintains blood pressure, blood volume and tissue water content by controlling the amount of water and hence the concentration of urine excreted by the kidney.

47
Q

what is the renin - anigiotension - aldoesterone system

A

regulates blood volume and systemic vascular resistance, which together influence cardiac output and arterial pressure.

48
Q

where is renin released from

A

mainly kidneys

49
Q

what does renin do

A

stimulates the formation of angiotensin in blood and tissues, which in turn stimulates the release of aldosterone from the adrenal cortex.

50
Q

what stimulates release of renin

A
  1. sympathetic nerve activation (acting through β1-adrenoceptors)
  2. renal artery hypotension (caused by systemic hypotension or renal artery stenosis)
  3. decreased sodium delivery to the distal tubules of the kidney.
51
Q

what is hyponatraemia

A

when the concentration of sodium in your blood is abnormally low.

52
Q

why does body need sodium

A

fluid balance, blood pressure control, as well as the nerves and muscles.

cardiovascular lectures (15 decks)

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