water and sodium homeostasis

Question 1

how is water distributed in body

Answer 1

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

Question 2

what is ECF made of

Answer 2

intravascular fluid
Interstitial fluid

Question 3

how does water move

Answer 3

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

Question 4

what is the main contributor to ECF

Answer 4

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

Question 5

what is the main contributor in ICF

Answer 5

predominant cation in cells is potassium

Question 6

what is interstitial fluid

Answer 6

surrounds the cells but does not circulate

Question 7

what is plasma

Answer 7

circulates as the fluid component of the blood

Question 8

how is plasma osmolality determined

Answer 8

by sodium and associated anions

Question 9

how do you estimate plasma osmolality

Answer 9

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

Question 10

what is end result for osmolality

Answer 10

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

Question 11

where do we get water from

Answer 11

food and drink
metabolism

Question 12

where do we lose water

Answer 12

skin
lugs
urine
faeces

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

Question 13

should water output and Input balance

Answer 13

yes

Question 14

what are IV fluids (intravenous fluids)

Answer 14

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

Question 15

why don’t we give water intravenously

Answer 15

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

Question 16

describe ECF osmolality

Answer 16

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

Question 17

how is ECF osmolality resotred

Answer 17

1) water deprivation / dehydration
2)

Question 18

describe ECF volume changes

Answer 18

slower response compared to osmolality

Question 19

Causes of water depletion in body

Answer 19

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

Question 20

symptoms of dehydration

Answer 20

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

Question 21

how does water excess occur

Answer 21

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

Question 22

what happens in water excess

Answer 22

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

Question 23

consequences of excess water

Answer 23

hyponatraemia
cerebral overhydration
- headache
- confusion
- conclusions

Question 24

define hydrostatic pressure

Answer 24

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

Question 25

define oncotic pressure

Answer 25

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

Question 26

what is oedema

Answer 26

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

Question 27

what is serous effusion

Answer 27

excess water in a body cavity

Question 28

pathogenesis of oedema and serous effusion

Answer 28

increased fluid leakage into interstitial spaces OR impaired reabsorption of fluid inflammatory venous lymphatic hypoalbuminaemic

Question 29

how much fluid in normal pleural space

Answer 29

around 10 ml

Question 30

what are pleural effusions

Answer 30

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

Question 31

what are pleura

Answer 31

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

Question 32

how much fluid in normal pleural space

Answer 32

about 10mL of fluid

Question 33

what causes pleural effusions

Answer 33

disruption of balance between hydrostatoc and oncotic forces in the visceral and parietal pleural vesses AND lymphatic drainage

Question 34

what is transudate

Answer 34

fluid pushed through the capillary due to high pressure within the capillary transudates have low protein content

Question 35

what is exudate

Answer 35

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

Question 36

why is plural fluid protein measured

Answer 36

to differentiate between exudative and transudative effusions

Question 37

what is normal range of plasma sodium

Answer 37

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

Question 38

what usually causes high or low sodium

Answer 38

gain or loss in water not sodium

Question 39

what are clinical effects of changes in plasma sodium

Answer 39

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

Question 40

what happens when too much sodium

Answer 40

hypernatraemia water deficit - poor intake - osmotic diuresis - diabetes insípidus sodium excess - mineralocorticoid (aldosterone ) salt poisoning

Question 41

what happens when too little sodium

Answer 41

hyponatraemia artefactural sodium loss - diuretics - addison’s disease excess water - IV fluids (iatrogenic) SIADH excess water and sodium - oedema

Question 42

effects of too much sodium

Answer 42

cerebral intra cellular dehydration tremors, irritability , confusion

Question 43

effects of too little sodium

Answer 43

cerebral intra cellular overhydration headache, confusion, convulsions

Question 44

what are IV fluids (intravenous fluids)

Answer 44

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

Question 45

describe steps of water homeostasis

Answer 45

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

Question 46

what is anti diuretic hormone

Answer 46

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.

Question 47

what is the renin - anigiotension - aldoesterone system

Answer 47

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

Question 48

where is renin released from

Answer 48

mainly kidneys

Question 49

what does renin do

Answer 49

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

Question 50

what stimulates release of renin

Answer 50

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.

Question 51

what is hyponatraemia

Answer 51

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

Question 52

why does body need sodium

Answer 52

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