Water and Sodium

Question 1

what is the distribution of water in the body?

Answer 1

60% of mass = water
20% Extracellular (more interstitial - less intravascular)
40% intracellular
7% plasma

Question 2

interstitial fluid + plasma = what?

Answer 2

extracellular fluid

Question 3

what does isotonic mean?

Answer 3

osmolality is the same

Question 4

what part of the brain watches plasma osmolarlity?

Answer 4

the hypothalamus

Question 5

what does ECF contain?

Answer 5

sodium, chloride, bicarbonate, glucose, urea,

Question 6

what does ICF contain?

Answer 6

predominantly potassium

Question 7

what is the equation for plasma osmolality?

Answer 7

2[Na] + 2[K] + urea + glucose mmol/L

Question 8

what effect on plasma osmolality does alcohol have?

Answer 8

alcohol increases plasma osmolality

Question 9

what is normal ECF osmolality?

Answer 9

275-295 mmol/kg

Question 10

why is water not given intravenously?

Answer 10

water is hypotonic vs cells - would cause haemolysis of blood cells

Question 11

what happens when someone is deprived of water?

Answer 11

there is an increase in ECF osmolality.
water moves from ICF to ECF - and the hypothalamus activates the ‘thirst centre’
releases ADH from posterior pituitary

renal water retention (less wee)

Question 12

what controls ECF volume?

Answer 12

the renin-angiotensin-aldosterone system

Question 13

what is renin?

Answer 13

a kidney enzyme that acts on the protein angiotensin to form angiotensin 1

Question 14

what synthesises aldosterone?

Answer 14

the adrenal cortex

Question 15

what does aldosterone do?

Answer 15

promotes sodium reabsoprtion and potassium secretion

Question 16

what is angiotensin 2?

Answer 16

a vasoconstrictor

Question 17

what happens when there is excess water in the body?

Answer 17

ECF osmolality decreases.

water moved into the ICF, and ADH is inhibited from the posterior pituitary gland.

Question 18

what is volume overload?

Answer 18

ECF volume expansion

Question 19

what can volume overload cause?

Answer 19

heart failure, 
loss of intravascular fluid into interstitial space
low effective circulation volume
renal sodium retention + water retention
loss of plasma protein

Question 20

what is oedema?

Answer 20

the accumulation of extra interstitial fluid - which disrupts filtration and osmotic forces.

Question 21

what is hydrostatic pressure?

Answer 21

the pressure exerted by fluid in equilibrium - caused by the heart

Question 22

what is oncotic pressure?

Answer 22

a form of pressure caused by proteins in fluid - mostly albumin

Question 23

how does oncotic pressure work?

Answer 23

proteins in capillaries can’t move across the well and thus pull water back into circulation

Question 24

what is serous effusion?

Answer 24

excess water in a body cavity

Question 25

what is pathogenesis?

Answer 25

increased fluid leakage into interstitial space or impaired reabsorption of fluid.

Question 26

what is venous oedema?

Answer 26

a blockage at one end which pushes water into the interstitial fluid

Question 27

what is lymphatic oedema?

Answer 27

when the lymphatic system is blocked and water builds up in the interstitial fluid

Question 28

what is hypalbuminaemic oedema?

Answer 28

low proteins, so can’t reabsorb the water as there are no proteins to pull the water back in.

Question 29

what is pleural effusion?

Answer 29

when the balance between hydrostatic and oncotic forces in the visceral and parietal pleural vessels is off so the pleural space becomes filled with more fluid.

Question 30

what is transudate?

Answer 30

when the fluid is pushed through the capillary due to high pressure within the capillary - low protein in the extravascular fluid