Renal Physiology IV - Water and Electrolyte Balance Flashcards
water is the major constituent of:
blood
lymphatic fluid
cerebrospinal fluid
aqueous humour
milk and colostrum
saliva
tears
sweat
bile
semen and secretions of sexual accessory glands
species difference - water balance?
dry climate animals have smaller faecal and urinary losses. some species can derive all the water they need from metabolic water
how can water be lost?
insensible losses (skin and lungs)
faecal loss
urinary loss
how can water be gained?
food and drink (90%)
metabolism (-10%)
(glucose, O2, CO2, H2O + ATP)
water intake needs to =
water loss
if not then there is disorder
what are elctrolytes?
these are minerals in your body that have an electric charge
where are electrolytes found?
in blood, urine, tissues and other body fluids
why are electrolytes important?
balance water
balance acid/base (pH) level
move nutrients into cells
move wastes out of cells
make sure that nerves, muscles, the heart and the brain function
what are all the electrolytes which are obtained through nutrition?
sodium, calcium, potassium, chlorine, phosphate and magnesium
dissolved compounds dissociate into:
ions
what are cations?
they are positively charged (move toward a negative cathode)
give examples of cations:
Na+, K+, Ca2+, H+, Mg2+
anions?
negatively charged (moved toward a positive anode)
give examples of anions?
Cl-
HCO3-
PO43-
non-electrolytes are…
uncharged
give examples of non-electrolytes:
urea, glucose and amino acids (some)
when can electrolyte levels change?
when the amount of water changes (dehydration or overhydration)
causes of electrolyte levels changing:
drugs
vomiting
diarrhoea
sweating
renal problems
what water disturbances can affect electrolyte levels?
water volume increase (oedema)
water volume decrease (dehydration)
give examples of electrolyte disturbances:
hypo/hypernatraemia (disturbances in blood Na+)
hypo/hyperkalaemia (disturbances in blood K+)
hypo/hypercalcaemia (disturbances in blood Ca2+)
hypo/hyperchloraemia (disturbances in blood Cl-)
three major compartments of the physiological fluid:
intracellular fluid (ICF)
interstitial fluid (part of ECF)
plasma fluid (part of ECF)
what is intracellular fluid?
fluid within all the cells of the body
what is interstitial fluid (or tissue fluid)?
it is a solution that bathes and surrounds the cells of multicellular animals
it is the main component of the extracellular fluid (ECF)
which also includes plasma and transcellular fluid
what is plasma fluid?
main constituent of blood
separated by capillary walls
permeable to all but large proteins
all interstitial fluid is extracellular fluid but not all extracellular fluid is interstitial fluid
remember
describe intracellular fluid:
separated by plasma membrane
permeable to water (via aquaporins)
impermeable to proteins
and impermeable to ions (except by specific channels and pumps)
where does the ICF lie?
it lies within cells and is the principal component of the cytosol/cytoplasm
what does the ICF make up?
makes up about 60% of the total body water
what does the ECF account for?
for the other 40% of the total body water
approx 20% of the ECF is plasma
approx 75% of the ECF is interstitial fluid (ISF/IF)
approx 5% of the ECF is ‘other’ fluid or transcellular fluid
describe what happens to the fluid during filtration:
fluid exits capillary since capillary hydrostatic pressure (35mm Hg) is greater than blood colloidal osmotic pressure (25mm Hg)
Arterial end net filtration pressure = +10 mm Hg
describe what happens to the fluid when there is no net movement:
no net movement of fluid since capillary hydrostatic pressure (25 mmHg) = blood colloidal osmotic pressure (25 mm Hg)
Mid capillary net filtration pressure = 0 mmHg
describe what happens to the fluid during reabsorption:
fluid re-enters capillary since capillary hydrostatic pressure (18 mm Hg) is less than blood colloidal osmotic pressure (25 mm Hg)
VENOUS END - NET FILTRATION PRESSURE = -7 mm Hg
what are the 9 major transport systems involved in electrolyte balance?
Na+/K+ ATPase
K+ channel
Epithelial Na+ channel
Voltage-dependent Na+ channel
Na+ - solute co-transporter
Voltage-gated Ca2+ channel
Organellar Ca2+/H+ pump
Plasma-membrane Ca2+/H+ pump
Na2+/Ca2+ exchanger
blood plasma has high concentrations of?
of sodium, chloride, bicarbonate and protein
what does the ISF have high concentrations of and low concs of?
sodium, chloride and bicarbonate but a relatively lower conc of protein
ICF has elevated amounts of?
of potassium, phosphate, magnesium and protein
Describe the way the Na+/K+ pump works:
powered by ATP to transfer Na+ out of the cytoplasm and into the ECF
The pump also transfers K+ into the cytoplasm
For every ATP molecule that the pump uses, three Na+ are exported and two K+ are imported
Net export of a single positive charge per pump cycle
more positive charge is gotten rid of in order to let K+ in so a positive ion makes the inside of the cell more negative
remember
describe a hypertonic solution:
higher solute content than ICF
water moves out of cells and cells shrivel (crenated)
describe an isotonic solution:
balanced solute content to ICF
free movement of water in balance
describe a hypotonic solution:
lower solute content than ICF
water moves into cells and cells swell or lyse
if we gave a hypertonic fluid - what would happen?
plasma volume expands and becomes more concentrated
free movement of water and ions from plasma leads to expansion of interstitial fluid
interstitial fluid becomes concentrated
osmotic potential draws water out of cells
cells lose water and shrink
intracellular-fluid concentrated
water movement if given a hypertonic fluid?
from plasma to ISF to ICF
if we gave a isotonic fluid - what would happen?
plasma volume expands
free movement of water and ions from plasma leads to expansion of interstitial fluid
fluid is isotonic so no osmotic potential generated between ISF and cells
intracellular fluid unaffected
describe the water movement when given an isotonic fluid:
plasma –> ISF
if we gave a hypotonic fluid - what would happen?
plasma diluted
oncotic pressure reduced
water moves into interstitial fluid
interstitial fluid diluted
osmotic potential generated between ISF and cells
Water moves into cells
intracellular fluid diluted
cells swell
describe the water movement when given a hypotonic fluid:
water movement from plasma –> ISF –> ICF
what is crystalloid fluid?
contains small solutes, mineral salts
what is colloid fluid?
contains large solutes
why would you give crystalloid to clinical case on slide 24?
need to replace lost water and lost electrolytes
why and when might you give a colloid?
blood pressure low and circulation is poor
low circulating volume - so give colloid to increase blood pressure
why give isotonic for clincial case slide 24?
to replace lost fluid and solutes without overloading ICF with fluid (hypotonic) or drawing fluid form ICF (hypertonic)
when may you give hypotonic?
hypotonic not very useful clinically as rarely have fluid loss without electrolyte loss as well
when may you give hypertonic?
hypertonic can function like colloid but only short-term as fluid will be lost from ICF as a result
animal can replace ICF with long term drinking so sometimes used in large animals
what routes could you give fluids?
orally, subcutaneous, IV
how to calculate how much fluid to give:
calculate fluid deficit, calculate maintenance requirements and add together
determine safe rate to administer (this will be covered in later years)
like w/ like
volume w/ volume
rate w/ rate
osmosis occurs through?
through semi-permeable membrane
cell membrane acts as a ?
a barrier to most molecules
why are the cell membranes semi-permeable?
specialised channels and transporters facilitate movement across the membrane
how does water move across membranes?
lipid bilayer is hydrophobic - therefore, only gases and molecules such as ethanol can diffuse across
only limited diffusion of water occurs too slow for most physiological processes
water crosses the plasma membrane via?
its own channels - aquaporins
three hormone systems play an important role in the regulation of extracellular fluid volume and osmolarity through their actions on renal absorption of Na+ and water - what are they?
ADH (anti-diuretic hormone)
the renin-angiotensin-aldosterone system
atrial natriuretic hormone
which two fluid compartments have the most similar compositions of fluid?
the compositions of the two components of the ECF - plasma and ISF - are more similar to each other than either is to the ICF
