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Flashcards in Fluid Balance Deck (14):

Intrinsic chemical factors influencing fluid balance

-Aldosterone - Stimulates reaborbtion of Na, therefore water retention

ADH - From RAAS, Angiotensin II causes systemic and renal vasoconstriction, reducing renal blood flow, stimulating release of ADH from posterior pituitary (made in hypothalamus). Release also regulated by osmoreceptors in hypothalamus, and baroreceptors in the atria. Acts on receptor V2 in the kidneys, increases permeability to water, also reabsorption of Na. Both to retain more water and regulate electrolyte concentration in the blood

ANP - Atrial natriuretic peptide - released from overstretched cardiac myocytes, a potent vasodilator itself and inhibits/initiates opposite effects of aldosterone, therefore causing diuresis via Na wasting


Major Body fluid compartments

Intracellular space - K is major lyte, 2/3of total BF

Extracellular space - Na major lyte, 1/3 of TBF, 15% interstitial, 4% intravascular

Transcellular Space - Normally only 1-2% of TBF, but the areas where fluids can accumulate pathologically, intraoccular, pleural, peritoneal, CSF etc. The "third space"


Which Lytes love to live in the extracellular compartment (Intravascular, interstitial)

Na, Cl, HCO3, Ca
Trace K, Phos, Mg


Which lytes are intracellular

K, Mg, Phos
Trace extracellular lytes


Pressures and their effect on fluid shift

Hydrostatic - pushing force, created by pump of heart, and pressure of fluid in the vessels

Oncotic - pulling force, created by the propensity for water to balance with solutes. Created by large colloidal molecules such as albumin


Difference between Osmolarity and osmolality

Osmolarity is the measure of solutes in liquid measures per litre

Osmolality is measured by kg of liquid


Forces affecting movement of water and solutes across a membrane

Hydrostatic pressure
Osmotic pressure
Membrane permeability


What is the movement of a solvent across and membrane called

Osmosis - movement of water from an area of low solute concentration to an area of high solute concentration across a semi-permeable membrane
Influenced by osmotic and hysteric pressures
Mediated primarily by Na


The movement of solutes

Diffusion - movement of solute from high concentration to low concentration


Name volume disorders

Hypervolemia - volume overloaded
Hypovolemia - dehydrated
Is called isotonic if its a pure volume problem, ie loss of blood or excess NS bolus
Eg. Isotonic Hypervolemia


Concentration disorder

Excess or insufficient Na (the primary extracellular ion), cause hyper or hypotonicity, which results in fluid shifts by osmosis

Most common being hypo or hypernatremia


Normal HCT range

Women 38-46%
Men 42-54%

Reflects relative concentration of RBC in plasma. Major effect is on afterload



Diabetes incipidus - trauma issues with pituitary and/or hypothalamus, not enough ADH, therefore massive diuresis, dec urine osmo, inc serum osmo with lesser and greater concentrations of solutes esp Na. Serum Na becomes concentration and therefore hypernatremia.



Issues with pituitary and or hypothalamus, tumour or somat
Too much ADH makes less urine output, incr urine osmo, dec serum osmo, dec Na with dilutional effect. Concentration disorder