Fluid Balance

Question 1

Intrinsic chemical factors influencing fluid balance

Answer 1

RAAS
-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

Question 2

Major Body fluid compartments

Answer 2

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”

Question 3

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

Answer 3

Na, Cl, HCO3, Ca

Trace K, Phos, Mg

Question 4

Which lytes are intracellular

Answer 4

K, Mg, Phos

Trace extracellular lytes

Question 5

Pressures and their effect on fluid shift

Answer 5

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

Question 6

Difference between Osmolarity and osmolality

Answer 6

Osmolarity is the measure of solutes in liquid measures per litre

Osmolality is measured by kg of liquid

Question 7

Forces affecting movement of water and solutes across a membrane

Answer 7

Hydrostatic pressure
Osmotic pressure
Membrane permeability

Question 8

What is the movement of a solvent across and membrane called

Answer 8

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

Question 9

The movement of solutes

Answer 9

Diffusion - movement of solute from high concentration to low concentration

Question 10

Name volume disorders

Answer 10

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

Question 11

Concentration disorder

Answer 11

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

Question 12

Normal HCT range

Answer 12

Women 38-46%
Men 42-54%

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

Question 13

DI

Answer 13

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.

Question 14

SIADH

Answer 14

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