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47 Cards in this Set
- Front
- Back
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osmolarity
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concentration of solute per liter of fluid (mosm/L)
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tonicity
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concen of a fluid relative to normal body fluids
isotonic = 300 mosm/L hypo and hyper |
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isotonic fluids
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normal saline and ringer's lactate
close to normal serum osmolarity. good for volume depleted. most efficient way. |
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hypotonic fluids
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1/2 normal saline and 5% dextrose in water
dextrose solution is metabolized to 0mosm/L quickly. not very useful bc you wanna give pts back whatever they are missing. and rare to be missing "1/2 of normal saline" bc a pt is missing either isotonic plasma or just water. |
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hypertonic fluids
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3% NaCl
this is close to seawater. |
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hypo/hy[ernatremia are...
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water problems
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hypo/hypervolumia are...
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sodium problems.
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sodium determines...
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extracellular volume.
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osmoles
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indiv particles in solution.
size doesn't matter. |
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how much of body is wtaer?
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50-60%. more in males.
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what determines where water flows?
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differences in osmoles in the different compartments.
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normal osmolarity
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280-290 mosm/L
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measuring osmolarity
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2*Na + gluc/18 + BUN/2.8
only do Na because the (-) charges balance so you just mult by 2. doesn't account for small amts of other things. |
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slide 8
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good to practice calculation of osmolarity.
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how to get direct measure of osmolarity?
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freezing point depression. the moresolute, the lower the freezing point is.
if more than 10mosm/L than calculated, a foreign substance is there (alcohol or paraprotein) |
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does urea draw fluid?
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no becasue it is freely permeable to all compartments.
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main determinant of plasma osmotic pressure
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albumin. it is confined to plasma.
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at beginning of capp bed
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tendency to push fluid out.
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at end of capp bed
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hydrostatic pressure falls, oncotic pressure rises, and fluid tends to push in.
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low albumin associated with...
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edema as fluid leaves the intravasc space for the interstitium.
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changes in cell volume especially affect...
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the brain. increase in cell volume after hyponatremia but skull lets the brain expand only so much.
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defense mech of the brain to hypovolemia
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doesn't change Na or K in the cell bc it messes with the membrane potential too much.
organic solutes are generated or removed. these are called idiogenic osmoles. takes 2-3 days for this to work. |
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___ is crucial in determining sx of changes in cell volume
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the rate of change in serum osmolarity.
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big sx of hypovolemia
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headache due to the brain swelling
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how is osmolarity monitored?
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osmoreceptors in the hypothalamus.
triggers changes in ADH |
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ADH increases with...
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increase in plasma osmolality or blood volume depletion.
body will sacrifice osmolality in order to maintain blood volume. in normal circumstances, osmolality is the main one. |
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ascending limb of LOH
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imperm to water. but NaCl is reabsorbed.
so interstit space in medulla of kidney become very hypertonic and tubule because very dilute. |
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in collecting system...
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there is a choice. let the water by drawn out by the hypertonic medulla or allow the water to be trapped in the duct and allwo the water to be excreted
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oliguria
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abnormally low amt of urine. less than 500cc per day.
due to taking in less than 500cc of water per day while the kidney HAS to excrete 600mosm/day i think... |
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most dilute urine can be
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50mosm/L
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water conservation is limited by...
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the medullary concentration gradient.
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free water excretion is regulated by...
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ADH but dependent on a minimal osmolar content. low osmolar intake will limit maximal water excretion.
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max osmolarity of urine
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1200 mosm/L
with loop diuretics - lower bc they impair medullary concentration. keeps you from reabs water. |
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thiazide diuertic impairs..
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ability to excrete water???
while a loop impairs abil to concentrate medulla. |
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atrial stretch receptors
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sense vol expansion and stim ANP release. This makes you pee.
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JGA senses...
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changes in Na+ flow rates. this stim RAA system.
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Baroreceptors in carotid sinus sense...
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decreased arterial pressure. this stim adrenergic system and ADH
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effective circ volume
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most important volume. changes with edema, venous obstruction, etc.
when there is fluid but it is nor perfusing things. classic ex is CHF. |
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increase in ECV
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most common reason is volume overload.
get HTN and edema. renal failure or abnorm fluid retention states (e.g. hyperaldosteronism) can maintain hypervolemia. |
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Decreased ECV
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often due to hypovolemia.
or pooling of fluid with normal blood volume - edema for example. total body volume is increased but there is hypoperfusion of organs. |
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main way to tell increased vs. decreased ECV
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hypoperfusion of organs.
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responses to low ECV
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increased CO
inc periph resistance increased intravasc volume (Na and water retention) |
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Na regulation
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VOLUME REGULATION!!!!
RAA aldosterone (the main effector hormone for conservation) and ANP/BNP (for dumping) |
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RAA
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releases REEEENIN in resp to renal hypoperfusion.
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AII effects
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most active at efferent arteriole bc if responding to low volume state you wanna constrict the efferent to conserve kidney function.
direct vasoconstrictor. doesnt change osmolarity. stimulates aldosterone. |
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aldosterone
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from adrenal cortex.
acts in CT... stim na abs and H secretion and K secretion |
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ANP
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direct vasodilator
red BP, dilates afferent arteriole to increase GFR. stim Na excretion. direct vasodilator. |
