1
I. Fluid shift issues
1. For our test questions about fluid shifts, Na+ (& its other form, NaCl) & proteins will be the solutes involved. They are the main
solutes that drive fluid shifts, which are based on osmosis --movement of water from area of lower solute concentration to area of higher
solute concentration.
(For questions involving K+ and Ca++, think electrical status—see Electrical Issues below.)
2. Remember that (for our purposes) changes in fluid status begin in the plasma space. So in any scenario you are given, think: in what
way has this scenario changed the solute status in the plasma space—has water been added or solutes removed (making the plasma
space more dilute)? Or has water been taken away or solutes added (making the plasma space more concentrated)? Also remember
that the tissue status (cells and interstitial space) remains normal initially —the “normal” number of solutes & “normal”
amount of water exist in the tissue at the beginning of the scenario. Therefore, when the plasma space dilution changes, think: “the
plasma has changed, but initially the tissue hasn’t YET—I have to figure out what happens next.” The situation will always be one of
these pictures (will discuss more at review):
took away water or added solutes to added water or took away solutes to
plasma space = more solutes than plasma space = less solutes than tissue
tissue
or? or?
tissue has normal tissue has normal
numbers of numbers of
solutes solutes
(**In studying your info, serum osmo (norm = 280- 295) serum Na+ (norm = 135-145) serum protein (oncotic pressure)
always think both “front
door” AND “back door.”) serum NaCl (norm = 0.9%)
Lab value low high
correlates with which terms?
hypo or hyper, high or low…
fluid goes which way?
(T to B or B to T?)
causes what pathologic fluid
status? S&S?
caused by what dz or
disorders?
compensation is done by
natriuretic peptides or RAAS?
, 2
II. Electrical issues
1. Associate K+ & Ca+ with electrical issues—they are the solutes that drive changes in excitability of cell membranes. Their movement
in & out of the blood & the cells is based on diffusion. (movement of molecules from area of higher solute concentration to area of
lower solute concentration.)
2. Normally there are slightly more anions than cations just inside the cell membrane, rendering the resting membrane potential (RMP)
slightly negative (norm = -90mV).
The more cations (and/or the less anions) there are inside the cell membrane, the more positive the RMP becomes, bringing it
closer to the depolarization goal of +30mv. The disorders that do this hypopolarize the cell; that is, bring its two poles—the
RMP & the depolarization point—closer together and make the cell more sensitive to signal stimulus. S&S include
“hypersensitive” cells—more prone to spasm & irritability. (Hypopolarization = hyperactive S&S).
The less cations (and/or the more anions) there are inside the cell membrane, the more negative the RMP becomes, making it
further from the depolarization goal of +30mv. The disorders that do this hyperpolarize the cell; that is, make its two poles—
the RMP & the depolarization point—farther apart and make the cell less sensitive to signal stimulus. S&S include
“hyposensitive” cells— they are slow to respond & the patient will be weak & lethargic. (Hyperpolarization = hypoactive S&S).
3. Two classic sets of situations have been discussed in class: hypo- and hyperkalemia, and hypo- and hypercalcemia.
Again, always think plasma space first in terms of changes. If the plasma becomes hypokalemic, K+ is going to diffuse into the
plasma space from the interstitial space & eventually out of the cells too. This leaves the cells hypokalemic & hyperpolarized
(less cations = more negative RMP). Similarly, if the plasma is hyperkalemic, K+ will eventually diffuse into the cells, leaving
them hyperkalemic & hypopolarized
But calcium is different. It has that special effect on Na+ So remember, if hypocalcemia (exists, it means the blood is low on
calcium, but DO NOT apply the usual diffusion process as you do to K+ states. Instead, think: “if hypocalcemia exists, it means
that the cells have become more permeable to INFLUX of Na+.” This means the cell will become more positive on the inside
(more Na+ = more cations), which means the RMP will become more positive = hypopolarized. Similarly, if the plasma is
hypercalcemic (high Ca+), it will cause Na+ to eventually diffuse OUT of the cells, leaving them with a more negative RMP &
they will be hyperpolarized (less cations = hypopolarized).
hypocalcemi hypercalcem
a ia
normal serum hypokalemia K+ hyperkalemia K+ K+ K+
Na+ Na+
levels K+
+30 +30 +30 +30 +30
K+ K+ K+ K+ K+ K+ K+ K+ K+ K+
Na+ -90 Na+ Na+ Na+ Na+ -90
-90 -90 -90
____ ____ ____ ____ ____
I. Fluid shift issues
1. For our test questions about fluid shifts, Na+ (& its other form, NaCl) & proteins will be the solutes involved. They are the main
solutes that drive fluid shifts, which are based on osmosis --movement of water from area of lower solute concentration to area of higher
solute concentration.
(For questions involving K+ and Ca++, think electrical status—see Electrical Issues below.)
2. Remember that (for our purposes) changes in fluid status begin in the plasma space. So in any scenario you are given, think: in what
way has this scenario changed the solute status in the plasma space—has water been added or solutes removed (making the plasma
space more dilute)? Or has water been taken away or solutes added (making the plasma space more concentrated)? Also remember
that the tissue status (cells and interstitial space) remains normal initially —the “normal” number of solutes & “normal”
amount of water exist in the tissue at the beginning of the scenario. Therefore, when the plasma space dilution changes, think: “the
plasma has changed, but initially the tissue hasn’t YET—I have to figure out what happens next.” The situation will always be one of
these pictures (will discuss more at review):
took away water or added solutes to added water or took away solutes to
plasma space = more solutes than plasma space = less solutes than tissue
tissue
or? or?
tissue has normal tissue has normal
numbers of numbers of
solutes solutes
(**In studying your info, serum osmo (norm = 280- 295) serum Na+ (norm = 135-145) serum protein (oncotic pressure)
always think both “front
door” AND “back door.”) serum NaCl (norm = 0.9%)
Lab value low high
correlates with which terms?
hypo or hyper, high or low…
fluid goes which way?
(T to B or B to T?)
causes what pathologic fluid
status? S&S?
caused by what dz or
disorders?
compensation is done by
natriuretic peptides or RAAS?
, 2
II. Electrical issues
1. Associate K+ & Ca+ with electrical issues—they are the solutes that drive changes in excitability of cell membranes. Their movement
in & out of the blood & the cells is based on diffusion. (movement of molecules from area of higher solute concentration to area of
lower solute concentration.)
2. Normally there are slightly more anions than cations just inside the cell membrane, rendering the resting membrane potential (RMP)
slightly negative (norm = -90mV).
The more cations (and/or the less anions) there are inside the cell membrane, the more positive the RMP becomes, bringing it
closer to the depolarization goal of +30mv. The disorders that do this hypopolarize the cell; that is, bring its two poles—the
RMP & the depolarization point—closer together and make the cell more sensitive to signal stimulus. S&S include
“hypersensitive” cells—more prone to spasm & irritability. (Hypopolarization = hyperactive S&S).
The less cations (and/or the more anions) there are inside the cell membrane, the more negative the RMP becomes, making it
further from the depolarization goal of +30mv. The disorders that do this hyperpolarize the cell; that is, make its two poles—
the RMP & the depolarization point—farther apart and make the cell less sensitive to signal stimulus. S&S include
“hyposensitive” cells— they are slow to respond & the patient will be weak & lethargic. (Hyperpolarization = hypoactive S&S).
3. Two classic sets of situations have been discussed in class: hypo- and hyperkalemia, and hypo- and hypercalcemia.
Again, always think plasma space first in terms of changes. If the plasma becomes hypokalemic, K+ is going to diffuse into the
plasma space from the interstitial space & eventually out of the cells too. This leaves the cells hypokalemic & hyperpolarized
(less cations = more negative RMP). Similarly, if the plasma is hyperkalemic, K+ will eventually diffuse into the cells, leaving
them hyperkalemic & hypopolarized
But calcium is different. It has that special effect on Na+ So remember, if hypocalcemia (exists, it means the blood is low on
calcium, but DO NOT apply the usual diffusion process as you do to K+ states. Instead, think: “if hypocalcemia exists, it means
that the cells have become more permeable to INFLUX of Na+.” This means the cell will become more positive on the inside
(more Na+ = more cations), which means the RMP will become more positive = hypopolarized. Similarly, if the plasma is
hypercalcemic (high Ca+), it will cause Na+ to eventually diffuse OUT of the cells, leaving them with a more negative RMP &
they will be hyperpolarized (less cations = hypopolarized).
hypocalcemi hypercalcem
a ia
normal serum hypokalemia K+ hyperkalemia K+ K+ K+
Na+ Na+
levels K+
+30 +30 +30 +30 +30
K+ K+ K+ K+ K+ K+ K+ K+ K+ K+
Na+ -90 Na+ Na+ Na+ Na+ -90
-90 -90 -90
____ ____ ____ ____ ____
