Distribution of Body Fluids
ICF
Transcapillary Transport
Transcapillary Hydrostatic and Osmotic Pressures
Distribution of Body Fluids
(in a 70 kg young man)
Intracellular
Fluid (25 L)
Total 60% (Cytoplasm)
Body Interstitial
Plasma 75% Fluid (13 L)
45% Blood Cells
Water Extracellular (2.5 L)
40% Transcellular
(42 L)
Fluid (17 L) Fluid (1 L)
Intravenous 7% Plasma
(5.5 L Whole Blood) Protein and Lipid
What is the fate of these solutions given IV? 55% Blood
• 1 L d5W Plasma (3 L)
• 1 L 0.9% NS
93% “Plasma Water”
• 200 mL PRBC
! Plasma is 7% protein/lipid and 93% aqueous with [Na] = 142 mM
! So protein- and lipid-free plasma has a [Na] = 142/0.93 = 153 mM
! That’s why the [Na] in 0.9% NS (100% aqueous) is 154/1.0 = 154 mM
! If a patient has severe hyperlipidemia with a 20% protein/lipid content, the lab
may report a [Na] = 122 mM, but the actual [Na] = 122/0.8 = 153 mM (normal)
! Note the osmolality of all compartments is the same, and that the additional 7
g/dL of plasma protein increases osmolality by only 1 mOsm.
Membrane Channels,
Transporters, and Pumps
Membrane Channels,
Transporters, and Pumps
In the Beginning There Were Pumps
and CHANNELS...
Na+ 3Na+ Na+
Na,K
Pump
K+ ATPase
ATPase
2K+
Na+ Na+
K+ K+ Channel
“I am made from the dust of the stars,
And the ocean flows in my veins…”
and it was GOOD! --Rush, 1989
SALT
Hypervolemia
Isotonic Saline Stores
Hypovolemia
WATER
Kalmon in a Salinarium
Hypotonicity
Positive Free Water
Zero Net Free Water
Hypertonicity
Negative Free Water
Effects of Adding IV Solutions
0.9% NS
1.5 L
Water (d5W)
1.5 L
NaCl
217.5 mM
Effects of Adding IV Solutions
Why Do People Lost at Sea Die of Thirst?
! Because the ocean no FREE WATER for a human
! “Water, water everywhere but not a drop to drink”
! Sea “water” is actually ~3% (hypertonic) NaCl
! Much more concentrated than human plasma (0.9% saline)
! So you die of water depletion (dehydration)
! if you drink from the ocean, you can actually be hypervolemic at the
same time you die from dehydration!
Na+ Balance
Na+ (ECF Volume) Balance
Edema
5g
2g Na+ Intake
SALT vs WATER
Volume Regulation Free Water Regulation
What is being Effective Circulating Plasma Tonicity
Sensed? Volume
Normal Setpoint NormoVolemia IsoTonicity = IsoAquemia
Sensors Baroreceptors (e.g., atrial) Osmoreceptor (hypothalamus)
Effectors Sympathetic Nervous System Thirst
Renin-Ang II-Aldosterone
Natriuretic peptides (e.g., Anti-Diuretic Hormone
ANP)
Anti-Diuretic Hormone
What is Affected? Sodium reabsorption Free water intake via thirst
Sodium excretion ADH-dependent free water
retention or excretion by the
kidney
Stress to organism
What are kidneys for? Free water Salt
[Na] Na+
Land Shortage Shortage
Freshwater Surplus Shortage
Seawater Shortage Surplus
Salt and Water:
Don’t Leave the Ocean Without It
Salt and Water:
Don’t Evolve Without It
It’s Great to “Get” Cholera