To: All Msg #231, Jun1693 12:24PM Subject: Seawater =/= blood, but. Sea water is not blood
From: James G. Acker
To: All Msg #231, Jun-16-93 12:24PM
Subject: Seawater =/= blood, but...
Organization: NASA Goddard Space Flight Center -- InterNetNews site
From: firstname.lastname@example.org (James G. Acker)
Sea water is not blood.
Well, that much should be obvious! Sea water is pure
and clear, while blood has got all sorts of things in it --
red and white blood cells, platelets, proteins, hormones,
waste products (urea, uric acid), etc. There really
shouldn't be much of a similarity between an essentially
biological fluid and a fluid that resulted primarily from
inorganic chemical reactions.
But, nonetheless, I attempted to compare the elemental
chemistry of blood to the elemental chemistry of seawater.
The numbers below are approximate: I couldn't compare the
density of blood serum to seawater. The blood numbers are
from Gould Medical Dictionary, Appendix, 3rd Edition, 1972
(what do you expect in an aerospace library?); the seawater
numbers are from _Aquatic Chemistry_, 2nd Edition, Stumm and
Morgan, available at fine marine science and hydrology
graduate departments nationwide.
Note that grams/kg is the most common method of expressing
elemental concentrations in seawater, so I converted the
blood numbers to this unit.
Element SW (g/kg) Blood (g/kg)
Bicarbonate .1424 .015
Calcium .4121 .05 (ionized) / .1 (serum)
Chloride 19.354 3.6
Copper 10E-8 .001 (10E-3)
Magnesium 1.29 .025
Phosphorus 2E-6 .0375
Potassium .399 .16
Sodium 10.77 3.2
Sulfate 2.712 .01
Order of concentration in SW: Cl, Na, Sulfate, Mg, Ca, K,
In blood: Cl, Na, K, Ca, Mg, bicarb, Sulfate.
Also, SW pH range is from 7.4 - 8.2 (higher in surface
waters), and blood is 7.38-7.44.
So, what have we gained from this comparison?:
Bicarbonate: in SW, controlled by carbon dioxide solubility
and calcium carbonate saturation; in blood, controlled by
respiration and gas exchange. Factor of 10 lower in blood.
Calcium: Factor of 4-8 lower in blood. (Factor of 8 is derived
from the "ionized" number.)
Chloride: Approximate factor of 5 lower in blood.
Copper: HUGE difference. Cu in seawater is controlled by
mineral solubility and carbonate complexation; there's a
lot of it in blood. Cu-hydroxyl complexes control
solubility in SW.
Mg: Factor of 50 less in blood compared to SW.
P: Much higher in blood (required for metabolism in
humans: energy source;) nutrient in SW.
K: Factor of 2.5 less in blood compared to SW: used in
muscles (I know this because K depletion can cause muscle
Na: Factor of 3.3 less in blood compared to SW.
Sulfate: Approx. 30 times more concentrated in SW.
Now, if we just look at Na, Cl, K, Ca, Mg, and Sulfate,
it's immediately apparent that Mg and sulfate are virtually
non-existent in blood, but important SW constituents.
Na, Cl, K, and Ca are (roughly) more dilute by factors
of 3-8 in blood than in SW. More sodium may be required to
balance the charge-balance problems due to the lack of Mg
(Mg is a doubly-charged cation) in blood. Ca is slightly
more dilute, but some Ca may be extracted for bone building
(and Ca participates in some other biochemical functions as
well.) Higher potassium levels (though I imagine these are
fairly variable) might also compensate.
Cu blew me away (I didn't bother comparing iron), but I
didn't realize there was so much Cu in blood.
So, seawater is clearly =/= blood. However, the
similarity of some of the dilution factors (for Na, Cl, Ca,
and K) is interesting. The absence of Mg and sulfate really
intrigues me; if I was to postulate that blood serum was
derived from SW, I'd first have to explain why Mg and
sulfate were eliminated. For sulfate, it's suggestive that
anaerobic processes rely on oxidation of sulfate to sulfides
(in anoxic muds), so sulfate is less likely to appear in an
oxic environment where respiration takes place. Mg is more
troublesome. I can't think of any biochemical processes in
humans that require Mg, so apparently we don't need it, and
therefore it isn't present in high concentrations. Of
course, we don't need chlorides either, other than to
balance the charge!
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