When physiological experimentation is performed with organs or
tissue removed from animal bodies, it is necessary to keep the specimen
moistened with a solution which contains the same ratio of major ions (Ca++,
Na+, K+) as is found in the ECF of the intact organism. This applies to
organ transportation during transplants also.
One such solution is called "Ringer's solution" after the British physiologist,
Sidney Ringer, who developed it.
The original discovery, as is so often the case in scientific
work, was a result of chance. It was the practice at the time to use a
simple solution of salt (Na+ and Cl- ions) for bathing tissues. On one
occasion, a particular batch of solution kept frog hearts alive much longer
than expected. It was found that a lab assistant had used tap water rather
than distilled water. The search was on for the other necessary ions and
Ringer's solution resulted.
Another interesting fact about the ratio of ions in the ECF of
animals can be seen by looking at Table 2. Sea water, the ECF of marine
invertebrates, and the ECF of vertebrates (including man) show a
striking similarity in the relative amounts of the ions present. The absolute
amount of the different ions varies more widely; the concentration of salts
in sea water and the ECF of marine invertebrates is roughly three times
that of the ECF in vertebrates. The similarity is sufficiently close that
workers in the Woods Hole Marine Biological Laboratories often substitute
diluted sea water (3 to 1) for Ringer's solution in routine physiological
experiments. This Woods Hole Ringer's serves the purpose admirably. The
ion ratios remain the same even when diluted, only the concentration changes.
The similarity between the ratio of ions in sea water and the
blood plasma of animals lends strong support to the idea that life arose
in the sea. Although animals now inhabit fresh water and the land, they
must actively regulate the composition of their self contained ECF so that
its ionic composition continues to be compatible with the processes of
life.
Table 3 shows the concentrations of electrolytes and protein in human
plasma.
Constituent
grams / l
millimoles / l
Sodium, Na+
3.39
144
Chloride, Cl-
3.55
100
Bicarbonate, HCO3-
1.50
25
Potassium, K+
0.17
4.4
Calcium, Ca++
0.10
2.5
Phosphate, HPO4--,or, H2PO4- 0.10
1.0
Magnesium, Mg++
0.04
1.5
Protein
70.00
2.5
To continue our look at the composition of the ECF, we look at
foods and vitamins.
Foods and vitamins: The ECF contains organic compounds which serve
as food or vitamins for the cells. Food substances serve as a source of
energy and as material for growth and repair. They include lipids, nitogen-containing
compounds such as amino acids, and most widespread of all, a carbohydrate
source such as glucose. The blood plasma of man contains 0.1 % of glucose,
or as its sometimes called, blood sugar. Homeostatic mechanisms maintain
this level within narrow limits in the ECF.
Hormones: Hormones are an important component of the ECF of vertebrates,
higher plants and perhaps all multicellular organisms. They are chemical
substances, released into the ECF by certain cells, which affect the metabolic
activities of other cells in the organism. Everything from digestion to
sweat and sexual activities. Over two hundred and forty major hormones
have been identified and perhaps as many a few thousand more are being
actively analyzed.
Wastes: The waste products of cell metabolism are also components
of the ECF. Among the most important to animals are the waste products
of protein and nucleoprotein (chromosomes) metabolism. These nitrogen-containing
wastes, such as ammonia and urea, are somewhat poisonous. Their level in
the ECF must not be allowed to exceed certain limits or death will result.
In most organisms, precise homeostatic devices have evolved (e.g. the kidney)
which regulate the level of these wastes in the ECF. Although there are
some cases where too low a level of a given waste in the ECF would be harmful,
the major emphasis is on preventing too great an accumulation of the waste.
It is not always easy to distinguish clearly between cell waste
in the ECF and some of the chemical messengers mentioned above. A substance
which is a waste product of one cell may well be necessary to the proper
functioning of some other cell. For example, the carbon dioxide discharged
into the ECF by all of our cells provides a necessary stimulus for that
part of the central nervous system that controls the rate of our breathing.
Here then, is a case where too low a level in the ECF of a given waste
would be as harmful as too high a level.
--to be continued--
Bless you, Bob Lee
--
oozing on the muggy shore of the gulf coast
l...@fbtc.net
--
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