Biomedical Engineering Reference
In-Depth Information
Table 2.3
Composition of the Extracellular and Intracellular Fluids
Plasma
(mOsm/L)
Interstitial
(mOsm/L)
Intracellular
(mOsm/L)
Solute
Na
+
K
+
Ca
2+
Mg
2+
Cl
−
HCO
3
−
HPO
4
−−
, H
2
PO
4
−−
SO
4
−−
142
4.2
1.3
0.8
108
24
2
0.5
139
4.0
1.2
0.7
108
28.3
2
0.5
14
140
0
20
10
10
11
1
Phosphocreatine
Carnosine
Amino acids
Creatine
Lactate
Adenosine triphosphate
Hexose monophosphate
Glucose
Protein
Urea
Others
45
14
8
9
1.5
5
3.7
2
0.2
1.2
2
0.2
1.2
5.6
1.2
4
4.8
5.6
0.2
4
3.9
4
4
10
Total (mOsmole/L)
301.8
300.8
301.2
Corrected osmolar
activity (mOsmole/L)
282.5
281.3
281.3
Total
π
(mmHg)
5,443
5,443
5,443
an increase in osmolarity of the extracellular fluids and from a reduction in plasma
volume. Cells within the hypothalamus can detect an increased extracellular fluid
osmolarity and initiate activity in neural circuits that results in a conscious sensa-
tion of thirst. Baroreceptors, specially adapted groups of nerve fibers within the
walls of a few blood vessels and the heart, can also influence the sensation of thirst.
When they detect a decrease in blood pressure, signals are sent to the central nerv-
ous system along sensory neurons to influence the sensation of thirst. Low blood
pressure associated with hemorrhagic shock, for example, is correlated with an
intense sensation of thirst.
EXAMPLE 2.9
0.9% NaCl, commonly called saline solution, is used clinically. What is the osmolarity of
this solution?
Solution: NaCl dissociates into Na
+
and Cl
−
ions. 0.9% NaCl solution contains 0.9 grams
NaCl per 100 mL of water or 9 grams per liter. MW of NaCl is 58.5. Thus, there is 9/58.5 or
0.154 mol or 154 mmol/L of NaCl of solution. Hence, osmolarity is 154 × 2
=
308 mOsM.
