Biomedical Engineering Reference
In-Depth Information
1.3
Plasma Constituents
Plasma represents approximately 55% of the blood volume. The remaining is
hematocrit
(Ht), i.e., percent of packed cells
5
(Ht 38-46% in women, 42-53% in
men). Plasma is mainly composed of water, a suspending fluid (or solvent) for
various solutes (Table
1.3
). Plasma contains 92% water, 8% proteins (
∼
7 g/dl), and
other substances.
1.3.1
Electrolytes
Electrolytes, or ions, contribute to the osmotic pressure (
), which is mainly
regulated by the kidneys. Major electrolytes are Na
+
,K
+
,Ca
2
+
,Mg
2
+
cations,
and HCO
3
,Cl
−
,HPO
2
−
Π
4
,andSO
2
4
anions.
Cations and anions are unevenly distributed in body fluid compartments (Ta-
ble
1.4
). Sodium ion (Na
+
) is the major cation and chloride (Cl
−
)themajor
anion outside the cell. Inside the cell, potassium ion (K
+
) is the major cation and
phosphate (HPO
2
−
4
) the major anion. At physiological pH, proteins are negatively
charged.
Ion transport through the cell membrane between the body fluid compartments
requires specialized plasmalemmal proteins (Fig.
1.1
and Vol. 3 - Chaps. 2.
Membrane Ion Carriers to 5. Receptors of Cellular Trafficking). Ion displacements
in the different compartments affect the blood volume.
Tabl e 1. 3.
Plasma approximate composition (%). Plasma, the suspending fluid for peripheral
blood cells, is composed of water, electrolytes, proteins (albumins 60-80%, globulins 16-36%,
and fibrinogen 4%), amino acids, lipoproteins, other lipids, and glucids. Hormones, vitamins, and
enzymes are conveyed by blood. The
normal plasma volum
e is 40 to 90 ml/kg of body weight.
Wat er
∼
92
Proteins
∼
7.0
Electrolytes
∼
0.9
Lipids
∼
0.6
Glucids
∼
0.1
5
Because erythrocytes (RBC) represent 97% of blood cell volume (Table
3.1
), Ht estimates RBC
concentration. The normal sex-dependent range has different limits according to different research
teams: Ht
=
.
±
.
=
.
±
.
0
47
0
07 and Ht
0
42
0
05 in male and female subjects, respectively.
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