The Human Cardiovascular System - Computational Hemodynamics: Theory, Modelling and Applications - page 33

Fig. 2.15 Composition of
blood. The hemacrotit is a
measure of the percentage of
blood is that contains formed
elements ( the RBC, WBC,
and platelets ), or plasma. On
average the formed elements
make up 45 % and plasma
make up 55 %

2.2.7 Blood

Blood circulates around the human body via the circulatory system, carrying with
it nutrients and oxygen. The cell components suspended in blood primarily consists
of the erythrocytes (red blood cells) that transport respiratory gases; the leukocytes
(white blood cells) that enhances immunity against diseases; and the thrombocytes
(platelets) that provide the mechanism for blood clotting. The proportion of blood
occupied by red blood cells is normally about 45 %. White blood cells and platelets
make up a very small portion of the blood and therefore are often included in this
percentage. The remaining proportion, approximately 55 %, is made up of plasma.
The hematocrit is a measure of the proportions of blood that are either cellular
(RBC) or liquid (plasma). For example normal haematocrit is approximately 48 %
for men and 38 % for women. This represents the percentage of blood by volume
that contains red blood cells.

Plasma is composed predominantly of water (making up to 93 % by volume), pro-
teins, glucose, mineral ions, hormones and carbon dioxide. It serves as a form of
protein reserve in the body, maintains the electrolyte level by intravascular osmosis,
and prevents infection or blood disorders. Blood plasma has a density of 1025 kg/
m 3 .

Erythrocytes (Red Blood Cells) Red blood cells are oxygen carriers of the blood
and have a lifetime of approximately 120 days. The hemoglobin, which is an iron-
based protein with molar mass of approximately 65,700 g/mol., gives the red blood
cell its color, and it also facilitates oxygenation of the blood and transport of oxygen
and respiratory gases.

Leukocytes (White Blood Cells) White blood cells protect the body against infec-
tion and non-biocompatible substances. The cells are manufactured in the bone
marrow (a hematopoietic stem cell), and have a lifespan of approximately 3 days.
They are then distributed to the human body and exist in both the circulation and
lymphatic systems.

Thrombocytes (Platelets) Platelets are micro-scale cell fragments of approxi-
mately 2 µm in diameter and have a lifespan of approximately 7 days. Platelets are