Biomedical Engineering Reference
In-Depth Information
CHAPTER 2
Biotransport
2.1 Overview
The human body is made of complex and delicate structures. These structures are
continuously subjected to various disturbances. For example, all cells require a
constant supply of nutrients such as oxygen, glucose, and water to support various
functions. There is unceasing continuous molecule and ion traffic in and out of the
cells and the body. Various biological membranes lining cells and tissues act as bar-
riers for transport of molecules while regulating biological functions at each level.
Thus, the transport of molecules can be visualized to occur at five levels (Figure
2.1):
1. Across different tissues;
2. Between different cell types;
3. Between the cells of the same type;
4. From the outside to the inside of the cell;
5. Within a cell.
For example, the flow of molecules and ions between the cell and its environ-
ment is precisely regulated by specific transport systems. Regulated movement of
various ions across the cell membranes leads to the presence of ionic gradients,
which are vital in stimulating nerves and muscles. Furthermore, vital functional
molecules such as insulin secreted by pancreatic
β
-cells needs to be transported to
the entire body.
A fundamental understanding of how homeostasis (a Greek word meaning “the
same” and “standing,” a state of relative constancy of its internal environment) is
maintained in various compartments of the body is critical to the design and devel-
opment of synthetic substitutes, which could effectively interfere and/or replace the
diseased or dysfunctional tissue. For example, external support devices such as di-
alysis machines, heart-lung machines, mechanical ventilators, and contrast agents
used during biomedical imaging have to assist in maintaining homeostasis. Dia-
lysate solution used in dialysis should only remove the toxins and excess water—
not important electrolytes. In addition, modeling various physiological processes
such as alterations in calcium fluxes during a cardiac cycle (and subsequent events)
helps to understand the process of tissue regeneration. Although molecular transfer
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