Biomedical Engineering Reference
In-Depth Information
Figure 2.1
Biotransport at multiple levels.
over large distances occurs in conjunction with fluid flow (termed as convective
flow), we will discuss the basic transport mechanisms across various biological
barriers in this chapter. First, the basic terminologies such as different compart-
ments, pH, pressure, and concentration are defined. Next, diffusion, osmosis, and
the transport of molecules across different tissues are described. Finally, movement
of macromolecules across single cells is discussed.
2.2 Fundamental Factors
2.2.1 Fluid Compartments
Water is the main fluid in the body through which biomolecules move from one
region to the other. Fluid in the body is either intracellular or extracellular. Intracel-
lular fluid is present inside the cells. The extracellular fluid is present outside the cell
body. Extracellular fluid is subdivided into the following compartments:
1. The plasma, which occupies the extracellular space within blood vessels
and the heart.
2. The interstitial fluid, which occupies the spaces between tissues excluding
blood vessels. A large fraction of blood in the capillaries surrounding a
tissue space is filtered into the tissue space as interstitial fluid. Thus, inter-
stitial fluid bathes the cells in the tissue space. Thus, all the requirements
of cells such as nutrients and signals and their synthesized products are
transported through interstitial space.
