Tissue-fluid interactions, determining

This external exposure may not necessarily correlate with internal exposure. The rate of absorption through the skin, the lung or the gastrointestinal tract determines the body burden of the chemical. Measurement of the chemical, its metabolites or products of the interaction of the chemical or its metabolites with cellular macromolecules such as proteins or DNA in body fluids and tissues determines internal exposure . Use of such biomarkers provides exact information on actual internal exposure (target dose) to an agent (Angerer et al. 2007 Boogaard 2007 Needham et al. 2007). When used in experimental studies in animals and humans they allow assessment of the individual and internal exposure as compared to external exposure. 

In attempting to understand the human body, much can be learned from material and fluids testing and cadaveric examination. These processes do not, in general, determine the relative forces and interactions between structures. They are also not able to determine the stresses within hard or soft tissue nor the patterns of flow due to the interaction of red blood cells within the vascular system. 

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