Anatomical and functional characteristics

Although the full-term neonate is bom with kidneys containing essentially the same number of nephrons as the adult, overall renal 

Another difference between adults and infants is that most of the cells are smaller in infants than in adults. Small cells have greater surface area in relation to mass compared with larger cells. This may have important implications for chemicals that come in contact with the cells in target organs (NRC, 1993). 

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Describe the anatomical and functional characteristics of each of the four layers of the digestive tract wall mucosa, submucosa, muscu-laris externa, and serosa... 

Deposition in the thoracic region is the sum of aerodynamic and thermodynamic deposition of particulate material. Aerodynamic deposition depends on aerodynamic particle size, total volumetric flow rate, anatomical dead space, tidal volume, functional residual capacity (FRC) (combined residual and expiratory reserve volume or the amount of air remaining in the lungs after a tidal expiration) and diameter of the airways. Thermodynamic deposition depends on anatomical and physical characteristics, such as tidal volume, anatomical dead space, functional residual capacity and the transit time of air within each region. Thermodynamic particle size, which is derived from the diffusion coefficient, particle shape factor and the particles mass density, influence thermodynamic deposition. 

This chapter summarizes the distinct characteristics of children across life stages that contribute to unique differences in their susceptibility to environmental exposures. These include anatomical, physiological, metabolic, functional, toxicokinetic, and toxicody-namic characteristics. The normal development of various organ systems is also addressed. Differences in exposure pathways and behavioural characteristics will be addressed in chapter 5. Different organ systems develop at different rates, and comparison across life stages will allow for identification of specific systems that are at risk during specific stages of development. 

Children s environmental health risks result from exposure of the parents before conception and of the child during the prenatal period and through childhood and adolescence. In this context, a child can be defined by a series of life stages from conception through adolescence, where each life stage has distinct anatomical, physiological, behavioural, and/or functional characteristics that contribute to potential differences in exposure, resulting in overall differences in susceptibility. 

These early studies support the concept that the heart is well designed, both anatomically and biochemically, for uninterrupted, rhythmic aerobic work. Although heart muscle has certain distinctive biochemical characteristics, many of the basic biochemical reaction patterns are similar to those of other tissues. In short, metabolism and function of the heart are inextricably linked (Fig. 1). 

Anatomical and Physiological Considerations. Fish possess a large number of unique features which distinguish them both structurally and functionally from other vertebrates. Many of these biological characteristics are germane to xenobiotic studies. 

For the safeguarding of the entire active system of man-machine-environment, exactly the same principles are applied as have been referred to in Reliability and Suitability of Machines. In the case of man, the pertinent procedures can likewise be subdivided into planning, control, and testing. During the planning of a man-machine-environment-system, the anatomical data of the human body and its physiological processes and functions must be taken into account as contributory prerequisites in the same way as the stress characteristics of a material used in the construction of a machine. 

Distinguish among arteries, arterioles, capillaries, and veins in terms of their anatomical characteristics and their functions... 

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