Pesticides in the Diets of Infants and Children (1993) / Chapter Skim
Currently Skimming:
2 SPECIAL CHARACTERISTICS OF CHILDREN
2 SPECIAL CHARACTERISTICS OF CHILDREN
Pages 23-48
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 23... ...
From birth through adolescence, physical growth and functional maturation of the body continue. The rates of physical growth and functional development vary from system to system, organ to organ, and tissue to tissue during this time.
|
From page 24... ...
Alteration in one of these domains can affect the development of each of the other three. Because of the dependence of behavioral development on physical and functional development, toxic effects occurring before maturation may permanently alter behavioral development.
|
From page 25... ...
Although infant and adult nonhuman animals differ in much the same way that human infants and adults differ, there are substantial interspecies differences among the young. For example, the newborn mouse or rat more nearly resembles the human fetus in the third trimester of gestation than the human infant at birth.
|
From page 26... ...
is never the same from moment to moment until growth processes are complete. Normal Human Growth After birth of the the full-term human infant, growth occurs at an average rate of 800 g/month or at an incremental rate of 25% of total body weight per month.
|
From page 27... ...
27 ._ cn _ it - (V ~ o ~ ~ ~ ._ o o ° hi: _ cn > ._ pa cn ~ U
|
From page 28... ...
Thus, as the child grows, his or her body consists of differing proportions of various tissues and organs that comprise the body. Various tissues brain, skeletal muscle, liver, heart, and kidney-have different metabolic rates and biochemical pathways, and their changing physical proportions will alter the disposition of xenobiotic compounds over time.
|
From page 29... ...
The effects on the mouse or hamster should be less pronounced than those on the dog, rabbit, or rat but still more pronounced than those on the human infant. However, if toxicity is related to absolute rates of growth, the order of increased sensitivity would be the hamster (36 days for a 10-fold increase in birth weight)
|
From page 30... ...
The animals were observed throughout their life span, and tumor incidence was compared with that in a nontreated control group (group 4~. Mammary adenocarcinomas occurred only in the rats treated at 3 months of age: 71% of group 1 and 32% of group 2 animals.
|
From page 31... ...
The authors pointed out that animals exposed early in life must be allowed to live out their full life span if appropriate tumor incidence is to be ascertained. When this was done, it was quite apparent that the animals exposed at the youngest age had, with an occasional exception, the highest incidence of a variety of tumors.
|
From page 32... ...
Ibe brain approaches adult size early in childhood, although behavioral development continues for many years. The uterus and testes grow slowly until adolescence, and the growth of the ovaries is similar to that of the kidney and spleen and to increase in total body weight.
|
From page 34... ...
Although the developmental sequences of tissue organization and cellular maturation are similar in various animal species, the specific rate of each sequence relative to other sequences and across species differs significantly (Rodier, 19801. The myelination of nerve tracts in the spinal cord and peripheral nerves is a process that continues throughout childhood.
|
From page 35... ...
Body water increases about 15-fold, but extracellular water only 10-fold. Total body protein increases almost 20-fold, whereas bone mineral increases by 25-fold and total body potassium by about the same amount as total body protein because protein is located primarily in cells and potassium is primarily an intracellular ion.
|
From page 36... ...
The change in intracellular water is to a large extent related to an increase in cell size. The changes in body water compartment sizes with increasing age may bear some relationship to changes in pesticide toxicity, depending on the distribution of the toxic compound.
|
From page 37... ...
The specific stage in tissue or organ development when environmental factors can modify the cells to produce an effect apparent only in later life are termed critical periods of development. For example, giving insulin or glucosamine to newborn animals may permanently alter the mature animal's insulin levels and blood glucose values (Csaba and Dobozy, 1977; Csaba et al., 1979~.
|
From page 38... ...
and impaired ability to withstand oxidant stress. Similarly, the increasing presence of chromosome aberrations in the cells of the older person, perhaps because of longer exposure to toxic substances in the environment, may contribute to the increased carcinogenic susceptibility of the elderly (Singh et al., 1986~.
|
From page 39... ...
Developmental Toxicity Studies Because so many bodily functions are at various stages of development throughout infancy and early childhood, toxic effects of chemical agents during these age periods not only produce the same sorts of direct injuries to established organ tissues and functions seen in adults, but also have the potential to affect the later development of anatomic, physiologic, and metabolic processes. During organogenesis, functional integrity does not necessarily coincide with morphological maturity, and relative organ size varies as development proceeds.
|
From page 40... ...
The complexity of the age-related changes in vascular responsiveness is illustrated by analysis of the changes in contractile function of the arterial smooth muscle in the rat. The responsiveness of the venous smooth muscle to the stimulant isoproterenol does not change with age, whereas the responsiveness of the arterial smooth muscle increases in the postnatal period and then declines with increasing maturity.
|
From page 41... ...
Without detailed knowledge of all such age-related physiological changes and their potential interactions, it is impossible to extrapolate the impact of xenobiotic effects from mature to young animals. It is therefore necessary to examine such effects in immature animals of various ages.
|
From page 42... ...
At present, toxicity data on mature animals are insufficient for extrapolation to immature animals. Conclusions · Human infants and children differ from human adults not only in size but also, and more importantly, in the relative immaturity of biochemical and physiological functions in major body systems; body composition in terms of proportions of water, fat, protein, and mineral mass, as well as the chemical constituents of these body components; the anatomic structure of organs; and the relative proportions of muscle, bone, solid organs, and brain.
|
From page 43... ...
· Studies should be conducted to examine age-related physiological changes and their potential interactions in immature animals of various ages. · Because of the variable rates of organ development within and be
|
From page 44... ...
Pp. 3-18 in Human Growth: Body Composition, Cell Growth, Energy and Intelligence.
|
From page 45... ...
1982. Body composition of reference children from birth to age 10 years.
|
From page 46... ...
Influence of age, sex and nutrition on body composition during childhood and adolescence. Pp.222-238 in Human Development, F
|
From page 47... ...
1968. Biological implications of body composition.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.