Directional Trends

Growth and development proceed in regular, related directions or gradients and reflect the physical development and maturation of neuromuscular functions (Fig. 5-1). The first pattern is the cephalocaudal, or head-to-tail, direction. Whereas the head end of the organism develops first and is large and complex, the lower end is small and simple and takes shape at a later period. The physical evidence of this trend is most apparent during the period before birth, but it also applies to postnatal behavior development. Infants achieve structural control of the heads before they have control of their trunks and extremities, hold their backs erect before they stand, use their eyes before their hands, and gain control of their hands before they have control of their feet.

Second, the proximodistal, or near-to-far, trend applies to the midline-to-peripheral concept. A conspicuous illustration is the early embryonic development of limb buds, which is followed by rudimentary fingers and toes. In infants, shoulder control precedes mastery of the hands, the whole hand is used as a unit before the fingers can be manipulated, and the central nervous system develops more rapidly than the peripheral nervous system.

These trends or patterns are bilateral and appear symmetric—each side develops in the same direction and at the same rate as the other. For some of the neurologic functions, this symmetry is only external because of unilateral differentiation of function at an early stage of postnatal development. For example, by the age of approximately 5 years, children have demonstrated a decided preference for the use of one hand over the other, although previously either one had been used.

The third trend, differentiation, describes development from simple operations to more complex activities and functions. From broad, global patterns of behavior, more specific, refined patterns emerge. All areas of development (physical, mental, social, and emotional) proceed in this direction. Through the process of development and differentiation, early embryonal cells with vague, undifferentiated functions progress to an immensely complex organism composed of highly specialized and diversified cells, tissues, and organs. Generalized development precedes specific or specialized development; gross, random muscle movements take place before fine muscle control.

Sequential Trends

In all dimensions of growth and development, there is a definite, predictable sequence, with each child normally passing through every stage. Children crawl before they creep, creep before they stand, and stand before they walk. Later facets of the personality are built on the early foundation of trust. The child babbles, then forms words, and finally sentences; writing emerges from scribbling.

Developmental Pace

Although development has a fixed, precise order, it does not progress at the same rate or pace. There are periods of accelerated growth and periods of decelerated growth in both total body growth and the growth of subsystems. Not all areas of development occur at the same pace. When a spurt occurs in one area such as gross motor, minimal advances may take place in language, fine motor, or social skills. After the gross motor skill has been achieved, development focus will shift to another area. The rapid growth before and after birth gradually levels off throughout early childhood. Growth is relatively slow during middle childhood, markedly increases at the beginning of adolescence, and levels off in early adulthood. Each child grows at his or her own pace. Distinct differences are observed among children as they reach developmental milestones.

Sensitive Periods

There are limited times during the process of growth when the organism interacts with a particular environment in a specific manner. Periods termed critical, sensitive, vulnerable, and optimal are the times in the lifetime of an organism when it is more susceptible to positive or negative influences.

The quality of interactions during these sensitive periods determines whether the effects on the organism will be beneficial or harmful. For example, physiologic maturation of the central nervous system is influenced by the adequacy and timing of contributions from the environment such as stimulation and nutrition. The first 3 months of prenatal life are sensitive periods for physical growth of fetuses.

Psychologic development also appears to have sensitive periods when an environmental event has maximal influence on the developing personality. For example, primary socialization occurs during the first year when the infant makes the initial social attachments and establishes a basic trust in the world. A warm relationship with a parent figure is fundamental to a healthy personality. The same concept might be applied to readiness for learning skills such as toilet training or reading. In these instances, there appears to be an opportune time when the skill is best learned.

External Proportions

Variations in the growth rate of different tissues and organ systems produce significant changes in body proportions during childhood. The cephalocaudal trend of development is most evident in total body growth as indicated by these changes. During fetal development, the head is the fastest growing body part, and at 2 months of gestation, the head constitutes 50% of total body length. During infancy, growth of the trunk predominates; the legs are the most rapidly growing part during childhood; in adolescence, the trunk again elongates. In newborn infants, the lower limbs are one third the total body length but only 15% of the total body weight; in adults, the lower limbs constitute half of the total body height and 30% or more of the total body weight. As growth proceeds, the midpoint in head-to-toe measurements gradually descends from a level even with the umbilicus at birth to the level of the symphysis pubis at maturity.

Biologic Determinants of Growth and Development

The most prominent feature of childhood and adolescence is physical growth (Fig. 5-3). Throughout development, various tissues in the body undergo changes in growth, composition, and structure. In some tissues, the changes are continuous (e.g., bone growth and dentition); in others, significant alterations occur at specific stages (e.g., appearance of secondary sex characteristics). When these measurements are compared with standardized norms, a child’s developmental progress can be determined with a high degree of confidence (Table 5-1). Growth in children with Down syndrome differs from that in other children. They have slower growth velocity between 6 months and 3 years and then again in adolescence. Puberty occurs earlier, and they achieve shorter stature. This population of patients is frequent users of the health care system, often with multiple providers, and benefit from the use of the Down syndrome growth chart to monitor their growth (Cronk, Crocker, Pueschel, and others, 1988; Myrelid, Gustafsson, Ollars, and others, 2002).

Linear growth, or height, occurs almost entirely as a result of skeletal growth and is considered a stable measurement of general growth. Growth in height is not uniform throughout life but ceases when maturation of the skeleton is complete. The maximum rate of growth in length occurs before birth, but newborns continue to grow at a rapid, although slower, rate.

At birth, weight is more variable than height and is, to a greater extent, a reflection of the intrauterine environment. The average newborn weighs from 3175 to 3400 g (7–7.5 pounds). In general, the birth weight doubles by 4 to 7 months of age and triples by the end of the first year. By the age of 2 to 2.5 years, the birth weight usually quadruples. After this point, the “normal” rate of weight gain, just as the growth in height, assumes a steady annual increase of approximately 2 to 2.75 kg (4.4–6 pounds) per year until the adolescent growth spurt.

Both bone age determinants and state of dentition are used as indicators of development. Because both are discussed elsewhere, neither is elaborated here (see next section for bone age; see also Chapters 10 and 12 for dentition).

Skeletal Growth and Maturation

The most accurate measure of general development is skeletal or bone age, the radiologic determination of osseous maturation. Skeletal age appears to correlate more closely with other measures of physiologic maturity (e.g., onset of menarche) than with chronologic age or height. Bone age is determined by comparing the mineralization of ossification centers and advancing bony form to age-related standards.

Bone formation begins during the second month of fetal life when calcium salts are deposited in the intercellular substance (matrix) to form calcified cartilage first and then true bone. Bone formation exhibits some differences. In small bones, the bone continues to form in the center, and cartilage continues to be laid down on the surfaces. In long bones, the ossification begins in the diaphysis (the long central portion of the bone) and continues in the epiphysis (the end portions of the bone). Between the diaphysis and the epiphysis, an epiphyseal cartilage plate (or growth plate) unites with the diaphysis by columns of spongy tissue, the metaphysis. Active growth in length takes place in the epiphyseal growth plate. Interference with this growth site by trauma or infection can result in deformity.

The first centers of ossification appear in 2-month-old embryos, and at birth, the number is approximately 400, about half the number at maturity. New centers appear at regular intervals during the growth period and provide the basis for assessment of bone age. Postnatally, the earliest centers to appear (at 5–6 months of age) are those of the capitate and hamate bones in the wrist. Therefore, radiographs of the hand and wrist provide the most useful areas for screening to determine skeletal age, especially before age 6 years. These centers appear earlier in girls than in boys.

Nurses must understand that the growing bones of children possess many unique characteristics. Bone fractures occurring at the growth plate may be difficult to discover and may significantly affect subsequent growth and development (Urbanski and Hanlon, 1996). Factors that may influence skeletal muscle injury rates and types in children and adolescents include (Caine, DiFiori, and Maffulli, 2006; Kaczander, 1997):

Neurologic Maturation

In contrast to other body tissues, which grow rapidly after birth, the nervous system grows proportionately more rapidly before birth. Two periods of rapid brain cell growth occur during fetal life, a dramatic increase in the number of neurons between 15 and 20 weeks of gestation and another increase at 30 weeks, which extends to 1 year of age. The rapid growth of infancy continues during early childhood and then slows to a more gradual rate during later childhood and adolescence.

Postnatal growth consists of increasing the amount of cytoplasm around the nuclei of existing cells, increasing the number and intricacy of communications with other cells, and advancing their peripheral axons to keep pace with expanding body dimensions. This allows for increasingly complex movement and behavior. Neurophysiologic changes also provide the foundation for language, learning, and behavior development. Neurologic or electroencephalographic development is sometimes used as an indicator of maturational age in the early weeks of life.

Lymphoid Tissues

Lymphoid tissues contained in the lymph nodes, thymus, spleen, tonsils, adenoids, and blood lymphocytes follow a growth pattern unlike that of other body tissues. These tissues are small in relation to total body size, but they are well developed at birth. They increase rapidly to reach adult dimensions by 6 years of age and continue to grow. At about age 10 to 12 years, they reach a maximum development that is approximately twice their adult size. This is followed by a rapid decline to stable adult dimensions by the end of adolescence.

Development of Organ Systems

All tissues and organ systems undergo changes during development. Some are striking; others are subtle. Many have implications for assessment and care. Because the major importance of these changes relates to their dysfunction, the developmental characteristics of various systems and organs are discussed throughout the book as they relate to these areas. Physical characteristics and physiologic changes that vary with age are included in age-group descriptions.

Metabolism

The rate of metabolism when the body is at rest (basal metabolic rate, or BMR) demonstrates a distinctive change throughout childhood. Highest in newborn infants, the BMR closely relates to the proportion of surface area to body mass, which changes as the body increases in size. In both sexes, the proportion decreases progressively to maturity. The BMR is slightly higher in boys at all ages and further increases during pubescence over that in girls.

The rate of metabolism determines the caloric requirements of the child. The basal energy requirement of infants is about 108 kcal/kg of body weight and decreases to 40 to 45 kcal/kg at maturity. Water requirements throughout life remain at approximately 1.5 ml/calorie of energy expended. Children’s energy needs vary considerably at different ages and with changing circumstances. The energy requirement to build tissue steadily decreases with age following the general growth curve; however, energy needs vary with the individual child and may be considerably higher. For short periods (e.g., during strenuous exercise) and more prolonged periods (e.g., illness), the needs can be very high.

Temperature

Body temperature, reflecting metabolism, decreases over the course of development (see inside back cover). Thermoregulation is one of the most important adaptation responses of infants during the transition from intrauterine to extrauterine life. In healthy neonates, hypothermia can result in several negative metabolic consequences such as hypoglycemia, elevated bilirubin levels, and metabolic acidosis. Skin-to-skin care, also referred to as kangaroo care, is an effective way to prevent neonatal hypothermia in infants. Unclothed, diapered infants are placed on the parent’s bare chest after birth, promoting thermoregulation and attachment (Galligan, 2006). After the unstable regulatory ability in the neonatal period, heat production steadily declines as the infant grows into childhood. Individual differences of 0.5° F to 1° F are normal, and occasionally a child normally displays an unusually high or low temperature. Beginning at approximately 12 years of age, girls display a temperature that remains relatively stable, but the temperature in boys continues to fall for a few more years. Females maintain a temperature slightly above that of males throughout life.

Even with improved temperature regulation, infants and young children are highly susceptible to temperature fluctuations. Body temperature responds to changes in environmental temperature and is increased with active exercise, crying, and emotional stress. Infections can cause a higher and more rapid temperature increase in infants and young children than in older children. In relation to body weight, an infant produces more heat per unit than adolescents. Consequently, during active play or when heavily clothed, an infant or small child is likely to become overheated.

Sleep and Rest

Sleep, a protective function in all organisms, allows for repair and recovery of tissues after activity. As in most aspects of development, there is wide variation among individual children in the amount and distribution of sleep at various ages. As children mature, there is a change in the total time they spend in sleep and the amount of time they spend in deep sleep.

Newborn infants sleep much of the time that is not occupied with feeding and other aspects of their care. As infants grow older, the total time spent in sleep gradually decreases, they remain awake for longer periods, and they sleep longer at night. For example, the length of a sleep cycle increases from approximately 50 to 60 minutes in newborn infants to approximately 90 minutes in adolescents (Anders, Sadeh, and Appareddy, 2005). During the latter part of the first year, most children sleep through the night and take one or two naps during the day. By the time they are 12 to 18 months old, most children have eliminated the second nap. After age 3 years, children have usually given up daytime naps except in cultures in which an afternoon nap or siesta is customary. Sleep time declines slightly from ages 4 to 10 years and then increases somewhat during the pubertal growth spurt.

The quality of sleep changes as children mature. As children develop through adolescence, their need for sleep does not decline, but their opportunity for sleep may be affected by social, activity, and academic schedules. The time spent in deep, restful sleep increases from 50% in infancy to 80% in older children.

Significance of Temperament

Observations indicate that children who display the difficult or slow-to-warm-up patterns of behavior are more vulnerable to the development of behavior problems in early and middle childhood. Any child can develop behavior problems if there is dissonance between the child’s temperament and the environment. Demands for change and adaptation that are in conflict with the child’s capacities can become excessively stressful. However, authorities emphasize that it is not the temperament patterns of children that place them at risk; rather, it is the degree of fit between children and their environment, specifically their parents, that determines the degree of vulnerability. The potential for optimum development exists when environmental expectations and demands fit with the individual’s style of behavior and the parents’ ability to navigate this period (Chess and Thomas, 1999) (see Growth Failure [Failure to Thrive], Chapter 11).

Early identification of temperament provides a useful tool for caregivers in anticipating probable areas of difficulty or risk associated with development. For example, “difficult” children may be prone to colic in infancy, active children require more vigilance to prevent injury, and school entry requires different approaches for children with different temperaments.

Research indicates that irritable and unadaptable infants can raise doubts in mothers about their competence (Beck, 1996). Additional research indicates that a child’s temperament can affect parent–child interactions and can influence the parents’ self-esteem, marital harmony, mood, and overall satisfaction as parents (Carey, 1998). Studies on the relationship between temperament and the ability to perform a task successfully (mastery motivation) have found that infants with high mastery are more cooperative and less difficult (Morrow and Camp, 1996). Principles that can be used by nurses in direct patient care and in providing anticipatory guidance are listed in Box 5-3.