1 INTRODUCTION : In this we are going to understand the meaning and process of growth, development, its stages and approaches to the study and different factors that control the process of growth at different stages. We shall also study the growth process and ecological conditions in the context of growth.
2 GROWTH PROCESS : Now we shall try to understand some of the basic terms concerning the growth process. The term growth and development are sometimes used as synonyms. But when we examine these two terms the meaning is slightly different. Growth can be defined as the increase in the size of organism or any of it parts by the way of multiplication of cells. Mainly growth is physical but development refers to the increase in functional capacity in perfect form resulting from specialized tissues. Development also depends on certain physiological functions in the body. At the same time, we cannot ignore the mental development for which we sometimes use the term personality. Personality can be defined as the overall complexity of an individual resulting from an interaction of physical, physiological and psychological attributes. In growth and development interaction of several processes are involved. Growth is primarily determined by hereditary component· but is also influenced by exogenous environmental factors. But in development though there is a hereditary base, but manifestation may be influenced mainly by external factors.
3 GROWTH MEASUREMENTS : Here, we will understand about the growth changes that occur from one age group to another age and also at different stages. To study the growth process, it is essential to make observations through measurements; in nutritional studies growth measurements give llS very valuable information. There are three basic types of measurements of growth. Firstly, the linear which are usually evaluated in terms of increase in length, e.g., stature, siting height, head length etc. Secondly, the circumferential measurements that include head circumference, chest circumference, mid-upper arm circumference, etc. Lastly, the ponderal measurements that refer to weight or mass. Growth is measured in inches, centimeters or millimeters and in kilograms and pounds.
4 GROWTH CURVES : Now let us discuss about the growth curves, which will give us the idea of the growth that takes place at different stages. The measurements taken at different ages are plotted in the form of a graph. Based on this, two types of curves call be drawn, namely distance curve and velocity curve. Growth is always considered as a form of motion. Hence, it can be observed at different ages and also at different stages. The growth movement is not same in all body dimensions. The first curve can be drawn for continuous growth. For example, the growth of the stature i· always in an upward direction from lower age group to higher age groups. It is also considered as fastest rate of growth when compared la other dimensions. This curve is called is distance curve. Secondly, in other dimensions, there i a different rate of growth in between age groups. For example, the curve drawn to denote growth of the head dimensions between two age groups is plotted in the Iorm of graph is interpreted as velocity curve. The velocity curve plots the amount gained in a given time, e.g. in one year. It measures the rate of growth at a given time for a particular body parameter, e.g. height.
5 TECHNIQUES OF STUDYING GROWTH: Let us now examine the different techniques used to measure the body dimensions. Firstly, the anthropometric technique wherein measurements on different parts of the body are recorded to know the extent of growth that takes places at different intervals. This technique involves many measurements which are recorded with the help of different landmarks on the human body to study growth. To take these measurements specialized instruments have been designed. To take measurements, it requires expertise on the part of the investigator who is involved in growth research. Secondly, let us see how the skeletal growth is studied to know the developmental aspects of growth. With the help of roentgenometric technique the X-ray photographs are taken on an individual to evaluate skeletal growth. This process gives us important clues about the stages of development of the different bones in the body. This technique can also be used to study dental maturity on the basis of stages of calcificaticr of teeth as seen in jaw X-rays in just the same way as we assess the skeletal growth.
6 METHODS OF STUDYING GROWTH : After knowing about techniques of studying growth, now it is essential for us to know about the different methods adopted by researchers to record the growth data. The first method is cross-sectional method, wherein the subjects involved in the study are measured only once in their life time. That means the subjects who are selected in a particular age group are not same ‘when measurements are recorded in some other age group the second time. This method is very popular because it is quicker, cheaper and less laborious. In most of the growth studies, this method is used. The next method is the longitudinal method wherein the individuals are measured more than once in their life time. Longitudinal studies give correct information on individual variations in the rate of growth in particular age-groups. Such studies are time consuming, costly, laborious and also require lot of patience on the part of the investigator. This study has its limitations. The third method is the mixed longitudinal method wherein children of a particular age-group are sometimes added to the already ongoing longitudinal study. But for certain reasons, some of the children may nbt be available for the next time measurement in a longitudinal study. They are then replaced by another set of . children to keep the continuity. This type of study is more complicated and special statistical tools are required to get maximum information out of mixed longitudinal growth data.
7 STAGES OF GROWTH : Now let us understand about the different stages of growth. A simple classification includes prenatal and post natal stages of growth. Prenatal growth includes the growth of the embryo and fetus. The post natal growth includes infancy, childhood, adolescence, puberty, adulthood and senescence.
- Prenatal growth :Prenatal growth includes embryonic and fetus stages. During embryonic stage, though the rate of growth is slow, it gives rise to the development of different parts like head, legs, arms and other parts. The cells are differentiated into specialized tissues, like nerves and muscles. When this stage is completed, embryo becomes childlike in appearance.
- Postnatal growth : This stage can be described from birth up to adulthood.
- Infancy : Infancy usually comprises the first year of postnatal life. During infancy the growth is very rapid. More than 50% of the birth length and 200% of birth weight takes place during the first year of life.
- Childhood : Childhood. generally spans from the end of infancy to the beginning of adolescent period. It may further be divided into early childhood, middle childhood and late childhood. The-early childhood is the period of eruption of deciduous or milk teeth. The permanent dentition also shows its beginning. The head in relation to the trunk: continues to predominate but in lesser degree. During this phase, the growth is relatively more in width than in height. The middle childhood period (sometimes also called juvenile period) is described between 7 and 10 years of age-group. During this time, the linear growth of the body takes place rapidly. The waistline becomes definable. Between 7 and 8 years a nominal acceleration in the rate of growth occurs. Normally the changes that take place during this period are termed juvenile growth spurt. Broadly, the late childhood begins from the pre-pubertal period and continues up to the time of puberty. The late childhood phase of growth starts from 7 to 8 years age group and continues till puberty (between 13 and 16 years among boys and between 12 and 15 years among girls). The secondary sexual characteristics normally appear during this phase in both the sexes. The growth changes that occur during this particular stage are al 0 referred to as the adolescent growth spurt.
- Adolescence : Childhood is followed by adolescence period. The adolescence period extends from the time of puberty till around 20 years. During this period there is a marked acceleration of growth, which is commonly known as the adolescence growth spurt. The acceleration of growth at adolescence causes many anatomical changes almost in all parts of the body. Differentiation in primary and secondary sexual characteristics also takes place during the adolescence period. This period is marked by changes in the reproductive organs, in body size and shape and in a variety of physiological functions. Under the influence of hormones, sexual maturation takes place during this period.
- Adulthood : An important sign of adulthood is reproductive maturity. In both the sexes we find lot of physical and physiological changes which lead to an altogether different type of appearance. During this period, we even find psychological changes. On an average, adult males are heavier and taller than adult females.
- Senescence : After the prime period of adulthood, senescence that is old age starts. The aging pattern shows great individual variation. The aging time also differs from person .to person and society to society, because the environment plays an important role. During this period, many molecular and cellular changes occur. These changes are measurable and also can be described, but these do not exhibit any specific pattern or well-defined sequence. It appears there is no definite biological plan for aging process but multi-casual mechanisms are involved in this process.
8 SECULAR TRENDS: Let us now try and follow the meaning of secular trend. The secular trend is the tendency over the last huncked or so years for each succeeding generation to mature earlier and grow larger. This trend has occurred worldwide. In the twentieth century, the mean body height from decade to decade has increased. Even the mean body weight has also increased. Other features, such as early menarche, have also demonstrated secular trend. One thing is clear that such data have’ been collected from children wh~ were regularly getting normal nutritional food. The adverse conditions have yielded nega.. v e results especially during World War I and World War II period. What causes these secular trends? Some researchers believe that a general improvement in nutritional, better sanitation, better health services and less tedious life styles are responsible. These factors have permitted individuals to come closer to their genetically determined potential weight and stature. Today a leveling off the secular trend appears to be occurring among the higher socio-economic urban population. It must be pointed out here that all positive secular trends are not desirable. For example, increased levels of adiposity without corresponding increase in height noticed in some parts of the world are associated with increased prevalence of obesity, particularly among children and adolescents, which is known to be a health risk.
9 THE INTERACTION OF HEREDITY AND ENVIRONMENT IN CONTROLLING GROWTH : In this sub-unit, it is very interesting for us to discuss about the interaction of heredity and environment in determining the growth process. Many factors that affect the rate of growth are known. Some are hereditary in origin and act by hastening or retarding physiological dietary restriction, season of the year or severe psychological stress originate in the environment and simply affect the rate of growth at the time they are acting. Others again such as socio-economic class reflect a complicated mixture of heredity and environmental influences.
10. GENETICS OF GROWTH: Genetic factors are clearly of immense importance. The genetic control of tempo of growth is exemplified most simply in the inheritance of age at menarche. Identical twin sisters reach menarche an average of two months apart and non-identical twin sisters an average of 10 months apart. The correlation coefficient between age at menarche of mother and daughter is about 0.4. Similarly, the skeletal maturity shows a close correspondence at all .ages in identical twins ..The time of eruption.
11 NON-GENETIC FACTORS OF GROWTH
- Race, Ecology and Growth : There are racial differences in rate and pattern of growth, leading to the differences seen in the adult buiId. Some of these are clearly genetically determined while others depend perhaps on climatic differences and certainly on nutritional ones. Many examples can be given on this issue from different racial populations distributed in different parts of the world. Altitude and climate are other factors associated with differences in the body size, body proportions and body composition. It has been found that people in colder climates show tendency to be heavier with relatively large trunks and shorter legs. On the other hand, in warmer climates they tend to have lighter and longer legged body. Populations living in warmer climates have large body surfaces than those in colder climates. The Africans who live in hot dry climate show tendency to be taller than in those who are living in hot-wet climates.
- Season of the Year: In most growth data, from industrialized countries in temperate areas a well-marked seasonal effect on growth velocity can be seen. Growth in height is on average fastest in spring and growth in weight fastest in the autumn. The average velocity of height from March to May is about twice that of from September to October in most of the western European data.
- Nutrition : Growth is closely linked with nutrition. An adequate supply of various nutrients such as proteins, carbohydrates; fats, vitamin, minerals, water, etc., is necessary for general growth of the body. Nutritional deficiencies retard normal growth during childhood and delays further growth process. During post-war periods (World War I and World War II) several studies were conducted in different parts of the world to assess the effects of diets on growth. During that period there was a shortage of food supply in some populations. The people were under nourished, As a result, the children of those populations were shorter and lighter. But after restoration of normal food supply both height and weight of these populations showed uniform increase. The children have the great recuperative capacity.
- Social-cultural and Economic Conditions: The social-cultural and economic conditions also play an important role in determining the course of growth process. It is very difficult to separate one element from the other. We can mention here about the role of socio-economic classes, size of the family and cultural behavior in growth studies. Some studies reveal that the children of upper socioeconomic classes are taller and heavier than those of the lower socioeconomic classes. The size of the family exerts an indirect influence on the rate of growth. In large families with limited income, children do not get adequate quantity of food. As a consequence their growth is affected. Cultural factors, such as taboos associated with various foods, may also influence growth,
- Psychological Disturbance: The secretion of growth hormone is affected by the emotional and psychological environment of a person. Hence, physical growth is related to psychological factors also, which are again associated with family and social environment. Under favourable psychological environment the endocrine system functions properly and as a result children show normal growth. Better living standard, medical care, .good hygiene and sanitation, etc., create normal psychological environment which is essential for normal growth process. We have now acquainted ourselves with some of the fundamental concepts of Human Growth and Development. In subsequent blocks you will learn these concepts in greater detail.