Physical development takes place over the course of the first 20 or so years of human life, but it is most concentrated during two periods: the prenatal phase and puberty. While childhood is marked by growth and significant brain development, organs and functions develop most markedly before a child is born and during the teenage years. Several factors affect physical development.
Function
The purpose of physical development is to produce body organs from undifferentiated cells and then to produce function within those body organs. In general, organs develop--though don't always develop complete function--during the embryonic phase of the prenatal period, according to Lauralee Sherwood, Ph.D., in her book "Human Physiology." Babies are then born with a complete set of organs, some of which have their full adult function and others that as yet don't. Later physical development during puberty rounds out the function of all organs.
Features
Physical development in utero is characterized by organogenesis, or the development of body organs, according to Gary Thibodeau, Ph.D., in his book "Anatomy and Physiology." He notes that one of the most important factors to affect development during this time is position of cells relative to other cells. Early in development, a developing cell ball gastrulates, meaning it folds into three layers. Based upon where cells are, they become different tissue types. Cells in the outer layer become the nervous system and skin, cells in the middle layer become muscles and bone, and cells in the inner layer become many of the body organs.
Considerations
Hormonal factors play a large part in physical development, not only during puberty but also during prenatal growth. For instance, while a developing baby may be a female, if the mother experiences severe, chronic stress during the pregnancy--if, for instance, she lives in a war zone--she could produce high levels of stress hormone that cross the placenta and act similarly to testosterone. The testosterone-like hormones can influence the child to begin showing masculine characteristics, such as male-like genitalia, notes Sherwood.
Misconceptions
During puberty, hormones again play a key role in development. Simple release of hormones from the pituitary gland and response to these by the gonads, however, isn't enough to launch puberty. Instead, the body--particularly if the child in question is a female--must have appropriate composition to support pubescent development. Girls with very low body fat often enter puberty later than normal, notes Thibodeau, despite appropriate hormone release, since they have insufficient fat stores to begin developing female reproductive abilities.
Other Influences
Physical development isn't just shaped by hormones and cell position. Outside influences, such as certain drugs and toxins, also can affect development. For instance, in the 1950s, a commonly prescribed antinauseant called thalidomide showed significant teratogenic effects, meaning that it crossed the placenta and adversely affected the development of the baby. Many babies exposed to thalidomide developed flipper-like arms. Sherwood notes that there are many such pharmaceuticals and drugs that can cross the placenta and affect a developing embryo.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
