Human Body

About 5 pages (1,346 words)

Human anatomy Summary

Human Body

Humans come in different shapes and sizes. There is no shape or size that is considered "right." Medical professionals have created healthy guidelines for people. When a baby is born, doctors track many variables to make sure it is developing correctly. These charts and guidelines are not perfect, but they form a framework from which to assess a person's health.

Tracking Growth

Over the years, physicians have developed various methods for tracking growth. Keeping a record of a child's growth patterns helps doctors determine if the child is developing properly. As a person ages, doctors continue to monitor growth, helping patients maintain a healthy weight. Physicians also review height to check for problems of the spine, bone, and other medical conditions.

Growth Charts. Pediatric growth charts have been used by medical professionals since 1977. The charts are used for many measurements of growth in a child. For example, when a child's height is measured, she is then placed into a percentile. If a child is in the seventy-fifth percentile in height, it means that she would be taller than 75 percent of all other children in her age group.

Originally, the sampling for growth charts was taken from a small portion of the population. These children were primarily Caucasian, formula-fed, and middle-class. This sample was problematic because it did not reflect the diversity of the United States. To help make charts that were representative of the whole, and in turn were more accurate, samples were taken from a much larger portion of the population and from people with varying backgrounds.

There are various mathematical concepts behind growth charts. Scaling is one important factor in charting growth in an infant. Though often associated with architecture, humans also undergo scaling. While an infant is much smaller than an adult, the support material remains the same: bone. Bone is a type of tissue that can only support a limited degree of force due to strain. This is evident in the number of broken bones humans can experience when faced with too much strain—for instance, as a result of activities such as sports. As humans grow, their bones also grow but only with a narrow tolerance for strain.

"Average" Height. The determination of "average" human dimensions is based on statistics and illustrates the statistical concepts of sampling, central tendency, and outliers. For example, rare genetic or medical conditions can cause a small percentage of the human population to be very tall or very short. Persons diagnosed with gigantism* may reach adult heights of more than 8 feet, whereas persons with dwarfism are commonly less than 4 feet, 10 inches tall.

*The tallest man in documented medical history was Robert Wadlow, who at 22 years old stood 8 feet, 11.1 inches tall, weighed 440 pounds, and wore a size 37AA shoe.

Because the heights of "average" people are statistically determined by excluding individuals with these rare conditions, the physical dimensions of tall or short people are therefore deemed "disproportionate" or "outside the average." Yet if the sampling set included only individuals with these special conditions, and excluded everyone else, then their statures would be considered well within average. Hence, what is considered average depends on the sampling and calculation methods by which it is derived.

Many consumer products are built for "average" people—they are constructed for persons within an average height and weight range and who are not physically challenged. Such construction can cause difficulties for those who are not "average." As a result, some manufacturers offer products to help people make the necessary adjustments. For example, some people could not drive automobiles comfortably without enhancements like adjustable foot pedals, which bring the brake and accelerator pedals closer or farther away from drivers. This allows shorter and taller people to drive more easily, keeping a safe distance from the car's steering wheel airbag. Gadgets also exist to help disabled drivers, including hand controls that can be used to brake or accelerate.

Allometry. Another mathematical principle known as allometry (from the Greek word alloios, which means different) is especially important in the study of how humans grow. Biological allometry and human anatomy are concerned with the different growth rates that an organism experiences throughout its lifetime. A human infant does not have the same proportions of limb-to-head-to-body ratios as a human adult. The head of an infant compared to its body size is much different from an adult's. As a human grows, limbs and body size increase considerably while the head does not. This change in ratio occurs in all kinds of animals. A baby horse is born with extraordinarily long legs compared to its body. As it grows, the body catches up with the legs.

An entire branch of science deals with the allometric changes of organisms. One of the modern methods of observing allometric change is to place imaginary points on the organism, in this case, a human infant's head. A computer scans for the imaginary points and constructs a grid system. As the infant grows, these points are continually tracked, and the points shift in position relative to one another. When the infant reaches adulthood, it is possible to see how the skull grew, where it grew the fastest and the slowest, and how the proportions have changed. The initial square grid looks wavy and distorted. Changes in body shape and physiology, such as in bone structure, breathing rate, and muscle strength can be expressed as variables and tracked. The basic allometric equations used to monitor these changes are as follows:

There is no such thing as an ideal weight. Instead, every person has a range of what is healthy for her based on a number of variables, including age, height, sex, and muscle mass.

y = a × x^b and logy = loga + b logx.

This equation is used by biologists to plot two variables on logarithmic coordinates (using logarithmic scales on the x and y axes of a Cartesian coordinate system). The result is a straight line. Many biological measurements that relate to change in body size use this general equation. The exponent b represents the slope of the line. This equation can help biologists track the changes in variables (the arbitrary points used to make an initial grid). Computers can track the three-dimensional (3-D) changes that occur with growth and produce allometric 3-D scaling grids.

How Much Should a Person Weigh?

The new indicator used for weight measurements is the Body Mass Index (BMI). Formerly, weight-for-stature charts had been used when assessing weight. With this type of chart, a person's weight was evaluated only in relation to one variable, his or her height. When looking at a person's BMI, other factors, such as age, are considered.

A BMI is the fraction of a person's weight divided by his height squared. If a person is between the range of 20–25, then he is said to fall within a healthy weight range. Once a person goes above a BMI of 25, he may suffer from weight-related health problems. Additionally, people with a BMI of less than 20 may also suffer health problems from being underweight. The BMI is the preferred way to chart weight because it looks at more variables than how much a person weighs and what his height is. The body mass index can also help doctors be aware of people who may be more predisposed to being either overweight or underweight.

While all growth charts are helpful in determining development, they really serve only as guidelines. There is no one correct height or weight for a person, only a range of what is healthy. Growth charts do not serve the purpose of locating an "ideal." Instead, they help to indicate whether someone is healthy.