How Do We Grow and Change?

animated picture of baby growing into adult

Our bodies are constantly changing. Each of us starts out in life as a single cell, about the size of the period at the end of this sentence. Over the next 40 weeks, we develop into a highly complex creature called a newborn. And after a lifetime of further growth and development, we die. For a brief overview of the growth and development process, read on.

Before Birth

animated diagram of the stages of human fetal development

The first body system to develop is the central nervous system—the brain and spinal cord. Then, the circulatory system forms, and the heart starts to beat. As the other systems develop, the fetus (unborn baby) swallows some of the fluid that surrounds it. The new digestive and excretory systems “practice” their functions with this fluid, but the fetus receives all its nutrients from its mother’s blood supply. The respiratory system also forms, but does not function. The fetus’s oxygen needs are supplied by its mother.

At Birth

At birth, the newborn no longer relies on its mother to supply oxygen and nutrients. The baby’s lungs inhale oxygen and exhale carbon dioxide. Its digestive system must absorb food in order for the baby to grow and have energy. Newborns’ muscular and skeletal systems are weak and immature, so babies must be handled gently. They are completely dependent on others to meet their needs for food, comfort, and warmth.

Childhood

children playing outside in a field

From birth through childhood, children grow and develop dramatically. They learn to control their muscles first by rolling over, then crawling, walking, running, and jumping. They develop fine-motor coordination, too, that allows them to color, thread beads on a string, and tie their shoes.

The most dramatic changes of all occur in the brain. Children learn language—listening, speaking, reading, and writing. They learn the relationship between cause and effect—if I push the blocks, they fall down. By playing with friends, they learn social skills like sharing and settling disputes. And they learn self-discipline: how to pay attention in school, to keep their word, to set goals, like learning to play a musical instrument, that take long-term commitment.

Puberty

At puberty, sex hormones produced in the testes (males) and ovaries (females) cause children’s bodies to begin changing into their adult form. Girls grow breasts, start growing body hair and begin having their monthly menstrual cycles. Boys start growing facial and body hair, their voices become deeper, and they begin producing sperm.

Adulthood

two adult couples sitting with each other

During adulthood, people graduate from college or learn a trade and work to support themselves. They seek out romantic partners and may marry and have children. Emotionally and mentally, adults continue to grow and learn, but not at the hectic pace of children. Healthy adults undergo few physical changes until they reach old age.

Old Age

People start some of the changes of old age as early as their 40s and 50s. Vision and hearing may become less acute. Muscle mass decreases, and it becomes harder to lose extra weight. But nowadays, “old” is usually considered over 70 years of age.

Healthy seniors who eat nutritious food and get regular exercise can remain physically and mentally active and vibrant well into their 80s, 90s, and beyond. Eventually, though, one or more of the body’s systems wears out. And even the healthiest among us dies.