Physical growth in humans is an ongoing process that most of us are blessed to witness. The earliest stage of development seems to be the germinal period, the first two weeks of conception. During this period the embryo and the zygote have started to form. The embryonic period, also known as the prenatal period, follows two to eight weeks after conception. The respiratory and digestive systems form at this time also. The middle layer of cells, called the mesoderm, will become the circulatory system, bones, muscle, excretory system, and reproductive system. The outer layer of cells, the ectoderm, will become the nervous system, the sensory receptors (eyes, nose, ears), and skin. The placenta, the umbilical cord and the amnion (fluid-filled sac) develop along with the embryo. The final developmental stage during conception would be the fetal period.
It begins two months after conception, lasting an average of seven months. Three months after conception the fetus becomes active, moving its arms and legs, opening and closing its mouth, and moving its head. The face, forehead, eyelids, nose, and chin are all distinguishable, as are the arms, hands and legs. At four months, a growth spurt occurs in the fetus’ lower parts. By the end of the fifth month the toenails and fingernails have formed and the fetus is more active. By the end of the sixth month the eyes and eyelids have completely formed, a grasping reflex is present and irregular breathing occurs. (1)
Infancy has now come into effect. The cephalocaudal, the first growth pattern in infants, will make the infants head look enormous. During this spurt the head takes up a fourth of the body while the legs take up a third. (7) One of my sons is almost two years old. He is still in the “big head-little body” stage. His shirts scarcely fit over his head, but are just right for his little neck and shoulders. The second growth pattern is called proximodistal. In this stage the arms and legs grow faster than the hands and feet, causing balance issues. Again, my youngest is extremely clumsy, due to the unaccounted growth in his limbs, but a joy to watch! Don’t worry, the rest of them will catch up quickly. (2)
By childhood most of rapid growth begins to slow down. The skeleton continues to change throughout early childhood. Near the end of the preschool years, a child begins to lose their baby teeth. (7) My oldest son is going to be six years old soon. He has his first loose tooth, along with excitement about meeting the “tooth-fairy.” Children tend to become sick more often due to the immune system not being fully developed. Ligaments are not fully attached to the bones yet so children will have seemingly abnormal flexibility.
Adolescence is a very special and difficult time for teenagers. Along with many social changes, physical changes also are very distinguishable. Puberty is a leading example of the physical changes they encounter. It is interesting to know that a female baby already has over one million follicles for eggs to develop in, which decreases to one hundred thousand by puberty.(3) Most females begin the stages of puberty before boys do. It is accompanied by increase in breast size, height increase, and (the ever dreadful) menstrual cycle, initiated by the thickening of the uterus caused by the cyclical changes in the presence of estrogens, otherwise known as the ‘period.'(3) Males tend to begin puberty after females have developed, although it will last longer. Males have a growth spurt due to testosterone, which is produced by the male testes. It initiates the growth spurt, and does so more effectively than estrogen, making most males on average taller than females.
After secretion of prolonged testosterone, the male shows secondary sex characteristics such as increased bodily hair, deepening of the voice and increased development of muscularity. The initial secretion of testosterone initiates sperm production, giving the male fertile gametes available for reproduction. (3)(4) Puberty also has many bearings on an adolescent’s social environment. You can read more about it at this web site: http://www.personal.psu.edu/faculty/n/x/nxd10/transition/group212/dating.html .And finally we come to the adulthood. This is the age when everything seemingly is balanced, between health and mentality.
This is when your body is supposed to be at its peak performance. (7) You will not notice many changes, physically, at this time. When you reach middle adulthood, on the other hand, this is the area of concern for a lot of individuals. At this point your physical appearance will start to deteriorate. The most noticeable physical change would be a person’s height. Your seeing and hearing will probably not be as good as it once was. You may start noticing grey hair in certain places or possibly no hair at all! Your skin will become loose and wrinkly as you continue to gain unwanted pounds. (6) But it is a part of the physical development ‘roller coaster’.
Imagine you’re on a roller coaster. When you first step into the seat (conception), to buckling your belt and getting excited as you are looking at everyone else (infancy), to the long, anticipated climb up the first drop-off (childhood), raising your hands with no fear as you begin to plunge into the overhang (adolescents), down and around the turns and loops of early ‘adulthood’, and finally enjoying the end of the ride and how fun it was getting there.