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In this presentation, we will focus on physical development and health over the lifespan through the endocrine and nervous system, genes and the environment impact growth. The function and growth of those systems may be optimized or inhibited. Environmental influences. Three principles guide physical development. First, development occurs and proximodistal manner. This means that humans develop from the center outward. In prenatal development, the chest and internal organs develop first, arms and legs develop. Next. Hands develop after arms, and fingers develop after hands. The second principle is cephalocaudal. This means that humans develop from top to bottom. The head develops first and is largest in proportion to your body as an infant. This picture demonstrates this phenomenon. The head is 25 percent of a newborn's link and 13 percent of its weight. In adulthood, the head is only 12 percent of height and 2% of weight. According to the cephalocaudal principle. In the first year of development after the head, the trunk develops. In Year 2 after the trunk legs develop. The third principle is ortho genetic. This means that cells begin undifferentiated and end up differentiated or specialized. As an embryo cells have the potential to develop into anything. And I, your foot, heart, liver, or spinal cord. With time, the cells become specialized such that they form a heart and work only as a heart. At that point. They cannot then also function as an I. The busiest time of physical development is infancy, even though it involves a small percentage of the lifespan. Infancy covers from the time of birth up to two years. The average American newborn measures 20 inches in length and weighs between 7.57 pounds. A newborn normally loses between five and 10 percent of their body weight during their first few days of life. 1 fifth or 20 percent of the lifespan is spent growing. The infant will experience dramatic changes in height and weight. They double their birth weight in the first six months, tripled their birth weight by the end of the first year, and quadruple their birth weight by age two years. By age of two, they have reached about half of their adult height. At birth, the infant skeleton contains soft cartilage tissue and overtime it gradually hardens into bones. In terms of physical appearance, infants have all species have very large eyes and large heads. Their legs are bent and stubby with protruding stomachs. This appearance is called the QP doll effect. This is true for puppies, kittens, bunnies, chicks, and Disney role to characters. Pathologists believe that babies have this appearance, which we as adults find to be cute. To promote their survival. The brain and spinal cord begin to develop during the first month of life in the embryonic stage of prenatal development. The first areas to develop are the lower portions of the brain, such as the spinal cord, brainstem, and midbrain. These areas controlled basic life functions such as breathing, reactions, alertness, and sleep cycles. By month five of prenatal development, the brain has developed unique human structures. Most importantly, the cortex, which is responsible for higher cognitive functions such as thinking and memory and planning. Neurons multiply exponentially in the prenatal period. It is estimated that neurons increase a number by 250000 every minute from conception to birth. It was previously believed that you are born with all the neurons you will ever have. But we now have evidence that even as late as in our seventies, we can produce new ones in the brain. Neurons migrate to the brain. And depending on where neuron ends up, it then differentiates or takes on a specific function of that area. Connections among the neurons increase throughout the lifespan. Development of function is assisted by the process of synaptogenesis. Synaptogenesis is the building of connections between neurons. This formation of specific synaptic connections allows the brain to fine tune functions. Throughout infancy and into childhood, neurons continue to increase in size and weight. Maturation of the brain consists primarily in the growth and branching in the cortex of the axons and dendrites into increasingly dense connective networks. The average infant has more neurons and neural connections than adults do. It is estimated that there is a five-fold increase in density within the cortex of the brain by two years of age. It's also estimated that the brain reaches about 90 percent of its adult weight. By five years of age, growth of the connections peak around two years and decline until around 16 years of age. Pathways that are used survive and those that are not used die. This is referred to as synaptic pruning. Neurons seldom stimulated, lose their connective fibers. Motor development in infants is primarily contain two reflexes. Reflexes are inborn automatic responses to a particular form of stimulation. Infants are born with several reflexes. Permanent survival reflexes stay with us throughout the lifespan. The first is breathing. This is repetitive for humans. Inhalation and exhalation, breathing is reflexive. It's not something we have to think about in order to do. Even though we do have some control over it with age, it promotes survival throughout the lifespan. The next to our eye blink and pupil reflexes. I blink is that whenever we see a flash of light or a puff of air, we automatically close our eyes. The pupil reflex is that pupils automatically constrict and expand to different levels of light. Both of these reflexes protect our eyes and maintain our site. Other early survival reflexes help a baby nurse. The first is the rooting reflex. If you touch an infant's cheek, they will automatically turn their head towards the touch. Mothers can use this to orient the baby to the breast to nurse. Babies also have a sucking reflex. Anything that comes into contact with their mouth is sucked on automatically. This also ensures feeding as an infant, the swallowing reflex is that if something is put into their mouth, they will automatically swallow. We do gain more control over this as an adult. But if something is placed far enough down into your mouth, it is still reflexive that you will swallow. There are also many primitive reflexes. Were unsure why we're born with these. They are used as a sign of normal neurological development. The first is the Babinski reflex. The Babinski is also referred to as the foot startle reflex. If you stroke the foot in a particular way, the toes will fan out and curl. This is also used to assess whether or not there is neurological damage in adults. If the Babinski reflex is not present for an adult, then you know something is wrong. For example, in an adult who is in a coma, the grasping reflex is that when you put something in a baby's palm, they will automatically close their fingers around it. The Moro reflex is called the startle reflex. If a baby is slightly dropped or if they think they're going to be dropped, they will arch their back, pulling their arms out and their legs out, and then bring arms and legs close to them. Babies also have a swimming reflex. If an infant is put into water, they will make arm and leg movements and in voluntarily hold their breath. Finally, there is the stepping reflex. If you place a baby upright with their feet touching a surface, they'll move their feet as if to step. Again, this is an automatic reaction. With development, movement becomes less reflexive and more voluntary. In other words, movements become less involuntary with more control and choice over time and development. A developmental norm is the average age of mastery of a skill. During the first two years, we first develop gross motor skills and then the fine motor skills. Gross motor skills include physical actions that involve many parts of the body. These help us to get around and include sitting, rolling over, standing, crawling, and walking. Fine motor skills include smaller actions that we usually perform while stable, including brisk movements, had rotation, coordination of fingers and grasping. By six months, babies can reach, grab, and hold on the objects. They start with their whole hand grasp. This is called the ulnar grasp. They then use their middle fingers and center of POME or index finger inside of POME. By nine to 14 months of age, they're able to use their thumb and forefinger together to grasp and release. This is the pincer grasp. Many believe because of a universality that motor development and sequence is determined by genetics, variations and the norms can be attributed primarily to inherited factors, such as activity level and rate of physical maturation. As with other areas of research, cross-cultural studies can give us an idea about whether these milestones are similar across cultures due to nature. Whether these milestones differ according to experience and are due to nurture environment or culture. For evidence, for nature among hoping Native Americans, the babies are raised strapped to a cradle board for the first several months of life. Nevertheless, they begin to walk at about the same time as healthy babies who aren't strapped to cradle boards. There are several tribes such as the kipp suggests and gander, where the mothers train their babies to hold up their head, sit and walk just a few months after birth. As a result, they do in fact, sit up and walk by themselves earlier than American babies. For most of the motor skills, if you leave kids alone, they will probably develop them without training. But the environment and culture play some roles as shifts and timing. However, the sequence of motor development is unlikely to very. Health issues for infants and their parents include managing issues associated with low birth weight babies as they develop during infancy. Other infants and their parents may encounter challenges from complications during delivery or from congenital malformations. Defects present at birth, either from genetic factors or prenatal events like heart defects, spina bifida, Down syndrome, and cleft palate. Maintaining a baby's health is a process that starts before and continues after birth.