Human Growth & Development Ch. 19 Sect. 2

Stages of Development Stages of development include infancy, childhood, adolescence, and adulthood. Stages are based on major developments that happen during each stage. Infancy – rapid development of nervous & muscular systems Childhood – ability to speak, read, write and reason. Adolescence – physically able to reproduce Adulthood – growth of muscular & skeletal system stops.

Fertilization Joining of the sperm and egg. Once sperm enters into the egg, the membrane changes which allows only one male and female cell to create a new human. Nuclei join fertilization is complete. Zygote (diploid cell)- fertilized egg Zygote contains an inner cell mass – baby. Multiple Births when inner cell mass divides

Multiple Births Identical Twins Fraternal Twins

Development Before Birth Implantation – the zygote enters the uterus and attaches to the thickened endometrium. After implantation the zygote can develop into a baby. Pregnancy – the period of development from fertilized egg to birth. Placenta – outer cells of the zygote and uterus. Umbilical cord – outer zygote cells form a rope like structure that attaches the offspring to the placenta.

Zygote to Embryo Embryo – from the time the zygote attaches to the uterus until the end of the 8th week of pregnancy. The cell grows and divides during this time: brain, heart, limbs, fingers, and toes form. Circulatory system is forming, embryo can take in nutrients and O₂ through the placenta. Bones and reproductive tissues develop. Ears & eyelids can be seen.

Embryo to Fetus Fetus – time between 9 weeks and birth Organ systems begin to function and fetus grows. Able to move arms & legs, heartbeat can be heard.

Birth When a fetus leaves the mother’s body and enters the world. Requires hormones (oxytocin) Labor helps the fetus leave the uterus. Cervix is the structure between the uterus and the vagina. It opens to allow the fetus to leave. Cesarean section (C-section) – surgical procedure where doctors deliver the fetus.

Infancy & Childhood During infancy, the baby depends on its own respiratory system and digestive systems. First 2 years of life, brain continues to develop, teeth form and bones grow and get harder. Infant grows in size, crawls, sit, walks and speak. Childhood- brain continues to grow and develop. Thinking improves, muscles strength increases and arms & legs grow longer.

Adolescence & Adulthood Adolescence - Grow taller, reproductive system matures (puberty). Males –voice deepens, muscles increase, pubic and facial and underarm hair grow. Females – breasts develop, pubic and underarm hair appear, fatty tissue is added to buttocks & thighs. Adulthood – growth stops, but aging continues.