Lecture Notes for Chapters 19 & 20

Life Science 2 Chapters 19 & 20: Gene Expression and Development -development: go thru changes ogrowth: in number of cells, cell size, or whole organism odifferentiation: cells specialized for different functions; divide omorphogenesis: whole organism à different shape; start to appear different -embryology: study of origin and development -prenatal period: oembryonic period (first 8 weeks): organs forming; 3 germ layers = 3 different sets of cells; basic body plan ofetal period: next 30 weeks, nothing new forms; organs bigger; sex and everything else determined -basic body plan: skin, bone, muscle; inner tube, kidney, outer body -first 6 days: start of embryonic period ofirst day: zygote = single celled o2 days: blastomere = cluster of cells; number of cells increases, cell size decreases o3 days: morula = all cells identical in function o4 days: blastocyst: cavity with fluid o6 days: blastocyst reaches/implants in uterus -fertilization: egg meets sperm o7 days: trophoblast = sac secretes fluid à cavity §inner cell mass gives rise to yolk sac and embryo o9 days: hypoblast = support/nourish embryo; connect to epiblast §epiblast = gives rise to embryo -week 2: 2 layered embryo oepiblast gives rise to 3 germ layers ? ecto/meso/endoderm §epiblast = cells of embryo; amniotic sac; constantly developing ohypoblast: yolk sac -week 3: 3 layered embryo; form mesoderm and notochord oprimitive streak = groove in epiblast layer; epiblast cells start to rise ogastrulation: cell migration §mesoderm?s mesenchyme cells have migrating ability onotochord: gives basic body plan oectoderm à skin, nervous system oneural plate: brain develops here oneural groove in neural plate -week 4: neurulation continues oneural crest: PNS oneural tube: CNS; one end = brain, other = spinal cord oend of week 4, NS completed osomites: body segments ointermediate mesoderm: tissue lateral to somites olateral plates: most lateral part of mesoderm §coelom becomes body cavities, where organs form §somatic mesoderm: apposed to ectoderm §splanchnic mesoderm: apposed to endoderm -weeks 5-8: second month oear, eye, heart, upper and lower limbs, somites -fetal period: maturation, rapid growth; cell differentiation during first half; 38 weeks = normal birth; premature = before 38 weeks obeginning: eyes and ears fully developed, looks human; large head; functional cardiovascular system; begins to form bone; 3cm ofirst to third week (9-12 weeks overall): large head; skin layers; begins red blood cells formation; sex determined; 9 cm o16 weeks: eyes flinch; body bigger than head; distinct bones; 14cm o21-30 weeks: §lanugo forms: type of hair baby loses after birth, found on skin to maintain warm temperature of unborn §eyes open §quickening: mom feels baby §limbs final proportion §19cm omonth 8 to birth: fat accumulates in hypodermis ? third lowest layer under skin; 36cm, 6-10 lbs