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Western University
Management and Organizational Studies
Management and Organizational Studies 1021A/B
Mark Cleveland

Chapter #4 Prenatal Development Prenatal Development: development that occurs at conception to beginning of the birth From Conception to Birth Zygote Germinal/Zygote Period: conception to implantation (organism becomes attached to wall of uterus) , 1 st stage -Zygote moves down the fallopian tube, towards the uterus it divides by mitosis into 2 cells, the 2 cells and all the rest continue to divide forming ball shaped structure Blastocyst: balls of cells forms when the fertilized egg begins to divide (contained 6-80 cells within 4 days) Embryo: inner layer of the blastocyst becomes the embryo, organism from 3-8 week after conception • Implantation: blastocyst attaching to the uterus -Communicates, positions itself, attaches and invades; occurs within 48 hours 7-10 days after ovulation -3/4 zygotes fail to survive the initial phase of prenatal development • Development of Support Systems -After implemented, blastocyst forms 4 major support layers for protection 1- Amnion: watertight membrane surrounds the developing embryo, regulates temperature and cushions against injuries.Yolk Sac: floats in the watery enviro of the amnion, produces blood cells until embryo can create its own 2- Chorion: attaches to the uterine tissues to gather nourishment for embryo 3- Placenta: multipurpose organ; provides respiration and nourishment of the unborn child and eliminates its waste 4-Allantois: forms the umbilical cord: soft tube containing blood vessels that connect the embryo to the placenta, transports CO2 and wastes from the embryo • Placenta Importance: -Fed by blood vessels from the mom and embryo -Semipermeable: allows some substances to pass through but not all -Oxygen, CO2, salt, nutrients -Blood cells are too large Embryo -From implantation, 3rd week- 8 week -The embryonic disc is differentiating into 3 layers 1- Ectoderm: outer layer; nervous system, skin and hair 2-Medoserm: muscles, bones and circulatory system 3- Endoderm: digestive system, lungs, urinary tract, vital organs- lungs pancreas Neural Tube: spinal cord that develops from the ectoderm, becomes the central nervous system th -By the 4 week, heart is formed and beats, eyes ears, nose and mouth are forming • 2 Month -Mthe human in appearance -5 week: eyes have corneas and lenses -7 week: ears formed -Brain develops rapidly -7 and 8 weeks: sexual development begins: male a gene on its Y chromosome triggers producing testes, if female gonads receive no such instruction and produce ovaries -Circulatory system functions on its own Fetus th -Fetus: organism is called this from the 9 week of pregnancy until birth -Quantifiable changes -Major organs function and fetus moves, senses and behaves -At this time, individuality emerges (develop unique characteristics) rd • 3 Month -Organ systems continue their rapid growth and become interconnected -Kicking legs, making fists, twisting bodies -The males testes secrete testosterone: responsible for penis and scrotum -The females genitalia form -By the end of this month sex of fetus can be known • 4 -6 Months ‘Second Trimester’ -Approx 20-25 cm long, 170g -Simple movements of the tongue, lips, pharynx and larynx increase -Kicks are strong enough to be felt by the mom -End of 16 week, looks human -5 and 6 month: nails harden, skin thickens -End of 6 month, fetus’visual and auditory senses are clearly functional Vernix: white cheesy substance that covers fetus to protect the skin from chapping Lanugo: fine hair covering the fetus’body helps the vernix stick to the skin • 7- 9 months ‘3 Trimester’ -Finishing phase, organ systems mature, prepnde for bthth Age of Variability: point between the 22 and 28 week when survival outside the uterus is possible -Becomes more regular and predictable in sleep cycles -Activity becomes less, sleep more during last 2 weeks before birth Environmental Influences Teratogens: external agents such as virus’, drugs, chemicals and radiation that can harm a developing embryo or fetus - Pregnant woman’s genetics and the prenatal environment play a role - Effects of them on a body part are worst during the period the structure is forming - Same defect can be caused by diff. teratogens - Longer the exposure, more serious the harm will be done - Embryos and fetus’can be affect by fathers’exposure to teratogens - Some aren’t apparent until later in life Sensitive Period: when organ is more susceptible to certain enviro influences -Embryo (3-8 of Development); women might not even know they are pregnant here -This time organs are most vuln
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