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PSYC 2110 (131)
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PSYC 2110
Gillian Wu

CH 4: PRENATAL DEVELOPMENT  Prenatal development: the process that takes place from conception until birth o An embryo becomes a fetus at 8 weeks (a full month before the women enters her 2 trimester From Conception To Birth  There are 3 stages of prenatal development o Period of the zygote: first 10 – 14 days o Period of the embryo: starts at the 3 week and ends at the 8 th o Period of the fetus: from the ninth week until birth PERIOD OF THE ZYGOTE  While the zygote is moving down the fallopian tube it will go through mitosis – during this time a nucleus (known as a blastocyst) will be created – it’s a ball shaped structure that will contain 60-80 cells w/in 4 days o Embryonic disk: the inner most layer of the blastocyst which will become the embryo; the outer layers will become tissue that protect the embryo  Implantation: at 6-10 days, tendrils will emerge from the blastocyst and will tap the mothers blood supply at the uterine wall (has a certain window of time that this needs to be done); should be implanted by 10-14 days (3/4 zygotes fail to survive this phase)  4 structures are created when the implantation happens to protect the inner layer of the blastocyst: o Amnion: sac that fills fluid from the mothers tissue – cushions the organism for protection and allows it move around o Chorion: yolk sac that surrounds the amnion and produces blood cells for the embryo until it can create its own o Placenta: eventually the chorion becomes this (multipurpose organ) o Allantois: will eventually become the umbilical cord  Placenta is formed to become a separation of the mothers and embryo’s blood – it has villi that prevent it from mixing (it is also semipermeable, so something’s like O 2 CO 2,lts and other nutrients can pass it – blood cells are just too large  Umbilical cord: connects the embryo to the placenta – transports waste away from the embryo and allows the oxygen delivered from the mother to get to the embryo (important for metabolic fns) PERIOD OF THE EMBRYO rd  Embryonic disk becomes 3 layers by the 3 week o Ectoderm: becomes the nervous system, skin, hair - by the 3 weekd some of the ectoderm folds to become the neural tube o Mesoderm: muscles, bones, circulatory system – heart forms at the 4 th week o Endoderm: all other organs, digestive system, lungs, urinary tract - The 2 Month  Limbs develop from the body outward; i.e. last part of the arm to form are the fingers (same goes for the legs) th th  Indifferent gonad: at the 7 -8 week this genital ridge is formed which gives rise to the embryos sexual development o So if male then the Y chromosome will trigger biochemical rxns to create testes; a female wont get these instructions so they will produce the ovaries THE PERIOD OF THE FETUS (the last 7 months of pregnancy)  All major organs are functioning at the beginning of this period and can move, sense and behave – also gives rise to individuality since the fetus creates different movement patterns and can express facial expression -The 3 Month  Connections bw different organs are starting i.e. nervous and motor system and the digestive and excretory systems  The male testes will secrete testosterone – this will allow the penis and scrotum to form o If not testosterone, then the female genitalia will form  End of the 3 an ultrasound can be used to detect the sex nd th th th th -The 2 Trimester (4 -6 months) – 13 to the 24 weeks  During this time the fetus can suck, swallow, cough and hiccup  Fetus will start kicking  By 16 weeks starts to look like a human (still cant live outside the womb)  20 weeks: heartbeat is strong enough that you can hear it by placing an ear on the women’s abdomen  Vernix is formed: white cheesy substance on the fetus – used for protection of the skin being chapped by the amniotic fluid  Lanugo is also formed: fine layer of body hair – helps the vernix stick to skin  End of six months: auditory and visual systems are formed and functioning rd th th -The 3 Trimester (7 -9 months)  Organ systems mature rapidly – getting ready for birth  Age of viability: 22-28 weeks, where living outside the uterus is possible  During these months the fetus assumes a fetal position since it is the most comfortable position they can get in the restricted uterus  Sleep increases by the ninth month  During the last month the uterus will start contracting and relaxing so the head of the fetus can be pushed to the pelvic bones ENVIRONMENTAL INFULENCES ON PRENATAL DEVELOPMENT Teratogens  Any disease, drug or other environmental agents that can harm an embryo or fetus  Long term effects of teratogens often depend on the quality of the postnatal environment  Embryos and fetuses can be effected by BOTH the father and mothers exposure to some teratogens  Some teratogens have “sleeper effects” – wont show the damage until later in life  Sensitive period: time when the organs are independently forming and when their most sensitive o Most things are forming during the period of the embryo, so this is known as critical phase of pregnancy MATERNAL DISEASES  Rubella (German measles): a mother than has this can lead to children being born blind, deaf, w/cardiac abnormalities, and mental retardation o As adolescence, these individuals are also more likely to develop psychotic disorders than controls o Most dangerous during the first trimester  Toxoplasmosis: a parasite found in many animals – can be given to a pregnant women that has ate undercooked meat or handling the feces of a cat that has ate an infected animal o Can lead only to a mild cold in the women, but can cause eye/brain st damage to the fetus (1 trimester) – can also induce a miscarriage later in the pregnancy  STI/STD’s: can cause birth defects or compromise developmental outcomes o Syphilis, genital herpes and AIDS are the most hazardous DRUGS  The thalidomide tragedy: in the 1960s a German drug company provided over the counter thalidomide - mild tranquilizers, to reduce morning sickness (had no –ve effects when studies of it were done on pregnant rats) o Thousands of babies during this time were born with severe birth defects – had deformed eyes, ears, hearts and some were born with phocomelia (all limb parts were missing so hands and feet were attached to the torso like flippers) o The drug had different effects on the fetus if taken during different times of pregnancy – a women that took
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