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Chapter 4

Developmental Chapter 4

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PSYC 2450
Jennifer Mc Taggart

CHAPTER 4 - Pregnancy and prenatal development Definitions cephalocaudalprinciple:principle that development proceeds in a head-to tail direction; that is, upper parts of the body develop before lower parts proximodistalprinciple:(Latin for near to far) principle that development proceeds from within to without; that is, parts of the body near the centre develop before the extremities germinalstage:first 2 weeks of prenatal development, characterized by rapid cell division, increasing complexity and differentiation, and the implantation in the wall of the uterus embryonicstage: second stage of gestation (2 to 8 weeks) characterized by rapid growth and development of major body systems and organs spontaneousabortion:natural expulsion from the uterus of an embryo or fetus that cannot survive outside the womb; also called miscarriage fetalstage: final stage of gestation (from 8 weeks to birth), characterized by increased detail of body parts and greatly enlarged body size ultrasound: prenatal medical procedure using high-frequency sound waves that detect the outline of a fetus and its movements, in order to determine whether a pregnancy is progressing normally teratogenic:capable of causing birth defects fetalalcoholsyndrome(FAS):combination of mental, motor, and development abnormalities affecting the offspring of some women who drink heavily during pregnancy acquiredimmunedeficiencysyndrome(AIDS): viral disease that undermines effective functioning of the immune system Chapter notes Prenataldevelopment:ThreeStages Gestational age usually takes place from the first age of an expectant mother’s last menstrual cycle, and usually has a normal range of 38-42 weeks. After conception happens (usually marked by a missed menstrual period), prenatal development takes place in three stages: germinal, embryonic and fetal. The genes responsible for this transformation are in a specific identifiable group and produce molecules called morphogens. Morphogens are turned on after fertilization and shape all the different parts of our bodies. Growth and motor development occur from the top down and from the centre of the body outward (see cephalocaudal and proximodistal principles). Cephalocaudal means “head to tail” in Latin and is demonstrated in that an embryo’s head, brain and eyes develop earliest and are disproportionately large until the rest of the body catches up. Germinal Stage (Fertilization to 2 weeks) During the germinal stage, the zygote undergoes cell division (mitosis), becomes more complex, travels down the fallopian tubes, and is implanted into the wall of the uterus. Before implanting in the wall of the uterus the zygote changes its form into a blastocyst, a fluid filled sphere that floats around the uterus for a day or two - after this point implantation occurs, but only around 10-20 percent of fertilized ova actually implant and continue to develop. Before implantation, a group of cells called the embryonic disk begin to form, which then change into two layers: the ectoderm (which will become the outer layer of skin, nails, hair, teeth, sensory organs and the nervous system) and the endoderm (which will become the digestive system, liver, pancreas, salivary glands, and respiratory system). Other parts of the blastocyst develop as well, such as a middle layer called the mesoderm (which will become the inner layer of skin, muscles, skeleton, and excretory and circulatory systems), as well as the placenta, umbilical cord, and the amniotic sac, all of which work to protect and nourish the unborn child. The placenta produces hormones that support pregnancy and is connected to the embryo by the umbilical cord, which delivers oxygen and food and removes waste. The mother’s and embryo’s circulatory systems are not directly connected, but diffusion of blood happens across the blood vessel walls. Embryonic Stage (2 to 8 weeks) During this stage the organs and major body systems (respiratory, digestive, and nervous) develop rapidly, and the embryo is especially vulnerable to destructive influences in the prenatal environment. This stage is critical for maintaining a healthy environment for the unborn, such as organs are still developing - defects that occur later in pregnancy are less likely to be as serious. The most seriously affected embryos rarely last past the first trimester, which can result in a spontaneous abortion - 3 out of 4 miscarriages occur during the first trimester. Males are more likely than females to be spontaneously aborted or stillborn, and continue be more susceptible to disorders after birth, even though males are more easily conceived than females Fetal Stage (8 weeks to birth) This stage is signaled by the first bone cells around 8 weeks, and during this stage the fetus grows rapidly to about 20 times its previous length and organs/body systems become more complex. At this stage fetuses are very mobile in the mothers uterus, and can feel pain (but most likely not before the third trimester). There are instruments available such as the ultrasound that we can use to monitor fetal movement, heart rate, changes in activity level, states of sleep and wakefulness and cardiac activity. Between 28 and 32 months a baby may show decreased signs of movement, this is because there is increasingly less space for them to move around in. Even with less space boys tend to move around more vigorously than female infants. Fetuses have signs of having senses such as touch and hearing when they are in the womb, such as they respond to their mother’s voice and to vibrations. There has been research indicating that infants show a preference towards sounds and speech patterns they heard before being born. In addition, from 12 weeks after gestation, fetuses swallow some amniotic fluid, which may stimulate their budding sense of smell and taste. Prenataldevelopment:Environmentalinfluences Maternal influences Since the prenatal environment is the mother’s body everything that affects the mother’s well-being affects the baby as well. Factors that are teratogenic are defect causing and the dose, duration and interaction with these factors can have varying effects in birth defects. Pregnant women need to gain weight and eat more than usual - pregnant women who gain between 10 and 20 kg are less likely to miscarry or have a stillborn or low birth-weight baby. Women who are having their first baby and overweight women are more at risk for having stillbirths or losing their baby in the first week of life, and underweight women are at danger of having small babies. The nutrition a baby gets from their mother can have long lasting effects and be a factor in health later in life. Taking vitamins as a malnourished mother can help improve a baby’s health, although some vitamins are harmful in large amounts. Iodine deficiency, unless corrected before the third trimester can cause cretinism, which may involve severe neurological or thyroid problems. Regular exercise can contribute to a more comfortable pregnancy and an easier delivery, but strenuous working conditions and stress may lead to premature birth. The baby is very vulnerable in the first few months of gestation and not only will they be effected by illegal drugs, medical drugs may also have an effect on the fetus. Some teratogenic medical drugs are tetracycline, barbiturates, opiates, and among others, certain anti-cancer drugs. In one study, Danish men whose mothers had
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