Chapter 3 - Prenatal Development and Birth.docx

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Mark Schmuckler

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By: Paraniya Prenatal Development and Birth o The ovum, or egg, once released from the mothers ovaries, lives only about three to five days. Prenatal development takes 38 weeks or approximately 9 months. 9 months of prenatal development are characterized in two ways: 1. Occurring in three trimesters (3 periods of 3 months) 2. Three periods of (a) the zygote, (b) the embryo, (c) the fetus o The period of the zygote is approximately the first two weeks of life. During which the sperm fertilizes the ovum, now referred to as zygote or fertilized egg, which then proceeds down the mothers fallopian tube and implants in the wall of the uterus About 7 days after conception the zygote is very small, but gradually the tendrils from the zygote penetrate the blood vessels in the wall of the uterus o Second prenatal period, the period of rapid growth the embryo which is in between the second and eight weeks of gestation; comprises the differentiation of the major physiological structures and systems The embryo also becomes recognizable as a tiny human being. From time of fertilization until the end of this period, the infant increases 2 million percent in size Three crucial structures develop to protect and support the growing life within the mothers uterus a. Amniotic sac a membrane containing a watery fluid that encloses the developing organism, protecting it from physical shocks and temperature changes b. Placenta a fleshy, disc-like structure formed by cells from the lining of the uterus and from the zygote, and that, together with the umbilical cord, serves to protect and sustain the life of the growing organism c. Umbilical cord a tube that contains blood vessels that carry blood back and forth between the growing organism and its mother by way of the placenta; it carries oxygen and nutrients to the growing infant and removes carbon dioxide and waste products Placenta and the umbilical cord transmit oxygen and nutrients to the infant and remove carbon dioxide and waste products from it, but they do not permit direct exchange of blood Inner mass of the developing organism differentiates into three layers: a. Ectoderm hair, nails, and parts of the teeth, the outer layer of the skin and skin glands, and the sensory cells and the nervous system develop b. Mesoderm -- muscles, skeleton, circulatory and excretory system and inner skin layer c. Endoderm gastrointestinal tract, trachea, bronchia, Eustachian tubes, glands, and vital organs, such as the lungs, pancreas, and liver By: Paraniya In about the fourth or fifth week of gestation, the neural folds begin to close. If something occurs to prevent them from closing completely, the chill will have spina bifida, a disorder in which the spinal cord and the membranes that protect it may protrude from the spinal column o Prenatal life is guided by two principles: 1. Cephalocaudal pattern of human physical growth in which the development begins in the area of the brain and proceeds downward to trunk and legs 2. Proximal-distal pattern of human physical growth wherein development starts in the central areas, such as internal organs, and proceeds to more distant areas, such as arms and legs End of the embryo growing period of the embryo, the growing organisms face and features are delineated, and fingers, toes, and external genitalia are present Most miscarriages, or spontaneous abortions, occur during this period; for one reason or another, the embryo becomes detached from the wall of the uterus and is expelled through the vaginal canal estimated 1 in 4 pregnancies o Third and final period of prenatal development, the fetus the term for the developing organism from the beginning of the third month of gestation to delivery experiences rapid growth in muscular development and the central nervous system Fetus has all of its body parts, including external genital organs. By the end of the fourth month, mothers usually report movement of the fetus Fifth month, the fetus develops nails and sweat glands, coarser, more adult- like skin, and soft hair, called lanugo, which covers the body shed before birth or after Six months, the eyes can open and close. If an infant is born prematurely at six months, the regulatory processes and nervous and respiratory systems are usually not mature enough for survival without intensive intervention Without surfactant, infants are often unable to breathe adequately, and they may develop respiratory distress syndrome, a condition of the newborn marked by labored breathing and a bluish discoloration of the skin or mucous membranes, and which often leads to death The age of 22 to 26 week , sometimes referred to as the age of viability is an important point in fetal development and which point the fetuss physical systems are well enough advanced that it has a change at survival if born prematurely o Many agents may cause developmental deviations in the fetus. These agents are called the teratogens which are an environmental agent, such as a drug, medication, dietary imbalance, or polluting substance, that may cause developmental deviations in a growing human organism; most threatening in the embryonic stage but capable of causing abnormalities in the fetal stage as well These may include prescription drugs or non-prescription drugs taken by mother and environmental toxins, such as pollution, other factors like mothersBy: Paraniya age, her diet, and her emotional state affect the response of mother and child to any given teratogen Teratogens exert their effects on prenatal development in specific ways 1. Teratogen exerts its effects largely during critical periods most vulnerable during embryotic stage 2. Each teratogen exerts certain specific effects rubella in mother affects mainly the fetuss heart, eyes, and brain. Drug thalidomide causes primarily malformations of the limbs 3. Either maternal or fetal genotypes may counteract a teratogen effect 4. Effects of one teratogen may intensify the effects of another 5. Different teratogen may produce the same defect 6. Longer a fetus is exposed to a particular teratogen and the greater the intensity of the teratogens effects, the more likely it is that the fetus will be seriously harmed dose-response principle at work ~ higher the dose, the more severe damage to the developing fetus o Illegal drugs, such as heroin, and other drugs in common use, such as alcohol and nicotine, are often harmful to human beings These substances can be extremely harmful even life-threatening to the prenatal infant According to one estimate nearly 90% of women take some sort of drug during pregnancy. In many cases these women do not yet realize they are pregnant. Even so, some over-the-counter d
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