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Chapter 4

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University of Guelph
PSYC 2450
Anneke Olthof

Chapter 4 - Prenatal Development Prenatal development: Development that occurs between the moment of conception and the beginning of the birth process. From Conception to Birth Prenatal development divided in to 3 major phases 1. Period of the zygote (germinal period)  from conception through implantation; when the zygote becomes firmly attached to the wall of the uterus. (10 to 14 days) 2. Period of the embryo  from the beginning of the third week through the end of the eight. Time when all the major organs are formed and the heart begins to beat. 3. Period of the fetus  from the ninth week until the child is born. All major organs begin to function. The Period of the Zygote  Zygote moves down fallopian tube towards uterus, divides by mitosis into two cells.  Those 2 cells and all other cells continue to divide and form a ball-shaped structure called blastocyst. (Contains 60 to 80 cells within 4 days of conception)  The inner layer of the blastocyst or embryonic disk becomes the embryo, whereas the outer layer of cells will develop into tissues that protect and nourish the embryo. Implantation - Blastocyst approaches the uterus 6 to 10 days after conception; small tendrils emerge from its outer surface. When reaching the uterine wall, tendrils burrow inward, tapping the mother’s blood supply  implantation (burrowing of blastocyst into lining of uterus) - Specific time where blastocyst must communicate with uterine wall to position and attach itself properly. - Process takes about 48 hrs. And occurs 7 to 10 days after ovulation. Entire process competed about 10 to 14 days after ovulation. Support Systems - After being implanted, the blastocyst’s outer layer forms four major support structures to protect and nourish the organism. - Amnion: Watertight sac that fills with fluid from the mother’s tissues. Amniotic fluid o Cushion the developing organism against blows, regulates its temperature, provides weightless environment to make it easier to move. o In watertight sac, there is another sac that produces blood cells until the embryo is capable of producing its own. - That yolk sac attaches to chorion: surrounds amnion and becomes the lining of the placenta. Gathers nourishment for embryo o Placenta: multipurpose organ. Provides for respiration and nourishment and elimination of metabolic wastes. - Fourth membrane: allantois: forms embryo’s umbilical cord: soft tube containing blood vessels that connects the embryo to the placenta. 1 Placenta - Fed by blood vessels from the mother and the embryo. - Prevents these two bloodstreams from mixing together - Oxygen, carbon dioxide, salts, sugars, proteins and fats can pass through. - Maternal blood delivers oxygen and nutrients to embryo through umbilical cord. Umbilical cord also transports carbon dioxide and metabolic wastes. - Wastes products cross-placental barrier, enter the mother’s bloodstream and are excreted along with her own wastes. See Figure 4.1 for Period of the Zygote Period of the Embryo rd th - From implantation (3 week) through 8 week. - By 3 week, embryonic disk is differentiating into 3 cell layers o Outer layer - ectoderm  will become nervous system, skin and hair o Middle layer - mesoderm  will become the muscles, bones and circulatory system. o Inner layer - endoderm  will become the digestive system, lungs, urinary tract, pancreas, liver. - 3 after conception, ectoderm folds into neural tube  becomes brain and spinal cord. - End of 4 week, heart starts beating - eyes, ears, nose and mouth are also forming/buds that will become arms and legs also appear. The Second Month - Primitive tail appears but soon enclosed  becomes the tip of the backbone and the coccyx. - Ears are formed, rudimentary skeleton. - Arms appear; upper arm first, followed by fore arms, hands and then fingers. - Leth folthw a few days later. - 7 or 8 week, genital ridge appears called the indifferent gonad. - Circulatory system now functions on its own, liver and spleen can now produce their own blood cells. Period of the Fetus - Rapid growth and refinement of all organ systems - Fetus begins to move, sense and behave. The Third Month - Organs become interconnected. o Ex. Coordination between nervous and muscular systems allow fetus to kick its legs, make fists, twist body. o Digestive and excretory system are also working together th th The Fourth through Sixth Month (Second Trimester - 13 to 24 ) - 15 or 16 weeks to 24 or 25 weeks  movement tongue, lips, pharynx, larynx, suck, swallow, cough, and snort… - 5 to 6 month  nails harden, skin thickens, eyebrows, eyelashes, scalp hair appear 2 - 20 weeks  sweat glands are functioning - Fetus is now covered in white, cheesy substance called vernix, and a fine layer of body hair called lanugo. o Vernix protects fetal skin against chapping during long exposure to amniotic fluid o Lanugo helpthvernix stick to the skin. o End of 6 month  Fetus’s visual and auditory senses are functioning Seventh to Ninth Month (Third Trimester) - Finishing phase - Between 22 and 28 weeks, fetus reaches age of viability: the point at which survival outside the uterus is possible. - Middle of ninth month  fetal activity slows and sleep increases See Table 4.1 for Summary Environmental Influences on Prenatal Development Teratogens  Any disease, drug, or other environmental agent that can harm a developing embryo or fetus by causing physical deformities, severely retarded growth, blindness, brain damage, and even death. - Effects worst during period when structure is forming and growing most rapidly. - Not all embryos or fetuses are affected the same way - Same effect can be caused by different teratogens - Variety of defects can result from one teratogens - The longer a structure is exposed to a certain teratogen, the worst the effect is going to be. - Embryos and fetuses can be affected by both mother and father’s exposure to teratogens - A long-term effect of teratogens depends on the quality of postnatal environment. - Some can cause sleeper effects - that may not be apparent until later in life. Each part of our body has a sensitive period  when it is most susceptible to teratogen agents. Teratogens can have a subtle effect on babies’ behavior that are not obvious at birth but influence their psychological development. (Ex. a mother that consumer 30ml a day of alcohol; the child will not have any physical deformities but it is more likely to be slower at processing information and have a lower IQ. Maternal Diseases Rubella: A disease that has little effect on a mother but may cause a number of serious birth defects in unborn children who are exposed in the first three to four months of pregnancy. - Blindness, deafness, cardiac abnormalities, mental retardation. - Most dangerous during first trimester Toxoplasmosis: Disease caused by a parasite found in raw meat and cat feces; can cause bi
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