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PSYB32H3 Lecture Notes - Morning Sickness, Pelvic Inflammatory Disease, Preterm Birth

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Mark Schmuckler

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Twinkle Arora (PSYB20)
CHAPTER 3: Prenatal Development and Birth
Stages of Prenatal development
- Conception takes place during a woman’s ovulation or within few days of it; the ovum or egg,
once released from the mother ovaries lives about 3- 5 days
- Prenatal development than encompasses the 38 weeks (9 months) b/w conception and birth
- 3 stages (trinesters) (1) Zygote (2) the embryo and (3) the fetus
- Zygote the developing organism from the time of the union of the sperm and the egg to about
the second week of gestation; the period of the zygote is comprised of the implantation of the
fertilized egg in the wall of the uterus
- Once the zygote is implanted in the mother’s uterus the second prenatal period begins
- Embryo - the developing organism b/w the second and eighth weeks of gestation the period of
the embryo comprises the differentiation of the major physiological structures and systems
- Gestation the carrying of an embryo or fetus during pregnancy usually for nine months
- During the embryo period 3 curcial structures develop to protect and support the baby - 1.
The amniotic sac 2. The placenta and 3. The umbilical cord
- Amniotic sac - A membrane containing a watery fluid that encloses the developing organism,
protecting it from physical shocks and temperature changes
- Placenta a fleshy, disk 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
- Umbilical cord - a tube that contains blood vessels that carry blood back and forth b/w the
growing organism and its mother by way of the placenta; it carries O2 and nutrients to the
growing infant and removes CO2 and waste products
- The semi permeable membranes within the placenta separate the bloodstreams of the infant
and mother
- During the embryo period the inner mass of the developing infant differantes into 3 layers : the
ectoderm, mesoderm and the endoderm
- Ectoderm - the hair, nails and parts of teeth
- Mesoderm forms muscles, skeleton, circulatory and excretory system
- Endoderm froms the gastrointestinal tract, trachea, bronchia, and vital glands (lungs)
- At the 4th week the neural folds (folds that form the CNS) being to close. If they fail to close the
infant can develop spina bifida disorder in the spinal cord
- Prenatal development is guided by 2 principles = cephalocaudal and proximal distal
- Cephalcaudal the pattern of human physical growth in which development begins in the area
of the brain and proceeds s downward to the trunk and legs
- Proximal distal wherein development starts in central areas such as internal organs and
proceeds to more distant areas such as arms and legs
- At 6 weeks the embryo is recognizable as a human being
- Miscarriages the natural end of pregnancy before the infant is capable of survival outside the
womb and generally defined in humans as prior to 20 weeks of gestation (range ¼ miscarriage)
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Twinkle Arora (PSYB20)
- The third and final period of prenatal development, the fetus the developing organism from
the 3rd month of gestation through delivery; during fatal development of bodily structures and
systems and becomes complete
- At 3 months the fetus has all its body parts
- At 4 moths mothers usually report movement of the fetus
- At 5 months reflexes such as sucking, swallowing and hiccupping usually appear
- Lanugo a fine, soft hair that covers the fetus’s body from about the 5th month of gestation on;
maybe shed before or after birth
- at 6 months - eyes begin to open and close
- if the infant is born prematurely at 6 months the regulatory processes and nervous system and
resspritiory systems are usually not mature enough for survival. At this time the fetus cannot
produce and maintain an adequate amount of surfactant
- surfactant - a liquid that allows lungs to transmit oxygen from the air to the blood
- respiratory distress syndrome a condition of the new born marked by laboured breathing and
a blush discolouration of the skin or mucous membranes and which can often leads to death
- age of viability the age of 22 -26 weeks, by which point the fetus’s physical systems are well
enough advanced that it has a chance at survival if born prematurely
Risks in the prenatal development
- teratogen an environmental agent, such as drug, medication, dietary imbalance or polluting
substance, they may cause developmental deviations in a growing human organism; most
threatening in the embryonic stage but capable of causing abnormalities in the fatal stage aswell
a teratogen exerts its effects largely during critical periods
each teratogen exerts certain specific effects - different teratogens influence different
developmental processes e.g. rubella (German Measles)
Either maternal or fetal genotypes may counteract a teratogen’s effects abnormalities
The effects of one teratogen may intensify the effects of another
Different teratogens may produce the same defect
The longer a fetus is exposed ti a particular teratogen and the greater the intensity of
the teratogen’s effects – the more likely it is that fetus will be seriously harmed
Environmental Dangers
- Heavy use of Asprin has been associated with low birth rate, lower IQ and poor motor control
- Caffeine can too affect the developing fetus by increasing risks of a miscarriage
- Smoking an d drinking are associated with disturbances in placental functioning and with
changes in maternal physiology that lead to oxygen deprivation and thus changes in the brain
- Sudden infant death syndrome (SIDS) in which infants under the age of 6 months stop
breathing and die w/o apparent cause, is more common in the offspring of mothers who drink
or smoke
- Prenatal nicotine exposure poorer performance on measures of verbal comprehension
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