Lecture 3 Flashcards
Ovaries of females contain precursors of all ova they will ever produce
Immature ova are called oocytes
Testes of males produce new sperm continually
Sperm and ova are called germ cells
Mature sperm and ova are called gametes
Sperm and ova contain 23 chromosomes each– half of the chromosomes
necessary (23 pairs or 46 chromosomes)
Sperm cells have half X and half Y sex chromosomes whereas all ova have one X sex chromosome. ( 2 X = female and X, Y = male)
Conception
Once fertilization has occurred and the ova and the sperm cell have contributed their 23 chromosomes each it is known as a zygote.
Zygotes undergo a two week rapid cell division, a process known as mitosis.
This two week period is known as zygotic or germinal phase and it covers from conception to implantation of the embryo into the uterus
Zygotic period
Embryonic stage is from two weeks to 8 weeks.
Fetus refers the time from the end of the 8th week until birth.
Zygotic & fetus period
The DNA – and genes that are sections of DNA- contain chromosomes inherited from both parents and help determine how humans develop.
Epigenetic mechanisms do not change the sequence of the building blocks in DNA but can turn on and off certain genes.
IMPORTANT PROCESSES IN PRENATAL DEVELOPMENT
Zygotic stage – cells have potential to develop into many different cell types and are referred to pluripotent cells
Epigenetic mechanisms remove or inactivate methyl groups on DNA during the zygotic stage
During cell division the daughter cells become more and more specialized
Specialized cells make different types of proteins causing cells in different tissues to have different shapes, membranes, structures and functions.
CELLULAR DIFFERENTIATION
Epigenetic process called X-Chromosome inactivation or lyonization
Early stage development one or the other of the X chromosomes in cells of females become inactivated so they do not have twice as many X chromosomes as males
X-linked conditions such as Duchenne muscular
dystrophy and Fragile X
Females were once thought not to be at risk of developing
Chromosome inactivation
Epigenetic process called Genomic imprinting
Genes can occur in alternative forms known as alleles
Alleles inherited from both the mother and the father
are expressed
Chromosomes that are subject to genomic imprinting this is not the case.
So genes on the maternal allele are expressed because the male allele is imprinted and turned off and vice versa
Interference with genomic imprinting can result in developmental disorders such as Prader-Willi syndrome and Angelman syndromes
genomic imprinting
Environmental factors in early development can affect health in adulthood
Example:
Inadequate nutrition prior to conception could result in a child that experiences high blood pressure, heart disease, or diabetes in later life.
Epigenetic process are believed to be involved in this physiological process, but
research is still in its infancy
metabolic programming
Metabolic programming or Perinatal programming explore the idea that environmental factors thought to change the way the infant’s brain genes express themselves, the way an infant develops, and may result in neurodevelopmental disorders
such as:
How mothers, fathers, and others interact with an infant
Bacterial and viral infections
Nutritional deficiencies after birth
Ex. A mother that has the flu during pregnancy is thought to increase risk of schizophrenia and autism in offspring. (Theory)
In animal studies, it is believed that the chemical oxytocin is responsible for positive maternal behavior and triggers the production of proteins called growth factors preventing certain genes in the brain from becoming methylated.
Perinatal programming
Teratogens are factors that interfere with normal embryonic and fetal differentiation e.g. certain medications, environmental factors etc.
Exert their effects via epigenetic mechanisms
Table 9.2, p. 117 gives a list of potential teratogens
Examples of some of the effects are:
Cleft lip/palate, anencephaly ( neural tube defect whereby a large part of the brain and skull are missing),
ventricular septal defects (whole in the heart at birth), and developmental disability
Fetal death, prematurity, growth retardation, and unexplained structural abnormalities suggest teratogenic effects
Disorders from teratogens can be prevented through community education
Teratogens
Four factors in ______ are:
Embryo/fetus age, or gestational age at the time of the exposure
Dosage of the teratogen
Fetal genotype which may make the fetus more or less vulnerable to the
teratogen
Maternal genotype; pregnant women differ in their ability to detoxify teratogens
teratogenicity
Most common complications:
Ectopic pregnancy – pregnancy that is not in the
uterus
Rh Negative Disease – mother has Rh Negative blood father has Rh positive
Group B streptococcus infection – present in the
gastrointestinal tract can be passed onto infant
Preterm Labor
Low gestational birth weight
Pregnancy complications
Complications can deprive the infant of oxygen or increase the risk of acquiring an infection and result is developmental delay, intellectual disability and/or physical disabilities
Complications include:
Premature labor and premature delivery
Labor that lasts too long
Abnormal presentation of the infant in the birth canal
Premature rupture of the membranes around the infant
Umbilical prolapse (Umbilical cord precedes the infant into the birth canal)
Complications of labour and delivery
Born before the 37th week of gestation considered to be premature
Complications associated:
Immature lungs
Increased risk of acquiring pneumonia
Other infections
Jaundice
Intraventricular hemorrhage (hemorrhage into the ventricles of the brain)
Inability to maintain body temperature
Immature digestive tracks
Premature birth complications
Ultrasound Scans
Maternal Serum Screening
Amniocentesis
Chorionic villus sampling (CVS)
Percutaneous umbilical blood Sampling (PUBS)
PRENATAL DETECTION OF DEVELOPMENTAL DISABILITIES
