111. twins, malformations, multiple pregnancy 112.113. birth defects envornment/genetic Flashcards
what is the reason for the increase in multiple pregnancies (twins triplets)
increasing age of mothers
more use of fertility treatments
dizygotic twins are more common than monozygotic (accounts for 90% of twins) what is the order of likelyhood
Male-Female twins
Female twins
Male Twins
Monozygotic Female
Monozygotic Male
How does dizygotic/ fraternal twins occur
2 oocytes are shed and fertilized by DIFFERENT spermatozoa
just like any other sibling DNA
the zygotes usually develop their own placenta, amnion, chorionic sac
erthyrocyte mosaicsm- fusion between placentas mean each twin jhas rbcs of 2 different types
How does monozygotic/ identical twins occur
develops from 1 egg fertilized by 1 sperm
zygote splits into 2
splitting happens at different stages
what are th different splitting for identical twin
split at 2 cell stage: blastocysts implant searately, separate placenta and chorionic sac
split at blastocyst stage: inner cell mass splits. The 2 embryos have same placenta nad chorionic cavity but different amniotic sac
rare, split at bilaminar germ disk: single placenta, chorionic and amniotic sac. blood supply well balanced tho
the later the embryo splits, the greater the similarity
What are some abnormalities associated with twins
approx 60% born preterm and underweight = 3x higher mortality
many twins die before birth (vanishing twin)
twin-twin transfusion syndrome= placental vascular anastomoses form resulting unequal blood flow
partial splitting of primative node/streak=conjoined twins
What is the term to describe the study of birth defects/ malformations etc
teratology/dysmorphology
congenital malformations is used to describe structural, behavioural, functional and metabolic disorders
What are some types of abnormalities
MALFORMATIONS-During formation of structures ie organogenesis ,3-8 week of gestation
Caused by environmental/genetic/both factors
DISRUPTIONS- alters already formed structures; caused by destructive process eg vascular acciedents leading to limb defects
DEFORMATIONS- mechanical force that ,olds part of fetus; may be reversible postnatally eg clubfeet due to compression amniotic cavity
Difference between syndrome and association
syndrome- group of anomalies occurring together that has common specific cause
association- non random 2 or more anomalies cause not known
When is the most critical period of development for the foestus
8 weeks after formation of zygote
When is the most critical period of development for the foetus
8 weeks after formation of zygote
environmental factors that can result in birth defects (tetrogens)
Alcohol- result in small head/body, underdeveloped physical/mental growth
Tobacco- nicotine gets into placenta, premature birth, growth restriction, increased chance of bleeding
Viral infections eg rubella non viral eg toxoplasmosis
drugs eg thalidomide
ionizing radiation- kills rapidly proliferating cells
Maternal obeseity/diabetes
capacity of an agent to produce birth defects have been defi ned and set forth as the principles of teratology:
- depends on the genotype of the embryo
2.Developmental stage at the time of exposure-sensitive period 3-8 week embryogenesis
3.Dose and duration of exposure to teratogen
4.Teratogens may act in a specific way that inhibits a biochemical process or pathogenesis may involve cell death
5.Manifestations of abnormal development are
death, malformation, growth retardation, and
functional disorders.
How can birth defects be caused by genetic factors
chromosomal defects
gene mutations
What are some chromosome defects
change in structure-translocations, deletions, duplications, inversions
change in number of chromosomes-aneuploidy, trisomy 18 (edwards syndrome)
Abnormalities of sex chromosomes
