congenital defects and embryology Flashcards
what does congenital mean?
present at birth
how many births have some defects? how many of these are minor abnormalities
20%
75% of these are minor abnormalities
how many births could be prevented if we knew the cause?
half
in how many births is the cause unknown?
70%
name some of the causes of birth defects?
- genetic/chromosomal
- drugs
- environmental
what drugs can cause birth defects?
accutane - anti-acne medication which contains an active form of Vitamin A. Vit A is fat-soluble so can be stored in the fat in toxic levels which can then pass onto the infant
thalidomide - given to women for morning sickness but wasn’t tested properly caused babies to be born without limb
what environmental factors can cause congenital defects?
o Infections agents (rubella – causes eye defects, CMV, Zika – causes microcephaly)
o Environmental agents (alcohol and smoking)
what does a lack of folic acid lead to?
birth defects
how can birth defects be prevented using folic acid?
prevent if women consume 400 micrograms of folic acid daily, prior (three months) and during the first trimester
why does an embryo have to be implanted into the endometrium by 5 weeks?
placenta needs to be formed and developed enough to give you an O2 supply bc embryo is 4mm – the limit of diffusion
when is the embryonic period?
between 3 and 5 weeks
when is the fetal period?
between 8 weeks and birth
what are major congenital defects defined as?
requiring medical/surgical treatment
what are minor congenital defects defined as?
anomaly that doesnt require intervention
name some major congenital defects
anencephaly cleft lip and palate omphalocele phocomelia spina bifida talipes equinovarus hypospadias congenital diaphragmatic hernia gastroschisis
what is anencephaly?
born without a skull
what is omphalocele?
intestines, liver and other abdominal organs outside body: failure of return of these contents in 9th week
what is phocomelia?
shortened limbs
what is spina bifida?
failure of closure of spinal cord and vertebral column
what is talipes equinovarus?
club foot
what is hypospadias?
urethra detached from penis
what is congenital diaphragmatic hernia?
diaphragm goes not close properly allow gastrointestinal contents (intestines) to push into the thorax and prevent proper development of lungs.
how can congenital diaphragmatic hernia be treated?
simple sutures
what is gastroschisis?
body wall has not closed so abdominal contents leak outside
name minor congenital defects
Auricular ear tag, supernumerary nipples, overlapping digits, micropenis
syndactyly, polydactyly, ankyloglossia, cryptorchidism
holoprosencephaly
cleft lip and cleft palate
congenital diaphragmatic hernia
what is syndactyly?
when fingers are fused together
what is polydactyly?
having an extra finger
what is ankyloglossia?
tongue tied
what is cryptorchidism?
undescended testes
how is cryptorchidism corrected?
usually spontaneously corrected within 3 months
what complications can arise if cryptorchidism isnt treated?
Gives 20x increased risk of developing testicular malignancy and can lead to male infertility
what is holoprosencephaly?
loss of midline structures
how can severity of holoprosencephaly differ?
o Severity can vary from mild to severe
what are the causes of holoprosencephaly?
genetic or environmental
why is it better to repair a cleft lip/palate in utero?
better regenerative capacity in utero and scar tissue doesn’t form bc immune system isn’t fully formed
how can a cleft lip/palate be repaired?
o Repairs can be done with simple sutures or synthetic patch such as Gor-tex (for large defects)
o In utero repair via laproscopy can allow lungs to develop
how is gastroschisis repaired?
Intestines are put into a plastic bag and sealed, fluids and anti-inflammatories are given to settle the inflammation. Intestines should fall back into the abdomen where the silo (bag) can be removed and everything can be sewn back together
where and when does fertilisation occur?
ampulla region of the uterine tube within 24 hours of fertilisation
when does the morula form?
3 days after fertilisation
when does the blastocyst implant?
hatches from zona pellucida and implants at day 6
what happens during week 2 of fertilisation?
- Trophoblasts differentiate into two layers: synctioblast, cytotrophoblast.
- Embryoblasts differentiate into 2 layers: epiblasts dorsally and hypoblast ventrally.
- Two cavities: amniotic cavity dorsal to epiblast. Yolk sac cavity ventral to hypoblast
what is the hydatidiform mole?
no fetus - only the placenta forms
what genes does the placenta come from?
paternal genes
how does the hydatidiform mole look?
Generally large, composed of grape-like clusters of swollen chorionic villi. Uterus fills with the placenta.
how is a hydatidiform mole treated?
Requires hysterectomy for removal – like a tumour. Grows into the endometrium
when does a hydatidiform mole form?
- Single spermatozoon fertilizes oocyte that lacks a nucleus, mitosis w/o cleavage.
- 2 spermatozoa may fertilize oocyte that lacks a nucleus (46XX, 46XY).
- 90% 46XX indicating that mono-spermic fertilisation is dominant.
what is a partial hydatiform mole?
some evidence of embryonic development can be found
what is the karyotype for partial hydatiform mole?
triploid (69XXX, 69XXY, 69XYY)
what causes partial hydatiform mole?
Often because of fertilisation of an oocyte containing female pronucleus by 2 spermatozoa or an abnormal diploid sperm
what happens during week 3 of fertilisation?
• Two layers are transformed into three layers as epiblasts travel to the midline, travel and push the hypoblasts outwards;
establishes body’s axis
what are the 3 layers formed in week 3 and what do they form?
o ectoderm – nervous system and skin
o mesoderm – muscle, connective tissue and bone
o endoderm – gut
what causes sirenomelia?
Epiblast cells stop invaginating too soon, insufficient mesoderm produced –> not enough cells in mesoderm to separate the legs.
why do few people with seronmelia survive?
Often associated with kidney and gastrointestinal defects, so few survive to have the legs separated
