10. Congenital Defects and Human Embryology Flashcards
Roughly what percentage of live births have some defect?
What are the 3 top systems that cause major problems if they do not develop correctly in an infant?
What is the cause of congenital defects?
What is added to many cereals in the USA to prevent neural tube defects, cleft lip and palate?
20% (of which 75% are minor abnormalities). Congenital birth defects = leading cause of infant mortality.
Heart and circulation, respiratory, head and NS
Multifactorial: genetic/chromosomal (e.g Downs), drugs (e.g. thalidomide), environmental (e.g. rubella, CMV, zika, alcohol). Diff countries have diff rates of certain congenital defects. Now older women and less spina bifida (due to Folic acid)
Folic acid. (UK: 400 micrograms/day).
Why should mothers take folic acid before and during pregnancy?
List some major and minor congenital malformations.
Embyronic period: 3 - 8 weeks. Most development of main organ systems in first 4 weeks = peak of when birth defects induced (woman may not know she’s pregnant then and still drink etc.). Foetal period: 8 - 38 weeks, all about growth.
Major: anencephaly (no skull), cleft lip and palate, omphalocele (GI system herniated out), gastroschisis (SI and LI outside body), hypospadias (cleft penis), phocomelia (limb defomation), spina bifida (neural tube), talipes equinovarus (club foot).
Minor: auricular ear tag/pit, supernumerary nipples, cryptorchidism (undescended testes), syndactyly (fused digits), rocker bottom feet, polydactyly, overlapping digits, micropenis, ankyloglossia (tongue tied)
What is this condition?
Anencephaly - some defects are not compatible with life.
What is this condition?
Hypospadias - opening of the urethra is on the underside of the penis. Classified as major defect but rarely life threatening.
What is this condition?
Cryptorchidism - undescended testis, 1-4% male live births, most spontaneously correct within 3 months. Can affect developing sperm and lead to testicular malignancy later in life, so need to operate on and if >1 year may remove it entirely.
What is this condition? What causes it?
Holoprosencephaly - varies from mild (L) to severe (R) and causes can be genetic or environmental (alcohol consumption). Due to loss of midline structures.
What is this condition?
Congenital diaphragmatic hernia: diaphragm (seperates thorax from abdomen) doesn’t close properly allowing GI system to enter thorax. Loops of intestines enter the chest and prevent proper lung development. Defect usually on L side of diaphragm. Treating depends on defect size - if small stictch up, if bigger - synthetic patch. Can have in utero repair.
What happens in week 1 of pregnancy?
Fertilisation in ampula region of uterine tube within 24h of ovulation. 3 days after -> ball of cells = morula then blastocyst which hatches from zona pellucida -> implantation (day 6). Cells around outside form placenta = cytotrophoblast (paternal but inner cell mass is maternal and paternal mix).
What happens in week 2 of pregnancy? (The week of two’s)?
What is a hydatidiform mole?
Trophoblast differentiates into 2 layers: cytotrophoblast and syncytiotrophoblast (multinucleated, bigger, fuse, will form placenta). Embryo differentiates into 2 layers: epiblast (most of you) dorsally and hypoblast ventrally. 2 cavities formed: amniotic cavity dorsal to epiblast, yolk sac cavity ventral to hypoblast.
Abnormal pregnancy - non-viable fertilized egg implants in uterus and will fail to come to term. No foetus in around 0.1-0.5% - only placenta forms. Or cells diploid but all chromosomes from father if e.g. 1 sperm fertilises oocyte that lacks nucleus, mitosis without cleavage. Moles large and made of grape-like clusters of swollen chorionic villi.
What is a partial hydatidiform mole?
Some evidence of embryonic development found. Karyotype usually triploid. Fertilisation of an oocyte containing female pronucleus by 2 spermatozoa or an abnormal diploid sperm. Lots of placenta.
What happens in week 3 of pregnancy? (Week of three’s).
What is sirenomelia?
Two layers transformed into 3 germ layers: ectoderm (will be NS and skin), mesoderm (will be most other things), endoderm (will be lungs, gut, genitourinary system). Establishes body axes: cranial/caudal, dorsal/ventral, left/right
Legs fused - epiblast cells stop invaginating too soon, insufficient mesoderm produced. Production done cranial to caudal so head and upper limbs OK. Often associated with kidney and GI defects, so few survive to have legs seperated.
What is situs inversis?
0.01% of population. Complete reversal of organs in body cavity: heart on R (dextrocardia), gut twists in opposite direction, liver on L etc.
