Embryology Flashcards
What is menstrual age in terms of pregnancy dating?
1) Used by obstetricians
2) From last menstrual period
3) Split into 3 equal trimesters
What is fertilisation age in terms of pregnancy dating?
1) Used by embryologists
2) From the date of fertilisation
3) 3 unequal periods based on major developmental events
What are the 3 periods in fertilisation age and what weeks are they?
1) Early development (Cell division, pre embryonic) ED 1-2 wks
2) Embryonic (organogenesis) period E 3-8wks
3) Foetal period F 9-birth
What are the 5 types of tetratogens and examples of each?
1) Infectious agents eg. viruses
2) Chemical agents eg. drugs
3) Physical agents eg. radiation
4) Maternal disease eg. diabetes
5) Nutritional deficiencies eg. obesity
What are the 5 main infectious agent teratogens?
T - toxoplasmosis O - other (hep b, syphilis) R - rubella C - cytomegalovirus H - herpes simplex virus
How many child deaths result from congenital abnormalities?
21%
How many babies have a congenital abnormality at birth and how many have one recognised by age 5?
Both 2-3%
Which infectious age teratogen can result in: hydrocephaly, microcephaly, micropthalmia?
Toxoplasmosis
How is toxoplasmosis spread?
Parasite
1/3 of the world population infected
Spread through undercooked meat/contact with cat faeces
Which infectious agent teratogen results can cause microcephaly, cataracts, heart defects and hearing loss?
Rubella
Which infectious agent teratogen can cause microcephaly, micropthalmia, cerebral calcification, intrauterine growth retardation?
Cytomegalovirus
How it cytomegalovirus spread?
Bodily fluids including, blood, vaginal fluid, semen, breast milk, urine
Which infectious agent teratogen results in skin lesions/scars,microcephaly, seizures, visual defectsʔ
ʜSV2 (genital herpes)
But intrauterine infection is rare, it is normally just spread during delivery
What did thalidomide result in and what is it now used to treatʔ
Shortened or absent limbs
ɴow used to treat leprosy and ʜɪV
What are the facial characteristics associated with foetal alcohol syndromeʔ
Smooth philtrum, thin upper lip. small eye openings
Other than abnormal facial characteristics what 3 other abnormalities are associated with foetal alcohol syndromeʔ
1) Prenatal and postnatal growth retardation
2) ɪntellectual disability
3) ɪmpaired motor ability and coordination
ʜow many days post fertilisation does the blastocyst hatch and initiate impantationʔ
day 5 or 6
ɪn the bilminar embryo, which layer forms the dorsal and which forms the ventral portionʔ
Epiblast = dorsal ʜypoblast = ventral
Full implantation of the blastocyst is achieved how many days post fertilisationʔ
Day 9
On what day post fertilisation is the secondary (Definitive) yolk sac formedʔ
Day 13
What sort of structure do you have by the end of week 2 post fertilisationʔ
Embryo with an amniotic cavity suspended in the secondary yolk sac by the connecting stalk - this will form part of the connecting stalk
What hormone is released that is detected in pregnancy testing, where is it released from and what is its role in pregnancyʔ
chorionic gonadotrophin hormone (cɢʜ)
Secreted by syncytiotrophoblast
ʜas a role in maintaining endometrium and may play a role in maternal immunotolerence
What is a hydatidiform mole, why does it occur and why does it give a positive pregnancy testʔ
Development of trophoblast without any embryonic tissue
Due to the fertilisation of an empty egg, lacking a nucleas
Suggests fathers genes favour the formation of a trophoblast at the expense of an embryo - imprinting
Trophoblast still releases cɢʜ so +ve pregnancy test
What is a lithopaedion and why does it formʔ
When blastocyst implants in the abdominal cavity, embryo develops and it goes undiagnosed and the foetus dies
Foetus gets calcified in the abdo cavity as it is too large to be reabsorbed - this is thought to protect the mother from the necrotic tissue of the foetus
Why is it possible for abdominal implantation to occurʔ
ɢap between the ovary and uterine tube so the egg can enter the abdomen
Where do the majority of ectopic pregnancies implantʔ
Tubal implantation - implantation in the uterine tube
80% in the ampulla
What is placenta previaʔ
Placenta forms near the head of the foetus, over the opening of the cervix, due to implantation near to the cervix, can cause severe bleeding in late pregnancy (as the head pushes on the pacenta)
What percentage of pregnancies have an abnormal implantation site and what percentage of pregnancy related deaths for the mother are related to abdominal implantation sitesʔ
Abnormal implantation sites occur in 2% of pregnancies
Abnormal implantation sites account for 9% of pregnancy related deaths for the mother
What is gastrulationʔ
Transformation into a trilaminar disc
What is kartagener’s syndromeʔ
Characterised by situs invertus and cilia which move in the wrong direction
What are the problems associated with situs inversusʔ
Often harmless but 20% have kartagener’s syndrome - (situs inversus + cilia moving in wrong direction)
ɢive an example of partial situs inversusʔ
Dextrocardia
What layer of the bilaminar embryo do the 3 layers of the trilaminar embryo (ectoderm, mesoderm, endoderm) come fromʔ
Ectoderm (formed from remaining epiblast cells next to amniotic cavity)
Mesoderm (formed from epiblast cells inbetween the ectoderm and definitive endoderm)
Endoderm (formed as the definitive endoderm from epiblast cells which move towards the primitve streak and then move to replace all of the hypoblast cells and are next to the definitive yolk sac)
What is the intraembryonic mesoderm continuous withʔ
Extraembryonic mesoderm
What germ layer does the CɴS, PɴS and skin come fromʔ
Ectoderm
What germ layer do the heart, muscles, bones, cartilage, major blood vessels, adrenal cortex, ureters and gonads come fromʔ
Mesoderm
What germ layer do most of your internal organs originate fromʔ
Endoderm
What 3 parts does the intraembryonic mesoderm differentiate into and what forms from each of theseʔ
1) Paraxial mesoderm - forms majority of skeleton, skeletal muscle and dermis of the skin
2) ɪntermediate muscle - forms the gonads, internal reproductive tracts and kidneys
3) ʟateral plate mesoderm - forms the lining of body cavities
On what day post fertilisation does the paraxial mesoderm begin to differentiate into somites, in what direction do they form, how many form per day and what can this be used forʔ
Day 20
Craniocaudal direction
3-4 pairs per day until have 42-44 pairs
ɢood predictor of fertilisation age
From what is the notochord formed and what is the processʔ
The primitive node (of the primitive streak) forms the notochordal process while the rest of the primitive streak regresses
ɴotochordal process fuses with the underlying endoderm to form the notochordal plate which seperates from the endoderm and fuses to form the solid notochord
What is neuralation and what initiates itʔ
ɴeuralation is the first step in the formation of the CɴS
ɪnitiated by the notochord
Formation of the neural tube, the notochord signals cause the overlying ectoderm to thicken and form the neural plate and then break off to from the neural tube
What is induction of neuralationʔ
Thickening of the overlying ectoderm to form the neural plate
What initiates and organises the formation of the vertebrae from somitesʔ
ɴotochord
What are the vertebrae formed fromʔ
Sclerotome from the somites (divisions of the paraxial mesoderm)
What 3 things do the somites differentiate into (initiated by the notochord)ʔ
1) Scleretomeː bone and cartilage
2) Myotomeː skeletal muscle
3) Dermatomeː dermis
ɪn the formation of vertebrae what is the difference between the vertebral body and vertebral archʔ
Sclerotome cells surround the notochord to from the vertebral body and the neural tube to form the vertebral arch
What happens to the notochord as the vertebral bodies formʔ
Majority of the notochord degenerates - the remnants persist as the nucleus pulposus of the intervertebral discs
Abnormal induction of the sclerotome results in what kind of defectsʔ
Spinal defects
What occurs in spina bifida occultaʔ
Section of the spinal chord only protected by subcutaneous fat, there is a section of vertebra missing, often get a tuft of hair and dimpling of skin where the vertebral body is missing. This section of the spinal chord is more prone to damage
What occurs in meningoceleʔ
Portion of meninges protrudes out of vertebral body and is therefore only protected by skin, this protruding portion of meninges (meningel sac) does not contain any nerve fibres
What occurs in myelomeningoceleʔ
Portion of meninges containing nerve fibres protrudes out of spinal column and is not covered by skin but is exposed (high risk of infection) and contains nerve fibres!
What is sirenomelia and why does it occurʔ
Abnormal gastrulation and insufficient mesoderm is formed in the caudal region of the embryo (somites form in craniocaudal direction) - abnormalities of the urogenital system and lower limbs (attached together)
What is sacrococcygeal teratoma (SCT) and why does it occurʔ
ʀemnants of primitive streak may persist and give rise to a tumour = SCT
Most common tumour of the newborn
80% occur in females
Most diagnosed in neonates are benign and the prognosis tends to be good after resection
When is neuralation complete?
When the anterior (cranial end) and posterior neural pores (caudal end) fuse
What are the first 2 steps in neuralation?
1) Notochord signals to the overlying ectoderm to thicken and form the neuroectoderm which gives rise to the neural plate
2) The lateral edges of the neural plate elevate to form neural folds
How does fusion of the neural folds occur?
The neural folds fuse in the midline to form the neural tube - as the neural folds fuse the neural tube becomes detached from the ectoderm
The fusion begins in the cervical (neck) region of the embryo then continues cranially and caudally
What does the cranial and caudal ends of the neural tube form?
Cranial end = brain
Caudal end = spinal chord
On what days do the anterior and posterior neural pores fuse?
Anterior = day 25 Posterior = day 28
What is anencephaly and how can it occur?
Failure of the anterior neuropore to fuse results in anencephaly
The forebrain doesnt form (responsible for cognition, speech, memory, vision and hearing)
Brainstem is still present which controls the heart, the lungs and some reflexes
Anencephaly normally results in still birth of death shortly after birth - rarely babies survive - Vittoria de Cristo
What is Rachischisis and when does it occur?
Failure of the posterior neuropore to fuse
Spinal chord does not from properly leading to paralysis
In addition open neural tube results in lack of formation of vertebrae - spina bifida
Flat plate of neural tube is exposed at birth - high risk of infection
What substance reduces neural tube defects and by what percentage?
Folic acid reduces neural tube defects by 50-70%
What is sometimes referred to as the 4th germ layer?
Neural crest cells
Where do neural crest cells originate from?
Cells from the lateral edges of neural folds which break off and migrate ventrally and dorsally as the neural folds fuse
Enteric plexuses originate from what germ layer?
The 4th germ layer - the neural crest cells
What is neurofibromatosis?
Its a genetic condition caused by a defect in neural crest cell development
There is a defect in neurofibromin gene 1 (NF1 gene) which is a tumour suppressor gene in neural crest cells which is switched off in neurofibromatosis leading to increased cell division
Get benign tumours of the nervous system, skin and cranial bones
Disease of the elephant man
In what week does craniocaudal and lateral folding occur?
Week 4
What forces craniocaudal and lateral folding to occur?
The differential growth of the yolk sac and the amniotic cavity, the amniotic cavity significantly increases in size and the yolk sac stays pretty much the same size
At what level is there a communicaton between the yolk sack and the gut?
At the level of the midgut
What is the vitelline duct?
Connection between the yolk sac and the midgut
What is the allantois?
Connected to the fetal bladder
What does the connecting stalk form?
The future umbilical chord
When does ectopia cordis occur?
Its a ventral body wall defect where the heart is left outside of the body because the lateral folds fail to fuse in the thoracic region, extremely rare, occurs in about 1 in 5 million live births
When does gastroschisis occur and how might it need to be corrected?
Its a ventral body wall defect and occurs when the intestines are outside of the body wall as the lateral folds fail to fuse in the abdominal region
May need a gastroschisis silo to cover the contents until the abdominal cavity has grown large enough to be able to fit the intestines back inside
Occurs in 3.5/10,000 births
How long is gestation? (from fertilisation to birth)
38 weeks
What is the difference in weeks between fertilisation and menstruation age?
Fertilisation age is 2 weeks less than menstruation age
