Abnormalities in Embryogenesis ✅ Flashcards
Why is embryology important when considering congenital abnormality?
It can help understand the evolution and configuration of many congenital abnormalities
What happens during the first 14 days of conception?
The development and implantation of the bilaminar germ disc occurs
What happens to the bilaminar disc?
The process of gastrulation and invagination occurs, transforming it into a trilaminar disc
When is the trilaminar disc formed?
By the end of the third week
What layers does the trilaminar disc consist of?
- Ectoderm
- Mesoderm
- Endoderm
What organs are derived from the ectoderm?
- CNS
- PNS
- Sensory epithelium (ear/eye)
- Skin, hair, and nails
- Pituitary, mammary, and sweat glands
What does the mesoderm differentiate into?
- Somites
- Intermediate mesoderm
- Parietal mesoderm
- Blood vessels
What do the somites differentiate into?
- Sclerotome
- Dermatome
- Myoterm
What does the sclerotome form?
The skeleton
What does the dermatome form?
The dermis
What does the myotome form?
The muscle
What does the intermediate mesoderm form?
The urogenital system
What does the visceral mesoderm form?
The GI and cardiac muscle
What does the parietal mesoderm form?
The body wall
What organs are formed from the endoderm?
- GI tract
- Respiratory organs
- Endocardium
What might be affected by a dysmorphogenic event occurring at the stage of trilaminar disc formation?
More than one of the essential events of blastogenesis
What are the essential events of blastogenesis?
- Fusion
- Lateralisation
- Decussation
- Segmentation
Give an example of a condition that results from a dysmorphogenic event occurring in early embryogenesis?
VACTERL association
What causes VACTERL association?
A field defect of embryonic mesoderm
When do the major organ systems develop?
From 4-8th weeks
What do the major organ systems develop from?
Secondary developmental fields
What forms the secondary developmental fields/
The cephalocaudal and lateral folding of the trilaminar disc
What causes cephalocaudal folding of the trilaminar disc?
The rapid growth of the neural tube
What causes lateral folding of the trilaminar disc?
The developing somites
What is the first step in CNS development?
Development of the neural plate
What does the neural plate develop from?
The ectoderm
What does the neural plate develop from?
The ectoderm
When does the neural plate form?
3rd wek
What is formed from the neural plate?
The neural tube
How is the neural tube formed from the neural plate?
Lateral folding
Where does neural tube fusion begin?
In the cervical region
When is neural tube fusion complete?
By the end of the 4th week
What does the cranial end of the neural tube develop into?
Three distinct dilations
What do the distinct dilations of the cranial end of the neural tube go on to become?
- Forebrain
- Midbrain
- Hindbrain
What does failure to neural tube to close cranially cause?
Anencephaly
What does failure of the neural tube to close caudally cause?
Spina bifida
What determines the severity of spina bifida?
The length and position of the defect
What does failure of skull ossification cause?
Meningoencephalocele
What region is most commonly affected by meningoencephalocele?
Occipital region
How long does development of rudimentary brain structures continue for?
Until the 8th week
What happens to the rudimentary brain structures throughout the fetal period?
They undergo further growth and elaboration
What is the clinical relevance of the long time frame for development of the CNS?
It increases the time frame during which the CNS is at risk of teratogenicity
When does neuronal proliferation begin?
Day 42
When is neuronal proliferation complete?
By 20 weeks
What aspect of CNS development is complete by term?
Neuronal migration and the establishment of major fibre pathways
When do primary sulci of the brain appear in an ordered manner?
From 8-26 weeks
When do the secondary sulci of the brain develop?
Weeks 30-35
What can defects of neuronal migration lead to?
Significant neurodevelopment sequelae
Give an example of a disorder of neuronal migration
Lissencephaly
What is the pathology of lissencephaly?
Disruption of normal pattern of sulci and gyri
How does lissencephaly present?
Severe developmental delay
What processes in brain develop continue after birth?
- Apoptosis
- Synaptogenesis
- Myelination
When does the process of apoptosis in brain development begin?
17 weeks gestation
When is the process of apoptosis in brain development complete?
Childhood
When does the process of synaptogenesis in brain development begin?
19 weeks gestation
When is the the process of synaptogenesis in brain development complete?
Late childhood
When does the process of myelination in brain development begin?
29 weeks gestation
How long does the process of myelination in brain development continue for?
Into adulthood
What causes folding of the endodermal layer?
Rapid growth of the ectoderm and mesoderm
What happens is the endoderm folds?
Part of the yolk sac is incorporated into the body cavity
What does the part of the yolk sac that is incorporated into the body cavity form?
The basis of the GI tract
What are the ends of the GI tract covered with?
Membranes
What happens to the membranes covering the ends of the GI tract?
They rupture, forming the mouth and anus
What happens to the foregut in the 4th week?
It develops respiratory, hepatic, and pancreatic buds
How does the respiratory bud separate from the foregut?
By formation of the oesophagotracheal septum
What happens if there is failure of the respiratory bud to separate from the foregut?
Tracheo-oesophageal fistula
What happens as the midgut undergoes rapid growth?
It herniates into the extra embryonic coelom
When does the midgut herniate into the extra embryonic coelom?
6th week
When does the normal embryonic return of the intestine to the abdominal cavity occur?
10 weeks gestation
What happens to the loops of the intestine as they return into the abdominal cavity?
The rotate
What happens if there is a failure of the embryonic intestine to return to the abdominal cavity?
Exomphalos
What happens if there is failure of the midgut to rotate adequately on return to the body cavity?
Malrotation with a shortened mesenteric pedicle
What is there a risk of if there is malrotation with a shortened mesenteric pedicle?
Volvulus
What cause gastroschisisis?
The bowel later (after 10 weeks gestation) herniating through an anterior abdominal wall defect
What is the first step in the formation of the urogenital system?
Formation of the urogenital sinus
How is the urogenital sinus formed?
The hindgut combines with the surface ectoderm
What happens to the urogenital sinus?
It separates into the urogenital system and rectum
When does the urogenital sinus separate into the urogenital system and rectum?
In the 7th week
What does a failure of separation of the urogenital sinus lead to?
Rectal fistula
When does the anal membrane rupture?
9th week
What does a failure of the anal membrane to rupture lead to?
Rectal atresia or imperforate anus
What do the head and neck develop from?
The frontonasal prominence and six pharyngeal arches
What separates the pharyngeal arches?
Five pharyngeal clefts
What happens to the first pharyngeal arch?
It divides into the maxillary and the mandibular prominence bilaterally , and fuses with the frontonasal prominent to form the mandible, upper lip, palate, and nose
What does failure of the pharyngeal arches to develop correctly give rise to?
- Lateral cysts and fissures
- Thyroglossal cysts and sinuses
What does a failure of the facial prominences to fuse correctly lead to?
A variety of clefts of the lip and palate
What causes cleft lip?
Failure of fusion of the maxillary and medial nasal prominences
What causes cleft palate?
When the two plates of the soul that form the hard palate are not completely joined
What happens to the uvula in cleft palate?
It is usually split
