Embryology Flashcards
What are the 4 cellular processes involved in embryological development?
Proliferation
Differentiation
Reorganisation
Apoptosis
What are the key developmental events that occur in the first 2 months of pregnancy?
Week 3: trilaminar disc (gastrulation), CNS, somite BVs form, placental villi (3mm)
Week 4: neural tube closes, face (limbs) initiated, placental villi elaborate (4mm)
Week 5: face + limbs continue (5-8mm)
Week 6: lots of other organs inc GIT and GU (10-14mm)
Week 7: continue and toes develop (17-22mm)
Week 8: lungs, liver and kidney (28-30mm)
What are the processes leading to spina bifida?
- 3 weeks PF: formation of neural tube (CNS precursor)
- Fusion should occur through neural tube
- Does not occur
- Location of gap in fusion process determines defect location, + tf effects
- “2 spines” - parallel tissues either side of spine often towards lower back, usually single
How may a cleft palate/lip arise?
- Grooves formed in midline
- Masses of tissue migrate from lateral side of face in towards midline to fill in these grooves
- Failure to fill these grooves leads to cleft palate/lip
- Upper lip consists of 2 grooves –> asymmetric defect
- Cleft palate = defect that occurs posterior to incisive foramen
How do the kidneys develop?
- Pronephros - precursor, grows down towards cloaca
- Gives rise to pronephric duct then begins to break down
- Mesonephros - intermediate, connects to cloaca
- BVs appear + mesonephros forms capsules
- Metanephros - definitive kidney (wk 5) excretory units from metanephric mesoderm
- Week 6-8: start down by ureters + ascend towards adrenal glands
- Ureters extend, arteries breakdown + reform
What complications can occur during renal development?
- Horseshoe kidney - kidneys fused below inferior mesenteric artery
- Renal agenesis (bilateral = Potter’s syndrome due to low amniotic fluid the ureteric buds don’t grow)
- Abnormal ureter/shaped kidneys
- Pelvic kidney (doesn’t ascend)
- Retention of extra artery (isn’t broken down) - may obstruct ureter –> enlarge renal pelvis
- Bladder exstrophy - problem w/cloaca - abdominal wall fails to cover bladder - abnormal distance btwn scrotum + penis
How does the heart develop?
Week 3 - heart at midline - cardiogenic cells develop in U pattern outside embryo proper
Week 4 - heart tubes fuse
Day 23 - heart loops - atria loop posteriorly and to the right so they end up more cranial to ventricles
Day 28 - heart septation - spiralling occurs
Week 7 - outflow tracts divide
- Vascular connections maintained, so major arteries connected to ventricles + veins to atria
- Valves develop –> unidirectionally flow ensured
- Foramen ovale between atria
- Main artery from RV connected to aorta by ductus arteriosus
How do cardiac abnormalities can occur?
- Problem w/heart looping day 23 = transposition of great arteries (aorta + PA swapped)
- Problem with heart septation day 28 = ventricular septal defect - deoxygenated blood into LV, patent foramen ovale
- Problem w/outflow tracts dividing wk 7 = pulmonary stenosis, truncus arteriosus
How is spina bifida prevented?
Folic acid before conception (3 months)
How do the lungs develop?
- Begins during 1st TM, not completed until after delivery
- Surfactant produced from 25 weeks PF + gradually increased during 3rd TM
- 5 stages of development (wks gestational age, since LMP)
- Week 0-6 = embryonic
- Week 6-16 = pseudoglandular
- Week 16-28 = canalicular
- Week 28-36 = saccular
- Week 36-birth = alveolar
How does the face develop?
- 2 halves of face develop separately
- Nasal pits begin where our eyes should be and eyes develop on sides of head
- Between wk5 and 10 PF, nose + eyes migrate inwards
- Eyes + nose begin on linear lvel
- Tissue btwn nasal pits apoptose via cleft formation
- Instead of new cell proliferation to fill up cleft, existing cells migrate centrally and pulls along with it the eyes + nose
- Process continues until 2 halves of face fuse
What is the Tetralogy of Fallot?
- Pulmonary stenosis (thickened, narrow pulmonary outflow tract)
- Thickened RV wall
- Ventricular septal defect
- Aorta overides septal defect
What happens in the embryonic stage of lung development?
0-6 weeks gestational age:
- Laryngotracheal groove folds into tube
- Tube divides into oesophagus + lung buds
- Buds grow into pleural passages + divide into lobes
What happens in the pseudoglandular stage of lung development?
6-16 weeks gestational age:
- Trachiobronchial tree forms as branching tubules resemble exocrine gland
What happens in the canalicular stage of lung development?
16-28 weeks gestational age:
- Ascinar units form terminal bronchioles and divide into resp bronchioles
- Capillaries approximate to potential air spaces but have little contact
- Type 1 and 2 alveolar cells + surfactant starts being made
