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
What happens in the saccular stage of lung development?
28-36 weeks gestational age:
- Barrier thins
- Increased maturation of surfactant
What happens in the alveolar stage of lung development?
36 weeks gestational age-birth:
- Primitive alveoli mature
Which cells make surfactant?
Type 2 alveolar cells
What is the role of surfactant?
Reduces surface tension
Produces constituent apoproteins
What causes respiratory distress syndrome?
Low surfactant
How can you increase surfactant production?
Injecting glucocorticoids
What layer of cells does the bladder develop from?
Mostly endoderm
Trigone is mesodermal (mesonephric duct)
- Trigone signals filling of bladder
Why does the mesonephric duct break down in females?
Gives rise to testes
When do the kidneys ascend?
Week 6-9 PF
What happens as the kidneys ascend?
- Need to rise up to lumbar region
- Don’t drag BVs with them
- Send out new and more cranial branches
- Caudal branches regress
- Mesonephros degenerates
- Gonads descend
Where do the gonads develop from?
Intermediate mesoderm within urogenital ridges
Where do the genital ducts arise from?
Paired mesonephric ducts (Wolfian duct - male) + Paramesonephric duct (Mullerian - female)
When do the genital ducts start to differentiate?
Week 7 PF
What does male sex rely on?
Activity of SRY protein
What are the main developmental abnormalities of the reproductive system?
Female:
- Congenital adrenal hyperplasia - mutation in CYP21A2
Male:
- Androgen insensitivity syndrome - mutant androgen R
- Result of inability to produce testosterone/anti-Mullerian hormone OR inability of target tissues to respond (Rs)
What causes regression of the paramesonephric female ducts?
Testosterione
**Anti-mullerian hormone
DHT
How do the gonads and reproductive tract develop?
- Gonads arise from intermediate mesoderm within urogenital ridges of embryo
- Genital ducts arise from paired mesonephric + paramesonephric ducts
- Mesonephric ducts give rise to MALE genital ducts (Wolffian system)
- Paramesonephric ducts give rise to FEMALE genital ducts (Mullerian system)
- Gonads and RTs are indifferent up until 7 weeks of development
- Differentiation is influenced largely by presence or absence of SRY (on Y chromosome)
- If SRY+, then development proceeds along male path
- If SRY-, then development proceeds along female path
