Embryology Flashcards
Sonic hedgehog gene
Produced: base of limbs (zone of polarizing activity)
Roles:
- A-P axis patterning
- CNS development
Mutation: holoprosencephaly
Wnt-7 gene
Produced: apical ectodermal ridge (at end of each developing limb)
Role: Organize along dorsal-ventral axis
FGF gene
Produced: apical ectodermal ridge
Role: mitosis of underlying mesoderm–> limb lengthening
Homeobox (hox) genes
Transcription regulators (code DNA-binding transcription factors)
Segmental organization of embryo cranial–> caudal
Mutations: appendages in wrong locations
Week 0-10 in development
Day 2= zygote
Day 3= morula
Day 5= blastocyst
Day 6= implantation in endometrium
Week 1= hCG secretion
Week 2= 2 layers (bilaminar disc= epi-, hypoblast)
Week 3= 3 layers (trilaminar disc)
- Epiblast invaginates–> primitive streak
- gastrulation= ecto-, meso-, endodermal layers
Week 4= neural tube closure, heartbeat
- 4 weeks= 4 limbs (limb bud formation)
Week 8= Fetal movement
Week 10= external F/M genitalia
**Weeks 3-8 (embryonic period)= organogenesis, v. susceptible to teratogens (malformations= intrinsic disruptions during embryonic period)
Ectodermal derivatives
Surface ectoderm:
- Epithelium and epidermis
- Anterior pituitary
- Sensory organs of ear
- Lens of eye
- Parotid, sweat, mamillary glands
Neuroectoderm:
- Brain (post. pit), retina, optic nerve, spinal cord
Neural crest cells:
- PNS
- Bones of skull
- Odontoblasts
- Aorticopulmonary septum
- Melanocytes (melanoma= neural-crest derived tumor)
Mesodermal derivatives
- Muscle, bone, cartilage, connective tissue
- Serous linings
- Spleen
- Defects= VACTERL:
- Vertebral defects
- Anal atresia
- Cardiac defects
- Tracheo-Esophageal fistula
- Renal defects
- Limb defects
** Notochord (mesodermal) induces ectoderm–> neuroectoderm (neural plate)–> nucleus pulposus of IV disc
Endoderm
Epithelium of internal structures Luminal epithelium derivatives: - Lungs - Liver, gallbladder, pancreas - Eustachian tube, thymus, Parathyroid, thyroid follicle cells (C cells= mesoderm)
Agenesis
Absent organ d/t absent primordial tissue
Aplasia
Absent organ despite present primordial tissue
Maternal diabetes
- Caudal regression syndrome (anal atresia–> sirenomelia): baby with denervated/weak lower limbs
- Congenital heart defects
- Neural tube defects
Twinning
Dizygotic twins (80%):
- 2 eggs, 2 sperm
- 2 aminiotic sacs, 2 chorions (placentas)
Monozygotic twins (20%):
- Divide at 2 cell stage (0-4 days): 2 + 2
- Divide at Morula (4-8 days): monochorionic, diaminiotic *most common
- Divide at blastocyst (8-12 days): monochorionic, monoamniotic
- Divide after embryonic disc formed (13 days)–> conjoined twins
Placental development
Fetal component:
- Cytotrophoblast: inner layer (cells)
- Synciotrophoblast: outer layer (hCG)
Maternal component:
- Decidua basalis= derived from endometrium; maternal blood in lacunae
Umbilical cord
Allantoid–> umbilical arteries/vein
2 Umbilical arteries: return DEoxygenated blood FROM feturs (internal iliacs) to placenta
1 umbilical vein: supplies oxygenated blood from placenta to fetus
- Drains: ductus venosus–> IVC
Urachal duct
3rd week: yolk sac allantois–> urogenital sinus–> urachus (duct btwn bladder and yolk sac)
- Patent urachus= urine discharge from umbilicus
- Vesicourachal diverticulum= outpouching of bladder (asymptomatic)