Embryogenesis terminology and timeline Flashcards
Where is sonic hedgehog gene produced? What patterning is it involved in?
Base of limbs in zone of polarizing activity. Anterior-posterior axis
What other major development process is SHH present in?
CNS development; mutation can cause holoprosencephaly.
Where is Wnt-7 produced? What patterning is it involved in?
Apical-ectodermal ridge: thickened ectoderm at distal end of each developing limb. Shapes dorsal/ventral axis.
Where is FGF gene produced? What is it responsible for?
Apical-ectodermal ridge. Stimulates mitosis of underlying mesoderm, providing for lengthening of limbs.
What are hox genes?
HOX genes are involved in segmental organization of embryo in a cranio-caudal direction. Codes for transcription factors. Hox mutations –> appendages in wrong locations.
What is considered “Day 0” of embryogenesis?
Fertilization by sperm
By what day does the zygote form?
2
By what day does the morula form?
3
By what day does the blastocyst form
5?
When does implantation in the endometrium occur?
Day6-10 (within week 1)
What occurs by the second week?
By 2 weeks, 2 layers: bilaminar disc
What are the layers of the bilaminar disc?
epiblast, hypoblast
What occurs by the third week?
3 weeks, 3 layers –> trilaminar disc.
What is gastrulation?
The process that forms the trilaminar embryonic disc. Starts with epiblast invaginating to form the primitive streak.
What are the layers of the trilaminar disc?
ectoderm, mesoderm, and endoderm germ layers
When does the neural plate begin to form?
Week 3
When is the neural tube closed by?
week 4
What occurs during weeks 3-8?
Organogenesis. Extremely susceptible to teratogens.
When does the hear begin to beat by?
Week 4
When are limb buds formed by?
4 weeks, 4 limbs.
By when is fetal cardiac activity visible by transvaginal ultrasound?
Week 6
By when do fetal genitalia have male/female characterisitics?
Week 10
What is the destination of ectoderm, mesoderm, and endoderm, generally?
Ectoderm: external/outer layer
Meso: Middle layer
Endoderm: Internal layer
What are the three components of ectoderm?
surface ectoderm, neuroectoderm, and neural crest
What are the derivatives of surface ectoderm?
Epidermis, anal canal below pectinate line. Gland related: -Adenohypophis (from rathke pouch) -parotid, sweat, mammary glands Sense related: - lens of eye, -epithelial linings of oral cavity, - sensory organs of ear - olfactory epithelium
What are the derivatives of neuroectoderm?
Brain+spinal cord (inc neurohypophyis, pineal gland)
Retina/optic nerve
What are the derivatives of neural crest?
PNS:
- dorsal root ganglia, cranial nerves, celiac ganglion, schwann cells, ANS
Melanocytes
Chromaffin cells of adrenal medulla
parafollicular C cells of thyroid
pia, arachnoid, bones of skull, odontoblasts, aorticopulmonary septum
What are the derivatives of mesoderm?
muscle, bone, connective tissue, serous linings of body cavities (eg peritoneum), spleen (derived from foregut mesentary), CV structures, lymphatics, blood, wall of gut tube, vagina, kidneys, adrenal cortex, dermis, testes, ovaries
What is the purpose of the notochord? What is its post-natal derivative?
Induces ectoderm to from neuroectoderm (neural plate). Its only post-natal derivative is the nucleus pulposus of the intervertebral disc.
What are the derivates of endoderm?
Gut tube epithelium (including anal canal above the pectinate line), most of urethra (derived from urogenital sinus), luminal epithelial derivatives (e.g., lungs, liver, gallbladder, pancreas, eustachian tube, thymus, parathyroid, thyroid follicular cells).
What is a craniopharyngioma derived from?
Surface ectoderm: benign rathke pouch tumor with cholesterol crystals and calcifications.
What does VACTERL stand for?
Mesoderm defects: Vertebral defects Anal atresia Cardiac defects Tracheo-Esophageal fistula Renal defects Limb defects (bone/muscle).
What is agenesis?
Absent organ due to absent primordial tissue.
What is aplasia?
Absent organ despite presence of primordial tissue.
What is hypoplasia?
Incomplete organ development; primordial tissue present.
What is deformation?
Extrinsic disruption; occurs after embryonic period.
What is disruption?
2° breakdown of previously normal tissue or structure (e.g., amniotic band syndrome).
What is malformation?
Intrinsic disruption; occurs during embryonic period (weeks 3–8).
What is a “sequence”
Abnormalities result from a single 1° embryologic event (e.g., oligohydramnios Potter sequence).
