GEP (Life Cycle) Week 4 Flashcards

Question

What are the development reg flags seen

Answer 1

**AT ANY AGE:** Parental concerns Asymmetry Regression Discordant development ** AT SPECIFIC AGES** At 10 weeks – no social smile At 6 months – persistent primitive reflexes (neonatal reflexes that are not lost), no interest in people, noise, hand preference At 8 months – not sitting At 12 months – no pincer grasp At 18 months – not walking, no words, drooling, mouthing At 2 years – no phrases (not joining two words together), not interactive At 4 years – unintelligible speech

Answer 2

* Morula – 16 cells Surrounded by zona pellucida.

Answer 3

32 cells Compaction of morula Fluid enters to form a cavity (blastocoele) Zona pellucida will dissolve, allowing implantation.

Answer 4

* Trophoblast – tropho (feed), blast (sprout). Trophoblast will one day become placenta which feeds the embryo * Syncytiotrophoblast – syn (together), cyto (cell). Together cells as there aren’t clear demarcation between each cell. * Hypoblast – hypo (lower) blast (sprout) * Epiblast – epi (upper), blast (sprout)

Answer 5

**Day 8 of embryogenesis: formation of the amniotic cavity** The blastocyst is partially implanted within the endometrial stroma. The embryoblast is surrounded by a mononuclear cell layer, the cytotrophoblast. From here, cells migrate into the syncytiotrophoblast, the part of the trophoblast that is in contact with the endometrium. The syncytiotrophoblast is a multinucleated layer that lacks cell boundaries. In the embryoblast, the germinal disk is formed from hypoblast and epiblast. Between the epiblast and cytotrophoblast, the amniotic cavity is formed. The amniotic cavity is lined on the cytotrophoblast side by amnioblast cells (from the epiblast). **Day 9 – formation of yolk sack ** Cells from the hypoblast migrate laterally (yolk sac epithelium), which gradually cover the entire blastocyst cavity and form the lining layer of the yolk sac epithelium (Heuser membrane). The Heuser membrane surrounds the former blastocyst cavity, which from this point on is referred to as the primary yolk sac. **Day 12 of embryogenesis: formation of the extraembyonic mesoderm ** The blastocyst implants into the endometrial stroma. The syncytiotrophoblast erodes the epithelium of the maternal sinusoids as it embeds into the endometrium, resulting in blood flow through the communicating trophoblast lacunae. This is exponential in comparison to the hypoblasts and epiblasts. The embryoblast increases in size in relation to the trophoblast and the resulting gaps between cytotrophoblast and embryoblast are filled by loose connective tissue, the extraembryonic mesoderm. This form cavities which then fuse together to form the chorinioc cavity. **Day 13 –** a large portion of the extraembryonic mesoderm is pinched off forming a smaller cavity, the secondary yolk sac. Bilaminar disc is joined to the trophoblasts by the connecting stalk (future umbilical cord) Syncytiotrophoblast begins secreting hCG (detectable in blood and urine one week and two weeks after conception, respectively)

Answer 6

* The differentiation of the bilaminar disc to 3 germ layers * 15 days post fertilization * Consists of ectoderm (outer), mesoderm (middle) and endoderm (inner) * Epiblasts will migrate through the primitive streak between epiblast and hypoblast layers and form intraembryonic mesoderm. * Hypoblast is replaced by epiblast forming the endoderm. * Original endoderm becomes ectoderm. ## Footnote Cranial end of hypoblast is the prochordal plate containing columnar cells. Cells migrate down from the epiblast and differentiate, this forms a macroscopically visible primitive streak At the cranial end, cells migrate quickly forming the primitive node. Gradually the primitive streak will elongate. Cells the differentiate into endoderm will replace the hypoblast layer. They are able to detach and slip into the interior of the embryo displacing the hypoblast completely and replacing it with the definitive endoderm. Cells which stay in the epiblast layer will differentiate into ectoderm. Some cells will force their way between the ectoderm and endoderm to form the mesoderm. Around day 16

Answer 7

* This begins with the development of the notocord. * Notochord will migrate along the primitive streak and ends at the prechordal plate. * It is made of epiblast cells that migrate from the primitive node and extend to the cranial aspect of the disc. **Neurulation:** Formation of the neural tube and neural crests after gastrulation Notochord will secrete signaling molecules -> triggers the differentiation of ectoderm cells to form neural cells This will form the neural plate. The neural plate will invaginate and become the neural groove. Folds are found on either side and will converge The neural groove will convert to a cylindrical neural tube. The most dorsal part forms the neural crest The neural crest will form peripheral nervous system neurons There are a cranial and caudal neuropores which should close. Neural tube forms and closes in week 4

Answer 8

* Due to failure of the neural tube to close -> associated with folic acid deficiency * * Anencephaly: Cranial neuropore fails -> no brain -> fatal * Craniorachischisis: Cranial and caudal neuropore fails -> no brain and spinal cord -> fatal * Spina bifida: caudal neuropore failure

Answer 9

**Somites = mesoderm mass formed from presomitic mesoderm after gastrulation.** * They are laid down sequentially from cranial to caudal end. * Controlled by developmental clock/wavefront - gene expression cycles. * Epithelial somites differentiate to: Sclerotome - verterbrae and ribs, heart tissue Myotome - muscle tissue, limb muscles, epimere and hypomere Dermatome - dorsal dermis Syndetome - tendons * This is a continuous process - akin to sausage making. Rapidly dividing cells being periodically segmented by opposing signalling mechanisms. ## Footnote Somites are blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo. Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Somites also determine the migratory paths of neural crest cells and of the axons of spinal nerves.

Answer 10

* Teratogen: an environmental factor that causes a permanent structural or functional abnormality, growth restriction, or death of the embryo or fetus **Teratogenic Drugs ** * Ethanol, valproate, warfarin, lithium * Thalidomide – morning sickness cum anti cancer drug * Retinoids – must be using contraception 1 month after finishing isotretinoin therapy FOR WOMEN ONLY