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WVSOM - Embryology-4
Early Morphogenesis (weeks 3 - 8)
| Question | Answer |
|---|---|
| Formation of the neural tube | Neurulation (progenitor of numerous tissues, particularly CNS) |
| What structures does the ectoderm generate? | CNS; PNS; sensory epithelia of ears, nose, eyes; epidermis including hair and nails; subcutaneous and mammary glands; pituitary gland; teeth enamel |
| What occurs at the beginning of week 3? | Notochord in anterior 3/4 of germ disc secretes GF that induce overlaying ectoderm to differentiate into neural plate |
| Neuroectoderm | Refers to thickened, columnar cells that compose neural plate |
| Neural folds | Lateral edges of neural plate that elevate (end of week 3) |
| Neural groove | Medium of neural plate depresses to form groove |
| Neural tube | Inversion and fusion of neural tube in anterior and posterior directions; begins in area that will develop into neck (4th somite) |
| Openings that persist before final closure | Cranial and caudal neurospores; open to the amniotic cavity |
| When does the cranial neurospore close? | ~day 25 (18-20 somite stage) |
| When does the caudal neurospore close? | Day 27 (25 somite stage) |
| What does the closure of the cranial and caudal neurospores indicate? | Completion of neurulation |
| What forms the spinal cord? | The narrow posterior region of the neural tube |
| What forms the brain vesicles? | The broad anterior portion of the neural tube |
| Neural crests | Lateral borders of the neural folds; after closure, neural crests dissociate & migrate thru mesoderm as mesenchymal cells (ex. of how mesenchyme not always mesodermal) |
| Neural crest cells | Ectodermal mesenchyme; from numerous structures (i.e. ganglia & cranial nerves, schwann cells, melanocytes, adrenal medulla, craniofacial bones, connective tissues, conotruncal heart cushions) |
| Mesenchyme | Loosely woven, embryonic stem cell derived from any germ layer |
| Mesoderm development | Produces muscle, connective tissue, cartilage, bone, blood vessels, kidneys, spleen, suprarenal cortex |
| Mesoderm differentiates into 3 regions | Paraxial, intermediate, lateral mesoderm |
| Lateral mesoderm differentiation | Coelom develops in lateral mesoderm by coalescence of intercellular spaces; lateral mesoderm lining dorsal surface of coelom = somatic mesoderm layer; ventral surface lining coelom = splanchnic mesoderm layer |
| Somatic (parietal) mesoderm layer | + overlaying ectoderm = somatopleura; will develop into lateral & ventral walls of body cavity; connects w/ extraembryonic mesoderm (covers amnion) |
| Splanchnic (visceral) mesoderm layer | + underlining endoderm = splanchnopleura; produces wall of gut; continuous w/ extraembryonic mesoderm covering yolk sac |
| Intermediate mesoderm | Located in cervical and thoracic regions; produces segmental clusters = nephrotomes (posteriorly produce unsegmented nephrogenic cord); both regions generate components of urinary system |
| Paraxial mesoderm | Segmented into somitomeres; each segment consist of concentric whorls of cells on each side of embryo |
| Neuromere | Somitomere in anterior region that forms beside neural plate segment; contribute to head mesenchyme |
| Somites | Somitomeres organized in medial and posterior regions; first develop in occipital region on day 20; give rise to segmental pattern on body |
| How many pairs of somites develop? | 42-44 pairs (4 occipital, 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 8-10 coccygeal); first occipital and last 5-7 coccygeal somites later disappear; others develop into axial skeleton |
| Sclerotomes | Somite ventral and medial walls that lose cohesion, producing mesenchymal cells that surround notochord |
| Dermomyotome | Remaining dorsal wall of each somite; laminates into 2 layers (myotome, dermatome) |
| What do sclerotomes produce? | Vertebra (cartilage to bone) |
| What do myotomes differentiate into? | Muscles, attached to each vertebra and limbs |
| What do dermatomes produce? | Underlying dermis of the skin |
| Endoderm development | Produces digestive tract, as well as epithelia and stromata for numerous other organs |
| Gut | Digestive tub that begins as a tube; formation = passive process (produced by inversiion of entire embryo due to disproportionate growth of ectoderm); rapid expansion of dorsal ectoderm elongates embryo; pulls ectoderm in anterior & posterior directions |
| Ectodermal elongation causes what to happen? | Embryo to buckle ventrally, constricting connectiion w/ yolk sac; at same time, somite growth inverts embryo laterally (helps fold endoderm into tubular gut); segregates majority of gut from yolk sac & coelom from chorionic cavity |
| Foregut | Anterior part of gut |
| Midgut | Medial part of gut |
| Hindgut | Posterior part of gut |
| Vitelline duct (yolk sac stalk) | Connection of midgut with yolk sac; by week 5, will merge w/ connecting stalk to form umbilical cord; later, midgut will separate from vitelline to become free in coelom |
| Oropharyngeal membrane | Anterior end of foregut anchored by prechordal plate; after week 3, membrane ruptures & opens gut to amniotic cavity; opening will develop into mouth |
| Cloacal membrane | Anchor for posterior of hindgut; in conjunction w/ portion of allantois, will form cloaca (develops into anus) |
| Embryonic circulatory system | Mid-week 3: blood vessels begin to develop thru-out embryonic & extraembryonic mesoderm; mesenchymal cells = clusters of angioblasts; center of angioblasts = blood cells; periphery of angioblasts = endothelial cells to produce blood vessels |
| What happens as the vessels proliferate? | They interconnect to establish embryonic circulatory system (runs thru-out mesoderm; includes heart tube, splanchnic extraembryonic mesoderm, somatic extraembryonic mesoderm, connecting stalk) |
| Chorionic villi | Composed of cytotrophoblast cells which become organized into columns that extend thru syncytiotrophoblast; major component of placenta |
| Primary villi | Consist of cytotrophoblast cells, surrounded by synctiotrophoblast |
| Secondary (placental) villi | Transformation of primary villi when extraembryonic mesoderm penetrates, producing mesodermal cores |
| Tertiary villi | Secondary villi with embryonic blood vessels in core |
| Outer cytotrophoblast shell | Cytotrophoblast cells that spread out between syncytiotrophoblast and endometrium to form epithelium |
| Stem (anchoring) villi | Villi that extend completely through syncytiotrophoblast |
| Terminal (free) villi | Villi that branch off of stem villi; purpose = nutrient exchange in placenta |
| Two components of the placenta | Embryonic (develops from chorion) and maternal component (derived from surrounding endometrium) |
| Maternal component of placenta | Known as decidua |
| Intervillous spaces | Lacunar network of decidua that expands and coalesces; forms between villi |
| Maternal blood flow | Through intervillous spaces |
| Embryonic blood flow | Through vessels w/i villi |
| Does maternal and fetal blood mix? | NO; discourages isoimmunization (immunorejection of genetically foreign fetal tissue) |
| How is nutrients and oxygen passed from mother to fetus? | Diffused across walls of villi |
| Progress of chorionic villi | Initially completely surround blastocyst; as development proceeds, they regress from abembryonic pole and become concentrated at embryonic pole, producing placenta |
| Fetal expansionAs the embryo grows into a fetus, where does it expand into? | Embryo into fetus -> amniotic cavity -> chorionic cavity; amniotic cavity supplants chorionic cavity |
| What is the membrane that surrounds the fetus composed of? | Amnion and chorion |
| "Water break" | Expulsion of amniotic fluid |
| Rh factors | Erythrocyte (RBC) surface antigens |
| Isoimmunization | Ex: mother = Rh-; feuts = Rh+; fetal blood in maternal circulatory system = mother's immune system produces antibodies against foreign Rh antigens |
| Erythroblastosis fetalis | Anti-Rh antibodies that cross placenta, resulting in fetal RBC hemolysis; results from isoimmunization; syndrome characterized by anemia, elevated bilirubin (accumulates in brain = brain damage), hydrops, pallor (blue baby), death |
| How is a severe case of erythroblastosis fetalis diagnosed? treated? | Diagnosed with spectrophotometric analysis of amniotic fluid; treated with intrauterine transfusion of RBC packed blood |
| How would fetal blood get into mother's circulatory system? | Placenta abruption; placenta ruptures/separates from uterine wall resulting in intrauterine bleeding; most common mechanism = fetal blood released into uterus when placenta extruded after birth |
| What is a problem with placenta abruption? | It can immunize mother against Rh+ factors, causing her body to attack subsequent pregnancies |
| What treatment is available for isoimmunization? | RhoGam (anti-Rh0D antibodies) -> D is most common isoform; treat Rh- mother with product to clear any fetal Rh+ RBCs from mother's circulatory system before they can elicit immune response |
| RhoGam sensitization | Reduces Rh- mothers from 10-20% to < 1% |
Created by:
JaneO
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