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UTSW Embryo 09
UTSW
| Question | Answer |
|---|---|
| What is the order of appearance of the 3 axes? | 1. dorso-ventral, 2. rostro-caudal, 3. Left-Right (medio-lateral) |
| describe dorso-ventral axis development: | occurs in blastocyst @ 4-5 days post-fertilization. side of inner cell mass facing blastocoele becomes ventral. Amniotic cavity forms @ 8 days over dorsal surface. |
| describe rostro-caudal axis development | @ 14 days, prochordal plate develops (rostral). primitive streak forms at caudal end @ 15 days & elongates rostraly. |
| describe left-right axis development | @ 15-16 days, cells in primitive streak form mesoderm (different protein expression on left vs. right). looping of heart @ 22-24 days = visible asymmetry. |
| Major Stages of Development | 1. Pregenesis (prior to fertilization), 2. Early Cell Divisions (0 - 1 1/2 weeks), 3. Embryogenesis (1 1/2 - 4 weeks, 4. Organogenesis (4-8 weeks), 5. Phenogenesis (8-38 weeks), Postnatal Maturation |
| Developmental Origin of Gametes | develop from primordial germ cells arising in the yolk sac wall @ 4 weeks. oocytes are produced in 5th month (fetal period) |
| Pre-Embryonic Period | 0-1 1/2 weeks (when implantation in uterine wall is complete). Cleavage, bilaminar disc. Zygote (cells called Blastomeres) -> Morula (3-4 days) -> Blastocyst |
| Determining Fetal Age | menstruation = 14 days after peak fertility. Age of fetus = 2 weeks + date of last period. |
| Embryonic Period | 1 1/2 - 8 weeks. (1-4 mm). implantation of blastocyst -> gastrulation (3 germ layers)-> neurulation (neural plate)-> trilaminar disc -> cylindrical embryo->organogenesis (heart beat, limb buds, 0.4-3 cm) |
| Fetal Period | 8-38 weeks. 3.5-35 cm. differentiation & growth of organ primordia, lung branching, facial definition. 10 weeks = external genitalia. |
| Postnatal Period | neonatal = 0-4 weeks post-birth: ductus closure, liver maturation, closing of patent ductus, lung expansion, liver metabolism, gain 0.5 oz/day. 13 months - puberty = childhood. Puberty - 18 years = adolescence. 18-death = adulthood. |
| Infantile Period growth rate | gain 0.5 oz/day until 1 month, double birth weight @ 5 months, triple birth weight at 1 year. |
| What % of couples are infertile? | 15% cannot conceive after trying for 6 months |
| What % of pregnancies end in spontaneous abortion or stillbirth? | 20% are miscarried (spontaneous abortion) / 4 % end in still birth (death after veal viability @24 weeks). |
| Deformities occurring during 1/12 - 4 weeks | = embryonic. during blastogenesis, gastrulation & neurulation. VATER syndrome. vertebral/anorectal/tracheo-esophageal fistula/ radial & renal defects. |
| Embryonic period deformities | single/multiple anomalies. miscarriage/malformed infant |
| Organogenesis abnormalities | 5-8 weeks post-fertilization. singular deformaties affecting single organ (e.g. congenital heart defect/spina bifida) |
| defects during the fetal period | abnormalities = subtle defects e.g. single palmar crease & normal variants e.g. stork-bite hemangioma. insult = immature lungs, growth retardation, limb deformation (e.g. arthrogryposis), porencephalic cyst in brain due to disrupted cerebral vasculature. |
| types of anomalies | isolated/single (usually sporadic), multiple (usually genetic), sequence or syndrome (single cause -> multiple primary anomalies. random). abnormal = defective vs. normal (e.g. birth marks). major = requires medical intervention vs. minor = <4% of people. |
| Extrinsic singular anomalies | Disruption = normal development disrupted by dugs/amniotic band constriction/blood vessel clotting or hemorrhage. Deformation = space constraints limit growth (e.g. clubfoot) |
| Intrinsic singular anomalies | Malformation = primordial structure is abnormal from genesis (e.g. polydactyly, holoprosencephaly). Dysplasia = tissue surrounding primordium fails to grow (e.g. in adhoncroplasia, limbs are short due to defective cartilage growth) |
| Associations | multiple major anomolies that have similar embryonic timing but no known cause(e.g. VATER @ 20-25 days of development). Few minor anomalies (e.g. small face, prominent occiput, clenched fists) |
| Sequence vs. Syndrome | Sequence = isolated defect. singular causative anomaly/mechanical factor. Syndrome = multiple defects. no known initiating factor. |
| Malformation vs. Dysplasia | malformation = morphological defect resulting from intrinsic anomaly. Dysplasia = disorganization of cells into tissues (e.g. hemangioma). |
| Blastomeres | produced by cleavage divisions, pluripotent |
| pre-implantation testing | 8-16 cell stage, remove single cell for genetic testing. |
| morula | same size as the ovum, enters the uterus 4 days post-fertilization |
| blastocyst | outer trophoblast layer (invades uterus -> chorion & placenta) & inner cell mass (forms embryo: ventral = inner, dorsal = outer. pluripotent stem cells). forms bilaminar disk @ 8 days (amniotic cavity = dorsal to disk/ yolk sac = ventral to disk) |
| prochordal plate | 2 layers of blastocyst bilayer plate fuse --> prochordal plate determines location of mouth, anterior-posterior axis of the embryo, head development |
| Gastrula | 3-4 weeks. primitive streak & primitive node induce migration into mesoderm layer. cells facing amniotic cavity -> ectoderm. cells facing yok sac -> endoderm. ecto & endoderm remain connected @ oropharyngeal membrane (-> mouth) & cloaca membrane (->anus) |
| 3 tissue layers | ectoderm -> skin, hair, nails, nervous system. mesoderm -> muscle & skeleton. endoderm -> gut & respiratory lining. |
| notochord | appears cephalad to the primitive node in the gastrula, provides rigid axis for embryo (mesoderm). induces overlying ectoderm -> neural plate |
| neural tube | formed by the folding of the neural plate. progenitor of the CNS. open at rostral & caudal ends (neuropores). lumen ->cerebral ventricles & spinal canal. |
| neural crest | = derived from ectoderm cells @ apex of dorsal fold in the neural plate as it forms the neural tube. -> mesenchyme (connective tissue, muscle, bones of face & skull) & spinal ganglia & support cells, melanocytes, adrenal medulla |
| limb buds | -> bones & muscles of limbs |
| Landmarks on Day 20 | axial/intermediate/lateral somites form, GI/mouth/anus/urinary tract(allantois) progenitors form, cardiac tube forms. |
| primitive streak | formed @ gastrulation (week3-4). cells migrate along to form mesoderm. shrinks, degenerates into structure @ base of spine, & disappears end of week 4. |
| landmarks on week 4 | mouth, heart & septum transversum (precursor to diaphragm) fold ventral so that mouth is most rostral. allantois, connecting stalk, & cloacal membrane move ventrally. lateral fold -> yolk sac pinched off, gut/pleural/pericardial/peritoneal cavities form. |
| chorionic villi | form from outer trophoblast cell layer of blastocyst. surround embryonic sac. portion under embryo -> placenta. remainder -> chorionic sac. |
| spontaneous abortion causes | failure of implantation (morula/blastocyst) w/in 2 weeks of fertilization (mistaken for normal period). 10-15% of pregnancies. |
| RU486 (Mefipristone) | inhibits progesterone R. prevents normal implantation (endometrial thickening & vascularization). effective before 7 weeks after last period. 96% effective in terminating pregnancy when taken w/prostaglandins. |
| Ectopic Pregnancy | 1 in 180-250 pregnancies (higher risk = older mom or low socioeconomic status). venereal disease scarring + tubal inflammation = predisposing factor. |
| Anencephaly | Faulty closure of rostral neuropore |
| myelomeningocele (spina bifida) | Faulty closure of the caual neuropore -> mass of tangled spinal nerve tissue on back. usually paralysis below the defect. |
| sacrococcygeal teratomas | ectoderm (hair), mesoderm (cartilage), & glandular (endoderm) tissues. normally degenerates @ end of week 4. non-malignant. |
| early heart development | E20 lateral mesoderm -> u-shaped primordium -> folds together w/2 conotruncal aortic rostral & 2 atrial caudal outlets. heart elongates & loops to bring ventricle caudal & atria cephalad. |
| development of internal heart divisions | endocardial cushions ->left & right canals. septum primum -> left & right atrium (flap over foramen ovale). septum secundum helps divide atrium. muscular interventricular septum grows up from apex. membranous septum grows down from endocardial cushions. |
| embryonic heart inputs & outputs | inputs = sinus venosus, umbilical/vitelline/cardinal veins. outputs = conotruncal region (bulbus cordis & truncus arteriosus)-> aortic sac -> branchial arches -> dorsal aortas |
| spiral septum (aorticopulmonary) | divides pulmonary trunk from aorta. from ridges from walls of bulbus cordis & truncus arteriosus (conotruncal region) |
| atrial septal defect | 1. persistence of foramen ovale (usually asymptomatic). 2. failure of septum primum/secundum to close completely (extreme = common atrium). 3. abnormal growth of endocardial cushions-> persistent ostium primum w/cleft mitral valve = ostium primum defect. |
| atrio-ventricular septal defect | severe failure of endocardial cushion fusion (common in Down syndrome) = severly abormal mitral & tricuspid valves = atrioventricular canal/endocardial cushion defect. |
| patent ductus arteriosus | common in premature infants. lungs are overloaded with fluid. |
| ventricular septal defect | membranous/muscular VSD. Severe = single ventricle. lungs overloaded when blood from left ventricle -> right ventricle. work stress -> heart failure. |
| persistent truncus arteriosus | when spiral septum fails to develop. mixed O2 in aorta + lungs overpressured. |
| transposition of the great arteries | when aorticopulmonary septum of truncus arteriosus doesn't spiral. right ventricle -> systemic. left ventricle -> lungs. |
| renal development | intermediate mesoderm-> pro/meso/meta-nephroi (cervical->caudal). metanephric diverticulum/ureteric bud-> ureter, renal pelvis/calices/collecting tubule. metanephroic mesoderm-> glomeruli & collecting tubules. kidneys start excreting urine @ 9 weeks. |
| bladder development | ventral cloaca & allantois -> urogenital sinus ->bladder & urethra. |
| genital development | primary sex cords from urogenital ridge -> undifferentiated gonad (SRY -> testis). mesonephric ducts -> Wolffian ducts (epididymus & vas deferens). paramesonephric ducts -> Mullerian -> uterus/vagina/oviducts (Mullerian Inhibiting Factor prevents). |
| renal agenesis = Potter syndrome | due to faulty development of metanephric diverticulum -> low fetal urination & oligohydramnios + anbormal facial features, lax skin, club feet + abnormal lung development & hypoplasia. death x multiple anomaly. |
| horseshoe kidney | fusion of kidneys @ lower pole. prevent ascent of kidneys by inferior mesenteric artery. common w/Turner syndrome. |
| Exstrophy of the bladder | faulty mesodermal migration to ventral abdominal wall -> bladder protrudes & pelvic bones splay. |
| Exstrophy of the cloaca | similar to exstrophy of the bladder + urorectal septum does not form. (faulty mesoderm migration) |
| androgen insensitivity syndrome | testes + testosterone but female external genitalia. Mullerian Inhibiting Factor -> no true uterus & oviduct. |
| gut development | gut tube suspended by dorsal & ventral mesenteries. ventral degenerates, dorsal provides neurovascular path to distal fore,mid,& hindgut. |
| derivatives of the foregut | pharynx, lungs, esophagus, stomach, proximal duodenum, liver, biliary tree, pancreas. |
| derivatives of the midgut | midgut herniates into umbilical cord & rotates around superior mesenteric artery -- later returns to abdomen. most of duodenum, small intestines, cecum, colon up to transverse (areas supplied by superior mesenteric artery) |
| derivatives of the hindgut | colon (after transverse), rectum, bladder epithelium, urethra. cloaca connects w/allantois. septum divides cloaca into urogenital sinus & rectal canal, -> anal membrane & urogenital membrane of cloaca. anal membrane ruptures= anus open to amniotic cavity. |
| duodenal atresia/stenosis | duodenal canal normally closes in week 5-6 & reopens in week 8. with duodenal atresia, it never reopens. presents w/vomiting. double-bubble in X-ray of abdomen. common in Down Syndrome. |
| Biliary atresia | incomplete connections of bile canaliculi to hepatic & common bile ducts. children present with hyperbilirubinemia (severe jaundice). |
| Omphalocele | protrusion of abdominal contents through hernia (covered w/thin membrane). persistence of normal midgut hernia that should reenter. |
| midgut volvulus | midgut twists too much in development, cuts off blood supply, can cause small intestine necrosis. |
| ileal diverticulum | = Meckel diverticulum. pouch remains where yolk sac joined midgut. may retain vascular & gastric tissue. bleeds. |
| Hirschprung disease | faulty migation of ganglion cells into distal colon causing narrowed aganglionic segment. |
| Imperforate anus | membranous anal atresia = persistence of anal membrane that usually perforates at 8 weeks. anorectal agenesis = faulty development of urorectal septum (fistulas w/bladder/vagina/urethra may be present) |
| respiratory tract early development | branches off of primitive foregut (week 4) = laryngotracheal diverticulum. mesenchyme surrounds. tracheoesophageal folds fuse -> tracheoesophageal septum. lung bud branches into 2 primary bronchi |
| respiratory tract later development | lungs grow until 26 weeks, terminal saccules ->28 weeks, immature alveoli -> 32 weeks (capable of function), alveoli continue to develop for several years |
| diaphragm development | septum transversum= between future thoracic cavity & yolk sac, partly separates thoracic from abdominal cavity. pleuroperitoneal folds from dorsum fuse w/ventral septum transversum -> diaphragm. left side fuses later than right. |
| respiratory distress syndrome | infants born before 26 weeks may not have enough alveoli/surfactant |
| pulmonary hypoplasia | decreased lung capacity with tachypnea, respiratory distress. caused by decreased amniotic fluid or lung compression (e.g. diaphragmatic hernia) |
| esophageal atresia | blind esophagus caused by posterior deviation of the tracheoesophageal septum. frequently associated w/tracheoesophageal fistula |
| tracheoesophageal fistula | faulty separation of the trachea & esophagus. "h" type = mild, food inhaled into lungs. severe = blockage of trachea/esophagus via esophageal atresia. |
| congenital diaphragmatic hernia | posterior gap in diaphragm allows intestines to enter chest & restrict lung development. usually on left. high mortality rate, cannot be surgically corrected. |
| secondary brain vesicles | HINDBRAIN: myelencephalon = medulla & 4th ventricle, metencephalon = pons, cerebellum, 4th ventricle. MIDBRAIN:mesencephalon = midbrain, aqueduct. FOREBRAIN: Diencephalon = Thalamus, 3d ventricle, telencephalon = cerebrum, lateral ventricles. |
| eye development | retina = from forebrain. lens placodes (ectoderm), choroid & sclera (mesoderm). |
| inner ear development | ectoderm (from otic placodes). |
| skin layers of the head | ectoderm -> epidermis. mesoderm -> dermis. |
| branchial arches, about | (=pharyngeal arches). end of week 4. from mesenchymal neural crest in neck + mesoderm. layered w/ecto & endoderm. 4 arches visible w/grooves (5 & 6 rudimentary), 1 aortic arch per branchial arch. pharyngeal pouch b/tw each arch (inner side). |
| branchial arch derivatives | 1: maxilla, mandible, mastication muscles & trigeminal nerve. 2: facial muscles & facial nerve. pharyngeal pouches -> middle ear. |
| facial development | frontonasal prominence induced by forebrain development -> nose & upper face (fuse to form primary palate). palatal shelves on walls of pharynx -> 2ndary palate. 1st pharyngeal pouch -> middle ear. prominences @ sides of 1st branchial groove -> outer ear. |
| palate development | primary (anterior) from fusion of frontonasal prominences. secondary from palatal shelves (walls of pharynx). shelves initially oriented caudally, but rotate ventrally above developing tongue & fuse. |
| congenital hydrocephalus | caused by abnormal closure of the neural tube -> CSF buildup in brain & head enlargement. severe conditions -> brain atrophy. can be caused by X-linked recessive mutation. |
| holoprosencephaly | defective prosencephalon differentiation can -> arrhinencaphaly, or undeveloped prosencephalon w/1 ventricle. mild= cleft palate. severe= ceocephaly (primate-like nose), hypotelorism (narrow-set eyes), cyclopia (single eye + proboscis instead of nose) |
| cleft palate | ANTERIOR= due to abnormal primary palate development or its abnormal fusion w/lateral palatine processes (shelves). POSTERIOR= abnormal fusion of lateral palatine processes. |
| lissencephaly | smooth brain w/no sulci & gyri. failure of cerebral neurons to migrate properly. |
| Pierre Robin sequence | 1st branchial arch anomaly -> small mandible, protruding tongue through palatal shelves w/out fusion. cleft soft palate & tongue protruding over jaw (glossoptosis) |
| hemifacial microsomia | small mandible & unilateral external ear anomalies. |
| Goldenhar syndrome | similar to hemifacial microsomia + extra tissue over sclerae, cleft eyelids, absent cervical & thoracic vertebre, scoliosis, cardiac septal defects (tetralogy of Fallot), urinary tract anomalies. |
| DiGeorge anomaly | small jaw, hypoparathyroidism, hypocalcemia, absent thymus (+ immune defects), interrupted aortic arch (coarctation of aorta). can be sporadic or caused by deletion of 22q11. multiple branchial arch developmental abnormalities. |
| cleft lip | CLEFT LIP: lateral = failure of maxillary & nasal prominences to fuse. midline = rare, usually due to arrhinencaphaly/holoprosencaphaly. |
| axial vs. appendicular skeleton | axial = vertebrae, ribs, sternum. appendicular = shoulder, pelvis, & limbs. |
| paraxial, intermediate, & lateral mesoderm | paraxial= lateral & ventral to neural tube-> somites, skin/muscle/bones of trunk. intermediate mesoderm= more lateral-> urogenital system. lateral mesoderm= more lateral-> pleural/pericardial/peritoneal membranes, heart, spleen & blood-forming tissues. |
| somite development | paraxial mesoderm -> dermatome, myotome, sclerotome of trunk. mesoderm -> mesenchyme (pluripotent) -> fibro-, chondro-, osteo-, & myoblasts. |
| bone development | from paraxial mesoderm -> somites. membranous bones (e.g. skull/jaw) from mesenchyme. echondral bones (e.g. long limb bones) from chondroblasts (cartilage matrix). vertebrae from osteoblasts, ribs grow from vertebrae. skull from somites & neural crest. |
| limb development | arm limb buds appear prior to leg. long bones have ends (epiphysis), necks (metaphysis), & shafts (diaphysis). primary ossification centers= in diaphyses (fetal). 2ndary ossification= in epiphyses (postnatal). muscles= from mesenchyme surrounding bones. |
| limb axes | proximal-distal (from apical epidermal ridge @ end of limb bud), dorso-ventral, preaxial-potaxial (e.g. thumb -> pinky). |
| ectrodactyly | lobster claw, due to bilateral defects of middle digital rays (2-4). may be associated w/Ectrodactyly-Ectodermal Dysplasia-Clefting syndrome OR as isolated anomaly or non-genetic birth defect. |
| syndactyly | digit fusion -> mitten hand. defects in apoptosis of digit rays. may be associated w/Apert Syndrome w/ Craniosynostosis, defects in FGFR2, or isolated congenital anomaly. |
| polydactyly | extra digits, usually ulnar(postaxial polydactyly) due to extra apoptotic centers. may be associated w/trisomy 13, Smith-Lemli-Opitz Syndrome (defect in cholesterol synthesis), or isolated anomaly. most common in African Americans. |
| Events in Week 1 of Development | Fertilization, Cleavage, Morula, Implantation |
| Events in Week 2 of Development | Bilaminar Disc, Placental Circulation, Axes |
| Events in Week 3 of Development | Primitive Streak, Notochord, Neural Plate, Neural Groove, Somites |
| Events in Week 4 of Development | Trilaminar Disc -> cylindrical embryo, Heart Beats, Neural folds fuse, Neuropores, Branchial Arches, Eye/Ear primordia, Limb Buds |
| Events in Week 5 of Development | Nasal Pits, Optic Cup, Hand/Foot Plates, Cerebral Vesicles |
| Events in Week 6 of Development | Upper lip, Digits defined, Palate |
| Events in Week 7 of Development | Eyelids, Primitive Genitalia |
| Events in Week 8 of Development | Arms bend @ elbows, primordia of all organs present |
| cleft lip | midline cleft lip= holoproencephaly. lateral= failure of frontonasal prominence fusion. |
Created by:
rbxbrown