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EMBRYOLOGY YR1 SLT EMILY BURTENSHAW
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Introduction to embryology Basic cncepts and principles How the embryo develops from fertilisation to implantation – brief overview, for information only Influences on the growth and development of the embryo; critical period concept Important stages in development: gastrulation, neurulation, development of the nervous system The neural crest cells – and their fate Embryonic development of the head and neck structures
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Directed study elements: Basic genetics To understand how the pharyngeal arches develop and contribute to the development of the structures of the face, neck and palate Relate this development to the structures of the head and neck you are currently studying
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https://insideoutsrikar.files.wordpr ess.com/2011/12/zygote.jpg
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https://en.wikipedia.org/wiki/File:Human_embryo_2.jpg
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https://en.wikipedia.org/wiki/File:HumanNewborn.JPG
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Why study embryology??
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Pregnancy: measured in trimesters http://totorus.blogspot.co.uk/
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In reality … Prenatal development: 3 stages of unequal length. Germinal stage: days 1 to 14 ie from conception to implantation Embryonic stage: begins at implantation approximately 2 weeks after conception and continues through weeks 3 to 8 (the period oforganogenesis )
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The Foetal Stage: from 9 th week to the birth (40 weeks from last period, or 38 weeks from fertilisation) Organs grow and continue differentiation Increase in weight
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Challenges in studying embryology: Complexity –CD rom and websites Personal experience Attitudes and beliefs Terminology
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Pre-embryonic period The first 14 days Cells can still repair themselves If damaged either repairs or dies (spontaneous miscarriage)
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Critical period: http://veganimal.wikispaces.com/4.1.7.-EL+DESAROLLO+EMBRIONARIO+EN+LOS+ANIMALES
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What can affect prenatal development?
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Chromosomal and genetic factors Teratogens: maternal disease, drugs Mutagens: radiation Other maternal influences on development: Diet, age, chronic illness, environmental hazards and maternal emotions
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Chromosomal & Genetic factors 90% of abnormal embryos are spontaneously aborted Only 1% of live newborns have a genetic abnormality
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Chromosomal abnormalities 23 pairs of chromosomes Over 50 different chromosomal abnormalities Too many chromosomes Too few chromosomes Vast majority of chromosomal abnormalities are lethal (spontaneous abortion)
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http://year9diseases.wikispaces.com/Down's+Syndrome
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http://ehumanbiofield.wikispaces.com/JH+Downsydrome
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eg:Down Syndrome Three copies of chromosome 21 1 in every 600 birth Learning disability (IQ averages 50) May have congenital eye, ear, heart defect Distinctive physical features: protruding tongue, short limbs, slightly flattened nose…
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Eg Angelman’s syndrome and Prader-Willi syndrome Genetic defect on chromosome 15 (maternal in case of Angelman’s syndrome, paternal in case of Prader-Willi syndrome)
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eg: Klinefelter’s Syndrome Sex chromosomes: XXY (boys) 1/500 births Poor coordination May have mild learning difficulties
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http://genmolecular.com/alteraciones-cromosomicas/
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Turner’s syndrome https://en.wikipedia.org/wiki/Turner_syndrome
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Genetic disorders Through dominant or recessive genes Eg Cystic fibrosis Phenylketonuria (PKU) –Lack of enzyme to digest food containing amino acid phenylalanine (e.g.milk) –Phenylpyruvic acid accumulates in the body and attacks the developing nervous system –Hyperactivity; learning difficulties –Test routinely given at birth –Treatment: diet
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Mutagens: Physical or chemical agents eg ionising radiation, certain chemicals Act on the DNA in cells, especially during cell division Alters the genes Mutation can be passed on, if it occurs in the gametes
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Teratogens Any disease, drug or other environmental agent that can harm the developing embryo or foetus. The effect is worse on a body part when that structure is forming or growing rapidly Critical period: Period when a body part is most sensitive to teratogenic agents
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Maternal disease Rubella –Most dangerous in first trimester –Blindness, deafness, cardiac abnormalities, mental retardation Syphilis –Most harmful in middle or later stages –Miscarriage, serious eye, ear, bone, brain damage
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Toxoplasmosis –¼ adults have this mild disease – similar to common cold. –Parasite (cat) –Powerful teratogen –Serious eye or brain damage, induce spontaneous abortion
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http://talubrinandoescritoschapadadoarapari.blogspot.co.uk/2012/09/a-minha-solidariedade-as-vitimas-da.html
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Drugs Thalidomide –In 60s –Drug against sickness given to pregnant women in first trimester –Violent teratogen –Badly deformed eyes, ears, nose, even missing limbs
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Smoking –Low birth weight (less than 2.5 kg) –Nicotine constricts blood vessels Reduces blood flow to placenta
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W Eugene Smith, 1972
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Alcohol: Foetal alcohol syndrome (FAS): –Microcephaly –Malformation of heart, limbs, joints, face –Smaller –Lower IQ - More likely to have learning difficulties (IQ < 85) –Even low drinking, social drinking
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http://disindevt3.wikispaces.com/Foetal+Alcohol+Syndrome
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Iterative processes in embryological development: Cell division (proliferation) Cell adhesion Separation of cell sheets to form cavities Cell migration Cell differentiation Cell induction
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http://eorif.com/syndactyly- 7551 APOPTOSIS
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Timing is everything: Cell proliferation : embryo/organ system vulnerable to genetic or environmental factors Cell migration: cells move into position; can be affected by matrix through which they travel Cell differentiation: cells assume their ultimate form or phenotype – less vulnerable to insult
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♫♪Let’s start at the very beginning♪♫
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Embryonic development: Weeks 1 and 2: Fertilisation Implantation Formation of the placenta and the early embryo
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l http://www.wisegeek.com/what-is-the-fertilization-process.htm
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Fertilisation to implantation: http://humanphysiology2011.wikispaces.com/15.+Reproductive+Physiology SYMBRYO video
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Day 1 Day 2 2 cells; Genes ‘switch on’
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8 to 16 cell stage (morula) Day3 https://en.wikipedia.org/wiki/File:Embryo,_8_cells.jpg
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Development of the blastocyst: http://www.conceive.ca/fertility-treatments/in-vitro-fertilization-ivf/
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Three sources of embryonic stem cells: http://www.intechopen.com/books/pluripotent-stem-cells/de-differentiation-of-somatic-cells-to-a-pluripotent-state
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Day 14: https://quizlet.com/7189248/bilaminar-and-trilaminar-flash-cards/
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"It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life." Lewis Wolpert (1986)
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GASTRULATION: a process that lasts 2 weeks Gastrulation At this point, I suggest you do a Google search of gastrulation images, as the best ones are unfortunately subject to copyright.
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The fate of the 3 germ layers: Ectoderm: CNS, PNS, epidermis, hair, nails, sensory epithelium (nose, ear, eye) Mesoderm: part of skull, muscles, vertebrae, urogenital system, serous membranes, body wall, limbs Endoderm: gut tube and its derivatives; glands, lungs, liver, gall bladder, pancreas
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Birth defects originating during gastrulation: situs inversus Teratoma (formed from epiblast cells – contain hair, skin, bone, liver etc cells) Caudal dysgenesis
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http://radiopaedia.org/cases/situs-inversus-9
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https://beyondthedish.wordpress.com/2013/05/
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http://body-system-broadcast.wikispaces.com/Musculo-Skeletal+System
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http://designermetin.deviantart.com/art/3D-Origami-Swan-303043684
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Weeks 3 to 4 Formation of the neural and gut tubes Embryo transformed from a trilaminar disc into something more recognisable!
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Neurulation: Formation of neural plate Elevation and curling of lateral edges ‘zippering’ and formation of the neural tube
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https://en.wikipedia.org/wiki/Neural_tube_defect,_folate-sensitive
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http://www.intechopen.com/books/neuroblastoma/
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neurulation video epic neurulation!
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Final destination neural crest cells: Connective tissue and bones of the face and skull C cells of thyroid gland Septum of the heart Odontoblasts Dermis in the face and neck Dorsal root ganglia Sympathetic chain and pre-aortic ganglia Parasympathetic ganglia of the GI tract Adrenal medulla Schwann cells Glial cells Arachnoid and pia mater melanocytes
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http://sharonap-cellrepro-p3.wikispaces.com/Creating+Bodies
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Week 3: 0.5 mm https://en.wikipedia.org/wiki/Somite
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https://en.wikipedia.org/wiki/Spina_bifida#/media/File:Spina-bifida.jpg
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Folding of the embryo: Dorsal surface – formation of the neural tube –‘zippering’ effect –cervical first, then caudally Ventral surface – formation of gut tube and body cavities Body stalk – eventual umbilical cord
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https://www.studyblue.com/notes/note/n/em bryology/deck/3740268
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http://philschatz.com/anatomy-book/contents/m46319.html
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Formation of the umbilical ring: Proliferation and differentiation of mesoderm Causes ventral folding along sides of embryonic axis; amnion surrounds embryo Formation of gut tube Brain grows Head and tail folding ‘purse strings’ effect
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folding of the embryo in two planes
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http://pregnancyweeks.wikispaces.com/Your+Baby%E2%80%99s+Development+and+Improvement+in+Week+4+of+Pregnancy Week 4 embryo
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Ontogeny replicates phylogeny
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https://en.wikipedia.org/wiki/Recapitulation_theory
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http://3-cups-of-tea.wikispaces.com/Pai+Yu+Cha+Tea
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http://sharonap-cellrepro-p3.wikispaces.com/Creating+Bodies
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Neural crest cells: in the head and neck region…… Form ganglia of the cranial nerves Connective tissue and some of the bones of the skull and face Dermis in the face and neck Odontoblasts Arachnoid and pia mater Glial cells
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https://www.studyblue.com/notes/note/n/em bryology/deck/3740268
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Week 3: 0.5 mm https://en.wikipedia.org/wiki/Somite
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Fate of the mesoderm: Paraxial mesoderm forms paired somites from occiput caudally along the length of the neural tube In the head region, somitomeres form part of skull, muscles, vertebrae, and dermis of the skin.
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Development of the Skull: Neurocranium (protective covering of the brain) derived from paraxial mesoderm –Membranous portion (flat bones) –Cartilagenous portion = Chondrocranium (base of the skull) Viscerocranium (skeleton of the face – the ‘middle third’ - & including the mandible) derived entirely from neural crest cells
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viscerocranium http://medical-dictionary.thefreedictionary.com/neurocranium
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Development of the brain vesicles: Cranial end of neural tube expands Neural tube closure complete in week 4 Brain vesicles form the future brain Anterior vesicle: prosencephalon This subdivides: telencephalon (future cerebral hemispheres) and diencephalon (optic and thalamic tissues and other structures)
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www.en.wikipedia.org
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(rhombencephalon) Primary Brain Vesicles https://en.wikipedia.org/wiki/File:Embry onicBrain.svg
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http://bookcoverimgs.com/fetal-brain-development-stages /
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Further development of the NS The nervous system continues to develop and changes occur up until the early 20’s The main changes include: Myelination Formation of synapses Synaptic pruning Apoptosis
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Synaptic pruning: Microglia -nerve cells which are usually involved in response to injury in the NS They also pluck off or ‘prune’ some of the synapses between neurons In conjunction with apoptosis of neurons, ensures that only the most- used ie strongest connections, remain Keeps the brain operating efficiently
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Synaptic pruning occurs: Prenatally In childhood At puberty “use it or lose it” Learning causes synaptic connections to increase in strength
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Implications for SLT: Aberrant synaptic pruning may be at the root of MND, MS AD – by the time it is identified, people have lost over HALF their synapses Children with ASD have increased cerebral volume, ? ? have not undergone the same extent of synaptic pruning?
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Myelination: Starts late in embryonic development and continues into adolescence/early adulthood Forebrain the last part to complete myelination Q what is the function of the myelin sheath?
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THE SPINAL CORD Extends from the foramen magnum to the level of the second lumbar vertebra. Shorter than the vertebral column because it does not grow as rapidly during embryonic development. Because the spinal cord is shorter, spinal nerves do not always exit the vertebral column at the same level as their origin in the spinal cord.
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https://it.wikipedia.org/wiki/Cauda_equi na https://quizlet.com/24950848/spinal-cord-flash-cards
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By the end of the 4 th week: Neural folds have closed Head region distinguished by presence of 3 brain vesicles
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Lens and otic placodes for eye and ear development; Primitive oral cavity (stomatodeum) 3 pairs of pharyngeal arches
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http://pregnancyweeks.wikispaces.com/Your+Baby%E2%80%99s+Development+and+Improvement+in+Week+4+of+Pregnancy Week 4 embryo
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Formation of the pharyngeal arches: Neural crest material grows from the rhombencephalic region (rhombomeres) Migrates and forms 6 paired bands These form the pharyngeal arches Each is accompanied by its own artery, nerve and cartilage
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http://www.med.umich.edu/lrc/coursepages/m1/embryology/embryo/09faceandpharynx.htm
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http://center-for-nonverbal-studies.org/pharynx.htm
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https://commons.wikimedia.org/wiki/File:PharyngealArchHuman.jpg
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https://odontologi.wikispaces.com/cranio-facial+development
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http://scienceblogs.com/pharyngula/2006/06/21/deep-homologies-in-the-pharyng
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http://medchrome.com/basic-science/anatomy/general-embryology-mnemonics/
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First arch deformities: Micrognathia Cleft palate (indirectly) Conductive hearing loss External ear malformations
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Abnormal neural crest migration/differentiation: Treacher-CollinsRobin sequence http://byebyedoctor.com/treacher-collins-syndrome/
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Goldenhar syndrome First AND second pharyngeal arches malformed https://en.wikipedia.org/wiki/Goldenhar_sy ndrome http://health9.org/goldenhar-syndrome/
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http://wps.aw.com/wps/media/objects/443/454121/developmentofexternalear.html
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https://syllabus.med.unc.edu/courseware/embryo_images/unit-ear/ear_htms/ear015.htm
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FORMATION OF THE FACE: formation of the face development of the head, neck, face and palate
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http://www.med.umich.edu/lrc/coursepages/m1/embryology/embryo/09faceandpharynx.htm
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Formation of the palate https://web.duke.edu/anatomy/embryology/craniofacial/craniofacial.html
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https://en.wikipedia.org/wiki/Incisive_foramen
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http://praxisprep.wikispaces.com/Cleft+Palate
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https://en.wikipedia.org/wiki/Embryo
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Week 8 https://en.wikipedia.org/wiki/Embryo
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