Intro To Embryology PDF - University of Bradford

CLS4011-U Systems, Physiology & Anatomy Introduction to Embryology Dr Keren Bielby-Clarke [email protected] 1 CLS4011-U: Introduction to Embryology  Learning Objectives Following this lecture an...

CLS4011-U Systems, Physiology & Anatomy Introduction to Embryology Dr Keren Bielby-Clarke [email protected] 1 CLS4011-U: Introduction to Embryology  Learning Objectives Following this lecture and self-directed learning, you should be able to: Understand the stages of fertilisation, formation of the zygote, and cleavage Explain the basic principles of blastulation and implantation, and understand the formation of the placenta from the blastocyst cells Explain the principles of gastrulation – formation of the germ layers from the bilaminar disc – and the significance of the germ layers for organ systems development Appreciate how longitudinal and lateral folding of the embryonic sheets creates the basic body structure 2 CLS4011-U: Introduction to Embryology  Why study embryology? Embryology – branch of science studying early formation and development Foundation for anatomy, physiology and developmental abnormalities 3 CLS4011-U: Introduction to Embryology  Terminology ANT towards head/beak front back towards po rail  Overview – day 0 to adult Development – from fertilisation to complex organism organ is a Enlargementovergrowth of Rapid ↑ in No/amount < Growth – by proliferation, hypertrophy or accretion growth/ ↑ by process of 2 gradual accumulation/addition Several/multiple cell types Differentiation – multipotency to specific fate Signalling –between cell groups to determine fate Organisation – often morphogens – tell cells what to become signalling molecules > Morphogenesis – changes in shape during development 5 CLS4011-U: Introduction to Embryology  Signalling molecules Simple ball of cells → complex, specific tissues and organ systems specialised groups of influence embryos of Surrounding that cells development in & Morphogens tissues and neighbouring cells How? Triggers – organisers and inducers Signalling molecules family Signalling proteins factors that signalling - A of or -cell to cell Secreted glycoproteins cell differentiation and ora trigger specific Paracrine signalling – egs Wnt, Hedgehog, developmental lumidora fibroblast growthA superfamily in changes factor (FGF’s), transforming > responsive Cells growth factor- of cytokines - Juxtacrine signalling cell's surface signalling molecules on one adjacent cell interact with receptors on an Transcription factors – egs Hox proteins - (encoded by Hox genes Important for patterning, axis formation, and organogenesis organ formation during development embryonic 6 CLS4011-U: Introduction to Embryology Embryonic & foetal periods - full term  Fertilisation Combination of genetic information from gametes Assuming ovulation and transfer of sperm into the female reproductive system female germ cell Also known. as egg cell or ovum layer offollicular cells Oocyte is surrounded by the corona radiata s needs maturation Once a sperm passes through the corona radiata, it binds to the zona pellucida and triggers the acrosome reaction, allowing membranes to fuse and cell contents to merge Enzymes released · are Oocyte releases cortical granules which alter the zona pellucida - prevents any other sperm from entering the oocyte turned into impenetrable - an membrane  Fertilisation enter the Before Spermatozoon can oocyte it need to undergo S capacitation and acrosome Enzyme released from Acrosomal capy reaction , speim undergone capacity - Haploid Meiosis II is triggered – forms definitive oocyte and second polar body Fertilised oocyte – ZYGOTE (has diploid set of chromosomes) Male pronucleus and female pronucleus align, DNA is duplicated, condenses, and mitosis continues – cell splits  Formation of the zygote Diploid cell 10 CLS4011-U: Introduction to Embryology  Formation of the zygote CELL DNA/chromosomes zygote combined and Split Division X Palluada is zoma still there 11 CLS4011-U: Introduction to Embryology  Fertilisation rotational cleavage 16 sell > fluid Apposed to uterine space wall  Zygote → blastocyst Zygote divides by mitosis (does not increase in size) Cells = blastomeres Morula = 12-cell stage embryo Forms inner cell develops mass (embryoblast) and outer cell mass (trophoblast) / Blastocoele - cavity 13 Gridmastocoele CLS4011-U: Introduction to Embryology  Zygote → blastulation Zygote Rotational cleavage Morula Hatch outside zona pellucida Helps to implant on to devine Blastocyst (IMC and blastocoele) surface Hatching 14 CLS4011-U: Introduction to Embryology  Implantation Morula enters uterus at ~4 days; forms blastocyst ~4.5 days (blastulation) Implantation – 6-7 days. Blastocyst has fluid-filled core (blastocoele), trophoblast (outer cell mass) and embryoblast (inner cell mass) Four stages: hatching (blastocyst exits zona pellucida); apposition; adhesion; invasion blackocyst sealed off Inner cell mass Is aligns with vierus coal in vierire Trophoblast contacts decidual cells of uterus, and inner cell mass rotates to closest to the point of contact - apposition 15 CLS4011-U: Introduction to Embryology  Day 6-7 spects into L layers Embryoblast: becomes BILAMINAR DISC (epiblast and hypoblast) Trophoblast: becomes cytotrophoblast and syncytiotrophoblast Syncytiotrophoblast - Proliferation of cells into uterine lining – cell membranes disintegrate and cytoplasm mixes – becomes placenta Cytotrophoblasts have well-defined cell margins  Day 8-9 Dorsal renta Epiblast: forms the embryo Hypoblast: forms extraembryonic membranes (amnion, yolk sac, chorion, allantoin) – exocoelomic membrane Primitive yolk sac develops below hypoblast (nutrients, red blood cells, primitive germ cells) Amniotic cavity forms above epiblast Fully embedded into uterus 17 CLS4011-U: Introduction to Embryology  Day 12-13 Extraembryonic mesoderm forms between cytotrophoblast cells and amnion/yolk sac Spaces develop – extra-embryonic cavities. Merge to form chorionic (extra-embryonic) cavity Surrounds amnion and yolk sac except at connecting stalk Extra embryonic mesoderm – splanchnic and somatic  Placenta Syncytiotrophoblasts – spread into endometrium Form lacunae (spaces) and release proteolytic enzymes Break down endometrial blood vessels – blood collects in lacunae  Placenta 20 CLS4011-U: Introduction to Embryology  Placenta Chorionic villi form – first, cytotrophoblasts proliferate into syncytiotrophoblast projections – primary villi Extra-embryonic mesoderm projects up within the cytotrophoblasts – secondary villi Blood vessels form and pass through the connecting stalk, into the chorionic villi, where they form capillaries – tertiary villi Exchange occurs between chorionic villi capillaries and maternal blood in lacunae 21 CLS4011-U: Introduction to Embryology  Placenta Tertiary villi: inner vascularised mesoderm; cytotrophoblast and syncytiotrophoblast layer 2 umbilical arteries, 1 umbilical vein in connecting stalk  Gastrulation Need to get from a bilaminar disc (epiblast and hypoblast) to a trilaminar disc with three germ layers (ectoderm, mesoderm, endoderm) Formation of axes – primitive node, primitive streak Cells in epiblast migrate towards and INTO streak Move under epiblast to replace or create new cells  Gastrulation View of epiblast layer of bilaminar disc 24 CLS4011-U: Introduction to Embryology  Gastrulation Invaginating cells first replace hypoblast cells to form the endoderm Cells move between epiblast and hypoblast to form mesoderm – paraxial, intermediate and lateral plate Gastrulation  closest Ectoderm to annniotic stoid “Outer” layer - dorsal External surface of embryo (epidermis of skin) (dermis from mesoderm) Nervous system – via neurulation (includes sensory structures) Neural crest cells – form (eg) PNS, skeletal facial structures, melanocytes,  Mesoderm Bones, cartilage and connective tissue of skeleton Striated skeletal and smooth muscle Cardiovascular system (majority); lymphatic system; reproductive system; parts of renal system, spleen Linings of cavities i.e. peritoneum Dermis of skin Cells of CV and immune system (from marrow) are also mesodermal derivatives  Endoderm Forms gastrointestinal tract Epithelia lining systems exposed to external substances (respiratory tract, GI tract), also bladder and urethra Respiratory system is derived from gut tube “Buds” form organs such as liver, gall bladder, pancreas, thyroid Tonsils, thymus, parathyroid glands  Embryonic folding – longitudinal Cranial-caudal (longitudinal) folding Heart tube – cranial end Folding of “flat sheet” begins at each end 30 CLS4011-U: Introduction to Embryology  Longitudinal folding At cranial end, oropharyngeal membrane (will become mouth) is pushed caudally, below brain Heart field cells move around to lie caudal to mouth Cloacal membrane moves underneath and connecting stalk is pulled towards umbilical region  Lateral folding Left and right sides grow down and Text under, meet in midline Germ layers meet and fuse Endoderm forms internal tube, mesoderm surrounds intraembryonic cavity 32 CLS4011-U: Introduction to Embryology  Formation of the body cavities Remember – coronal section As the mesoderm develops, cavities arise in the lateral plate region 33 CLS4011-U: Introduction to Embryology  Formation of the body cavities Intraembryonic cavity is continuous at this stage with extraembryonic cavity  Formation of the body cavities 21-day embryo: lateral folding brings left and right sides close together on ventral surface 28-day embryo: germ layers fuse  Overview Following this lecture and self-directed learning, you should be able to: Understand the stages of fertilisation, formation of the zygote, and cleavage Explain the basic principles of blastulation and implantation, and understand the formation of the placenta from the blastocyst cells Explain the principles of gastrulation – formation of the germ layers from the bilaminar disc – and the significance of the germ layers for organ systems development Appreciate how longitudinal and lateral folding of the embryonic sheets creates the basic body structure 36 CLS4011-U: Introduction to Embryology  References Drake, RL, Vogl, AW & Mitchell, AWM “Grays Anatomy for Students” 2020, 4th Edition, Elsevier Naish, J & Syndercombe Court D “Medical Sciences” 2019, 3rd Edition, Elsevier Sadler, TW “Langman’s Medical Embryology” 2019, 14th edition, Wolters Kluwer (612.64 SAD) Webster, S & de Wreede, R “Embryology at a glance” 2016, 2nd edition, Wiley Blackwell 37 CLS4011-U: Introduction to Embryology