DOCSLIB.ORG

Revisedental.Com Implantation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Revisedental.Com Implantation Embryology Sumamry This lesson will cover fertilisation, implantation, gastrulation and neurulation. The first 4 weeks of embryology. Pregnancy is split into three trimesters. Semesters one and two contribute to the embryonic period and semester three becomes the fetal period. The first of these trimesters is a critical time period, because this is when all the main organ systems begin to develop. The second trimester is when we start to look more human and our organ systems are near complete ready to move into the third trimester, which shows rapid fetal growth and organ function. This process takes between 38-40 weeks, which is when birth occurs. Week 1: Key Words: Fertilisation Zygote Cleavage Blastomere Morula Blastocyst Trophoblast EmbryoblastsReviseDental.com Implantation Cell actions: Proliferate, Migrate and Differentiate. Fertilisation: The optimum time for fertilisation to occur is between 12-24hrs after ovulation (when the secondary oocyst leaves the ovary). However, due to the ability of sperm being able to remain viable for 48hrs, there is a 3 day window around the time of ovulation for fertilisation to take place. Sperm and ova are haploid cells. This means they have half the amount of chromosomes of a human cell. Therefore, on fusion (syngamy) a diploid cell is created, now known as a zygote. The Zygote now has the correct number of chromosomes: 46. Diagram schematicReviseDental.com of a sperm and ova The sperm cells are specially equipped to enter the ova, having acrosome enzymes to penetrate the cell wall and a powerful flagella (tail) for motility. On entrance, to prevent polyspermy (multiple sperm entering), the ova cell wall depolarises alongside deactivation of cell receptor, making the ova's zona pellucida impenetrable. Cleavage: Mitotic cell division occurs around day 2-3 forming a morula (16 cells). When the cell population reaches 32, the mass is now known as a blastula. The cells are still within the zona pellucida and therefore show no increase in size, but cell density has increased (compaction), these cells are known as blastomeres.ReviseDental.com Around days 4-5 an accumulation of fluid (blastocoel) occurs within the morula via cavitation, alongside the zona pellucida degradation, and the blastocyst is created. The blastocoel fluid is derived from the endometrium and provides nourishment for the cells. The blastocyst now shows two clear cell populations. The inner cell mass are the embryoblasts (what becomes us). The outer cell mass are the trophoblasts, which play an important role during implantation. Implantation: Implantation occurs around day 6 and firm attachment to the endometrium is seen by the end of the first week of theReviseDental.com embryonic period. As the blastocyst burrows, it becomes fully surrounded by the endometrium and an increase in vascularity occurs. This area of the endometrium is called the decidua and provides glycogen and lipid to the developing embryonic cells and later contributes to formation of the placenta. Week 2: Key Words: Trophoblasts: Syncytiotrophoblasts and Cytotrophoblasts = Chorion Bilaminar disc: Hypoblasts and Epiblasts Yolk sac Amnion Sinusoids Trophoblasts: Around day 8 the trophoblasts have differentiated into two distinct layers with distinct functions. The syncytiotrophoblasts go on to assist with the embedding of the blastocyst by secreting enzymes as well as secreting human chorionic gonadotrophin (hCG), which prevents menstruation (note: pregnancy test). Syncytiotrophoblasts have no distinct cell boundaries and also contribute to the surrounding vascular supply. The cyctotrophoblasts are clearly demarcated cells and become the out lining cells of the developing embryo. Bilaminar Disc: Day 8 also shows the Embryoblast cells differentiate to form two cell layers; the hypoblasts and the epiblasts. The hypoblasts migrate and surround the original fluid filled cavity of the blastocyst, now known as the yolk sac. The yolk sac is the nutrient supply until the development of the placenta takes over, and has many other functions e.g. contains primitive stem cells which will contribute to the gut and gonads. The Epiblast layer (which will become us), also cavitates, to form a small amniotic cavity. The amniotic cavity is lined by amnion cells at its roof and the epiblasts on its floor. The amnion will eventually surround the embryo completely, and will become the large amniotic cavity as we know which contains the amniotic fluid. The amniotic fluid has many roles and is initially filled with constituents of maternal blood. It acts as a shock absorber, helps regulate body temperature, keeps the developing cells moist (preventing adhesion) and later in the pregnancy acts as a waste collector (e.g. fetal urine).ReviseDental.com Sinusoids: As mentioned above the syncytiotrophoblasts contribute to the vascular supply to the developing cells. Around days 9-12, they do this by creating lacunae spaces, which fuse to form the lacunar networks. Endometrial capillaries dilate around these networks and form sinousoids. Nutrient and waste exchange occurs at these boundaries. Chorion: Cells from the yolk sac migrate and form the extraembyronic mesoderm. This connective tissue will eventually surround the whole embryo and cavitate to form the extraembyronic coelom. The chorion consists of the trophoblastic layers and the extraembyonic mesoderm. This network of cells provides nutrient supply, protection from the mother's immune cells, and secretes hCG. It fuses with the amnion and the developing coelom (mentioned above) now becomes the chorionic cavity. These structures will become the embryonic part of the future placenta. Week two is demarcated by a clear bilaminar disc consisting of hypoblasts and epiblasts. The development of the connecting stalk has also occurred between the bilaminar disc and trophoblasts, which will go on to becoming the future umbilical cord. ReviseDental.com ReviseDental.com Week 3: Key words: Gastrulation Primitive streak and node Trilaminar disc Endoderm Mesoderm Ectoderm Epithelial and mesenchyme Somites Angiogenesis Notochord Neurulation Neural plate/ groove/ fold/ tube Crest cells General note: The development of 3 primary germ layers and the primitive nervous system. Key cell activities involve: differentiation, migration and rearrangement. Gastrulation: Around day 15, the epiblasts from the bilaminar disc start to migrate. This early migration is seen as the primitive streak, as they invaginate and migrate inwards to displace the hypoblast layer. The epiblasts develop into the three primary germ layers: the ectoderm, mesoderm and endoderm. The disc is now a trilaminar disc. At the head end of the primitive streak, a depression is seen, known as the primitive node. The ectoderm and endoderm are epithelial cell layers, and the mesoderm is a loose connective tissue layer known as mesenchyme. ReviseDental.com Below is a table of the key systems each germ layer will eventually develop into: Notochordal process: At day 16 the mesoderm layer begins to develop a crucial structure called the notochord, which completes around the end of the third week. The notochord is a key influencer by inducing other cells to become active and specialised. At the same timeReviseDental.com as the notochord develops, an oropharyngeal membrane at the head end also begins to develop, as well as the cloacal membrane at the tail end. These areas are made up of ectoderm and endoderm only. At this stage the yolk sac creates an out pouch known as the allantois, a structure that will contribute to early vessels and the urinary system. Somites: During week three, the mesoderm which lies adjacent to the notochord develops into three sections. The paraxial mesoderm forms adjacent to the notochord, the intermediate mesoderm forms next to this and furthest away from the notochord forms the lateral plates. The paraxial mesoderm further sections into somite regions: myotome (muscle), dermatome (connective tissue and dermis), sclerotome (vertebrae and ribs). The intermediate mesoderm contributes to the kidneys and gonads. The lateral plates divides into two sections; splanchnic and somatic, due to the development of the intraembryonic coelom. The splanchnic region which develops into the heart/ circulation (heart beat around 21days) and the somatic region which forms the bones, ligaments and many other structures. Angiogenesis and the placenta: Vessels develop first in the chorion, yolk sac and connecting stalk (remember the chorion is the trophoblasts and the extra embryonic mesoderm that surrounds the embryo, amniotic cavity and yolk sac). Mesoderm cells differentiate in angioblasts which group to form blood islands. Lumens begin to develop in the islands by the angioblasts rearranging to form the endothelial cells of the vessel walls, and eventually the tunic layers. Blood cells and plasma develop first in the chorion and yolk sac vessels As mentioned in week one, during implantation lacunae were formed, which fill with maternal blood. Projections now start to emerge from the chorion, along with its new vessel network. These projects are known as the chorionic villi which become surrounded by the lacunae and are bathed in the mother's blood. Nutrient and waste transfer occurs here and is transported back to the embryo along the connecting stalk (umbilical cord) and the new vascular network (consisting of two main arteries and one main vein). The placenta consists of tissue contributed by two separate individuals; the mother and future child. Its consists of the chorionic
Load more

Recommended publications
  • Human Pluripotent Stem Cells As a Model of Trophoblast Differentiation in Both Normal Development and Disease
    Human pluripotent stem cells as a model of trophoblast differentiation in both normal development and disease Mariko Horiia,b,1, Yingchun Lia,b,1, Anna K. Wakelanda,b,1, Donald P. Pizzoa, Katharine K. Nelsona,b, Karen Sabatinib,c, Louise Chang Laurentb,c, Ying Liud,e,f, and Mana M. Parasta,b,2 aDepartment of Pathology, University of California, San Diego, La Jolla, CA 92093; bSanford Consortium for Regenerative Medicine, University of California, San Diego, La Jolla, CA 92093; cDepartment of Reproductive Medicine, University of California, San Diego, La Jolla, CA 92093; dDepartment of Neurosurgery, Center for Stem Cell and Regenerative Medicine, University of Texas Health Sciences Center, Houston, TX 77030; eThe Senator Lloyd and B. A. Bentsen Center for Stroke Research, University of Texas Health Sciences Center, Houston, TX 77030; and fThe Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, University of Texas Health Sciences Center, Houston, TX 77030 Edited by R. Michael Roberts, University of Missouri–Columbia, Columbia, MO, and approved May 25, 2016 (received for review March 24, 2016) Trophoblast is the primary epithelial cell type in the placenta, a Elf5 (Ets domain transcription factor) and Eomes (Eomeso- transient organ required for proper fetal growth and develop- dermin), also have been shown to be required for maintenance of ment. Different trophoblast subtypes are responsible for gas/nutrient the TSC fate in the mouse (8, 9). exchange (syncytiotrophoblasts, STBs) and invasion and maternal Significantly less is known about TE specification and the TSC vascular remodeling (extravillous trophoblasts, EVTs). Studies of niche in the human embryo (10, 11).
    [Show full text]
  • NUMB and Syncytiotrophoblast Development and Function: Investigation Using Bewo Choriocarcinoma Cells by Julie Carey This Thesis
    NUMB and Syncytiotrophoblast Development and Function: Investigation Using BeWo Choriocarcinoma Cells By Julie Carey This thesis is submitted as a partial fulfillment of the M.Sc. program in Cellular and Molecular Medicine Faculty of Medicine, University of Ottawa May, 2012 © Julie Carey, Ottawa, Canada, 2012 ABSTRACT The role of NUMB, a protein important for cellular differentiation and endocytosis in non-placental cells, was investigated in syncytiotrophoblast development and function in the human placenta. The BeWo choriocarcinoma cell line was used as a model for villous cytotrophoblast cells and syncytiotrophoblast to investigate NUMB’s involvement in differentiation and epidermal growth factor receptor (EGFR) endocytosis. NUMB isoforms 1 and 3 were found to be the predominant isoforms and were upregulated following forskolin-induced differentiation. Overexpression of NUMB isoforms 1 and 3 did not mediate differentiation or EGFR signaling. Immunofluorescence analysis revealed that NUMB colocalized with EGFR at perinuclear late endosomes and lysosomes following EGF stimulation. We have demonstrated for the first time that NUMB isoforms 1 and 3 are expressed in BeWo cells, are upregulated in forskolin- differentiated BeWo cells and are involved in ligand-dependent EGFR endocytosis in BeWo cells. ii TABLE OF CONTENTS ABSTRACT …………………………………………………………………………….. ii LIST OF TABLES ……………………………………………………………………... v LIST OF FIGURES ………………………………………………………………...…. vi LIST OF ABBREVIATIONS ………………………………………………...……… vii ACKNOWLEDGEMENTS ……………………………………………...…..……….
    [Show full text]
  • The Placenta: Transcriptional, Epigenetic, and Physiological Integration During Development
    The placenta: transcriptional, epigenetic, and physiological integration during development Emin Maltepe, … , Anna I. Bakardjiev, Susan J. Fisher J Clin Invest. 2010;120(4):1016-1025. https://doi.org/10.1172/JCI41211. Review Series The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface relies on coordinated interactions among transcriptional, epigenetic, and environmental factors. Here we describe these mechanisms in the context of the differentiation of placental cells (trophoblasts) and synthesize current knowledge about how they interact to generate a functional placenta. Developing an understanding of these pathways contributes to an improvement of our models for studying trophoblast biology and sheds light on the etiology of pregnancy complications and the in utero programming of adult diseases. Find the latest version: https://jci.me/41211/pdf Review series The placenta: transcriptional, epigenetic, and physiological integration during development Emin Maltepe,1,2,3,4 Anna I. Bakardjiev,1,2,5 and Susan J. Fisher2,3,4,6,7 1Department of Pediatrics, 2Biomedical Sciences Program, 3Center for Reproductive Sciences and the Department of Obstetrics, Gynecology and Reproductive Sciences, 4Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research, 5Program in Microbial Pathogenesis and Host Defense, 6Department of Anatomy, and 7Human Embryonic Stem Cell Program, University of California, San Francisco. The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface relies on coordinated interactions among transcriptional, epigenetic, and environmental factors. Here we describe these mechanisms in the context of the differentiation of placental cells (tro- phoblasts) and synthesize current knowledge about how they interact to generate a functional placenta.
    [Show full text]
  • Mechanisms of Human Embryo Development: from Cell Fate to Tissue Shape and Back Marta N
    © 2020. Published by The Company of Biologists Ltd | Development (2020) 147, dev190629. doi:10.1242/dev.190629 REVIEW Mechanisms of human embryo development: from cell fate to tissue shape and back Marta N. Shahbazi* ABSTRACT activated ion channels (Coste et al., 2010), mechanosensitive Gene regulatory networks and tissue morphogenetic events drive the transcription factors (Dupont et al., 2011) or directly by the nucleus emergence of shape and function: the pillars of embryo development. (Kirby and Lammerding, 2018). Once sensed, mechanical cues – Although model systems offer a window into the molecular biology of are transduced into biochemical signals a process known as cell fate and tissue shape, mechanistic studies of our own mechanotransduction (Chan et al., 2017). The conversion of development have so far been technically and ethically challenging. mechanical cues into biochemical signals leads to changes in However, recent technical developments provide the tools to gene expression and protein activity that control cell behaviour, cell describe, manipulate and mimic human embryos in a dish, thus fate specification and tissue patterning. opening a new avenue to exploring human development. Here, I Current consensus focuses on two main ideas to explain the discuss the evidence that supports a role for the crosstalk between emergence of tissue patterns in response to morphogen (see Glossary, ‘ ’ cell fate and tissue shape during early human embryogenesis. This is Box1)signals.Inthe positional information model (Wolpert, a critical developmental period, when the body plan is laid out and 1969), the concentration of a morphogen serves as a coordinate of the many pregnancies fail. Dissecting the basic mechanisms that position of a cell within a tissue.
    [Show full text]
  • Early Embryonic Development Till Gastrulation (Humans)
    Gargi College Subject: Comparative Anatomy and Developmental Biology Class: Life Sciences 2 SEM Teacher: Dr Swati Bajaj Date: 17/3/2020 Time: 2:00 pm to 3:00 pm EARLY EMBRYONIC DEVELOPMENT TILL GASTRULATION (HUMANS) CLEAVAGE: Cleavage in mammalian eggs are among the slowest in the animal kingdom, taking place some 12-24 hours apart. The first cleavage occurs along the journey of the embryo from oviduct toward the uterus. Several features distinguish mammalian cleavage: 1. Rotational cleavage: the first cleavage is normal meridional division; however, in the second cleavage, one of the two blastomeres divides meridionally and the other divides equatorially. 2. Mammalian blastomeres do not all divide at the same time. Thus the embryo frequently contains odd numbers of cells. 3. The mammalian genome is activated during early cleavage and zygotically transcribed proteins are necessary for cleavage and development. (In humans, the zygotic genes are activated around 8 cell stage) 4. Compaction: Until the eight-cell stage, they form a loosely arranged clump. Following the third cleavage, cell adhesion proteins such as E-cadherin become expressed, and the blastomeres huddle together and form a compact ball of cells. Blatocyst: The descendents of the large group of external cells of Morula become trophoblast (trophoblast produce no embryonic structure but rather form tissues of chorion, extraembryonic membrane and portion of placenta) whereas the small group internal cells give rise to Inner Cell mass (ICM), (which will give rise to embryo proper). During the process of cavitation, the trophoblast cells secrete fluid into the Morula to create blastocoel. As the blastocoel expands, the inner cell mass become positioned on one side of the ring of trophoblast cells, resulting in the distinctive mammalian blastocyst.
    [Show full text]
  • Modulation of Bax Expression in Physiological and Pathological Human Placentas Throughout Pregnancy
    in vivo 21: 777-784 (2007) Modulation of Bax Expression in Physiological and Pathological Human Placentas Throughout Pregnancy LUIGI COBELLIS1*, MARIA DE FALCO2*, MARCO TORELLA1, ELISABETTA TRABUCCO1, FRANCESCA CAPRIO1, ELISABETTA FEDERICO1, LUCREZIA MANENTE3, GABRIELE COPPOLA3, VINCENZA LAFORGIA2, ROBERTO CASSANDRO4, NICOLA COLACURCI1 and ANTONIO DE LUCA3 Departments of 1Gynecology, Obstetric and Reproductive Science and 3Medicine and Public Health, Section of Clinical Anatomy, Second University of Naples, Naples; 2Department of Biological Sciences, Section of Evolutionary and Comparative Biology, University of Naples "Federico II", Naples; 4San Giuseppe Hospital, Service of Pneumology, Milan, Italy Abstract. Apoptosis is intimately involved in placental The human placenta is formed by an inner layer of homeostasis, growth and remodelling, and apoptotic rates mononucleated trophoblasts, called the cytotrophoblast, that increase progressively during normal pregnancy as part of surrounds the blastocoel (1). On direct contact with maternal normal placental development. Moreover, apoptosis increases tissues, the cytotrophoblast fuses to form an outer layer of in pregnancies complicated by some pathologies such as postmitotic multinucleated cells, called the preeclampsia, fetal growth restriction and diabetes. In the syncytiotrophoblast (1, 2), which grows by continued present study, we describe differences in the expression of pro- incorporation of new mononucleated trophoblasts from a apoptotic protein Bax, in first trimester voluntary termination proximal subset of stem cells (3). Some mononucleated of pregnancy, first trimester abortion (reserved abortion), cytotrophoblast cells break through the syncytiotrophoblast caesarean birth, spontaneous birth, preeclampsia and diabetes. and invade the uterine stroma forming the trophoblastic cell We first observed a strong increase of Bax expression in the columns; such cells are called extravillous trophoblasts cytotrophoblast, stroma, endothelial cells and decidua of (EVT) (1).
    [Show full text]
  • 26 April 2010 TE Prepublication Page 1 Nomina Generalia General Terms
    26 April 2010 TE PrePublication Page 1 Nomina generalia General terms E1.0.0.0.0.0.1 Modus reproductionis Reproductive mode E1.0.0.0.0.0.2 Reproductio sexualis Sexual reproduction E1.0.0.0.0.0.3 Viviparitas Viviparity E1.0.0.0.0.0.4 Heterogamia Heterogamy E1.0.0.0.0.0.5 Endogamia Endogamy E1.0.0.0.0.0.6 Sequentia reproductionis Reproductive sequence E1.0.0.0.0.0.7 Ovulatio Ovulation E1.0.0.0.0.0.8 Erectio Erection E1.0.0.0.0.0.9 Coitus Coitus; Sexual intercourse E1.0.0.0.0.0.10 Ejaculatio1 Ejaculation E1.0.0.0.0.0.11 Emissio Emission E1.0.0.0.0.0.12 Ejaculatio vera Ejaculation proper E1.0.0.0.0.0.13 Semen Semen; Ejaculate E1.0.0.0.0.0.14 Inseminatio Insemination E1.0.0.0.0.0.15 Fertilisatio Fertilization E1.0.0.0.0.0.16 Fecundatio Fecundation; Impregnation E1.0.0.0.0.0.17 Superfecundatio Superfecundation E1.0.0.0.0.0.18 Superimpregnatio Superimpregnation E1.0.0.0.0.0.19 Superfetatio Superfetation E1.0.0.0.0.0.20 Ontogenesis Ontogeny E1.0.0.0.0.0.21 Ontogenesis praenatalis Prenatal ontogeny E1.0.0.0.0.0.22 Tempus praenatale; Tempus gestationis Prenatal period; Gestation period E1.0.0.0.0.0.23 Vita praenatalis Prenatal life E1.0.0.0.0.0.24 Vita intrauterina Intra-uterine life E1.0.0.0.0.0.25 Embryogenesis2 Embryogenesis; Embryogeny E1.0.0.0.0.0.26 Fetogenesis3 Fetogenesis E1.0.0.0.0.0.27 Tempus natale Birth period E1.0.0.0.0.0.28 Ontogenesis postnatalis Postnatal ontogeny E1.0.0.0.0.0.29 Vita postnatalis Postnatal life E1.0.1.0.0.0.1 Mensurae embryonicae et fetales4 Embryonic and fetal measurements E1.0.1.0.0.0.2 Aetas a fecundatione5 Fertilization
    [Show full text]
  • Implantation, Bilaminar Embryo. Fetal Membranes, Umbilical Cord
    Implantation, bilaminar embryo. Fetal membranes, umbilical cord. Structure of the placenta, placentar circulation. Events in the female genital tract (1st week) BLASTULATION Within the BLASTOCYST an inner cell mass (ICM) is separated, this contains the EMBRYOBLASTS The surrounding cells form TROPHOBLASTS, they are responsible for the formation of the chorion. HATCHING OF THE BLASTOCYST - enters the uterus 0.1 - 0.2 mm - „hatches" from the zona pellucida The implantation starts 5 - 6 days after the ovulation, the blastula descends into the uterine cavity, then adheres to the endometrium (the trophoblasts produce enzymes which pierce the endometrium) APPOSITION (the embryo turns towards the endometrium with the ICM being deep) - The superficial proteoglycans bind to the cells - hCG, progesterone release grows Pregnancy test!! The glands enlarge The endometrium thickens A richer vascular network grows IMPLANTATION MOLECULAR FACTORS OF IMPLANTATION Events in the wall of the uterus in 2nd week 3-syncytiotrophoblast 4-cytotrophoblast Implantation (embedding) Criteria: • Blastula (stage) • Uterus (endometrium: 19-24. day, „window”) Endometrium, Secretory phase •Str. compactum •Str. spongiosum •Str. basale ----------------- Myometrium Perimetrium Uterus, endometrium decidual transformation!!! STEPS OF IMPLANTATION APPOSITION – the ICM faces the endometrium ADPLANTATION – the endometrial cells grow processes (they swell and catch the blastocyst - reversible binding) ADHESION – the microvilli of the trophoblasta interact with the cells of the endometrium (proteoglycans) irreversible binding DIFFERENTIATION - trophoblast derivatives - syncytiotrophoblast - cytotrophoblast IMPLANTATION – the syncytiotrophoblasts form a syncytiumot and penetrate the membrana basalis as well as the endometrium DECIDUAL REACTION – apoptosis within the endometrial cells, then the stroma cells undergo an epitheloid transformation. The extracellular vacuoles will be filled with blood and merge to form the LACUNAE the invasive growth will be stopped by the zona compacta By week 2.
    [Show full text]
  • VI SEMESTER B. Sc ZOOLOGY PRACTICALS STUDY of EMBRYOLOGICAL SLIDES
    VI SEMESTER B. Sc ZOOLOGY PRACTICALS STUDY OF EMBRYOLOGICAL SLIDES FROG BLASTULA 1. The egg cleaves and forms blastula at 8 cell stage. 2. The blastula contains a blastocoelic cavity surrounded by unequal blastomeres. 3. The smaller blastomeres are called micromeres, found in the upper half and contain dark pigments. 4. The larger blastomeres are called macromeres, found more in the lower half and laden with yolk. 5. The lower side or vegetal hemisphere is composed of large yolky megameres. Because of their large size, the blastocoel is excentric, lying towards the animal pole. CHICK BLASTULA 1. Chick Blastula is known as Discoblastula 2. Discoblastula consists of a disc - shaped mass of blastomeres overlying a large yolk mass. 3. This blastula is the result of meroblastic discoidal cleavage 4. There is no blastocoel, instead a slit like cavity called subgerminal cavity appears in between the blastoderm and the yolk mass. 1 FROG GASTRULA 1. First part of gastrulation is the formation of a blastopore on surface of blastula 2. The cells begin to fold inward 3. Further folding of the blastopore results in a cavity called the archenteron. The future gut 4. Blastopore becomes anus 5. The blastocoel is being displaced 6. Continued morphogenic movements result in enlarging the archenteron, reducing the blastocoel and forming a yolk plug over the blastopore 7. In mature frog gastrula there are three germ layers 8. Ectoderm which are the outer cells, Endoderm which line the archenteron, and mesoderm which is in between endoderm and ectoderm CHICK GASTRULA 1. Gastrulation begins within four or five hours after the onset of incubation 2.
    [Show full text]
  • Reproductive Organs Basics– Differences Between Species
    Reproductive Organs Basics– Differences between Species Klaus Weber, PhD, DVM, MSBiol AnaPath GmbH, Switzerland In Cooperation with BSL Scientific Laboratories GmbH, Planegg, Germany Embryonic Development Type of Eggs (Oocytes) • Oocytes with nucleus and cytoplasm, complete apparatus for synthesis • Special is the deposition of larger amounts if reserve substances = yolk • Rule: as more intense the brood care as less eggs and as more yolk (except mammals with alimentation by materna organism) Cleavage: Cygote to Blastula • Cell division without gowth • No differentiation at beginning • aegual/in-aequal cleavage (depending on distribution of yolk), discoidal, superficial • holoblastic (complete) cleavage: bilateral (nematodes, chordates) , radial (porifers, echinodermates), rotational (mammals) , and spiral (turbellaria, annelides, molluscs) • Morula • Blastula – hollow sphere of cells (cells of wall more or less of same size) filled with fluid (exceptions are blastulas of e.g. coelenterates with compact sterroblastula) Relationship: Oocyte and Cleavage a- or equal oligolecithal Echinodermates Branchiostomata total in- equal many Avertebrates telolecithal and Amphibia Cephalopoda, discoidal Fish, Sauropsida total super- Arthropodes centrolecithal ficial Blastopore • Opening into the archenteron • Primitive gut • In protostome development, the blastopore, becomes the animal's mouth (nematodes, plathelminths, molluscs etc). • In deuterostome development, the blastopore becomes the animal's anus (echinodermates, chordates). http://waynesword.palomar.edu/images/gastru1.gif Cleavage: Gastrula • Reorganization of single-layered blastula into three- layered structure. • Ectoderm gives rise to epidermis, neural crest, nervous system. • Mesoderm gives rise to somites, which form muscle; cartilage of ribs/vertebrae; dermis, notochord, blood/vessels, bone, connective tissue. • Endoderm gives rise to epithelium of digestive system and respiratory system, liver and pancreas. • Following gastrulation, cells in the body are organized into sheets of connected cells (e.g.
    [Show full text]
  • 17. Formation and Role of Placenta
    17. FORMATION AND ROLE OF PLACENTA Joan W. Witkin, PhD Dept. Anatomy & Cell Biology, P&S 12-432 Tel: 305-1613 e-mail: [email protected] READING: Larsen, 3rd ed. pp. 20-22, 37-44 (fig. 2-7, p. 45), pp. 481-490 SUMMARY: As the developing blastocyst hatches from the zona pellucida (day 5-6 post fertilization) it has increasing nutritional needs. These are met by the development of an association with the uterine wall into which it implants. A series of synchronized morphological and biochemical changes occur in the embryo and the endometrium. The final product of this is the placenta, a temporary organ that affords physiological exchange, but no direct connection between the maternal circulation and that of the embryo. Initially cells in the outer layer of the blastocyst, the trophoblast, differentiate producing an overlying syncytial layer that adheres to the endometrium. The embryo then commences its interstitial implantation as cells of the syncytiotrophoblast pass between the endometrial epithelial cells and penetrate the decidualized endometrium. The invading embryo is first nourished by secretions of the endometrial glands. Subsequently the enlarging syncytiotrophoblast develops spaces that anastomose with maternal vascular sinusoids, forming the first (lacunar) uteroplacental circulation. The villous placental circulation then develops as fingers of cytotrophoblast with its overlying syncytiotrophoblast (primary villi) extend from the chorion into the maternal blood space. The primary villi become secondary villi as they are invaded by extraembryonic mesoderm and finally tertiary villi as embryonic blood vessels develop within them. During the first trimester of pregnancy cytotrophoblasts partially occlude the uterine vessels such that only plasma circulates in the intervillous space.
    [Show full text]
  • Pre-Implantation Mammalian Development and Derivation of Embryonic Stem Cells (HS Lecture 1)
    Pre-implantation mammalian development and derivation of embryonic stem cells (HS lecture 1) The mouse is not an immediately obvious choice of model system for developmental biology. Its embryos are small, develop relatively slowly and are inaccessible to experimental manipulation because most of development must take place in utero. However, mice are at least as easy to study as any other eutherian (placental - not marsupial) mammal and, being mammals ourselves, we have a particular interest in understanding mammalian development. The early stages of mammalian development are quite different from those of other vertebrates such as Xenopus and so need to be studied in a mammal. Moreover, mouse genetics is comparatively well developed (lots of mutants) and techniques exist for manipulating gene function (knocking genes out and turning them on), which are not available in any other model vertebrate. Early mouse development The fertilized egg divides and develops as it travels along the oviduct to the uterus. In mice this process takes 4-5 days.The egg has a protective membrane, the zona pellucida, which stops it from implanting in the oviduct wall. By the time it reaches the uterus the egg has undergone many cell divisions to form a blastocyst, which hatches from the zona to implant into the uterine wall. Pre-implantation mouse development can be studied in culture - prior to implantation embryos can survive and can develop in liquid media. One reason mammalian early development is different from that of other vertebrates is that the extra-embryonic membranes (amnion and chorion) play a much more important role (they generate much of the placenta).
    [Show full text]