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History of embryology

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History of embryology

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History of embryology

  1. 1. Outline  History  Definition of Embryology  Techniques used in Prenatal Screening (Humans)  Other concepts in embryology  Techniques used in the study of Embryonic Development
  2. 2. History  Embryonic development has been a source of wonder…  Aristotle’s (384-322 B.C.) studies –a shift from superstitions to observation.  Galen (130-200 A.D) – learned about advanced fetuses but the minute dimensions resisted analysis
  3. 3.  caused a lag in the growth of knowledge about the embryo until the development of microscope.  De Graaf in 1672 – described ovarian follicle  Hamm and Leeuwenhoek in 1677 – have seen the sperm cells  significance were not understood
  4. 4. Theory of Preformation  Spermists - sperm contained new individual in miniature and only nourished in the ovum  Ovists- thought the same and that the seminal fluid only stimulates it.  Bonnet (1745) – discovered eggs of some insects undergoing parthenogenesis  Spallanzani (1729-1799) – demonstrated that both male and female sex products are necessary for the initiation of development
  5. 5.  Wolff (1733–1794) – thesis on epigenesis (embryological development occurs through progressive growth and differentiation)  Von Baer (1828) – discovered mammalian egg, first emphasized that the more general basic features of any animal group appear earlier in the development than do special features of different members of the group – von Baer’s law  Demonstrated existence of germ layers
  6. 6.  The formulation of cell theory by Matthias Schleiden and Theodore Schwann laid down the foundation of modern embryology as a science.  Ernst Haeckel (1834 -1919) – drafted the Biogenetic Law of Muller and Haeckel – Haeckel’s Law of Recapitulation  Ontogeny recapitulates phylogeny  Tail in vertebrates
  7. 7. Embryology as a science  Embryology- study of animal development between fertilization and birth  May include gametogenesis  Weismann (1834-1914) – distinguished between soma and germ cell
  8. 8. Special Fields  Descriptive embryology (1880-1890) – serial sections and three dimensional wax plate reconstruction  computer softwares  Comparative embryology (late 1800s) – provided insights on recapitulation theory; started with invertebrates (evolution)
  9. 9.  Experimental – directed to causative factors that regulate developmental processes.  Chemical embryology – information about the chemical and physiological events in the embryo.  Included the role of DNA and RNA - how it fabricates specific chemical and structural components of embryo
  10. 10.  Teratology – concerned with the study of malformations  Reproductive biology – problems of conception and contraception  Developmental biology – approach, includes even postnatal processes.
  11. 11. Prenatal Diagnosis  Designed to detect  Malformations  genetic abnormalities  overall fetal growth  complications of pregnancy, such as placental or uterine abnormalities.  “Their use and development of in utero therapies have heralded a new concept in which the fetus is now a patient. “
  12. 12. Ultrasound  may be transabdominal or transvaginal (produces images with higher resolution)  developed in the 1950s- advanced to detection of blood flow , movement of heart valves, fluid flow in the trachea and bronchi  safe and commonly used, with approximately 80% of pregnant women US
  13. 13. Ultra…  Parameters revealed :  characteristics of fetal age and growth  presence or absence of congenital anomalies  status of the uterine environment, including the amount of amniotic fluid (Fig. 7.4A);  placental position and umbilical blood flow;  whether multiple gestations are present (Fig.7.4B).  Among the factors used to determine proper approaches for management of the pregnancy.
  14. 14.  Fetal age and growth assessed by:  crown-rump length during the fifth to tenth weeks of gestation.  combination of measurements, including the biparietal diameter (BPD) of the skull, femur length, and abdominal circumference (Fig. 7.5).  Multiple measures of these parameters over time improve the ability to determine the extent of fetal growth.
  15. 15.  Congenital malformations determined by ultrasound:  the neural tube defects anencephaly and spina bifida  abdominal wall defects, such as omphalocele and gastroschisis ;  Heart defects  facial defects (cleft lip and palate).
  16. 16. Maternal Serum Screening  In search for biochemical markers of fetal status  first of these tests assessed serum alpha- fetoprotein (AFP)concentrations.  AFP produced normally by the fetal liver, peaks at approximately 14 weeks, and “leaks” into the maternal circulation via the placenta.
  17. 17.  AFP conc. increase in maternal serum in the second trim; begin a steady decline after 30 weeks of gestation.  AFP levels increase in amniotic fluid and maternal serum in  neural tube defects and other abnormalities i.e omphalocele, gastroschisis, bladder exstrophy, amniotic band syndrome, sacro-coccygeal teratoma, and intestinal atresia,
  18. 18.  AFP conc. decrease in Down syndrome, trisomy 18, sex chromosome abnormalities, and triploidy.  During amniocentesis, a needle is inserted transabdominally into the amniotic cavity (identified by ultrasound; Fig. 7.4A) and approximately 20 to 30 ml of fluid are withdrawn.
  19. 19. Amniocentesis  a needle is inserted transabdominally into the amniotic cavity (identified by ultrasound; Fig. 7.4A)  20 to 30 ml of fluid are withdrawn.  not usually performed before 14 weeks gestation  risk of fetal loss 1%
  20. 20.  fluid analyzed for AFP and acetyl- cholinesterase  fetal cells in the amniotic fluid recovered for metaphase karyotyping and other genetic analyses  major chromosomal alterations, such as translocations, breaks, trisomies, and monosomies, can be identified.
  21. 21. THE HUMAN CHROMOSOMES
  22. 22. Chorionic villus sampling  CVS involves inserting a needle transabdominally or transvaginally into the placental mass and aspirating approximately 5 to 30 mg of villus tissue  Reserved only for high risk pregnancy
  23. 23. Fetal Therapy  FETAL TRANSFUSION  In cases of fetal anemia produced by maternal antibodies or other causes, blood transfusions for the fetus can be performed. Ultrasound is used to guide insertion of a needle into the umbilical cord vein, and blood is transfused directly into the fetus.
  24. 24.  FETAL MEDICAL TREATMENT  Treatment for infections, fetal cardiac arrhythmias, compromised thyroid function, and other medical problems is usually provided to the mother and reaches the fetal compartment after crossing the placenta. In some cases, however, agents may be administered to the fetus directly by intramuscular injection into the gluteal region or via the umbilical vein.
  25. 25.  FETAL SURGERY  Because of advances in ultrasound and surgical procedures, operating on fetuses has become possible.  “Modern medicine has also made the fetus a patient who can receive treatment, such as transfusions, medications for disease, fetal surgery, and gene therapy.”  www.scribd.com/doc/7733260/Langmans-Medical-Embryology
  26. 26. Other concepts in Embryology  Totipotency – capability to form all possible types of cells - zygote  Pluripotency – all possible cell types with some exceptions – placental stem cells  Multipotency – multiple types of cells but not all possible types – adult stem cells  Monopotency – one particular cell type - monocyte
  27. 27.  Gurdon and colleagues use somatic cells of Xenopus to show somatic pluripotency
  28. 28. Types of Stem Cell Source Potency 1. Early Embryonic Stem Cell Newly fertilized egg that starts to divide TOTIPOTENT! They can become any kind of cell in the body 2. Blastocyst Embryonic Stem Cell Inner cell mass of blastocyst (7 days after fertilization) PLURIPOTENT! they have the ability to become almost any kind of cell in the body 3. Fetal Stem Cell Fetus ( 8 weeks after fertilization) PLURIPOTENT! 4. Umbilical Cord Stem Cell Blood from the umbilical cord MULTIPOTENT! can differentiate into only a limited range of cell types (blood & immune cells) 5. Adult Stem Cell From developed tissues UNIPOTENT! MULTIPOTENT!
  29. 29.  Restriction - reduction of developmental options  Determination – commitment to single developmental fate  Formation of cornea  Differentiation – formation of specialized cell
  30. 30.  Restriction of ectoderm
  31. 31. Mammals
  32. 32.  Morphogenesis – entire group of processes that mold internal and external configuration of an embryo (axes)  Role of homeotic genes
  33. 33.  Apoptosis - genetically determined cell death  Induction – embryonic signal calling; effect of embryonic tissue on another  Regulation  Morphogenetic fields  Regeneration
  34. 34.  Recapitulation - Biogenetic law  Growth  Differential growth  Determinate growth  Indeterminate growth
  35. 35. Methods in the Embryology  Microcinematography  Fixed Material  Histochemical Methods – chem. activity  Autoradiography - isotopes  In situ hybridization – for RNA  Tracing Methods – using dyes  HRP - injected  Japanese quail cells  Retroviruses – carry reporter gene
  36. 36.  Immunological  Microsurgical  Ablation  Transplantation  Explantation  Autografting  Heterografting  Xenografting
  37. 37.  Culture techniques  Biochemical and molecular techniques  Isoenzymes  PCR  Irradiation techniques  Use of mutants  Transgenic animals
  38. 38. References  Carlson B.M. 2003. Patten’s Foundations of Embryology. 6th Ed. New York: McGraw-Hill, Inc. Book Company  www.scribd.com/doc/7733260/langmans-medical -embryology

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