Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Human Embryology II


Published on

Human Embryology Histology lecture 2 by Professor Tatiana Bororinkina, First Moscow State Medical University I.M. Sechenov, Moscow, Russia

Published in: Health & Medicine
  • Be the first to comment

Human Embryology II

  1. 1. Human Embryology II
  2. 2. Embryonic period – the third week of development  The 2nd stage of gastrulation  Germ layer initial differentiation and axial organ formation  Primitive cardiovascular system formation  Subsequent chorion development  Allantois appearance  Folding
  3. 3. The second stage of gastrulation  results in - trilaminar embryonic disk formation  occurs - on the 14th to 15th day of development
  4. 4. Only epiblast participates in the 2nd stage of gastrulation Hypoblast does not take part in the embryo body formation  Epiblast gives rise to embryonic - ectoderm - endoderm - mesoderm  Hypoblast is displaced to - extraembryonic regions
  5. 5. Primitive streak is the key structure of the 2nd stage of gastrulation  Epiblastic cells at the disk cranial end - proliferate - migrate along the disk margins - converge at the disk caudal end - turn back to the disk cranial end towards the midline ß primitive streak Þ cranial end caudal end
  6. 6. Primitive streak anterior portion thickens to form the primitive knot or Hensen’s nodule  Primitive groove - develops in the primitive streak - is continuous with the primitive pit in the primitive knot Û
  7. 7. Primitive streak is a source of the embryonic mesoderm and embryonic endoderm  Primitive streak cells migrate Þ - into the primitive groove - inwardly between the epiblast and hypoblast early-migrating cells Þ endoderm later-migrating cells Þ mesoderm
  8. 8. Gastrulation is completed with the trilaminar disk formation  As soon as the primitive streak gives rise to - embryonic endoderm - embryonic mesoderm Û remaining epiblastic cells are referred to as - embryonic ectoderm
  9. 9. Duplication of the primitive streak results in twinning Удв оен ие Ü duplication of the primitive streak Ü monochorial monoamniotic twins ~30% ~70% ~4%
  10. 10. Conjoint twins (~1% of monozygotic twins) result from the primitive streak duplication partial duplication of the primitive streak (Y-shaped) ß complete duplication of the primitive streak but incomplete duplication of the germ layers ß bifurcation of the spinal cord and vertebral column fusion of soft tissues (Siamese twins)
  11. 11. Siamese twins  may be separated surgically Þ
  12. 12. Initial germ layer differentiation and the axial organ formation  Complex of the axial organs includes - notochord - neural tube - mesodermal somites
  13. 13. Notochord is the first to appear concurrently with mesoderm  Primitive pit - extends into the primitive knot - forms the notochordal canal  Primitive knot cells - migrate through the canal - give rise to the notochord
  14. 14. Notochordal process looks like a cellular rod  extends - cranially from the primitive knot - between the ectoderm and endoderm wing-like mesoderm is on each side of the notochord Ü Þ
  15. 15. Notochord forms the embryo midline axis around which the vertebral column develops  Notochord - disappears where it becomes surrounded by the vertebral bodies - persists as the nucleus pulposus of the intervertebral disks - induces the overlying ectoderm to form the neural plate Þ
  16. 16. Neurulation or the neural tube formation is induced by the notochord with the adjacent mesoderm Stages of the neural tube development  neural plate (15 – 16 days)  neural groove and neural folds (18 – 21 days)  neural tube (23 – 25 day) Û
  17. 17. Neuroectoderm includes the neural tube and neural crest  Neural tube ß Brain Spinal cord Retina Olfactory epithelium  Neural crest ß Neural ganglia Pia mater and arachnoid Skin melanocytes Adrenal medulla Thyroid gland C-cells
  18. 18. Surface ectoderm remains after the neural tube separation  Gives rise to - skin epidermis - sweat and sebaceous glands - nails and hair - mammary glands - salivary glands - tooth enamel - oral cavity epithelium - corneal epithelium
  19. 19. Mesoderm subdivision  Paraxial mesoderm Þ somites - myotome - dermotome - sclerotome  Intermediate mesoderm (somite cord) Þ nephrogonadotome  Lateral mesoderm Þ parietal layer or somatopleure visceral layer or splanchnopleure Ü coelom in the lateral mesoderm
  20. 20. Subsequent mesoderm differentiation  Myotome Þ skeletal muscles  Dermatome Þ skin dermis  Sclerotome Þ bones and cartilages  Nephrogonadotome Þ kidney and gonads  Coelom Þ - pericardial - pleural - peritoneal cavities  Somatopleure Þ mesothelium  Splanchnopleure Þ - mesothelium - myocardium - epicardium - adrenal cortex Þ
  21. 21. Some mesodermal cells migrate and become mesenchyme  Mesenchyme gives rise to - blood - blood and lymphatic vessels - all types of connective tissue - smooth muscle cells - microglial cells - endocardium
  22. 22. Embryonic endoderm differentiation  Gastrointestinal tract epithelium  Pancreas parenchyma  Liver parenchyma  Gallbladder epithelium  Lung epithelial parts
  23. 23. Primitive cardiovascular system formation  Angiogenesis begins in the provisory organs - yolk sac - connecting stalk - chorion
  24. 24. Embryonic vessels begin to develop about two days later  embryonic vessels and primitive heart arise from the mesenchyme
  25. 25. Angiogenesis and hemopoiesis occur concurrently  Primitive blood cells - differentiate from mesenchyme - inside the embryonic vessels ß intravascular hemopoiesis
  26. 26. Cardiovascular system is the first system to attain a functional state - by the end of the 3rd week  сhorionic and embryonic vessels become connected via the connecting stalk Û
  27. 27. Chorionic villi become tertiary villi  Composition of tertiary villi - syncytiotrophoblast - cytotrophoblast - extraembryonic mesoderm - chorionic blood vessels ß
  28. 28. Chorionic villi provide maternal-fetal blood exchange  are bathed by maternal blood from lacunae  Chorionic villi are - stem or anchoring villi - branch villi
  29. 29. Allantois appears on the 16th day of embryonic development  is a finger-like projection - of an embryo endoderm - into the connecting stalk
  30. 30. Allantois exists for two months Its remnant will be a part of the umbilical cord  Allantois is involved in - blood formation - angiogenesis - the urinary bladder development
  31. 31. Folding – the body fold formation  begins on the 21st day of development  There are two pairs of folds - longitudinal folds - transversal folds
  32. 32. Longitudinal – cranial and caudal - folds  convert the embryonic disk into C-shaped structure ß
  33. 33. Transversal folds  include - surface ectoderm - somatopleure - splanchnopleure - endoderm  move down to meet each other  converge below the embryo body
  34. 34. Transversal fold results  embryonic disk is converted to a cylinder-like structure Û
  35. 35. Folding consequences  Embryo acquires - cylindrical C-like body shape - primitive gut  . . . and separates - from the yolk sac
  36. 36. Embryonic period from the 4th to the 8th weeks  All tissues and organs differentiate, develop, and begin to function 7th week embryo Û  The period is the most critical period of embryogenesis because any disturbances may give rise to congenital malformations
  37. 37. Placentation or placenta development  begins after implantation  is completed by the 8th week Û
  38. 38. Embryo by the 8th week – the end of the embryonic period  is disposed in the amnion and bathed by amniotic fluid  amnion fills the chorionic cavity Þ  amniotic wall underlies the chorion Ü  chorion fills the uterine cavity  uterine cavity obliterates  umbilical cord connects the embryo and chorion
  39. 39. Umbilical cord arises from the connecting stalk  contains - two arteries - a vein - mucoid connective tissue - remnants of the yolk sac and allantois  is covered by amniotic epithelium
  40. 40. Umbilical cord functions to connect  fetal cardiovascular system with chorionic vessels
  41. 41. Endometrium in pregnancy is called the decidua graviditas  Decidua basalis - underlies the implantation site  Decidua capsularis - covers the implantation site  Decidua parietalis - remaining endometrium
  42. 42. Endometrium by the 8th week of development  Decidua basalis - takes part in placenta formation  Decidua capsularis - fuses with decidua parietalis when the uterine cavity obliterates
  43. 43. Chorion by the 8th week of development is subdivided into  Smooth chorion - almost lacks villi - is associated with the decidua capsularis  Villous chorion - possesses large and branched villi - is associated with the decidua basalis
  44. 44. Smooth chorion is one of the amniochorionic membranes  that form the fetal bladder wall - amnion wall - smooth chorion - decidua capsularis
  45. 45. Villous chorion or chorion frondosum  takes part in placenta formation
  46. 46. Placenta is a combined organ  is formed by - maternal body – the decidua basalis - fetal body – the villous chorion  Two placental parts are involved in the maternal-fetal circulation exchange Þ
  47. 47. Human placenta is discoid in shape  It is determined by the circular form of the villous chorion fetal part Þ Ü maternal part placenta after parturition
  48. 48. Fetal part of placenta  Chorionic plate  Tertiary villi  Umbilical cord is attached to the fetal surface  Amniotic epithelium surrounds the umbilical cord and covers the fetal placenta part
  49. 49. Chorionic plate  is a layer of extraembryonic connective tissue  contains blood vessels coming from the umbilical cord  is covered with amniotic epithelium  gives rise to chorionic villi Ü
  50. 50. Chorionic villi arise from the chorionic plate  project into intervillous spaces or lacunae  are bathed by maternal blood Û
  51. 51. Chorion attaches itself to the decidua basalis  Stem or anchoring villi - are attached to the endometrium - form cytotrophoblastic shell at the site of attachment  Branch or floating villi - arise from the stem villi - float in lacunae with maternal blood - provide the main fetoplacental exchange
  52. 52. Chorionic villi are tertiary villi  syncytiotrophoblast  cytotrophoblast  extraembryonic mesoderm  villous blood vessels villi are bathed by the maternal blood Ü
  53. 53. Fibrinoid material arises from the decidua basalis necrosis  results from the syncytiotrophoblast enzyme activity  contains fibrin and immunoglobulins  covers villi and the endometrium  separates the fetal tissues from maternal tissues  takes part in immune defence
  54. 54. Maternal part of placenta  Decidua basalis with decidual cells  Placental septa  Lacunae with maternal blood
  55. 55. Decidua basalis  is a layer of the lamina propria connective tissue  contains ruptured blood vessels and gland remnants Û  is underlined by the decidual plate - remains after parturition - is involved in the endometrium regeneration
  56. 56. Decidual cells result from decidual reaction  arise from the endometrial stromal cells  are rich in glycogen and lipids  Functions Þ - restrict the trophoblast invasion - provide some nourishment for the embryo and fetus - create a layer of the placenta separation in parturition - secrete hormone relaxin responsible for the cervix softening Ý
  57. 57. Placental septa are wedge-like areas of the endometrium  project from the decidua basalis to the chorionic plate (never attach themselves)  divide placenta into 15 to 20 lobules – cotyledons Cotyledon includes - two or more stem villi - numerous branch villi
  58. 58. Cotyledons are visible on the placenta maternal surface maternal part Ü fetal part placenta after parturition
  59. 59. Lacunae or intervillous spaces  result from syncytiotrophoblast enzymatic activity  contain maternal blood  surround chorionic villi  communicate with each other Û
  60. 60. Uteroplacental circulatory system  Maternal blood - enters the placenta through ruptured spiral arteries - flows into the intervillous spaces - circulates in the intervillous spaces - leaves the placenta through the endometrial veins - brings O2 and nutrients - carries away CO2 and waste products
  61. 61. Fetal blood enters the placenta through  paired umbilical arteries ß  chorionic plate vessels ß  chorionic villus vessels ß  a single umbilical vein Ü capillary network in the small branch villi - is in close association with maternal blood-filled lacunae - takes part in fetal-maternal blood exchange
  62. 62. Placental barrier separates fetal blood and maternal blood  includes only fetal tissues - syncytiotrophoblast - cytotrophoblast - trophoblastic basal membrane - villous connective tissue - villous capillary wall Þ Ü fetal blood never mixes with maternal blood
  63. 63. Placental barrier ultrastructure  Syncytiotrophoblast  Cytotrophoblast  Trophoblastic basal membrane  Endothelium basal membrane  Endothelial cells ß Þ ß ß Ý
  64. 64. Placental barrier by the last trimester of pregnancy  becomes very thin, facilitating maternal-fetal exchange  lacks - cytotrophoblast (degenerates) - connective tissue (disappears)  includes Ý - syncytiotrophoblast - villous capillary wall Þ
  65. 65. Placenta functions  Selective fetal-maternal blood exchange - gases, water, electrolytes - nutrients, hormones, antibodies - medicine, drugs, infection agents  Synthesis of some nutrients - glycogen, cholesterol, fatty acids  Release of enzymes to erode the endometrium  Hormone production - progesterone, estrogens, - human chorionic gonadotropin (hCG) - human placental lactogen (hPL) Ý - relaxin hCG in the villus syncytiotriophoblast
  66. 66. The End Thank you for attention!