Bms

• Embryology


  The study of the development of an organism from fertilization through birth

  
• Significance of embryology


  • Beginning of human beings
  • Background for understanding adult structures - gross anatomy
  • Congenital malformations – teratology (gene therapy)
  • Various related fields – obstetrics, pediatrics, pediatric surgery
• Developmental anatomy


  The study of the development of the structure of an organism
• Embryo


  The early stage of development of a multicellular organism, before the major features have developed

  
• Fetus


  The unborn offspring in the postembryonic period, from the ninth week after conception to birth

  
• Stages of pregnancy


  • Embryonic development (fertilization - 8 weeks)
  • Fetal development (9 weeks - birth)
  • Postnatal Development (birth to maturity)

  
• Prenatal Development


  The development that occurs before birth, including both embryonic and fetal development

  
• Embryonic and Fetal Development

  1. Division and differentiation of cells

  2. Changes that produce and modify anatomical structures
• Stages of embryonic development

  • Embryonic Period (fertilization - 8 weeks)
  • Fetal Period (9 weeks - birth)

  
• First trimester


  The first 3 months of pregnancy, when the embryo develops its basic structures

  
• Second trimester


  The middle 3 months of pregnancy, when the fetus grows and develops

  
• Third trimester


  The final 3 months of pregnancy, when the fetus grows rapidly and prepares for birth

  
• Gametogenesis


  1. Spermatogenesis

  2. Oogenesis
• Fertilization


  1. Sperm capacitation

  2. Acrosomal reaction

  3. Fusion of gametes
• Early embryonic development


  1. Cleavage

  2. Morula formation

  3. Blastocyst formation

  
• Implantation


  Attachment of blastocyst to uterine wall
• Gastrulation


  1. Formation of primitive streak

  2. Migration of cells from epiblast to form ectoderm, mesoderm and endoderm
• Notochord


  The primitive axial skeleton that induces the formation of the neural tube
• Neurulation


  Formation of the neural plate, neural folds and neural tube
• Primary germ layers


  • Ectoderm
  • Mesoderm
  • Endoderm
• Somite


  A block of mesoderm that develops into the vertebrae, ribs, and skeletal muscles of the trunk
• Cardiovascular system development


  1. Formation of primordial heart tubes

  2. Heartbeat detection
• Embryo folding


  1. Longitudinal (cephalocaudal) folding

  2. Lateral (transverse) folding
• Lateral plate mesoderm splits into

  1. Somatic mesoderm (cover amnion)

  2. Splanchnic (visceral) mesoderm (cover yolk sac)
• Intraembryonic coelom


  Will become body cavity (Peritoneal cavity, Pericardial cavity, Pleural cavity)
• Primordial Cardiovascular System is the first system to start functioning in the embryo
• Primordial heart tubes develop

  During 3rd week
• Heartbeat can be detected 7 weeks after last menstrual period
• Folding of the embryo

  1. Longitudinal (cephalocaudal)

  2. Lateral (transverse)
• Head fold


  Causes the heart tube to move anteriorly and enter the pericardial cavity
• Head fold


  Causes the yolk sac to be incorporated into the embryo, forming the foregut
• Tail fold


  Forms the hindgut
• Lateral fold


  • 1. Forms the midgut
  • 2. Intraembryonic coelom surrounds the gut tube
  • 3. Vitelline duct forms as the connection between intra- and extra-embryonic coelom narrows
• Fetal membranes


  • Amnion
  • Chorion
  • Yolk sac
  • Allantois
• Yolk sac


  First extraembryonic membrane to appear (day 10), site of early blood cell formation

  
• Amnion


  Membrane that lines the amniotic sac and protects the embryo, forms from the germ layers but is not part of the embryo
• Allantois


  Develops during week 3, forms the urinary bladder
• Chorion

  Derived from trophoblast of blastocyst and mesoderm, surrounds the embryo early on and later forms the embryonic part of the placenta

  
• Placenta


  • Maternal portion (endometrium of uterus)
  • Fetal portion (chorion)
• Placental hormones


  • Relaxin
  • Human placental lactogen
  • Placental prolactin
  • Corticotropin-releasing hormone