done - chapter 5

• Cleavage


  • Zygote formation
  • Journey from fallopian tubes to uterus
  • Rapid cell divisions
  • Turns single cell zygote into embryo

  
• Types of cleavage

  • Indeterminate cleavage
  • Determinate cleavage
• Indeterminate cleavage

  • Each cell has potential to develop into any cell type
• Determinate cleavage

  • Fate is predetermined and each cell can only turn into one type of cell
• First 3 cleavages happen at 32, 60, 72 hours after fertilization


  • 8 celled embryo reaches uterus as a result
• Morula


  • Embryo after more divisions
  • Solid ball of cells

  
• Blastulation

  • Morula becomes blastula (hollow sphere)
  • Characterized by blastocoel (fluid filled cavity)

• Main cell groups

  • trophoblast
  • Inner cell mass
• Trophoblast

  • Forms outer layer, which becomes placenta
• Inner cell mass

  • Group of cells located inside the blastula that form the actual embryo
• Implantation

  • Zygote becomes embryo
  • Travels to uterus
  • Blastocyst implants into uterine lining (endometrium)
• Implantation occurs 8 days after fertilization
• Progesterone

  Hormone that prepares uterine lining for embryo attachment
• Implantation allows embryo to connect with mother's blood supply and get nutrients/oxygen
• Gastrulation

  Forms 3 distinct layers
• Germ layers

  • Ectoderm
  • Mesoderm
  • Endoderm
• Ectoderm

  Outer layer forms skin, hair, nails, nervous system
• Mesoderm

  Middle layer forms muscles, bones, circulatory system, other internal structures
• Endoderm

  Inner layer forms lining of digestive/respiratory systems, parts of organs like liver and pancreas
• Selective transcription

  Process by which cells become different types using genes only needed for their specific function
• Inducers

  Chemical signals that influence nearby cells to change their development or behavior
• Neurulation

  1. Development of nervous system

  2. Comes from outer layer (ectoderm)
• Neurulation steps

  • Notochord formation
  • Neural folds and groove
  • Neural tube
  • Neural crest cells

  
• Fetal respiration

  • Involves placenta and umbilical cord handling nutrients and gas exchange between mother and fetus
• Chorion

  Membrane formed by placenta that connects fetus through umbilical cord
• Placenta provides fetus with necessary oxygen and nutrients
• Membranes surrounding fetus

  • Allantois
  • Amnion
  • Yolk sac
• Allantois

  Early fluid exchange
• Amnion

  Fluid that protects fetus like a cushion
• Yolk sac

  Important for early blood vessel formation
• Placenta allows nutrients and waste to move between mother and fetus without mixing their blood
• Higher concentration of oxygen is in maternal blood
• Fetal hemoglobin binds more strongly to adult hemoglobin
• Placenta protects fetus from many infections and harmful substances
• Fetus relies on placenta for oxygen as lungs are not yet functioning
• Oxygen comes from mother's blood via the placenta
• Fetal shunts

  • Foramen ovale
  • Ductus arteriosus
  • Ductus venosus
• Foramen ovale

  Allows blood to flow directly from the right atrium to the left atrium, bypassing right ventricle and lungs
• Ductus arteriosus

  Directs leftover blood from pulmonary artery to the aorta, bypassing the lungs
• Ductus venosus

  Directs blood from the umbilical vein to the inferior vena cava, bypassing the liver