embryology

• What is the link to the helpful video in Module Information?

  https://www.youtube.com/watch?v=yXUv4MPuNTA
• What are the terms used in embryology nomenclature?


  • Rostral (cranial/superior) = head end
  • Caudal (inferior) = tail end
  • Dorsal (posterior) = back
  • Ventral (anterior) = front
  • Proximal = near body center
  • Distal = further from body center
• What are the stages of human development and their time frames?

  1. Pre-embryonic: Day 1 to Week 3
  2. Embryonic: Weeks 3 to 8
  3. Foetal: Week 8 to Birth
• What is fertilisation in human development?


  It is the process where a sperm fuses with an ovum, creating a zygote.
• What are gametes?


  Gametes are sex (or “germ”) cells: sperm and ovum.
• What is the largest single biological cell known to scientists?

  The ovum (mature egg).
• What does haploid mean?


  It means containing a single chromosome set (23 chromosomes).
• What does diploid mean?


  It means containing two sets of chromosomes (23 from each parent, totaling 46).
• What is a zygote?


  A zygote is a fertilised egg with 46 chromosomes.
• What are the steps involved in fertilisation?

  1. Sperm dissolves and penetrates the zona pellucida of the oocyte.
  2. Sperm head fuses with the oocyte's plasma membrane.
  3. Pronuclei from the ovum and sperm fuse to form a diploid nucleus.
  4. The diploid cell is now called a zygote.
• What occurs from fertilisation to implantation?

  1. Fertilisation occurs 12-24 hours after ovulation.
  2. Cleavage begins (2-cell stage on Day 1).
  3. Morula forms (solid ball of cells on Day 4).
  4. Blastocyst forms (Day 5).
  5. Implantation occurs (Day 6).
• What is the morula?


  The morula is a solid ball of cells formed by Day 4.
• What happens during cleavage?


  Cleavage involves rapid mitotic divisions of the zygote.
• When does the first cleavage occur?


  The first cleavage starts at 24 hours after fertilisation.
• What is the blastocyst?


  The blastocyst is a structure formed from the morula that contains an inner cell mass and a trophoblast.
• What are the two cell populations that arise from the blastocyst?


  1. Embryoblast (Inner Cell Mass, ICM) - will become the embryo.
  2. Trophoblast - will become the outer chorionic sac.
• What is the role of the trophoblast?


  The trophoblast forms the placenta and facilitates nutrient/waste exchange between mother and embryo.
• What happens to the zona pellucida during implantation?


  The zona pellucida disintegrates and is replaced by trophoblasts.
• What occurs during implantation?

  1. The blastocyst hatches from the zona pellucida.
  2. It attaches to the endometrium by Day 6.
  3. The endometrium becomes more vascularised.
  4. The blastocyst secretes enzymes and burrows into the endometrium.
• What is the bilaminar embryonic disc?


  The bilaminar embryonic disc is formed from the epiblast and hypoblast layers.
• What are the two layers formed from the trophoblast and inner cell mass?


  1. Trophoblast forms:

  • Cytotrophoblast
  • Syncytiotrophoblast

  1. Inner cell mass forms:

  • Epiblast
  • Hypoblast
• What is the role of the epiblast?


  The epiblast forms the three germ layers and some extra-embryonic membranes.
• What is the function of the yolk sac?


  The yolk sac provides nutrients and shrinks by the end of the third trimester.
• What is gastrulation?


  • It is the process that replaces the hypoblast layer with the endoderm germ layer.
  • It forms a trilaminar structure called the gastrula.
  • It generates the three germ layers: ectoderm, mesoderm, and endoderm.
• What are the three germ layers formed during gastrulation?


  1. Ectoderm
  2. Mesoderm
  3. Endoderm
• What does the ectoderm develop into?


  • Epidermis (skin)
  • Nervous system (PNS, CNS)
  • Retina, nose, and ears
• What does the mesoderm develop into?


  • Dermis, bones, cartilage, connective tissue
  • Cardiovascular, reproductive, lymphatic systems
  • Muscle (striated, smooth, cardiac), kidneys, and spleen
• What does the endoderm develop into?


  • Epithelial lining of gut, lungs, and respiratory tract
  • Epithelia of urethra and bladder, thyroid, tonsils, thymus
  • Liver and pancreas
• What is the significance of the primitive streak during gastrulation?


  The primitive streak establishes the embryo's body axis and forms the endoderm and mesoderm layers.
• How does the structure of the mesoderm differ from the ectoderm and endoderm during gastrulation?


  The mesoderm is less organized with cells more loosely connected compared to the tightly-connected epithelial sheets of the ectoderm and endoderm.
• What is the next process after gastrulation?


  • Neurulation
  • Formation of the neural tube
  • Development of the nervous system
• What is the link to the gastrulation video?


  https://www.youtube.com/watch?v=3AOoikTEfeo&t=24s
• What resources are available for learning about embryonic folding?


  • Neurulation video
  • Chapter 29 of Tortora
  • Detailed animations in Module Information of GCU