Gastrulation | what happens during gastrulation? | week 3 of embryonic development

00:11:18
https://www.youtube.com/watch?v=g75Q4-nRk_0

Résumé

TLDRThe video explores the process of gastrulation, a critical phase in embryonic development where coordinated cell movements in the blastula lead to the formation of three primary germ layers: ectoderm, mesoderm, and endoderm. Each of these layers is pivotal for various organogenesis functions. The gastrulation process involves dynamic movements such as invagination, ingression, and others, guided by structures like the Primitive Streak and Primitive Node. Understanding this complex choreography is essential as it lays the foundation for subsequent developmental processes such as neural tube formation, which will be covered in a subsequent video.

A retenir

  • 🧬 Gastrulation is crucial for establishing three germ layers in embryonic development.
  • 🔄 Involves coordinated movements like ingression, invagination during cell migration.
  • 📏 Primitive Streak plays a central role in organizing cell movement and layer formation.
  • 🌿 Germ layers—ectoderm, mesoderm, endoderm—are vital for organogenesis.
  • 🧠 Ectoderm leads to nervous system and skin; mesoderm forms kidneys, heart; endoderm forms GI tract.
  • 🔬 Gastrulation phase is a key milestone in embryogenesis, setting foundations for future development.
  • 🔄 Movements are not haphazard; they follow a coordinated choreography.
  • 🔍 Different types of movements occur, guided by molecular signaling.
  • 🌐 Patterns of gastrulation vary across the animal kingdom.
  • 🔗 Following gastrulation, neural tube formation begins.

Chronologie

  • 00:00:00 - 00:05:00

    Gastrulation is a critical phase in embryonic development characterized by coordinated cell movements, where cells in the blastula migrate to form body axes and germ layers (endoderm, ectoderm, mesoderm). These movements, including invagination, involution, and others, vary across species and are crucial for establishing the structure of the embryo. At around the second week of human gestation, the blastocyst implants in the uterine wall, and structures like the epiblast and hypoblast begin forming distinct layers that contribute to the embryo's overall development.

  • 00:05:00 - 00:11:18

    The formation of distinct germ layers (endoderm, mesoderm, ectoderm) involves specific cell movements, notably through the primitive streak, allowing cells to move inward, known as ingression. In humans, this occurs around day 16 of gestation. The epithelial to mesenchymal transition is pivotal as epiblast cells ingress to form the definitive endoderm and mesoderm, with ectoderm forming afterwards. Gastrulation thus sets the stage for organogenesis, as each germ layer contributes to different organ systems. This process is followed by neural tube formation, which will be discussed in a subsequent video.

Carte mentale

Vidéo Q&R

  • What is gastrulation?

    Gastrulation is a set of coordinated cell movements that establish body axis and germ layers in embryonic development.

  • Why is gastrulation important?

    Gastrulation is essential because it forms the three germ layers—ectoderm, mesoderm, and endoderm—crucial for organ development.

  • What happens during gastrulation?

    During gastrulation, epiblast cells undergo movements like ingression, invagination, and involution to form germ layers.

  • What are the three germ layers?

    The three germ layers are ectoderm, mesoderm, and endoderm, each responsible for forming different organs and tissues.

  • How do germ layers form during gastrulation?

    Germ layers form through coordinated movements and cellular processes like epithelial to mesenchymal transition (EMT).

  • What is the Primitive Streak?

    The Primitive Streak is a structure that forms during gastrulation, guiding cell movements and germ layer formation.

  • What role does the Primitive Node play?

    The Primitive Node is critical for gastrulation; it serves as a signaling center and site for cell movement initiation.

  • What are some movements involved in gastrulation?

    Some movements include invagination, involution, ingression, delamination, and epiboly.

  • Why is the process of ingression important?

    Ingression allows individual cells to migrate and form the definitive endoderm and other structures.

  • What does the ectoderm layer form?

    The ectoderm forms the central nervous system, brain, skin, and adrenal medulla, among other structures.

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Sous-titres
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  • 00:00:00
    in this video we'll talk about the
  • 00:00:01
    process of gastrulation and focusing on
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    the human gastrulation angle
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    gastrulation is a set of coordinated
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    movement which is very important for an
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    embryonic development according to the
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    famous embryologist Louis walpart it's
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    not birth marriage or death but
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    gastrulation which is truly the most
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    important time of your life so what
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    really happens during gastrulation
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    during the gastrulation process the
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    cells of blastula are given new
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    positions they migrate into a new
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    neighborhood in a very coordinated
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    fashion and that's the key time to
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    establish body axis and different Jam
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    layers
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    so here is AP blast and the cells of the
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    AP blast would be reorganized in a
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    coordinated fashion to give rise to
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    layers like endoderm ectoderm and
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    misoderm in short that is the process of
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    gastrulation
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    now this movement is not haphazard this
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    movement is highly coordinated and each
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    movement has features and there are
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    different kinds of movement that can
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    possibly occur during gastrulation like
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    invagination involution integration
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    delamination or even epiboli now all
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    these movements are not happening all at
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    once
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    there could be a combination of movement
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    that can occur in one organism and this
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    kind of morphogenetic movements are
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    different throughout the different
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    Animal Kingdom I have a different video
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    on morphogenetic movement
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    so in this video if we cut a long story
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    to short we would understand that
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    gastrulation is all about coordinated
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    movements of a pool of cells
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    and this movement involves the entire
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    embryo
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    and patterns of gastrulation could vary
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    throughout the animal kingdom there
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    could be different types of movements
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    happening during gastrulation
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    now all the patterns of movement doesn't
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    happen at once a combination of these
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    morphogenetic movements that we
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    discussed happens during gastrulation
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    and we'll take an example of the human
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    embryo to understand this better
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    so this is about the end of second week
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    of human gestation
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    point of time
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    the blastocyst is implanted into the
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    uterine wall
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    So at around day 15 you can see a
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    distinct chorionic cavity here is the
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    Primitive stock and you can see the
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    embryo is hanging through the Primitive
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    stock
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    so now let's look at the embryo in 3D so
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    here in red you can see the AP blast
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    which would eventually give rise to the
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    embryo and here is the hypoblast which
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    would give rise to the yolk sac
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    so basically it's amniotic cavity which
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    is in between the epiblast cells and it
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    is yolk Sac between the hypoglass cells
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    during the process of gastrulation the
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    bilaminar embryonic disc
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    which is composed of epiblast and
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    hypoblast ultimately gives rise to
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    ectoderm mesoderm and endoderm
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    and this process happens in a
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    coordinated fashion over a period of
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    time
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    so let's look at the embryo in 3D so we
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    can look at the embryo hanging in the
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    chorionic cavity and here is the
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    amniotic cavity in the embryo and here
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    is a yolk sac
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    so at this point of time at the caudal
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    end of the embryo A Primitive streak
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    forms
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    and this is a thickening
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    which contains a midline Groove
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    and it forms the mid sagittal plane of
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    the embryonic disc
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    over the course of next day this
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    thickening which is known as the
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    Primitive streak elongates and occupy
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    almost half the
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    span of the embryonic disc
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    and thereby the Primitive Groove is
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    formed
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    so at the cranial end of this primitive
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    streak
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    there is a formation known as the
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    primitive node
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    so this primitive node is really
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    important to understand the process of
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    gastrulation
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    and a depression at around the Primitive
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    node is formed which is known as the
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    Primitive pit it contains a depression
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    now the cells move through the Primitive
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    streak
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    inside
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    the embryo and this is this process is
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    known as ingression
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    so let's leave the jargon and try to
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    understand what is ingression but during
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    gastrulation AP blast cells move towards
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    the Primitive streak enter through the
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    Primitive streak and then migrate away
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    from the Primitive streak as an
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    individual cell so overall lot of
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    cellular aspects are associated with
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    this process let us try to understand
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    this better
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    so Follow the arrow to look at the cell
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    movement first of all these cells are
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    moving towards the Primitive streak
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    through the permissive streak and moving
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    away the Primitive streak inside from
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    the inside of the embryo
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    so this is the integration process now
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    if we look at the cross section of the
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    embryo we can appreciate this movement
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    look at the arrow and see how the cells
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    move first inward then downward and then
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    again Inward and this movement is
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    ingression and it is key to understand
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    the formation of the charm layers
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    now here we are looking at the epiblast
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    and hypoblast from our top view
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    and this if we cut a cross section along
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    this angle we would have a view like
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    this
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    one thing is to one thing is important
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    to note that there is a pro or
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    pre-codile plate which is defining the
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    cranial end of the embryo the
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    pre-cordial plate contributes to the
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    oropharyngeal membrane a two layered
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    membrane that would eventually be
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    ruptured to give rise to the mouth
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    opening also this pre-cordial or Pro
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    chordal plate works like an important
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    signaling Center which is crucial for
  • 00:06:34
    the neural tube formation
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    now if we Orient ourselves towards the
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    embryo this is the chordal end there is
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    a cranial and Left Right End
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    now there are certain signaling
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    happening which is allowing the
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    formation of the Primitive trick
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    so the Primitive streak induction
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    happens
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    via activity of wind TGF beta Etc
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    and in the cranial end there are uh
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    molecules which counteracts this wind
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    activity and thereby a gradient is
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    generated and along this gradient a
  • 00:07:11
    cranial to caudal axis is formed so this
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    is the induction of the Primitive streak
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    and this is the formation of the
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    Primitive streak which triggers the
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    process of ingression
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    now formation of the definitive endoderm
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    is the next process at around day 16
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    many of the AP blast cells move inside
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    by the process of ingression which is
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    one type of morphogenetic movement and
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    they populate the inside of the embryo
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    eventually they replace the cells in the
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    hypoblast layer and eventually form the
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    definitive endoderm
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    so first the
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    cells need to detach from the epiblast
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    layer and this happens via process known
  • 00:08:01
    as epithelial to mesenchymal transition
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    if you want to learn more about EMT
  • 00:08:06
    click on the I button
  • 00:08:08
    so the first Ingress ingressing AP blast
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    cells invent the hypoblast and displace
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    its cells to create the definitive into
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    term
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    some of the epithelial cells migrating
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    migrating through the Primitive streak
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    diverge into the space between the
  • 00:08:25
    epiblast and the definitive Hindu term
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    and this is kind of like the intra
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    embryonic mesoderm so this layer in
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    Violet would be eventually becoming the
  • 00:08:40
    mesoderm of the embryo so this Violet
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    cells are actually going to give rise to
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    the misoderm
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    and at the last the
  • 00:08:49
    term forms so once the formation of the
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    definitive endoderm and intra-embryonic
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    mesoderm is complete AP blast cells no
  • 00:08:59
    longer need to move towards an Ingress
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    through the Primitive streak so they
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    eventually give rise to the ectoderm
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    layer and thereby three germ layer
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    formation is kind of complete
  • 00:09:11
    so what we learned so far gastrulation
  • 00:09:14
    is nothing but choreographed series of
  • 00:09:16
    movements which helps to form three
  • 00:09:19
    important jump layers known as ectoderm
  • 00:09:23
    mesoderm and endoderm and each of these
  • 00:09:25
    germ layers are important for
  • 00:09:27
    organogenesis for example if we look at
  • 00:09:29
    the ectoderm it give rise to central
  • 00:09:33
    nervous system brain skin Adrenal
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    medulla to name a few
  • 00:09:38
    then mesoderm give rise to kidney
  • 00:09:40
    reproductive system bone heart and
  • 00:09:43
    spleen whereas endoderm give rise to GI
  • 00:09:47
    tract liver endocrine system urethra
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    bladder Etc so obviously gastrulation is
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    the first Milestone that has to be
  • 00:09:55
    achieved during the process of
  • 00:09:57
    development eventually there would be
  • 00:10:00
    many modifications and influences from
  • 00:10:02
    inside and outside environment
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    the very next thing that happens is the
  • 00:10:08
    neural tube formation
  • 00:10:10
    neural tube formation is a complicated
  • 00:10:12
    process and in the next video we would
  • 00:10:15
    talk about the neural tube so if you
  • 00:10:17
    look at the embryo from a top view right
  • 00:10:19
    now and a cross section view you can
  • 00:10:21
    completely imagine that this flat sheet
  • 00:10:24
    of ectodermal cells are eventually
  • 00:10:27
    folding to form a tube-like organization
  • 00:10:31
    and this is the neural tube eventually
  • 00:10:34
    our brain is nothing about but a tube at
  • 00:10:37
    one side it is blown up like a balloon
  • 00:10:40
    in the brain side and other side it's
  • 00:10:42
    tippering in the spinal cord so in a
  • 00:10:45
    next video we'll talk about the neural
  • 00:10:47
    tube folding process and the defects
  • 00:10:49
    associated with neural tube folding
  • 00:10:52
    so stay tuned for more you can get more
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Tags
  • Gastrulation
  • Embryogenesis
  • Germ Layers
  • Primitive Streak
  • Cell Movement
  • Epiblast
  • Ectoderm
  • Mesoderm
  • Endoderm
  • Embryo Development