Term
| Explain the development of the vertebrate limbs |
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Definition
- The forelimb develops before the hindlimb
- The limbs develop as limb buds (these are made of two components: a loose core of mesenchymal cells (derived from the mesoderm that form skeletal tisse) and a thickening in the ectoderm called the apical ectodermal cap.
- Proliferation takes place and specification till hand and foot plates are formed.
- The digits are formed via apoptosis whereby the spaces between the digits are formed.
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Term
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Definition
| Somites in vertebrate embryos are segmented blocks of mesoderm lying on either side of the notochord. They give rise to the body and limb muscles, the vertebral collumn and the dermis. |
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Term
| How do we know where these somites end up? |
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Definition
We can transplant somites of a quail embryo from the site of the future wing bud is transplanted into a chick embryo. The resulting quail-chick chimera embryo has wing tissues that contain quail cells, but not anyother wing tissues.
Therefore we know this somite gives rise to muscle tissue and the bones form from elsewhere.
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Term
| What is the transverse structure of the neural region before somite differentiation? |
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Definition
There is a sheet of epidermis covering everything.
Underneath in the centre you have the neural tube like an empty hot dog bun running along the anterior/posterior axis. The notochord (like a tube) is underneath and the somites are either side (they don't run the whole length- they are dotted along the whole length of the A/P axis). |
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Term
| What is the structure of the mesoderm before any major differentiation? |
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Definition
| The neural tube runs down the middle. Chordamesoderm runs underneath that (forms notochord) and paraxial mesoderm runs either side (forms somites). Outside of these you have the intermediate mesoderm and then the lateral mesoderm. |
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Term
| How do the somites differentiate? |
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Definition
- From the beginning the somite can be split into scleretosome cells and dermamyotome cells.
- The scleretome cells loose their adhesion to one another and migrate towards the neural tube.
- The remaining dermamyotome region forms medial cells that congregate beneath them. The dermamyotome also elongating outwards from the neural tube.
- The medial cells form a layer of myotome (which becomes muscle mass).
- Ventral sclerotome cells form the vertebral body and dorsal sclerotome cells form the vertebral arch.[image]
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Term
| How does the lateral plate grow into two? |
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Definition
The lateral plate unzips into two. The top half is the somatic mesoderm layer which forms the future body wall. The bottom half is the splanchnic mesoderm layer that goes on to form the circulatory system and the future gut wall.
The proliferation of the lateral mesoderm generates the limb bud. |
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Term
| How do we know that the intermediate mesoderm plays a role in limb bud formation? |
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Definition
If there is an impermeable barrier placed between the intermediate mesoderm and the lateral plate of the mesoderm then no limb bud is induced. If the intermediate mesoderm is destroyed or removed the limb bud is reduced.
This means the intermediate mesoderm plays a key role in the signalling of the limb bud induction. |
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