S8600021 at 03:25, 24 August 2011

2011-08-24T03:25:48Z

← Older revision		Revision as of 14:25, 24 August 2011
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	Note intraembryonic coelomic cavity communicates with extraembryonic coelom (space outside the embryo) through portals (holes) initially on lateral margin of embryonic disc.		Note intraembryonic coelomic cavity communicates with extraembryonic coelom (space outside the embryo) through portals (holes) initially on lateral margin of embryonic disc.

			{{2011Lab5Footer}}

S8600021 at 03:15, 24 August 2011

2011-08-24T03:15:40Z

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			{{2011Lab5}}
	==Introduction==		==Introduction==
	Begin by very briefly covering the first 3 weeks of development. Our story of GIT development begins in the third week with the formation of the 3 germ cell layers, one layer the endoderm will form the lining of the entire gastrointestinal tract and also contibute the respiratory tract and other organs.		Begin by very briefly covering the first 3 weeks of development. Our story of GIT development begins in the third week with the formation of the 3 germ cell layers, one layer the endoderm will form the lining of the entire gastrointestinal tract and also contibute the respiratory tract and other organs.

S8600021: /* Week 1 and 2 */

2011-08-24T03:05:12Z

Week 1 and 2

← Older revision		Revision as of 14:05, 24 August 2011
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	Note that the description below, and throughout the practical, has been substantially simplified.		Note that the description below, and throughout the practical, has been substantially simplified.

	~~==Week 1 and 2==~~
	~~[[File:Week1 summary.jpg\|thumb\|Week 1 and 2]]~~

	Fertilization/Blastocyst Formation: an egg released into the uterine tube has been fertilized by a single sperm to form the first diploid cell (zygote). This cell then undergoes rapid division to form first a solid ball of cells (morula) and then a hollow ball (blastocyst) with an outer cell layer, an inner cell mass and a fluid filled cavity. All this has occurred in the uterine tube (horn, oviduct, fallopian tube) prior to implantation in the uterus.

	~~<br>~~
	~~<Flowplayer width="640" height="186" autoplay="true">Week1_001.flv</Flowplayer><br>~~

	~~[[Quicktime_Development_Animation_-_Week_1\|Quicktime]] \| [[Development_Animation_-_Week_1\|Flash]]~~

	==Week 3==		==Week 3==

S8600021: Created page with "==Introduction== Begin by very briefly covering the first 3 weeks of development. Our story of GIT development begins in the third week with the formation of the 3 germ cell laye..."

2011-08-24T03:04:59Z

Created page with "==Introduction== Begin by very briefly covering the first 3 weeks of development. Our story of GIT development begins in the third week with the formation of the 3 germ cell laye..."

New page

==Introduction==
Begin by very briefly covering the first 3 weeks of development. Our story of GIT development begins in the third week with the formation of the 3 germ cell layers, one layer the endoderm will form the lining of the entire gastrointestinal tract and also contibute the respiratory tract and other organs.

Note that the description below, and throughout the practical, has been substantially simplified.

==Week 1 and 2==
[[File:Week1 summary.jpg|thumb|Week 1 and 2]]

Fertilization/Blastocyst Formation: an egg released into the uterine tube has been fertilized by a single sperm to form the first diploid cell (zygote). This cell then undergoes rapid division to form first a solid ball of cells (morula) and then a hollow ball (blastocyst) with an outer cell layer, an inner cell mass and a fluid filled cavity. All this has occurred in the uterine tube (horn, oviduct, fallopian tube) prior to implantation in the uterus.

<br>
<Flowplayer width="640" height="186" autoplay="true">Week1_001.flv</Flowplayer><br>

[[Quicktime_Development_Animation_-_Week_1|Quicktime]] | [[Development_Animation_-_Week_1|Flash]]

==Week 3==

Gastrulation/Neuralation: The inner cell mass forms a flat sheet of cells and cells migrate through a specific region of the sheet (primitive streak) turning the single layer into first 2 then 3 layers (trilaminar embryo).

==Folding==
The next process to follow is the folding of the embryonic disc which will form the "tube" of the GIT. Forming the ends of this tube are the 2 membranes which form the upper and lower limits of the GIT.

[[File:Endoderm cartoon.jpg]]

Note that in addition to gastrulation, neuralation (forming the early neural tube that makes the nervous system) and somitogenesis (segmentation of the mesoderm forming the axial skeleton) are the other major processes occuring in week 3 to 4.

Folding of the embryonic disc occurs ventrally around the notochord, which forms a rod-like region running rostro-caudally in the midline.

In relation to the notochord:

* Laterally (either side of the notochord) lies mesoderm.
* Rostrally (above the notochord end) lies the buccopharyngeal membrane, above this again is the mesoderm region forming the heart.
* Caudally (below the notochord end) lies the primitive streak (where gastrulation occurred), below this again is the cloacal membrane.
* Dorsally (above the notochord) lies the neural tube then ectoderm.
* Ventrally (beneath the notochord) lies the mesoderm then endoderm.

The ventral endoderm (shown yellow) has grown to line a space called the yolk sac. Folding of the embryonic disc "pinches off" part of this yolk sac forming the first primative GIT.
{|
| <wikiflv width="280" height="322" autostart="true" position="left">Endoderm 002.flv|File:Endoderm 002 icon.jpg</wikiflv>
| <wikiflv width="388" height="500" autoplay="true">Week3_folding.flv|Week3_folding icon.jpg</wikiflv><br>
|-
| [[Quicktime_Development_Animation_-_Endoderm|Quicktime]] | [[Development_Animation_-_Endoderm|Flash]]<br>
| [[Quicktime Development Animation - Week 3|Quicktime]] | [[Development Animation - Week 3|Flash]]
|}

==Week 4==

Carnegie stage 10, 23 day, 5-11 somite pairs

[[File:Stage10 sem10.jpg|600px]]

[[File:Stage10_sem1.jpg|600px]]

==Membranes==

During the process of gastrulation the embryonic disc formed 3 layers, except in 2 specific membrane regions where ectoderm and endoderm have no mesoderm between them: buccopharyngeal membrane and cloacal membrane. These will form the upper and lower extend of the GIT.

===Buccopharyngeal membrane===
also called mouth or oral membrane

Carnegie stage 10 (21 days, 4-5 somite pairs, ventral sem)

[[File:Stage10_sem4.jpg|600px]]

Carnegie stage 11 (25 days, 20 somite pairs)
<gallery>
File:Stage11 sem4c.jpg|Low power ventral view of the Buccopharyngeal Membrane
File:Stage11 sem3c.jpg|Higher power ventrolateral view of the Buccopharyngeal Membrane
File:Stage11 sem2c.jpg|Close up view of the degenerating Buccopharyngeal Membrane
</gallery>

Cloacal membrane - not clearly visible in the above section

==Splanchnic Mesoderm==
[[File:Mesoderm_cartoon4.gif]]

The cartoon above is a section through the trunk of the trilaminar embryo showing the further development of the 3 layers and the space (coelom) that forms in the mesoderm ('''only the righthand side is shown, lefthand side would be identical''').

Within the embryonic disc lateral plate mesoderm a space (coelom) forms, it lies within the embryo and so is called the intraembryonic coelom. This single "horseshoe-shaped" space will form the 3 major body cavities: pericardial (around the heart), pleural (around the lungs) and peritoneal (around the GIT and visceral organs).

The mesoderm adjacent to the endoderm is now called the splanchnic mesoderm which forms the connective tissue and muscular wall of the GIT.

Note intraembryonic coelomic cavity communicates with extraembryonic coelom (space outside the embryo) through portals (holes) initially on lateral margin of embryonic disc.

2011 Lab 5 - Trilaminar Embryo - Revision history

S8600021 at 03:25, 24 August 2011

S8600021 at 03:15, 24 August 2011

S8600021: /* Week 1 and 2 */

S8600021: Created page with "==Introduction== Begin by very briefly covering the first 3 weeks of development. Our story of GIT development begins in the third week with the formation of the 3 germ cell laye..."