Difference between revisions of "2011 Lab 2 - Week 3"

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==Introduction==
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{| class="prettytable"
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|-
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| [[File:Human_embryo_day_18.jpg|300px]]
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| Gastrulation means "gut forming" and converts the inner cell mass which then formed the bilaminar embryo (epiblast, hypoblast) into the trilaminar embryo (ectoderm, mesoderm, endoderm).
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The process involves the migration of cells from the epiblast layer through the primitive streak to form first the endoderm layer and then a second intermediate layer the mesoderm layer. Once all cells have left the epiblast layer it now becomes the ectoderm layer.
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These three germ cell layers (ectoderm, mesoderm, endoderm) will form in a layer specific manner all the future tissues of the developing embryo.
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'''Approximate cross-section of an 18 day human conceptus.'''
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Identify the 3 layers of the trilaminar embryo: ectoderm (columnar cells), intraembryonic mesoderm (mesenchymal cells, endodermal cells (cuboidal single layer). Identify primitive groove with dense cluster of primitive streak cells below it.
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(Image: Nishimura etal., 1977)
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|-
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|}
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== Conceptus Cavities Week 2 and Week 3 ==
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{| border='0px'
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|-
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| <wikiflv width="214" height="220" autoplay="true" position="left">Chorion 001.flv|File:Chorion 001 icon.jpg</wikiflv>
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| Animation shows the events following implantation and focuses on changes in the the spaces surrounding the embryonic disc, the extraembryonic coelom. The blastoceol cavity is converted into two separate spaces: the yolk sac and the chorionic cavity. The third space lies above the epiblast, the amniotic cavity.
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'''blue''' - epiblast layer
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'''yellow''' - hypoblast layer
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'''red cells''' - extraembryonic mesoderm layer
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'''green''' - trophoblast layer
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'''red spaces''' - blood-filled spaces, maternal lacunae
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'''white cells''' - (left) endometrial gland (right) endometrial epithelium
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:[[Media:Chorion_001.mov|Quicktime version]]
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|-
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|}
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==Germ Layers and Dynamic Processes==
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:''From 1 layer of cells to 3 layers that define all tissues of the entire embryo.''
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The [[C#conceptus|conceptus]] is now fully implanted in the uterine wall. This time is now when a small cluster of cells (the inner cell mass) will differentiate into two simple cell layers ([[E#epiblast|epiblast]] and [[H#hypoblast|hypoblast]]). From the single epiblast layer cells will migrate through a narrow region ([[P#primitive streak|primitive streak]]) to form firstly two layers epiblast and endoderm, then later the three layers ectoderm, mesoderm and endoderm. These final three layers (germ layers) are the trilaminar embryo and will form all the tissues of the body.
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During implantation cells on the outside (trophoblast layer) of the conceptus are forming part of the early placenta. The cells on the inside (inner cell mass) now begin to form the three germ layers that will form the entire embryo. Note that as the conceptus also forms the fetal component of the placenta, not all cells from our blastocyst will form part of the developing embryo.
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The images below show the embryo (week 3 between 15 to 17 days) as a disc 0.4 mm diameter in size.
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[[File:Stage7_features.jpg]]
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[[File:Stage7-sem1.jpg|300px]]
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[[File:Stage7-sem4.jpg|300px]]
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[[Carnegie_stage_7|Stage 7 Human Embryo (15 to 17 days)]]
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[[Carnegie_stage_10|Stage 10 Human Embryo (22 to 23 days)]]
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'''Please just make note of the events that occur at this time, we do not have time to discuss these events in detail, this will occur in BGD.'''
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== Stage 7 ==
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{|
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|-
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| [[File:Stage7-sem2.jpg|300px]]
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| [[File:Stage7_features.jpg]]
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|-
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| '''Features:''' embryonic disc, primitive node, primative streak, primitive groove, yolk sac
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'''Facts:''' Week 3, 15 - 17 days, 0.4 mm
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'''View 1:''' embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.
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'''Events:''' Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm.
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Mesoderm lies between the ectoderm and endoderm as a continuous sheet except at the buccopharyngeal and cloacal membranes. These membranes have ectoderm and endoderm only and will lie at the rostral (head) and caudal (tail) of the gastrointestinal tract.
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| '''Gastrulation:''' Through the '''primitive streak '''cells migrate continuously through week 3 into week 4. Initial cells replace hypoblast as an epithelial layer the '''endoderm'''. Later migrating cells spread between the two epithelial layers to form '''mesoderm'''.
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|-
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| [[File:Stage7_primitive_streak_labelled.jpg]]
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| [[File:Stage7 axes.jpg]]
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|-
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| '''Axes:''' embryonic disc is shown rostral (head) to top and caudal (tail) to bottom. Left and right are the lateral margins of the disc as shown.
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|-
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|}
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== Gastrulation ==
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Carnegie Stage 7 and 8, gastrulation, migration of cells through the primitive streak to form endoderm and mesodermal layers of embryo.
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[[File:Chicken-gastrulation3.jpg]]
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[[File:Trilaminar_embryo.jpg]]
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Scanning electron micrograph showing the early forming 3 layers: ectoderm, mesoderm and endoderm.
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[[File:Mesoderm 001 icon.jpg|200px|link=Development_Animation_-_Mesoderm]]
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{{Template:2011Lab2}}
 
{{Template:2011Lab2}}

Revision as of 11:23, 4 August 2011

2011 Lab 2: Introduction | Week 1 | Week 2 | Week 3 | Online Assessment | Group Project

Introduction

Human embryo day 18.jpg Gastrulation means "gut forming" and converts the inner cell mass which then formed the bilaminar embryo (epiblast, hypoblast) into the trilaminar embryo (ectoderm, mesoderm, endoderm).

The process involves the migration of cells from the epiblast layer through the primitive streak to form first the endoderm layer and then a second intermediate layer the mesoderm layer. Once all cells have left the epiblast layer it now becomes the ectoderm layer.

These three germ cell layers (ectoderm, mesoderm, endoderm) will form in a layer specific manner all the future tissues of the developing embryo.


Approximate cross-section of an 18 day human conceptus.

Identify the 3 layers of the trilaminar embryo: ectoderm (columnar cells), intraembryonic mesoderm (mesenchymal cells, endodermal cells (cuboidal single layer). Identify primitive groove with dense cluster of primitive streak cells below it.


(Image: Nishimura etal., 1977)

 


Conceptus Cavities Week 2 and Week 3

File:Chorion 001 icon.jpg</wikiflv> Animation shows the events following implantation and focuses on changes in the the spaces surrounding the embryonic disc, the extraembryonic coelom. The blastoceol cavity is converted into two separate spaces: the yolk sac and the chorionic cavity. The third space lies above the epiblast, the amniotic cavity.

blue - epiblast layer

yellow - hypoblast layer

red cells - extraembryonic mesoderm layer

green - trophoblast layer

red spaces - blood-filled spaces, maternal lacunae

white cells - (left) endometrial gland (right) endometrial epithelium

Quicktime version


Germ Layers and Dynamic Processes

From 1 layer of cells to 3 layers that define all tissues of the entire embryo.

The conceptus is now fully implanted in the uterine wall. This time is now when a small cluster of cells (the inner cell mass) will differentiate into two simple cell layers (epiblast and hypoblast). From the single epiblast layer cells will migrate through a narrow region (primitive streak) to form firstly two layers epiblast and endoderm, then later the three layers ectoderm, mesoderm and endoderm. These final three layers (germ layers) are the trilaminar embryo and will form all the tissues of the body.

During implantation cells on the outside (trophoblast layer) of the conceptus are forming part of the early placenta. The cells on the inside (inner cell mass) now begin to form the three germ layers that will form the entire embryo. Note that as the conceptus also forms the fetal component of the placenta, not all cells from our blastocyst will form part of the developing embryo.

The images below show the embryo (week 3 between 15 to 17 days) as a disc 0.4 mm diameter in size.

Stage7 features.jpg Stage7-sem1.jpg Stage7-sem4.jpg

Stage 7 Human Embryo (15 to 17 days)

Stage 10 Human Embryo (22 to 23 days)

Please just make note of the events that occur at this time, we do not have time to discuss these events in detail, this will occur in BGD.


Stage 7

Stage7-sem2.jpg Stage7 features.jpg
Features: embryonic disc, primitive node, primative streak, primitive groove, yolk sac

Facts: Week 3, 15 - 17 days, 0.4 mm

View 1: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.

Events: Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm.

Mesoderm lies between the ectoderm and endoderm as a continuous sheet except at the buccopharyngeal and cloacal membranes. These membranes have ectoderm and endoderm only and will lie at the rostral (head) and caudal (tail) of the gastrointestinal tract.


Gastrulation: Through the primitive streak cells migrate continuously through week 3 into week 4. Initial cells replace hypoblast as an epithelial layer the endoderm. Later migrating cells spread between the two epithelial layers to form mesoderm.
Stage7 primitive streak labelled.jpg Stage7 axes.jpg
Axes: embryonic disc is shown rostral (head) to top and caudal (tail) to bottom. Left and right are the lateral margins of the disc as shown.

Gastrulation

Carnegie Stage 7 and 8, gastrulation, migration of cells through the primitive streak to form endoderm and mesodermal layers of embryo.

Chicken-gastrulation3.jpg

Trilaminar embryo.jpg Scanning electron micrograph showing the early forming 3 layers: ectoderm, mesoderm and endoderm.


Mesoderm 001 icon.jpg


2011 Lab 2: Introduction | Week 1 | Week 2 | Week 3 | Online Assessment | Group Project