2010 BGD Practical 6 - Week 3: Difference between revisions

Revision as of 10:40, 16 May 2010

Introduction

Introduction

Key events of human development during the third week (week 3) following fertilization or Clinical week 5 (LMP). Note that during this time the conceptus cells not contributing to the embryo are contributing to placental membranes and the early placenta.

Somitogenesis

The later migration of cells forms the mesoderm germ layer. An embryonic connective tissue (mesenchyme) which forms nearly all the connective tissues of the body (the head is different). Somitogenesis is when part of this layer segments during week 3 to form balls of mesoderm called somites.

Folding

There are two major folding processes that take place during this time.

Folding of the ecoderm will form a neural groove, then closing to form a neural tube, separating the neural ectoderm from the embryo surface ectoderm.

Folding of the whole embryonic disc ventrally, separates the endoderm to form the epithelial lining of the gut.

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.

Movies - Endoderm folding | Folding overview

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 righhand side is shown).

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 adjacennt 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.

Neurogenesis

The remaining cells that do not migrate from the epiblast layer remain and form the ectoderm. An epithelial layer of cells which contributes all neural (brain, spinal cord, peripheral nervous system) and the external epithelium (surface layer of the skin) of the embryo. Neurogenesis begins towards the end of week 3, when the neural tissues separate from this germ cell layer.

Week 2 and 3 Movies


Implantation	Mesoderm	Chorionic Cavity	Amniotic Cavity	Week 3

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

Detailed Week by Week

The following information is a detailed timeline of embryonic development between week 3 to 8 and content does not form part of the current practical class.

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2024, May 20) Embryology 2010 BGD Practical 6 - Week 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_6_-_Week_3

What Links Here?

@@ Line 39: / Line 39: @@
 ==Neurogenesis==
 The remaining cells that do not migrate from the epiblast layer remain and form the ectoderm. An epithelial layer of cells which contributes all neural (brain, spinal cord, peripheral nervous system) and the external epithelium (surface layer of the skin) of the embryo. Neurogenesis begins towards the end of week 3, when the neural tissues separate from this germ cell layer.
-==Embryo Stages and Events==
-{| class="prettytable"
-| width= "50px" |'''Day'''
-| width= "100px" |'''Stage'''
-| '''Event'''
-|-
-| <center>15</center>
-|
-|
-|-
-| <center>16</center>
-| [[Carnegie stage 7|Stage 7]]
-| [[Image:Stage7.jpg|120px|left]] '''Primitive node''' (Hensen's node, primitive knot) The small circular region located at the cranial end of the primitive streak, where gastrulation occurs, and is a controller of this process. The second role is to act as an initial generator of the left-right (L-R) body axis.
-|-
-| <center>17</center>
-| &nbsp;
-| &nbsp;
-|-
-| <center>18</center>
-| [[Carnegie stage 8|Stage 8]]
-| [[Image:Stage8_human.jpg|120px|left]] [http://embryology.med.unsw.edu.au/Notes/neuron.htm Neural]  neurogenesis, neural groove and folds are first seen
-|-
-| <center>19</center>
-| &nbsp;
-| [[Image:Stage8_SEM1.jpg|120px|left]]
-|-
-| <center>20</center>
-| [[Carnegie stage 9|Stage 9]]
-| [[File:Stage9_bf1c.jpg|200px|link=Carnegie stage 9]] [http://embryology.med.unsw.edu.au/Notes/skmus6.htm Musculoskeletal]  somitogenesis - first somites form and continue to be added in sequence caudally
-[http://embryology.med.unsw.edu.au/Notes/neuron.htm Neural] - three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open
-|-
-| <center>21</center>
-| &nbsp;
-| [http://embryology.med.unsw.edu.au/Notes/heart.htm Heart]  cardiogenesis - week 3 begins as paired heart tubes.
-|}
 ==Week 2 and 3 Movies==