Difference between revisions of "2010 BGD Practical 6 - Week 4"

From Embryology
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* '''stage 13''' (4 weeks) the neural tube is normally completely closed
 
* '''stage 13''' (4 weeks) the neural tube is normally completely closed
  
[[File:Stage13-CNS-icon.jpg|120px|link=Movie_-_Central_Nervous_System_3D_stage_13]]
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[[File:Stage13-CNS-icon.jpg|200px|link=Movie_-_Central_Nervous_System_3D_stage_13]]
  
 
==Placodes==
 
==Placodes==

Revision as of 14:12, 16 May 2010

Introduction

BGDsmall.jpg

Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Quiz


Introduction

Key Events of Human Development during the fourth week (week 4) following fertilization or Clinical week 6 (LMP).

These notes cover the fourth week of embryonic development, which is the beginning of organogenesis, (specific tissues and systems are beginning to differentiate) from the trilaminar embryo. With many parallel processes, descriptions begin to get complicated! Many of the described processes begin and extend over a broader range of time. Some developmental processes will be discussed later in the practical to simplify matters.

Ectoderm on the embryo surface undergoes segmentation: The central portion of the embryonic disc forms the neural plate, the edge of this plate forms neural crest and the remainder outside this forms the epitheium of the skin and other structures.

Neurogenesis

  • Central Nervous System (CNS) - the neural plate undergoes morphological changes to form the primitive central nervous system. 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.
  • Peripheral Nervous System (PNS) - the neural crest cells in the body region migrate and spread to different regions of the embryo forming the PNS and many other embryonic tissues. Neural crest cells in the head region form skeletal and other structures.

Placodes

In the head region, ectoderm small patches form pairs of specialised placodes that eventually contribute to specific sensory components, cranial ganglia and the anterior pituitary (adenohypophysis).

Limb Buds

Limb buds form from ectoderm and mesoderm (somitic and somatic) components and are the "paddle-like" projections from the trunk which will form all the upper and lower limb components. (An overview of limb development will be covered in week 8).

Cardiogenesis

Within the embryo mesoderm, the heart tube and vascular development continues. Cardiogenesis will be covered in week 5, when septation begins.

Neurogenesis

Primary Brain Vesicles
  • Central Nervous System (CNS) - the neural plate undergoes morphological changes to form the primitive central nervous system. 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.
  • Peripheral Nervous System (PNS) - the neural crest cells in the body region migrate and spread to different regions of the embryo forming the PNS and many other embryonic tissues. Neural crest cells in the head region form skeletal and other structures.

Human Neuralation - Early Stages

The stages below refer to specific Carneigie stages of development.

  • stage 8 (about 18 postovulatory days) neural groove and folds are first seen
  • stage 9 the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open
  • stage 10 (two days later) neural folds begin to fuse near the junction between brain and spinal cord, when neural crest cells are arising mainly from the neural ectoderm
  • stage 11 (about 24 days) the cranial neuropore (rostral, cephalic or anterior) closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in several areas simultaneously. The two lips, however, behave differently.
  • stage 12 (about 26 days) The caudal (posterior) neuropore takes a day to close
  • the level of final closure is approximately at future somitic pair 31
  • corresponds to the level of sacral vertebra 2
  • stage 13 (4 weeks) the neural tube is normally completely closed

Stage13-CNS-icon.jpg

Placodes

otic placode forms the otocyst

In the head region, ectoderm small patches form pairs of specialised placodes that eventually contribute to specific sensory components, cranial ganglia and the anterior pituitary (adenohypophysis).

Embryo Stage 13

Movies - Embryo Carnegie stage 13 - These are rotating animations based upon reconstruction of individual serial slice images of the stage 13 embryo.


Stage13-CNS-icon.jpg Stage13-GIT-icon.jpg Stage13-CVS-icon.jpg
Central Nervous System Gastrointestinal Cardiovascular

Week 4 Movies

Note that many of the movies start in week 4 and continue on through later embryonic development.

Ectoderm

Neuralplate 001 icon.jpg Neuraltube 001 icon.jpg
Neural Plate Neural Tube

Mesoderm

Mesoderm 001 icon.jpg Somite 001 icon.jpg Vertabra 003 icon.jpg
Mesoderm Somite Structures Vertebra

Endoderm

Endoderm 002 icon.jpg


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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Quiz



   

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.

Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8

Embryo Stages and Events

Day Stage Event
22
Stage 10 Stage10 dorsal1.jpg Stage10-dorsal2.jpg

Neural

  • neural folds begin to fuse near the junction between brain and spinal cord
  • rostral neural tube forms 3 primary brain vesicles (week 4)

Neural Crest

  • differentiation at spinal cord level from day 22 until day 26
  • cells are arising mainly from the neural ectoderm
  • trigeminal, facial, and postotic ganglia components visible PMID: 17848161
  • migration of vagal level neural crest cells begins (7-10 somite stage)

Respire

  • Week 4 - laryngotracheal groove forms on floor foregut
23
  Heart begins to beat in Humans by day 22-23, first functioning embryonic organ formed.
24
Stage 11 Stage11 bf1c.jpg

Thyroid thyroid median endodermal thickening in the floor of pharynx

Neural rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in two areas simultaneously. The two lips, however, behave differently.

Optic ventricle appears

25
Stage 12 Stage12 bf1c.jpg

Pituitary Week 4 hypophysial pouch, Rathke’s pouch, diverticulum from roof

GIT - Liver septum transversum forming liver stroma and hepatic diverticulum forming hepatic trabeculae PMID: 9407542

Neural caudal neuropore takes a day to close (closure is approximately at future somitic pair 31/sacral vertebra 2)

Neural secondary neurulation begins

Neural Crest cardiac crest, neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there the truncus arteriosus PMID: 17848161

Neural Crest vagal neural crest enter the foregut (20-25 somite stage)

26
   
27
   
28
Stage 13 Stage13 bf1c.jpg Neural the neural tube is normally completely closed, ventricular system now separated from amniotic fluid. Neural crest at spinal level is segregating, and spinal ganglia are in series with the somites. Spinal cord ventral roots beginning to develop. PMID: 3354839

telencephalon cavity appears

GIT - Liver epithelial cord proliferation enmeshing stromal capillaries PMID: 9407542

Sense - Smell Crest comes from the nasal platesPMID: 15604533

Skin 4 weeks - simple ectoderm epithelium over mesenchyme

Skin 1-3 months ectoderm- germinative (basal) cell repeated division of generates stratified epithelium; mesoderm- differentiates into connective tissue and blood vessels

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. (2021, May 17) Embryology 2010 BGD Practical 6 - Week 4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_6_-_Week_4

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G