BGDA Practical 3 - Week 3 Summary: Difference between revisions
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If you have finished and need some more help understanding this period of development, I have included some links to Online References. | If you have finished and need some more help understanding this period of development, I have included some links to Online References. | ||
If you have finished and are interested in looking at tissues involved in this period of development, I have included some links to Histology Images. | If you have finished and are interested in looking at tissues involved in this period of development, I have included some links to Histology Images. | ||
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Note that this Practical has discussed mainly development of the embryo as placental development will be covered in detail in another practical ('''Practical 14 - Placenta and Fetal Membranes'''). | Note that this Practical has discussed mainly development of the embryo as placental development will be covered in detail in another practical ('''Practical 14 - Placenta and Fetal Membranes'''). | ||
The next Practical will continue on through embryonic development ( | The next Practical will continue on through embryonic development ([[BGDA Practical - Implantation to 8 Weeks|Implantation to 8 Weeks]]). | ||
Revision as of 12:55, 9 May 2016
Practical 3: Oogenesis and Ovulation | Gametogenesis | Fertilization | Early Cell Division | Week 1 | Implantation | Week 2 | Extraembryonic Spaces | Gastrulation | Notochord | Week 3 |
Introduction
This page is a overview of events that occur in human development up to week 3 post-fertilization. From this Practical understand concepts of: fertilization, blastocyst development, implantation, bilaminar and trilaminar embryo formation, development of embryonic cavities and brief understanding of early placenta development.
By the end of week 3, segmentation of the trilaminar embryo 3 germ layers has begun:
- Ectoderm - central neural plate and lateral parts form epidermis
- Mesoderm - midline notochord, adjacent somites, formation of the internal embryonic space (intraembryonic ceolom)
- Endoderm - epidermal lining of gastrointestinal tract and yolk sac lining
Note
Use the links to Carnegie stage 7, Carnegie stage 8 and Carnegie stage 9 to see a number of different views of the human embryo in the third week of development.
The timeline at the bottom of this page should give you a better perspective of the sequence of early developmental events. You would not be expected to know exact days (as they are only approximate anyway) it is more important to get the weeks and sequence right.
Stage 7
Facts
Human embryonic stage 7 occurs during week 3 between 15 to 17 days.
The embryo is now 0.4 mm diameter in size.
The initial images are displayed unlabeled to allow you to explore the embryo for yourself, linked labeled versions are also available for some images.
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.
From the primitive node a tube extends under the ectoderm in the opposite direction to the primitive streak. This tube forms first the axial process then notochordal process, then finally the notochord.
The notochord is a key to embryonic folding and regulation of ectoderm and mesoderm differentiation. It lies in the rostrocordal axis and the embryonic disc will fold either side ventrally, pinching off a portion of the yolk sac to form the lining of the gastrointestinal tract.
Carnegie Stage 8
Facts
Human embryonic stage 8 occurs during week 3 between 17 to 19 days.
The embryo is now 1.0 - 1.5 mm in size.
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.
From the primitive node a tube extends under the ectoderm in the opposite direction to the primitive streak. This tube forms first the axial process then notochordal process, then finally the notochord.
The notochord is a key to embryonic folding and regulation of ectoderm and mesoderm differentiation. It lies in the rostrocordal axis and the embryonic disc will fold either side ventrally, pinching off a portion of the yolk sac to form the lining of the gastrointestinal tract.
Identify
- embryonic disc
- primitive node, primative streak, primative groove
- connecting stalk
- cut amniotic membrane
Carnegie Stage 9
Facts
Human embryonic stage 9 occurs during week 3 between 19 to 21 days.
The embryo is now 1.5 to 2.5 mm in size and somites have begun to form and number between 1 to 3 somite pairs during this stage.
The initial images are displayed unlabeled to allow you to explore the embryo for yourself, linked labeled versions are also available for some images.
Events
Ectoderm - Neural plate brain region continues to expand, neural plate begins folding over the notochord. Gastrulation continues through the primitive streak region.
Mesoderm - Paraxial mesoderm segmentation into somites begins (1 - 3 somite pairs). Lateral plate mesoderm begins to vacuolate, dividing it into somatic and splanchnic mesoderm and to later form the intra-embryonic coelom. Prechordal splanchnic mesoderm begins to form the cardiogenic region, from which the primordial heart will develop.
Endoderm - Notochordal plate still visible which will form the notochord. Endoderm is still widely open to the yolk sac and germ cells form part of this layer. Extra-embryonic mesoderm on the yolk sac surface begins to form "blood islands".
Identify
- Neural groove and neural folds, the mesoderm showing first somite bulges, that segments beside the neural groove to form somites but extends laterally to margin of embryonic disc lateral plate mesoderm, where it merges with the covering extraembryonic mesoderm.
- The intra-embryonic coelom develops in the middle of the lateral plate mesoderm.
- Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline
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. |
Human Development Timeline
The table below shows human development features and approximate timing during the menstrual cycle to fertilization and the first 3 weeks of development.
The timing assumes fertilization the day after ovulation and the "weeks" refer to embryonic development and differ from Gestational Age (GA, clinical weeks shown in brackets, from last menstrual period) and "stages" refer to Carnegie stages of development.
Week -2
(GA week 1, clinical week 1)
Event | ||
Menstrual Phase |
Menstrual Cycle changes: Uterine endometrium (loss), Ovary (Follicle Development) | |
Proliferative Phase | Menstrual Cycle changes: Uterine endometrium (proliferation), Ovary (Follicle Development) | |
Week -1
(GA week 2, clinical week 2)
Menstrual cycle | Event | |
Proliferative Phase | ||
Menstrual Cycle - Mid proliferative | ||
Menstrual Cycle - Late Proliferative | ||
Ovulation
Capacitation |
Week 1
Week 1 (GA week 3, clinical week 3)
Week 2
Week 2 (GA week 4, clinical week 4)
Event | ||
Implantation | ||
Stage 6 | Chorionic Cavity | |
Week 3
Week 3 (GA week 5, clinical week 5)
Event | ||
Stage 7 | ||
Stage 8 | Neural neurogenesis, neural groove and folds are first seen | |
Stage 9 | Musculoskeletal somitogenesis, first somites form and continue to be added in sequence caudally
Neural the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open Neural Crest mesencephalic neural crest is visible PMID: 17848161 | |
Heart cardiogenesis, week 3 begins as paired heart tubes. |
Next
Finished Lab 3 !
If you have finished and would like to apply your knowledge, I have also included some Clinical Questions based around this period of development.
If you have finished and need some more help understanding this period of development, I have included some links to Online References.
If you have finished and are interested in looking at tissues involved in this period of development, I have included some links to Histology Images.
Note that this Practical has discussed mainly development of the embryo as placental development will be covered in detail in another practical (Practical 14 - Placenta and Fetal Membranes).
The next Practical will continue on through embryonic development (Implantation to 8 Weeks).
BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | Tutorial
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
Cite this page: Hill, M.A. (2024, April 24) Embryology BGDA Practical 3 - Week 3 Summary. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_3_-_Week_3_Summary
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G