BGDA Lecture - Development of the Embryo/Fetus 1: Difference between revisions
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[[File:BGDsmall.jpg|left]] | [[File:BGDsmall.jpg|left]] | ||
==Introduction== | ==Introduction== | ||
[[File:Human development timeline graph 02.jpg|thumb|400px]] | [[File:Human development timeline graph 02.jpg|thumb|400px|link=One Minute Embryology#Human Timeline]] | ||
In medicine foundations you were given a broad overview of human development. Now in BGDA we will be working through the human development process in more detail, focussing on key events. | |||
<br><br> | |||
[[Media:2018 BGDA Lecture - Development of the Embryo-Fetus 1.pdf|'''2018 Lecture PDF''']] | |||
* Begin by reviewing the recent Foundations [[Foundations Lecture - Introduction to Human Development|Lecture]] and [[Foundations Practical - Introduction to Human Development|Practical]]. | * Begin by reviewing the recent Foundations [[Foundations Lecture - Introduction to Human Development|Lecture]] and [[Foundations Practical - Introduction to Human Development|Practical]]. | ||
* This lecture covers conceptus development from fertilization to implantation to trilaminar embryo formation. | * This BGDA lecture covers conceptus development from fertilization to implantation to trilaminar embryo formation. | ||
** Note that {{fertilization}} and [[week 1]] concepts have already been covered in an earlier BGDA lecture. | |||
* The lecture will also introduce early fetal membranes and placentation. | * The lecture will also introduce early fetal membranes and placentation. | ||
<br> | |||
{{OneMinuteClock}} | |||
==Textbooks== | [[One_Minute_Embryology#Human_Timeline|'''1 Minute Embryology''']] | [http://thebox.unsw.edu.au/video/1-minute-embryology-human-timeline UNSW theBox] | ||
===The Developing Human: Clinically | <br><br> | ||
[[Media:2019 BGDA Lecture - Development of the Embryo-Fetus 1.pdf|'''2019 Lecture PDF''']] | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Lecture Archive | |||
|- | |||
| [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_1&oldid=335824 2018] | [[Media:2018 BGDA Lecture - Development of the Embryo-Fetus 1.pdf|2018 PDF]] | |||
[[Media:2017 BGDA Lecture - Development of the Embryo-Fetus 1.pdf|2017 PDF]] | [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_1&oldid=248130 2016] | | |||
[https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_1&oldid=179121 2015] | [[Media:2015BGDA Lecture - Development of the Embryo-Fetus 1.pdf|2015 PDF]] | [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_1&oldid=139846 2014] | [[Media:BGDA_Lecture_2014_-_Development_of_the_Embryo-Fetus_1.pdf|2014 PDF]] | [http://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_1&oldid=122686 2013] | | |||
<br> | |||
|} | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Textbooks | |||
|- | |||
| | |||
===UNSW Embryology=== | |||
{| | |||
| valign=top|[[File:Logo.png|90px]] | |||
| {{Embryo citation}} | |||
* [[BGDA_Practical_-_Fertilization_to_Implantation|BGDA Practical 3 - Fertilization to Implantation]] | |||
* {{menstrual cycle}} | {{oocyte}} | {{spermatozoa}} | {{meiosis}} | {{mitosis}} | {{ovary}} | {{testis}} | |||
* {{fertilization}}| {{zygote}} | {{morula}} | [[Blastocyst]] | [[Implantation]] | |||
* {{gastrulation}} | {{Somitogenesis}} | |||
* [[Week 1]] | [[Week 2]] | [[Week 3]] | |||
* [[Lecture - Fertilization]] | [[Lecture - Week 1 and 2 Development|Lecture - Week 1 and 2]] | |||
* [[Movies]] | [[Movies#Week_1|Week 1]] | [[Movies#Week_2|Week 2]] | [[Movies#Week_3|Week 3]] | |||
|} | |||
===The Developing Human: Clinically Oriented Embryology=== | |||
{{MPT2015APAcitation}} (links only function with UNSW connection) | |||
{| | {| | ||
|- | |- | ||
| [[File:The Developing Human, | | valign=top|[[File:The Developing Human, 10th edn.jpg|90px]] | ||
| | | | ||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=23 Introduction to the Developing Human] | |||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=34 First Week of Human Development] | |||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=65 Second Week of Human Development] | |||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=81 Third Week of Human Development] | |||
{{UNSW textbook - The Developing Human}} | |||
|} | |} | ||
===Larsen's | ===Larsen's Human Embryology=== | ||
{{Larsen2015APAcitation}}(links only function with UNSW connection) | |||
{| | |||
|- | |||
| [[File:Larsen's human embryology 5th ed.jpg|90px]] | |||
| | |||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=32 Gametogenesis, Fertilization, and First Week] | |||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=61 Second Week: Becoming Bilaminar and Fully Implanting] | |||
# [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=75 Third Week: Becoming Trilaminar and Establishing Body Axes] | |||
{ | {{UNSW textbook - Larsen's Human Embryology}} | ||
|} | |} | ||
[[Embryology_Textbooks|More Textbooks?]] | |||
|} | |} | ||
===BGDA Practical Classes=== | |||
{| border="1" cellpadding="10" | |||
| [[BGDA_Practical_-_Fertilization_to_Implantation|'''Practical 3 - Fertilization to Implantation''']] | |||
| [[BGDA_Practical_-_Implantation_to_8_Weeks|'''Practical 6 - Implantation to 8 Weeks''']] | |||
| [[BGDA_Practical_-_Fetal_Development|'''Practical 12 - Fetal Period''']] | |||
|- | |||
| | |||
| colspan="2" | <center>[[BGDA_Practical_-_Placenta_and_Fetal_Membranes|'''Practical 14 - Placenta and Fetal Membranes''']]</center> | |||
|} | |||
==Human Reproductive Cycle== | ==Human Reproductive Cycle== | ||
* | * '''{{meiosis}}''' in gonad produces haploid gametes ({{oocyte}}, egg) and ({{spermatozoa}}, sperm) | ||
{| | |||
! Female | |||
! Male | |||
|- | |||
| | |||
* [[Menstrual Cycle]] a regular cycle of reproduction (28 days) | * [[Menstrual Cycle]] a regular cycle of reproduction (28 days) | ||
* begins at puberty | * prenatal all oocytes produced | ||
* begins at puberty, release of 1 egg (oocyte) every cycle | |||
* Endocrine controlled (HPG axis) | * Endocrine controlled (HPG axis) '''H'''ypothalamus - '''P'''ituitary - '''G'''onad | ||
** | | | ||
* | * postnatal continuous production of spermatozoa | ||
* begins at {{puberty}}, release millions of spermatozoa | |||
* Endocrine controlled (HPG axis) '''H'''ypothalamus - '''P'''ituitary - '''G'''onad | |||
|} | |||
[[File:XXhpgaxis.jpg|300px]] [[File:Menstrual_cycle.png|500px]] | [[File:XXhpgaxis.jpg|300px]] [[File:Menstrual_cycle.png|500px]] | ||
==Gametogenesis== | ==Gametogenesis== | ||
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<gallery> | <gallery> | ||
File:Historic-testis.jpg|Historic testis drawing | File:Historic-testis.jpg|Historic testis drawing | ||
File:Testis_histology_006.jpg|Child Seminiferous tubule | |||
File:Seminiferous-tubule-HEx40.jpg|Adult Seminiferous tubule showing spermatozoa developmental stages | File:Seminiferous-tubule-HEx40.jpg|Adult Seminiferous tubule showing spermatozoa developmental stages | ||
File:Testis_histology_2.jpg|Seminiferous tubule cross-section and supporting cells | File:Testis_histology_2.jpg|Seminiferous tubule cross-section and supporting cells | ||
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</gallery> | </gallery> | ||
Human spermatozoa take about 48 days from entering meiosis until morphologically mature spermatozoa. | Human {{spermatozoa}} take about '''48 days''' from entering meiosis until morphologically mature spermatozoa. | ||
{| | |||
| | |||
* Spermatogonia - are the first cells of spermatogenesis | |||
* Primary spermatocytes - large, enter the prophase of the first meiotic division | |||
* Secondary spermatocytes - small, complete the second meiotic division | |||
* Spermatid - immature spermatozoa | |||
* Spermatozoa - differentiated gamete | |||
::'''Spermatozoa development:''' primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa | |||
::'''Spermatozoa development:''' | |||
'''{{Sertoli cell}}s''' (support cells) '''Interstitial cells''' or Leydig cells (produce hormone testosterone) | |||
| [[File:Seminiferous tubule cartoon.jpg|400px]] | |||
|} | |||
{{Spermatozoa Terms collapse table}} | |||
===Female=== | ===Female=== | ||
The | The {{ovary}} has two main functions. | ||
# produce the female gametes or '''oocytes''' | # produce the female gametes or '''oocytes''' | ||
# produce female hormones, | # produce female hormones, '''estrogen''' and '''progesterone''' (secondary sex characteristics, menstrual cycle) | ||
<gallery> | <gallery> | ||
File:Infant_ovary.jpg|infant ovary | |||
File:Ovary5x.gif|overview of ovary | File:Ovary5x.gif|overview of ovary | ||
File:Ovary10x.jpg|three stages of follicle development | File:Ovary10x.jpg|three stages of follicle development | ||
File:Ova41he.jpg|primary follicle | File:Ova41he.jpg|primary follicle | ||
File:Ova20he.jpg| | File:Ova20he.jpg|tertiary follicle | ||
</gallery> | </gallery> | ||
In an adult human female the development of a primordial follicle containing an oocyte to a preovulatory follicle takes in excess of 120 days. | In an adult human female the development of a primordial follicle containing an oocyte to a preovulatory follicle takes in excess of '''120 days'''. | ||
[[File:Human_ovary_follicle_development.jpg|600px]] | |||
Human ovary follicle development | |||
::'''Ovarian Follicle Stages:''' | ::'''Ovarian Follicle Stages:''' primordial follicle - primary follicle - secondary follicle - preovulatory follicle | ||
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{{Oocyte terms collapse table}} | |||
:'''Links:''' {{spermatozoa}} | {{oocyte}} | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3716 MBoC - Figure 20-18. Influence of Sry on gonad development] | [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=endocrin&part=A972&rendertype=box&id=A1230 Endocrinology - Comparative anatomy of male and female reproductive tracts] | |||
==Fertilization== | ==Fertilization== | ||
[[ | [[File:Early_zygote_labelled.jpg|thumb|Early zygote showing polar bodies]] | ||
* | * {{Oogenesis}} - 1 gamete produced/meiosis + 3 polar bodies, meiosis is slow, 1 egg produced and released at ovulation | ||
* | * {{Spermatogenesis}} - 4 gametes produced/meiosis, meiosis is fast, 200-600 million sperm released at ejaculation | ||
[[File:Ovulation_icon.jpg|90px|link= | [[File:Ovulation_icon.jpg|90px|link=Rabbit Ovulation Movie]] [[File:Fertilization 001 icon.jpg|90px|link=Mouse Fertilization Movie]] | ||
===Fertilization Site=== | ===Fertilization Site=== | ||
* Fertilization usually occurs in first 1/3 of uterine tube (oviduct, Fallopian tube) | * Fertilization usually occurs in first 1/3 of uterine tube (oviduct, Fallopian tube) | ||
* Fertilization can also occur outside uterine tube associated with | * Fertilization can also occur outside uterine tube associated with Assisted Reproductive Technologies ({{ART}}, IVF, GIFT, ZIFT...) and {{ectopic pregnancy}} | ||
* The majority of fertilized eggs do not go on to form an embryo | * The majority of fertilized eggs do not go on to form an embryo | ||
===Fertilization - Spermatozoa === | ===Fertilization - Spermatozoa=== | ||
* '''Sperm Binding''' - | |||
* | * '''Capacitation''' - alteration of the spermatozoa metabolism and surface proteins | ||
** enzymes to digest the zona pellucida | * '''Sperm Binding''' - zona pellucida protein {{ZP3}} acts as receptor for sperm | ||
** exposes sperm surface proteins to bind ZP2 | * Acrosome Reaction - exocytosis of acrosome contents (Calcium mediated) [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3741 MBoC - Figure 20-31. The acrosome reaction that occurs when a mammalian sperm fertilizes an egg] | ||
* '''Membrane Fusion''' - between sperm and egg, allows sperm nuclei passage into egg cytoplasm | ** enzymes to digest the {{zona pellucida}} | ||
** exposes sperm surface proteins to bind {{ZP2}} | |||
* '''Membrane Fusion''' - between sperm and egg, allows sperm nuclei passage into egg cytoplasm | |||
<br> | |||
{{Human Fertilization Movie 2 frame table}} | |||
===Fertilization - Oocyte=== | ===Fertilization - Oocyte=== | ||
* '''Membrane Depolarization''' - caused by sperm membrane fusion, primary block to polyspermy | * '''Membrane Depolarization''' - caused by sperm membrane fusion, primary block to polyspermy | ||
* | * Cortical Reaction - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3743 MBoC - Figure 20-32. How the cortical reaction in a mouse egg is thought to prevent additional sperm from entering the egg] | ||
** enzyme alters ZP3 so it will no longer bind sperm plasma membrane | ** enzyme alters ZP3 so it will no longer bind sperm plasma membrane | ||
* '''Meiosis 2''' - completion of 2nd meiotic division | * '''Meiosis 2''' - completion of 2nd meiotic division | ||
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[[File:Week1_summary.jpg]] | [[File:Week1_summary.jpg]] | ||
[[File: | [[File:Human embryo day 5 label.jpg|300px]] [[File:Human embryo day 5 label2.jpg|300px]] | ||
[[File:Human_blastocyst_day_1-6.jpg|link=Blastocyst Day 3-6 Movie]] | |||
===Week 2 Implantation=== | ===Week 2 Implantation=== | ||
* Bilaminar embryo - {{Epiblast}} and {{Hypoblast}} | |||
* Bilaminar {{trophoblast}} - Cytotrophoblast and Syncytiotrophoblast | |||
[[File:Week2_001 icon.jpg|200px|link=Implantation Movie]] [[File:Chorion 001 icon.jpg|200px|link=Chorionic Cavity Movie]] | |||
= | {| | ||
|-bgcolor="CEDFF2" | |||
! Uterine Implantation | |||
! Ectopic Implantation | |||
|- | |||
| | |||
* Uterine body | * Uterine body | ||
** posterior, anterior, superior, lateral (most common posterior) | ** posterior, anterior, superior, lateral (most common posterior) | ||
** inferior implantation | ** '''Placenta Previa''' inferior implantation, placenta overlies internal os of uterus | ||
| | |||
* Outside Uterine body | |||
* | |||
** external surface of uterus, ovary, bowel, gastrointestinal tract, mesentery, peritoneal wall | ** external surface of uterus, ovary, bowel, gastrointestinal tract, mesentery, peritoneal wall | ||
** | ** '''Tubal pregnancy''' - (uterine tube) most common ectopic | ||
|- | |||
| [[File:Galletti1770 placenta previa.jpg|200px]] | |||
| [[File:Tubal_pregnancy.gif|200px]] | |||
|} | |||
===Early Placenta=== | ===Early Placenta=== | ||
{| | |||
| | |||
* interaction between implanting conceptus and uterine wall (endometrium) | * interaction between implanting conceptus and uterine wall (endometrium) | ||
* The uterine lining following implantation (Decidua) | * The uterine lining following implantation (Decidua) | ||
** forms 3 distinct regions, at approx 3 weeks | ** forms 3 distinct regions, at approx 3 weeks | ||
** Decidua Basalis - implantation site | ** '''Decidua Basalis''' - implantation site | ||
** Decidua Capsularis - enclosing the conceptus | ** '''Decidua Capsularis''' - enclosing the conceptus | ||
** Decidua Parietalis - remainder of uterus | ** '''Decidua Parietalis''' - remainder of uterus | ||
* uterine cavity is lost by 12 weeks | * uterine cavity is lost by 12 weeks | ||
| [[File:Bailey494.jpg|400px]] | |||
|} | |||
==Week 3 Gastrulation== | ==Week 3 Gastrulation== | ||
[[File: | {| | ||
| [[File:Stage7-sem2.jpg|300px]] | |||
[[File: | | [[File:Stage7 primitive streak labelled.jpg|300px|Stage7 primitive streak]] | ||
| [[File:Chicken-gastrulation3.jpg|300px]] | |||
|- | |||
| Embryonic disc | |||
| Primitive Streak | |||
| Gastrulation | |||
|} | |||
* | * '''Primitive node''' - region in the middle of the early embryonic disc epiblast from which the primitive streak extends caudally (tail) | ||
** nodal cilia establish the embryo left/right axis | ** nodal cilia establish the embryo left/right axis | ||
** axial process extends from the nodal epiblast | ** axial process extends from the nodal epiblast | ||
* | * '''Primitive streak''' - region of cell migration (gastrulation) from the epiblast layer forming sequentially the two germ cell layers ({{endoderm}} and {{mesoderm}}) | ||
{| | |||
| Gastrulation, (Greek = belly) | |||
Means the formation of gut, but has been used in a more looser sense to to describe the formation of the trilaminar embryo. The epiblast layer, consisting of totipotential cells, derives all 3 embryo layers: | |||
# {{ectoderm}} | |||
# {{mesoderm}} | |||
# {{endoderm}} | |||
The primitive streak is the visible feature which represents the site of cell migration to form the additional layers. Historically, gastrulation was one of the earliest observable morphological event occurring in the frog embryo. | |||
| {{Week 3 mesoderm movie}} | |||
| [[File:Trilaminar_embryo.jpg|300px]] | |||
Trilaminar embryo (SEM) | |||
|} | |||
[[File:Trilaminar_embryo_cartoon.jpg|400px|Trilaminar embryo]] | [[File:Trilaminar_embryo_cartoon.jpg|400px|Trilaminar embryo]] | ||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Virtual Slides - Human Embryo (stage 7) | |||
|- | |||
| {{VirtualSlidesStage7}} | |||
|} | |||
== Notochord == | == Notochord == | ||
[[ | [[File:Stage7 axial process.jpg|thumb|300px|Stage7 axial process]] | ||
The | The {{notochord}} is a structure which has an early '''mechanical role''' in embryonic disc folding and a major '''signaling role''' in patterning surrounding embryonic tissue development. This signaling role patterns many different tissues (neural plate, neural tube, somites, endodermal organs). It has its own sequence of development from a primitive axial process and is a developmental feature not present in the adult anatomy. | ||
[[File:Notochord 02 icon.jpg|160px|link= | [[File:Notochord 02 icon.jpg|160px|link=Notochord Movie]] | ||
[[ | [[Notochord Movie|Page]] | ||
* '''axial process''' an initial epiblast hollow epithelial tube which extends in the midline from the primitive pit, cranially in the embryonic disc (toward the oral membrane). | * '''axial process''' an initial epiblast hollow epithelial tube which extends in the midline from the primitive pit, cranially in the embryonic disc (toward the oral membrane). | ||
** '''neuroenteric canal''' is a transient communication between the amnionic cavity and the yolk sac cavity formed by the axial process. | ** '''neuroenteric canal''' is a transient communication between the amnionic cavity and the yolk sac cavity formed by the axial process. | ||
* '''notochordal plate''' forms from the axial process merging with the endoderm layer. | * '''notochordal plate''' forms from the axial process merging with the {{endoderm}} layer. | ||
* '''notochord''' forms from the notochordal plate which then separates back into the mesoderm layer as a solid column of cells lying in the midline of the embryonic disc and running rostro-caudally (head to tail). | * '''notochord''' forms from the notochordal plate which then separates back into the mesoderm layer as a solid column of cells lying in the midline of the embryonic disc and running rostro-caudally (head to tail). | ||
** An alternate name for the notochord is "axial mesoderm". | ** An alternate name for the notochord is "axial mesoderm". | ||
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==Somitogenesis== | ==Somitogenesis== | ||
[[File:Stage_9_SEM1.jpg|thumb|stage 9 Embryo]] [[File:Stage10 bf6b.jpg|thumb|stage 10 Embryo]] | [[File:Stage_9_SEM1.jpg|thumb|stage 9 Embryo]] [[File:Stage10 bf6b.jpg|thumb|stage 10 Embryo]] | ||
'''Mesoderm''' means the "middle layer" and it is from this layer that nearly all the bodies connective tissues are derived. In early mesoderm development a number of transient structures will form and then be lost as tissue structure is patterned and organised. Humans are vertebrates, with a "backbone", and the first mesoderm structure we will see form after the notochord will be '''[[S#somite|somites]]'''. | '''Mesoderm''' means the "middle layer" and it is from this layer that nearly all the bodies connective tissues are derived. In early {{mesoderm}} development a number of transient structures will form and then be lost as tissue structure is patterned and organised. Humans are vertebrates, with a "backbone", and the first mesoderm structure we will see form after the notochord will be '''[[S#somite|somites]]'''. | ||
<gallery mode="packed-hover" caption="Mesoderm and Ectoderm Cartoons"> | |||
File:Mesoderm-cartoon1.jpg|Trilaminar Embryo | |||
File:Mesoderm-cartoon2.jpg|Paraxial and Lateral Plate | |||
File:Mesoderm-cartoon3.jpg|Somites | |||
File:Mesoderm-cartoon4.jpg|Somatic and Splanchnic | |||
</gallery> | |||
'''Coelom''', meaning "cavity", and major fluid-filled cavities can be seen to form both within the embryo (|intraembryonic coelom) and outside the embryo (extraembryonic coelom). | |||
The '''intraembryonic coelom''' is the single primitive cavity that lies within the {{mesoderm}} layer that will eventually form the 3 major anatomical body cavities ('''pericardial, pleural, peritoneal'''). | |||
[[File:Stage11 sem100c.jpg|thumb|stage 11 Embryo]] | |||
Somite initially forms 2 main components | |||
* '''sclerotome''' - (ventromedial) forms axial skeleton - vertebral body and intervertebral disc | |||
* '''dermomyotome''' - (dorsolateral) forms dermis and skeletal muscle | |||
== | <gallery mode="packed-hover" caption="Somite Cartoons"> | ||
File:Somite cartoon1.png|paraxial | |||
File: | File:Somite cartoon2.png|early somite | ||
File: | File:Somite cartoon3.png|sclerotome and dermomyotome | ||
File: | File:Somite cartoon4.png|dermatome and myotome | ||
File: | File:Somite cartoon5.png|somite spreading | ||
</gallery> | </gallery> | ||
==Neural== | |||
* midline | Week 3 {{ectoderm}} - 2 parts | ||
* lateral surface ectoderm (cuboidal cells) | * midline - neural plate (columnar cells) | ||
** central nervous system (CNS) | |||
* edge of neural plate - {{neural crest}} | |||
** peripheral nervous system (PNS), and many other structures. | |||
* lateral - surface ectoderm (cuboidal cells) | |||
** epidermis of skin, hair, glands, anterior pituitary, teeth enamel | ** epidermis of skin, hair, glands, anterior pituitary, teeth enamel | ||
** head region - sensory placodes | |||
== | <gallery mode="packed-hover" caption="Ectoderm"> | ||
File:Neural_plate_movie_icon.jpg|Neural plate | |||
File:Mesoderm-cartoon1.jpg|Neural plate | |||
File:Mesoderm-cartoon3.jpg|Neural groove | |||
File:Mesoderm-cartoon4.jpg|Neural tube and Neural crest | |||
</gallery> | |||
* extends from | * extends from buccopharyngeal membrane to primitive node | ||
* forms above | * forms above notochord and paraxial mesoderm | ||
* neuroectodermal cells | * neuroectodermal cells | ||
** broad brain plate | ** broad brain plate | ||
** narrower spinal cord | ** narrower spinal cord | ||
* 3 components form: | * 3 components form: floor plate,neural plate, neural crest | ||
{| | |||
| valign="bottom"|{{Neural plate movie}} | |||
| valign="bottom"|{{Neural tube movie}} | |||
| valign="bottom"|{{Neural Tube Closure 1 movie}} | |||
|} | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Week 4 Embryo (dorsal view) | |||
|- | |||
| {{SlideStage10bf10}} | |||
[[Embryo Virtual Slides]] | |||
|- | |||
| | |||
<gallery> | |||
File:Stage10_SEM1.jpg|[[Carnegie_stage_10|Stage 10]] (22 - 23 days) | |||
File:Stage10_sem2.jpg|[[Carnegie_stage_10|Stage 10]] (22 - 23 days) | |||
File:Stage11 sem6.jpg|[[Carnegie_stage_11|Stage 11]] (23 - 26 days) | |||
File:Stage12_SEM3.jpg|[[Carnegie_stage_11|Stage 11]] (26 - 30 days) | |||
</gallery> | |||
|} | |||
{| | |||
! Neural Tube Defects | |||
|- | |||
| {{Ultrasound Spina-Bifida}} | |||
| [[File:Anencephaly ultrasound.jpg|200px]] | |||
| [[File:Neural tube defect meningomyelocele.jpg|200px]] | |||
|- | |||
| Spina-Bifida | |||
| Anencephaly | |||
| Meningomyelocele | |||
|} | |||
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==Cardiogenesis== | ==Cardiogenesis== | ||
[[File: | [[File:Heart_Tube_Fusion.jpg|thumb|200px|alt=Heart Tube Fusion|Heart Tube Fusion]] | ||
[[File:Early_Development_of_Heart_Tube.jpg|600px]] | |||
Early Development of Heart Tube | |||
[[File:Human heart SEM1.jpg]] | [[File:Human heart SEM1.jpg]] | ||
The Human Heart from day 10 to 25 (scanning electron micrograph) | The Human Heart from day 10 to 25 (scanning electron micrograph) | ||
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===Blood Formation=== | ===Blood Formation=== | ||
[[File:Mouse hematopoietic stem cell.gif|thumb|Mouse hematopoietic stem cell location]] | [[File:Mouse hematopoietic stem cell.gif|thumb|Mouse hematopoietic stem cell location]] | ||
* blood formation from stem cells occurs initially in the | * blood formation from stem cells occurs initially in the extra-embryonic mesoderm of the yolk sac | ||
* then later (week 5) throughout embryonic mesenchyme | * then later (week 5) throughout embryonic mesenchyme | ||
* blood stem cells then migrate into the liver | * blood stem cells then migrate into the liver | ||
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===Red Blood Cells=== | ===Red Blood Cells=== | ||
The only cells in the blood are | The only cells in the blood are initially entirely fetal red blood cells (RBC). | ||
These red blood cells differ from adult red blood cells in: | These red blood cells differ from adult red blood cells in: | ||
* | * may remaining nucleated | ||
* contain | * contain fetal haemoglobin - has different oxygen and carbon dioxide binding characteristics | ||
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The trophoblast layer has now differentiated into two morphologically distinct cellular layers. | The trophoblast layer has now differentiated into two morphologically distinct cellular layers. | ||
*''' | *'''Syncitiotrophoblasts''' - form a multinucleated cytoplasmic mass by cytotrophoblast cell fusion and both invade the decidua and secrete hCG | ||
*''' | *'''Cytotrophoblasts''' - form a cellular layer around the [[B#blastocyst|blastocyst]], proliferates and extends behind syncitiotrophoblasts | ||
Early Utero-Placental exchange - transfer of nutrition from maternal lacunae filled with secretions from [[U#uterine gland|uterine glands]] and maternal blood from blood vessels. | Early Utero-Placental exchange - transfer of nutrition from maternal lacunae filled with secretions from [[U#uterine gland|uterine glands]] and maternal blood from blood vessels. | ||
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There are three stages of villi development: | There are three stages of villi development: | ||
# '''Primary Villi''' - | # '''Primary Villi''' - cytotrophoblast | ||
# '''Secondary Villi''' - | # '''Secondary Villi''' - cytotrophoblast + extraembryonic mesoderm | ||
# '''Tertiary Villi''' - | # '''Tertiary Villi''' - cytotrophoblast + extraembryonic mesoderm + blood vessels | ||
<gallery> | <gallery> | ||
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There are two main types of early villi: | There are two main types of early villi: | ||
* Anchoring villi - attached to | * '''Anchoring villi''' - attached to decidua | ||
* Floating villi - not attached to | * '''Floating villi''' - not attached to decidua, floating in maternal lacunae. | ||
== | ==Abnormalities== | ||
Critical periods, Genetic and Environmental factors leading to abnormal development will be covered in the associated practical classes. | |||
{{ | {{BGDAFooter}} |
Latest revision as of 15:24, 2 May 2019
Embryology - 18 Jun 2024 Expand to Translate |
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Introduction
In medicine foundations you were given a broad overview of human development. Now in BGDA we will be working through the human development process in more detail, focussing on key events.
2018 Lecture PDF
- Begin by reviewing the recent Foundations Lecture and Practical.
- This BGDA lecture covers conceptus development from fertilization to implantation to trilaminar embryo formation.
- Note that fertilization and week 1 concepts have already been covered in an earlier BGDA lecture.
- The lecture will also introduce early fetal membranes and placentation.
1 Minute Embryology | UNSW theBox
2019 Lecture PDF
Lecture Archive |
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2018 PDF
2017 PDF | 2016 |
2015 | 2015 PDF | 2014 | 2014 PDF | 2013 |
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BGDA Practical Classes
Practical 3 - Fertilization to Implantation | Practical 6 - Implantation to 8 Weeks | Practical 12 - Fetal Period |
Human Reproductive Cycle
- meiosis in gonad produces haploid gametes (oocyte, egg) and (spermatozoa, sperm)
Female | Male |
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Gametogenesis
Male
The testes have two functions.
- produce the male gametes or spermatozoa
- produce male sexual hormone, testosterone (internal and external genitalia, sex characteristics)
Human spermatozoa take about 48 days from entering meiosis until morphologically mature spermatozoa.
sertoli cells (support cells) Interstitial cells or Leydig cells (produce hormone testosterone) |
Spermatozoa Development (expand to see terms) | ||
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Note there are additional glossaries associated with genital, spermatozoa, oocyte and renal.
See also: Spermatozoa Terms collapse table
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Female
The ovary has two main functions.
- produce the female gametes or oocytes
- produce female hormones, estrogen and progesterone (secondary sex characteristics, menstrual cycle)
In an adult human female the development of a primordial follicle containing an oocyte to a preovulatory follicle takes in excess of 120 days.
Human ovary follicle development
- Ovarian Follicle Stages: primordial follicle - primary follicle - secondary follicle - preovulatory follicle
Follicle cells (support cells) Theca cells (produce hormone)
Oocyte Development (expand to see terms) | ||
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Note there are additional specific term glossaries available listed at bottom of this table.
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- Links: spermatozoa | oocyte | MBoC - Figure 20-18. Influence of Sry on gonad development | Endocrinology - Comparative anatomy of male and female reproductive tracts
Fertilization
- oogenesis - 1 gamete produced/meiosis + 3 polar bodies, meiosis is slow, 1 egg produced and released at ovulation
- spermatogenesis - 4 gametes produced/meiosis, meiosis is fast, 200-600 million sperm released at ejaculation
Fertilization Site
- Fertilization usually occurs in first 1/3 of uterine tube (oviduct, Fallopian tube)
- Fertilization can also occur outside uterine tube associated with Assisted Reproductive Technologies (ART, IVF, GIFT, ZIFT...) and ectopic pregnancy
- The majority of fertilized eggs do not go on to form an embryo
Fertilization - Spermatozoa
- Capacitation - alteration of the spermatozoa metabolism and surface proteins
- Sperm Binding - zona pellucida protein ZP3 acts as receptor for sperm
- Acrosome Reaction - exocytosis of acrosome contents (Calcium mediated) MBoC - Figure 20-31. The acrosome reaction that occurs when a mammalian sperm fertilizes an egg
- enzymes to digest the zona pellucida
- exposes sperm surface proteins to bind ZP2
- Membrane Fusion - between sperm and egg, allows sperm nuclei passage into egg cytoplasm
Approximate Timing of Early Human Events (in vitro) | ||||
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20 min - components | 28 min - spermatozoa penetrates zone pellucida | 31 min - spermatozoa penetrates oocyte - fertilization | ||
See also clock in lower righthand corner for the approximate timing of events. | ||||
Reference: PMID 22695746 J Assist Reprod Genet. |
Fertilization - Oocyte
- Membrane Depolarization - caused by sperm membrane fusion, primary block to polyspermy
- Cortical Reaction - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules MBoC - Figure 20-32. How the cortical reaction in a mouse egg is thought to prevent additional sperm from entering the egg
- enzyme alters ZP3 so it will no longer bind sperm plasma membrane
- Meiosis 2 - completion of 2nd meiotic division
- forms second polar body (a third polar body may be formed by meiotic division of the first polar body)
Week 1 and 2
Week 2 Implantation
- Bilaminar embryo - epiblast and hypoblast
- Bilaminar trophoblast - Cytotrophoblast and Syncytiotrophoblast
Uterine Implantation | Ectopic Implantation |
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Early Placenta
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Week 3 Gastrulation
Embryonic disc | Primitive Streak | Gastrulation |
- Primitive node - region in the middle of the early embryonic disc epiblast from which the primitive streak extends caudally (tail)
- nodal cilia establish the embryo left/right axis
- axial process extends from the nodal epiblast
- Primitive streak - region of cell migration (gastrulation) from the epiblast layer forming sequentially the two germ cell layers (endoderm and mesoderm)
Gastrulation, (Greek = belly)
Means the formation of gut, but has been used in a more looser sense to to describe the formation of the trilaminar embryo. The epiblast layer, consisting of totipotential cells, derives all 3 embryo layers: The primitive streak is the visible feature which represents the site of cell migration to form the additional layers. Historically, gastrulation was one of the earliest observable morphological event occurring in the frog embryo. |
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Trilaminar embryo (SEM) |
Virtual Slides - Human Embryo (stage 7) | ||||||||||||||||
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Notochord
The notochord is a structure which has an early mechanical role in embryonic disc folding and a major signaling role in patterning surrounding embryonic tissue development. This signaling role patterns many different tissues (neural plate, neural tube, somites, endodermal organs). It has its own sequence of development from a primitive axial process and is a developmental feature not present in the adult anatomy.
- axial process an initial epiblast hollow epithelial tube which extends in the midline from the primitive pit, cranially in the embryonic disc (toward the oral membrane).
- neuroenteric canal is a transient communication between the amnionic cavity and the yolk sac cavity formed by the axial process.
- notochordal plate forms from the axial process merging with the endoderm layer.
- notochord forms from the notochordal plate which then separates back into the mesoderm layer as a solid column of cells lying in the midline of the embryonic disc and running rostro-caudally (head to tail).
- An alternate name for the notochord is "axial mesoderm".
Somitogenesis
Mesoderm means the "middle layer" and it is from this layer that nearly all the bodies connective tissues are derived. In early mesoderm development a number of transient structures will form and then be lost as tissue structure is patterned and organised. Humans are vertebrates, with a "backbone", and the first mesoderm structure we will see form after the notochord will be somites.
Coelom, meaning "cavity", and major fluid-filled cavities can be seen to form both within the embryo (|intraembryonic coelom) and outside the embryo (extraembryonic coelom).
The intraembryonic coelom is the single primitive cavity that lies within the mesoderm layer that will eventually form the 3 major anatomical body cavities (pericardial, pleural, peritoneal).
Somite initially forms 2 main components
- sclerotome - (ventromedial) forms axial skeleton - vertebral body and intervertebral disc
- dermomyotome - (dorsolateral) forms dermis and skeletal muscle
Neural
Week 3 ectoderm - 2 parts
- midline - neural plate (columnar cells)
- central nervous system (CNS)
- edge of neural plate - neural crest
- peripheral nervous system (PNS), and many other structures.
- lateral - surface ectoderm (cuboidal cells)
- epidermis of skin, hair, glands, anterior pituitary, teeth enamel
- head region - sensory placodes
- extends from buccopharyngeal membrane to primitive node
- forms above notochord and paraxial mesoderm
- neuroectodermal cells
- broad brain plate
- narrower spinal cord
- 3 components form: floor plate,neural plate, neural crest
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Week 4 Embryo (dorsal view) | |||
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Neural Tube Defects | |||||
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Spina-Bifida | Anencephaly | Meningomyelocele |
Cardiogenesis
Early Development of Heart Tube
The Human Heart from day 10 to 25 (scanning electron micrograph)
- forms initially in splanchnic mesoderm of prechordal plate region - cardiogenic region
- growth and folding of the embryo moves heart ventrallly and downward into anatomical position
- week 3 begins as paired heart tubes that fuse to form single heart tube
- begins to beat in Humans- day 22-23
Blood Islands
- 2 populations of cells
- peripheral- form endothelial cells that form the lining of all blood vessels
- core- form blood cells (haemocytoblasts)
- all vessels (arteries and veins) appear initially the same
Blood Formation
- blood formation from stem cells occurs initially in the extra-embryonic mesoderm of the yolk sac
- then later (week 5) throughout embryonic mesenchyme
- blood stem cells then migrate into the liver
- then spleen, bone marrow, lymph nodes
Red Blood Cells
The only cells in the blood are initially entirely fetal red blood cells (RBC).
These red blood cells differ from adult red blood cells in:
- may remaining nucleated
- contain fetal haemoglobin - has different oxygen and carbon dioxide binding characteristics
- Links: Basic Cardiac Embryology
Early Placentation
The trophoblast layer has now differentiated into two morphologically distinct cellular layers.
- Syncitiotrophoblasts - form a multinucleated cytoplasmic mass by cytotrophoblast cell fusion and both invade the decidua and secrete hCG
- Cytotrophoblasts - form a cellular layer around the blastocyst, proliferates and extends behind syncitiotrophoblasts
Early Utero-Placental exchange - transfer of nutrition from maternal lacunae filled with secretions from uterine glands and maternal blood from blood vessels. The development of trophoblast villi extending into the uterine decidua.
There are three stages of villi development:
- Primary Villi - cytotrophoblast
- Secondary Villi - cytotrophoblast + extraembryonic mesoderm
- Tertiary Villi - cytotrophoblast + extraembryonic mesoderm + blood vessels
There are two main types of early villi:
- Anchoring villi - attached to decidua
- Floating villi - not attached to decidua, floating in maternal lacunae.
Abnormalities
Critical periods, Genetic and Environmental factors leading to abnormal development will be covered in the associated practical classes.
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, June 18) Embryology BGDA Lecture - Development of the Embryo/Fetus 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Lecture_-_Development_of_the_Embryo/Fetus_1
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G