Lecture - Ectoderm Development: Difference between revisions
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Development of the epidermis (integumentary) and sensory placodes (sensory) and later development of neural, neural crest, will be covered in future topic specific lectures. The current lecture will also introduce the significance of environmental factors, such as maternal diet, to embryonic development. | Development of the epidermis (integumentary) and sensory placodes (sensory) and later development of neural, neural crest, will be covered in future topic specific lectures. The current lecture will also introduce the significance of environmental factors, such as maternal diet, to embryonic development. | ||
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! colspan=2|2017 Medicine Lecture Video - Neural | |||
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| I think this is the lecture with poor audio quality. While I do not have a Science Lecture available I have added the Medicine equivalent content. Note that the lecture slides from Dr Beverdam's lecture are the examinable theory content. | |||
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==Objectives== | ==Objectives== | ||
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==Lecture Resources== | ==Lecture Resources== | ||
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'''Secondary neurulation''' begins at stage 12 - is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate. Above text modified from | '''Secondary neurulation''' begins at stage 12 - is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate. Above text modified from{{#pmid:8005032|PMID8005032}} | ||
{{Carnegie stages}} | {{Carnegie stages}} | ||
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===Maternal Diet=== | ===Maternal Diet=== | ||
[[File:Monitoring the health impacts of mandatory folic acid and iodine fortification 2016.jpg|thumb|150px|alt=AIHW Report - Folic acid and iodine fortification (2016)|Folic acid and iodine fortification (2016)]] | |||
====Folate==== | ====Folate==== | ||
Found that supplementation of maternal diet with folate reduces incidence of NTDs. | Found that supplementation of maternal diet with folate reduces incidence of NTDs. | ||
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{{Neural terms}} | {{Neural terms}} | ||
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[[Category:Ectoderm]] [[Category:Neural]] [[Category:Neural Crest]] [[Category:Week 3]] [[Category:Week 4]] | [[Category:Ectoderm]] [[Category:Neural]] [[Category:Neural Crest]] [[Category:Week 3]] [[Category:Week 4]] |
Latest revision as of 09:53, 9 October 2019
Embryology - 10 Jun 2024 Expand to Translate |
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Introduction
Covering the same period as the previous mesoderm lecture, lets now look at changes to the ectoderm.
The ectoderm will from the entire nervous system (both central and peripheral), the epidermis of the skin and in the head region specialised placodes.
Development of the epidermis (integumentary) and sensory placodes (sensory) and later development of neural, neural crest, will be covered in future topic specific lectures. The current lecture will also introduce the significance of environmental factors, such as maternal diet, to embryonic development.
2017 Medicine Lecture Video - Neural | ||||
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I think this is the lecture with poor audio quality. While I do not have a Science Lecture available I have added the Medicine equivalent content. Note that the lecture slides from Dr Beverdam's lecture are the examinable theory content. |
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Objectives
- Understanding of events during the third and fourth week of development
- Understanding the process of early neural development
- Brief understanding of neural crest formation
- Brief understanding of epidermis formation
- Understanding of the adult components derived from ectoderm
- Brief understanding of early neural abnormalities
Lecture Resources
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References | |
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Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved June 10, 2024, from https://embryology.med.unsw.edu.au |
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Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders. | The following chapter links only work with a UNSW connection. |
Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone. | The following chapter links only work with a UNSW connection.
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Development Overview
1 trilaminar - neural plate | 2 neural plate to groove |
3 groove folding | 4 neural tube and neural crest |
see also the cartoon animation
Notochord
- forms initially as the Axial Process, a hollow tube which extends from the primitive pit , cranially to the oral membrane
- the axial process then allow transient communication between the amnion and the yolk sac through the neuroenteric canal.
- the axial process then merges with the Endodermal layer to form the Notochordal Plate.
- the notochordal plate then rises back into the Mesodermal layer as a solid column of cells which is the Notochord.
Ectoderm
Two parts
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Neural Plate
<html5media height="520" width="320">File:Neuralplate_001.mp4</html5media> | Development of the neural plate region at the embryonic disc stage.
Dorsal view of the embryonic disc from the amniotic cavity side showing the ectoderm with the central region developing into the neural plate. The neural plate extends from buccopharyngeal membrane to primitive node and forms above the notochord and paraxial mesoderm.The neuroectodermal cells form a broad brain plate and narrower spinal cord region. Three specific regions medial to lateral can also be identified: midline region floor plate, neural plate, edge of neural plate neural crest
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Neural Determination- neuronal populations are specified before plate folds
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Neural Groove
<html5media height="480" width="480">File:Neuraltube_001.mp4</html5media>
Click Here to play on mobile device
This animation of early neural development from week 3 onward shows the neural groove fusing to form the neural tube.
View - Dorsolateral of the whole early embryo and yolk sac. Cranial (head) to top and caudal (tail) to bottom. Yolk sac is shown to the left.
Beginning with the neural groove initially fusing at the level of the 4th somite to form the neural tube and closing in both directions to leave 2 openings or neuropores: a cranial neuropore (anterior neuropore) and a caudal neuropore (posterior neuropore).
The animation also shows as the embryo grows and folds it increases in size relative to the initial yolk sac. Note also the increasing number of somites over time.
- forms in the midline of the neural plate (day 18-19)
- either side of which are the neural folds which continues to deepen until about week 4
- neural folds begins to fuse, beginning at 4th somite level
Neural Tube
<html5media height="440" width="380">File:Mouse neural tube 01.mp4</html5media> | ||
Mouse neural tube closure | Human Stage 10 neural groove to tube | Human Stage 11 forming neuropores |
- the neural tube forms the brain and spinal cord
- fusion of neural groove extends rostrally and caudally
- begins at the level of 4th somite
- closes neural groove "zips up" in some species.
- humans appear to close at multiple points along the tube.
Last parts of neural groove to close are the Neuropores
- two openings at either end of the embryo
- cranial (rostral, anterior) neuropore closes (day 25) about 2 days before caudal
Secondary Neurulation
<html5media height="320" width="320">File:Secondary_neurulation_01.mp4</html5media> | This animation shows the early developmental process often described as secondary neurulation.
Red - site of secondary neurulation | Blue - neural tube
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Neural Crest
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Neural Crest Derivitives
- dorsal root ganglia (DRG)
- autonomic ganglia
- adrenal medulla
- drg sheath cells, glia
- pia-arachnoid sheath
- skin melanocytes
- connective tissue of cardiac outflow
- thyroid parafollicular cells
- craniofacial skeleton
- teeth odontoblasts
Early Brain Structure
Primary Vesicles
- rostral neural tube forms 3 primary brain vesicles (week 4)
- 3 primary vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)
Secondary Vesicles
From the 3 primary vesicles developing in week 5 to form 5 secondary vesicles
- prosencephalon- telencephalon (endbrain, forms cerebral hemispheres), diencephalon (betweenbrain, forms optic outgrowth)
- mesencephalon
- rhombencephalon- metencephalon (behindbrain), myelencephalon (medullabrain)
Ventricles
MH - this will be covered in detail in later neural development
- cavity within tube will form the contiguious space of the ventricules of the brain and central canal of spinal cord
- space is filled initially with amniotic fluid, later with CerebroSpinal Fluid (CSF)
- CSF is secreted by a modified vascular structure, the chorioid plexus, lying within the ventricles (More? Ventricular System)
Brain Flexures
Rapid growth folds the neural tube forming 3 brain flexures
- cephalic flexure - pushes mesencephalon upwards
- cervical flexure - between brain stem and spinal cord
- pontine flexure - generates 4th ventricle
Carnegie stage 13 Embryo showing neural tube and brain flexures.
Neural Layers
- neural stem cells lie in the layer closest to the ventricular space, the ventricular layer
- this layer generates both neuroblasts and glioblasts
Neuroblasts - neurons arise first as neuroblasts and migrate along radial gial, their migration stops at cortical plate. Glioblasts - glia arise later as glioblasts
Both neurons and glia undergo a complex process of growth, differentiation and interaction over a long developmental time period.
Spinal Cord Axes
Identified by experimental manipulation of interactions.
- Initial experiments looked at how isolated tissues may influence the development of the spinal cord.
- Repositionining of specific tissues both in vivo and in vitro
- specific markers of or alteration of differentiation.
- today molecular signals - Sonic Hedgehog (ventral), Dorsalin (dorsal), Hox (rostrocaudal)
Additional Information - Spinal Cord Axes |
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Students do not need to know the details within this table.
Ventral Axis
Dorsal Axis
Rostro-Caudal Axis
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Ectodermal Placodes
- Specialized ectodermal "patches" in the head region
- Contribute sensory structures - otic placode (otocyst), nasal placode, lens placode
- Contribute teeth
- Covered in Head and Sensory Development Lectures
Human Neuralation - Early Stages
Carnegie stage 8 (about 18 postovulatory days) neural groove and folds are first seen. | Carnegie 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. | Carnegie 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. |
Carnegie stage 11 (about 24 days) the 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 several areas simultaneously. The two lips, however, behave differently. | Carnegie stage 12 (about 26 days) The caudal neuropore takes a day to close. Level of final closure is approximately at future somitic pair 31, corresponds to the level of sacral vertebra 2. | Carnegie stage 13 (4 weeks) the neural tube is normally completely closed. |
Secondary neurulation begins at stage 12 - is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate. Above text modified from[1]
- 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
Abnormalities
Neural Tube Defects (NTD)
Failure of neural tube closure either incorrectly or incomplete
- Dysraphism is the term often used to describe the defective fusion of the neural folds. The position and degree of failure of fusion will result in either embryonic death or a range of different neural defects. The way (mode) in which the human neural tube fuses has been a source of contention. In humans, fusion appears to initiate at multiple sites but the mode is different from that found in many animal species used in developmental studies.
- severity dependent upon level within the tube and degree of failure
- caudal failure - spina bifida cranial failure - anancephaly
Maternal Diet
Folate
Found that supplementation of maternal diet with folate reduces incidence of NTDs.
- A randomised controlled trial conducted by the Medical Research Council of the United Kingdom demonstrated a 72% reduction in risk of recurrence by periconceptional (ie before and after conception) folic acid supplementation (4mg daily).
- Women who have one infant with a neural tube defect have a significantly increased risk of recurrence (40-50 per thousand compared with 2 per thousand for all births)
In the U.S.A. the Food and Drug Administration in 1996 authorized that all enriched cereal grain products be fortified with folic acid, with optional fortification beginning in March 1996 and mandatory fortification in January 1998. The data in the above graphs show the subsequent changes in anencephaly and spina bifida rate over that period.
Iodine
A second maternal diet requirement for later neural growth and development.
- Iodine is required for fetal thyroid hormone synthesis.
Holoprosencephaly
Holoprosencephaly (HPE) is developmental abnormality where the forebrain does not divide into the two separate hemispheres and ventricles.
Critical Periods of Human Development
Exposure to teratogens during these "critical periods" results in specific abnormalities.
- most systems are susceptible during embryonic development (first trimester)
- the earlier the exposure the more severe the effects
- each system has a different critical period
- longest critical periods
- longest developing systems (neural, genital)
- complicated developmental origins (sensory systems)
The table below identifies approximate windows of time, "critical periods", that following exposure to teratogens can lead to developmental abnormalities (anomalies, congenital). In general, the effects for each system are more severe (major anomalies) in the embryonic period during organogenesis in the first trimester. Later teratogen exposure are less severe (minor anomalies) in the fetal period during continued growth and differentiation in the second and third trimester.
Conceptus | Embryonic development (weeks) | Fetal period (weeks) | |||||||||||||||||
Neural | |||||||||||||||||||
Heart | |||||||||||||||||||
Upper limbs | |||||||||||||||||||
Lower limbs | |||||||||||||||||||
Ear | |||||||||||||||||||
Eye | |||||||||||||||||||
Palate | |||||||||||||||||||
Teeth | |||||||||||||||||||
External genitalia | |||||||||||||||||||
Loss | Major abnormalities | Functional and Minor abnormalities |
Neural Development Terms
Only brief descriptions are given below, more complete definitions can be found in the glossary.
Neural Terms |
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Neural Development
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Other Terms Lists |
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Terms Lists: ART | Birth | Bone | Cardiovascular | Cell Division | Endocrine | Gastrointestinal | Genital | Genetic | Head | Hearing | Heart | Immune | Integumentary | Neonatal | Neural | Oocyte | Palate | Placenta | Radiation | Renal | Respiratory | Spermatozoa | Statistics | Tooth | Ultrasound | Vision | Historic | Drugs | Glossary |
2017 ANAT2341 - Timetable | Course Outline | Group Projects | Moodle | Tutorial 1 | Tutorial 2 | Tutorial 3 |
Labs: 1 Fertility and IVF | 2 ES Cells to Genome Editing | 3 Preimplantation and Early Implantation | 4 Reproductive Technology Revolution | 5 Cardiac and Vascular Development | 6 CRISPR-Cas9 | 7 Somitogenesis and Vertebral Malformation | 8 Organogenesis | 9 Genetic Disorders | 10 Melanocytes | 11 Stem Cells | 12 Group |
Lectures: 1 Introduction | 2 Fertilization | 3 Week 1/2 | 4 Week 3 | 5 Ectoderm | 6 Placenta | 7 Mesoderm | 8 Endoderm | 9 Research Technology | 10 Cardiovascular | 11 Respiratory | 12 Neural crest | 13 Head | 14 Musculoskeletal | 15 Limb | 16 Renal | 17 Genital | 18 Endocrine | 19 Sensory | 20 Fetal | 21 Integumentary | 22 Birth | 23 Stem cells | 24 Revision |
Student Projects: 1 Cortex | 2 Kidney | 3 Heart | 4 Eye | 5 Lung | 6 Cerebellum |