Placodes: Difference between revisions
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In human development, during [[week 4]] a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region. | In human development, during [[week 4]] a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region. | ||
Recent research suggests that all sensory placodes | Recent research suggests that all sensory placodes arise from common panplacodal ectoderm (PPE) a horseshoe-shaped region of ectoderm surrounding the anterior neural plate and neural crest .Each placode then differentiates to eventually have different developmental fates. These sensory placodes will later contribute key components of each of our special senses (vision, hearing and smell). Note that their initial postion on the developing head is significantly different to their final position in the future sensory system. | ||
* Adenohypophyseal placode | * Adenohypophyseal placode | ||
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===Reviews=== | ===Reviews=== | ||
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<pubmed>20801420</pubmed> | <pubmed>20801420</pubmed> | ||
<pubmed>20460364</pubmed> | <pubmed>20460364</pubmed> | ||
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[[Category:Placode]] | [[Category:Placode]] |
Revision as of 14:44, 12 February 2015
Introduction
Placodes are ectodermal thickenings which have important roles in development of special sensory systems.
In human development, during week 4 a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region.
Recent research suggests that all sensory placodes arise from common panplacodal ectoderm (PPE) a horseshoe-shaped region of ectoderm surrounding the anterior neural plate and neural crest .Each placode then differentiates to eventually have different developmental fates. These sensory placodes will later contribute key components of each of our special senses (vision, hearing and smell). Note that their initial postion on the developing head is significantly different to their final position in the future sensory system.
- Adenohypophyseal placode
- Otic placodes - the first placodes visible on the surface of the embryo.
- Olfactory (Nasal) placodes - has 2 components (medial and lateral) and will form the nose olfactory epithelium.
- Optic (Lens) placodes - lies on the surface, adjacent to the outpocketing of the nervous system (which will for the retina) and will form the lens.
- Profundal/trigeminal placodes
Other species have a number of other placodes which form additional sensory structures (fish, lateral line receptor).
- Epibranchial placodes
- Lateral line placodes
- Hypobranchial placodes
Other Placodes? | ||
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Note that a second, later developing, form of ectodermal placode development occurs with the development of hair follicles and other integumentary specialisations. This topic does not directly relate to the specialised placodes of the head region covered here. (More? Hair Development | Integumentary_System Development) |
Placode Links: placode | Week 4 | sensory | Otic Placode | Optic Placode | Nasal Placode | Category:Placode | ||||||||||||||||
Some Recent Findings
Preplacodal DevelopmentPreplacodal development model[9]
(Above text from figure legend[9]) Otic PlacodeThe otic placode is the first of the sensory placodes visible on the surface of the developing human embryo. This placode will differentiate to contribute almost entirely the components of the inner ear. The images below show the first appearance on the embryo surface during week 4 and the eventual disappearance from the surface by week 5. This is only the beginning of the complex development of this structure, influenced by the surrounding epidermis, neural tube and neural crest. Stage 11The scanning EM of the week 4 human embryo Carnegie stage 11 shown below is a superior dorsal view of the paired otic placodes sinking into the surface at the level of the hindbrain between day 24 and day 25. Stage 12By Carnegie stage 12 26 days, only a small opening of the developing otic vesicle (otocyst) remains visible on the embryo surface located behind the second pharyngeal arch. Stage 13By week 5 Carnegie stage 13 the otic vesicle (otocyst) is completely formed and is no longer visible on the embryo surface. Cross-sections of the embryo head at this stage show the otocyst now lies within the embryo as a hollow fluid-filled epithelial "ball", located between the epidermis and the neural tube (hindbrain).
Adenohypophyseal PlacodeThe hypophysis, or pituitary, is an endocrine gland that links the brain to peripheral endocrine organs and systems of the body through several specific hormones. The developmental origin of the hypophysis is unique, with epithelial origins from neural ectoderm (posterior) and from surface ectoderm (anterior) the adenohypophyseal placode.
Drosophila and mouse placode similarity[11]
Olfactory Placodes(Nasal) Optic PlacodesOptic placodes (Lens) lie on the embryo surface, adjacent to the out-pocketing of the nervous system (forms the retina) and will form the lens. surface ectoderm -> lens placode -> lens pit -> lens vesicle -> lens fibres -> lens capsule and embryonic/fetal nucleus.
Trigeminal Placodes(Profundal)
Epibranchial PlacodesEpibranchial ganglia sensory neurons formed by the facial, glossopharyngeal, and vagal placodal regions. These ganglia neurons relay from the sensory organs such as gustatory taste buds, heart baroreceptors, gut sensory enteric nerves.
Sensory System
References
Online Textbooks
Reviews<pubmed>24491817</pubmed> <pubmed>24495912</pubmed> <pubmed>20801420</pubmed> <pubmed>20460364</pubmed> <pubmed>9927591</pubmed> Articles17205191 15380243 10906460 Search PubmedJune 2010 "placode development" All (852) Review (90) Free Full Text (285) Search Pubmed placode development | otic placode development | optic placode development | nasal placode development |
adenohypophyseal placode development
External LinksExternal Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
Glossary Links
Cite this page: Hill, M.A. (2024, May 21) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
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