Secondary palate development
Encyclopedia
The development of the secondary palate
commences in the sixth week of human embryological development
. It is characterised by the formation of two palatal shelves on the maxillary prominences, the elevation of these shelves to a horizontal position, and then a process of palatal fusion between the horizontal shelves. The shelves will also fuse anteriorly upon the primary palate, with the incisive foramen
being the landmark between the primary palate and secondary palate. This forms what is known as the roof of the mouth, or the hard palate
.
The formation and development of the secondary palate occurs through signalling molecules SHH
, BMP-2, FGF-8
among others.
Failure of the secondary palate to develop correctly may result in a Cleft palate disorder.
The specific mechanism by which the medial edge epithelium disappears has been differed over by academics. The three most distinguished theories related to the explanation of palatal fusion are as follows:
Secondary palate
The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates.In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medially and their mutual fusion in the midline...
commences in the sixth week of human embryological development
Embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...
. It is characterised by the formation of two palatal shelves on the maxillary prominences, the elevation of these shelves to a horizontal position, and then a process of palatal fusion between the horizontal shelves. The shelves will also fuse anteriorly upon the primary palate, with the incisive foramen
Incisive foramen
The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...
being the landmark between the primary palate and secondary palate. This forms what is known as the roof of the mouth, or the hard palate
Hard palate
The hard palate is a thin horizontal bony plate of the skull, located in the roof of the mouth. It spans the arch formed by the upper teeth.It is formed by the palatine process of the maxilla and horizontal plate of palatine bone....
.
The formation and development of the secondary palate occurs through signalling molecules SHH
Sonic hedgehog
Sonic hedgehog homolog is one of three proteins in the mammalian signaling pathway family called hedgehog, the others being desert hedgehog and Indian hedgehog . SHH is the best studied ligand of the hedgehog signaling pathway. It plays a key role in regulating vertebrate organogenesis, such as...
, BMP-2, FGF-8
Fibroblast growth factor
Fibroblast growth factors, or FGFs, are a family of growth factors involved in angiogenesis, wound healing, and embryonic development. The FGFs are heparin-binding proteins and interactions with cell-surface associated heparan sulfate proteoglycans have been shown to be essential for FGF signal...
among others.
Failure of the secondary palate to develop correctly may result in a Cleft palate disorder.
Formation of palatal shelves
The formation of the vertical palatal shelves occurs during week 7 of embryological development, on the maxillary processes of the head of embryo, lateral to the developing tongue.Palatal shelf elevation
The elevation of the palatal shelves from a vertical position to a horizontal one occurs during week 8 of embryological development. It is unknown as to what exactly is the direct cause of this movement is, but a number of possibilities have been identified as follows:- Muscular contraction;
- Hydrostatic forces exerted by Glycosaminoglycans and HyaluronanHyaluronanHyaluronan is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues...
; - Mesenchymal reorganisation;
- Mesenchyme cell contraction;
- Epithelial reogranisation
- Movement of the developing tongue
Suggested mechanisms for palatal fusion
Fusion between the two palatal shelves occurs during week 9 of embryonic development. In this time, the elevated palatal shelves join together to form one continuous structure, with the medial edge epithelium (the shelf surfaces which are closest to each other) disappearing.The specific mechanism by which the medial edge epithelium disappears has been differed over by academics. The three most distinguished theories related to the explanation of palatal fusion are as follows:
- Epithelial apoptosisApoptosisApoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
; - Epithelial-to-mesenchymal transformation;
- Epithelial cell migrationCell migrationCell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryonic development, wound healing and immune responses all require the orchestrated movement of cells in particular directions to specific locations...
.