The development of the

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 medi ...

commences in the sixth week of

human embryonic development Human embryonic development, or human embryogenesis, is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of de ...

. It is characterised by the formation of two palatal shelves on the

maxillary prominence Continuous with the dorsal end of the first pharyngeal arch, and growing forward from its cephalic border, is a triangular process, the maxillary prominence (or maxillary process), the ventral extremity of which is separated from the mandibula ...

s, 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 Around the 5th week, the intermaxillary segment arises as a result of fusion of the two medial nasal processes and the frontonasal process within the embryo. The intermaxillary segment gives rise to the primary palate. The primary palate will form ...

, with the

incisive foramen In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood ves ...

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 hard palate is a thin horizontal bony plate made up of two bones of the facial skeleton, located in the roof of the mouth. The bones are the palatine process of the maxilla and the horizontal plate of palatine bone. The hard palate spans ...

. The formation and development of the secondary palate occurs through signalling molecules SHH,

BMP-2 The BMP-2 (''Boyevaya Mashina Pekhoty'', , literally "combat machine/vehicle (of the) infantry") is an amphibious infantry fighting vehicle introduced in the 1980s in the Soviet Union, following on from the BMP-1 of the 1960s. Development hist ...

FGF-8 Fibroblast growth factor 8 (FGF-8) is a protein that in humans is encoded by the ''FGF8'' gene. Function The protein encoded by this gene is a member of the fibroblast growth factor (FGF) family. FGF family members possess broad mitogenic and ...

, among others. Failure of the secondary palate to develop correctly may result in a

cleft palate A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The te ...

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 the 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. The direct cause of this movement is unknown, but a number of possibilities have been identified as follows: * Muscular contraction; *

Hydrostatic Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...

forces exerted by

glycosaminoglycan Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units). The repeating two-sugar unit consists of a uronic sugar and an amino sugar, except in the case ...

s and

hyaluronan Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglycans ...

; * Mesenchymal reorganisation; *

Mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...

cell contraction; * Epithelial reorganisation; * 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

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

; * Epithelial-to-mesenchymal transformation; * Epithelial

cell migration Cell 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 dire ...

References

External links

Craniofacial, Cleft Palate

{{Embryology of head and neck Embryology

Formation of palatal shelves

Palatal shelf elevation

Suggested mechanisms for palatal fusion

See also

References

External links