Palate development, cleft defects

Palate forms a division between the nasal and oral cavities and consist of hard and soft palate. During the development of palate, the primary and secondary palate joins to form the definitive palate.

Primary palate development

Primary palate formation begins on week 6 and is formed from the 2 maxillary processes and 2 medial nasal processes. The maxillary processes undergoes cell proliferation and comes in contact with lateral nasal processes and then with the medial nasal process, allowing the lateral and medial nasal processes to come into contact (the connecting part will then form the superior future nasal epithelium and future oral epithelium inferiorly) The mesenchymal continues to proliferate between the maxillary processes and then and the epithelium are being pulled apart. By the end of 6th week, the membrane formed in between will then be ripped open, resulting in primitive choana, which connects the nasal cavity to the oral cavity.

Secondary palate development

By the start of 7th week, the medial aspect of maxillary processes produces a pair of extension known as palatial shelves and are directed obliquely downward on each side of the tongue (end of 6th week) and later as horizontal position above the tongue (7th week) and fuse to form the secondary palate. The shelve then fuse with the primary palate anteriorly and is marked by the incision foramen. At the same time, the nasal septum browns down and joins with the cephalopods aspect of newly formed palate.

Cleft defects

Clefts defects are often caused by malformation or disruption of development of palate. The most common defects are cleft lip and cleft palates, which can lead to difficulties with speech and abnormal facial appearance.

• Lateral cleft lip, cleft upper jaw, cleft between primary and secondary palates are often caused by partial or complete lack of fusion of the maxillary prominence with the medial nasal prominence on one or both sides.
• Cleft palate (and cleft uluva) - lack of fusion of palate shelves , failure to elevate shelves, inhibition of the fusion process, failure of the tongue to drop between shelves
• Van der Woude syndrome - most common syndrome associated with cleft lip (and sometimes cleft palate). It is an autosomal dominant disease which causes a mutation in interferon regulatory factor 6.
• oblique facial clefts - failure of maxillary prominence to merge with its corresponding lateral nasal prominence along the line of nasolacrimal groove, causing the nasolacrimal duct to be exposed on the surface
• median cleft lip - incomplete merging of the 2 median nasal prominences in the midline. This can also cause brain abnormalities due to low of midline tissue.

Bibliography

Sadler, T.W. (2015) Langman’s medical embryology. 13th edition. ISBN 978-1-4511-9164-6