EMBRYOLOGY Medical Assignment Help

EMBRYOLOGY

To understand the causes. of oral clefts, a review of nose, lip and palate embryology is necessary. The entire process takes place between the fifth and tenth weeks of fetal lifer’ During the fifth week, two fast-growing ridges, the atemand media! nasa/ swellings, surround the nasal- vestige (Fig. 27,-3). The lateral swellings will form the alae of the nose; the medial swellings will give rise to four areas: (1) the middle portion of the nose, (2) the middle portion
of the upper lip, (3 ) the middle portion of the maxilla,and (4) the entire primary palate. Sim

FtG. ~7-3 Frontal aspect.of face. A, Five-week-old embryo. B, Six-week-old embryo. Nasal swellings are gradually separated from maxillary swelling by deep furrows. At no time during normal development does this tissue break down. C, Seven-week-old embryo. 0, Ten-week-old embryo. Maxillary swellings gradually merge with nasal folds, and furrows are filled with mesenchyme. (From Langman J: Medical embryology, ed 3, Baltimore, 1975, Williams & Wilkins.)

FtG. ~7-3 Frontal aspect.of face. A, Five-week-old embryo. B, Six-week-old embryo. Nasal swellings
are gradually separated from maxillary swelling by deep furrows. At no time during normal development
does this tissue break down. C, Seven-week-old embryo. 0, Ten-week-old embryo. Maxillary
swellings gradually merge with nasal folds, and furrows are filled with mesenchyme. (From Langman J:
Medical embryology, ed 3, Baltimore, 1975, Williams & Wilkins.)

.During. the next 2 weeks, the appearance of the face .changes considerably. The maxillary swellings continue to grow in a medial direction and  ompress themedial nasal swellings toward the midline. ‘Subsequently these swellings simultaneously merge with each other and with the maxillary swellings laterally. Hence the upper lip is, formed by the two medial. nasal swellings and the two maxillary swellings. The two medial swellingsmerge not only at the surface but also at the deeper level. The structures formed by the two merged swellingsare known together as the intermaxilar  segmellt (Fig.27-4), which is comprised of three components: (1) a labial component, which forms the philtrum of the upper lip; (2) an upper jaw component, which carries the four incisor teeth; and (3) a palatal component, which forms the triangular primary palate. Above, the intermaxillary segment is continuous with the nasal septum, which is formed by the frontal prominence. Twoshelflike outgrowths from the maxillary swellings form the.secondary palate. These palatine shelves appearin the sixth week of development and are directed obliquely downward on either side of the tongue. In the seventh week, however, the palatine shelves ascend to
attain a horizontal position above the’ tongue and fuse with each other, thereby forming the secondary palute.Anteriorly the shelves fuse with the triangular primary palate, and the incisive foramen is formed at this junction. At the same time, the nasal septum grows down and’ joins the superior surface of the newly formed palate. The palatine shelves fuse with each other and with the primary palate between the seventh and tenth weeks of development Clefts of the primary palate result from a failure of
mesoderm to penetrate into the grooves’ between the – medial nasal’ and maxillary processes, which prohibits their merging with one another. Clefts of the secondary palate are caused by a failure of the palatine shelves to
fuse with one another. The causes for this are speculative ‘and include failure of the tongue to descend int.g the  oral cavity

FIG. 27-4 A, Frontal section through head of 61/2-week-old·embryo. Palatine shelves are located in. vertical position on each side of tongue. B, Ventral view of same. Note clefts between primary triangular palate and palatine shelves, which are still in vertical position. C, Frontal section through head of . 71/2-week-old embryo. Ton~ue has moved downward, and palatine shelves have reached horizontal position.D, Ventral view of same. Shelves are in horizontal position. E, ~rontal section through head of 10-week-old embryo. Two palatine shelves have fused with each 'other and with nasal septum. F,Ventral view of same. (From Lang.'Tlan J: Medical embryology, ed 3, Baltimore, 1915, WiII!ams & Wilkins.)

FIG. 27-4 A, Frontal section through head of 61/2-week-old·embryo. Palatine shelves are located in.
vertical position on each side of tongue. B, Ventral view of same. Note clefts between primary triangular
palate and palatine shelves, which are still in vertical position. C, Frontal section through head of .
71/2-week-old embryo. Ton~ue has moved downward, and palatine shelves have reached horizontal
position.D, Ventral view of same. Shelves are in horizontal position. E, ~rontal section through head of
10-week-old embryo. Two palatine shelves have fused with each ‘other and with nasal septum.
F,Ventral view of same. (From Lang.’Tlan J: Medical embryology, ed 3, Baltimore, 1915, WiII!ams & Wilkins.)

 

 

 

 

 

 

 

 

 

 

 

 

 

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