Early Development of the Nose in Human Embryo: A Stereomicroscopic and Histologic Analysis / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: We aimed to analyze the morphologic features of the nose in the human embryo from 4th to 8th developmental weeks according to the Carnegie stage. MATERIALS AND METHOD: A total of 27 cases of embryos, ranging from Carnegie stage of 13 to 23, were analyzed. The external morphology was observed with a stereomicroscope, photographed and analyzed. The histologic features were observed with a light microscope in the horizontally-transected specimens stained with hematoxylin-eosin staining. RESULTS: The nasal placode was observed at the stage 13, and it became flat or even concave at the stage 14. At the stage 15, the nasal pit was formed. At the stage 16, the nasal sac and nasal fin were observed. At the stage 17, the oronasal membrane was formed by thinning of the nasal fin. At the stage 18, the primitive choana was established by rupture of the oronasal membrane. At the stage 19, the lateral palatine process projected vertically below the level of the tongue. The cartilaginous nasal capsule was formed at the stage 20. At the stage 21, the olfactory area was localized to the upper portion of the lateral nasal wall and the nasal septum. At the stage 22, the lateral palatine process developed in a somewhat horizontal orientation. At the stage 23, the premaxilla and primitive choana were formed. CONCLUSION: The development of the nose is most active from the Carnegie stage of 13 to 19, which corresponds to the end of the 4th embryonic week to the end of the 7th week. Thus, this period is considered to be the most important period in human nasal embryonic development.

Embryological background for fetal surgery

Congenital malformations are one of the main topics, which must be addressed in the 21st century. Fetal surgery is expected to become a routine procedure for malformed fetal patients in the near future. This paper presents some important aspects of the embryological background required for fetal surgery and shows normal human embryos between the 4th and the 8th week of development.

Development of the lip and palate in staged human embryos and early fetuses

Cleft lip and palate are the most common congenital malformations in humans. Using 43 staged human embryos and early fetuses ranging from the 4th to 12th week of development, we investigated the development of the lip and palate in order to provide the basic developmental concepts required for managing these anomalies. The lower lip appeared as bilateral mandibular arches at Carnegie stage 11, and these were completely merged at stage 15. The components of the upper lip, medial nasal prominence and maxillary process, appeared at stage 16, and completely merged at stage 20. The median palatine process appeared at stage 16, and the lateral palatine process, at stage 17. The palatine processes and the nasal septum started to fuse abruptly at stage 23, and from external observation seemed to be fused at the 9th week. However, complete fusion did not take place until the 12th week of development. The tongue was prominent at stage 16, showed differentiation of the muscular tissue at stage 21, and was located superior to the lateral palatine process before stage 23. These results may be used in understanding the different mechanisms present in the formation of various congenital anomalies in this region.

Morphological characteristics of the developing human brain during the embryonic period

Many features of the developing nervous system are visible from external observations of intact human embryos. In this study, a photographic atlas from the 4th to the 7th week after ovulation (Carnegie stages 10-18) is provided. The neural folds began to fuse at stage 10, and the rostral and caudal neuropore were closed during stages 11 and 12, respectively. The three primary divisions of the brain were distinguishable before closing of the neural tube. The five secondary brain vesicles were formed during stages 14-15. The development of the cerebellum and cerebrum were first observed at stages 14 and 15, respectively. The mesencephalic flexure was seen at stage 12, and the cervical flexure and pontine flexure at stage 14. After stages 18-19, it became increasingly difficult to identify detailed features of the brain from the surface. Results from this study will help to correlate the characteristic findings of the developing central nervous system of human embryos from stereomicroscopical and light microscopical observations and to locate the exact parts of the developing human brain for other purposes.

Morphogenic development of the pancreas in the staged human embryo

The Carnegie stage is widely applied in the field of human embryology, and it is more logical to analyze the embryos by this stage than CR length or menstrual age. In this study, the early development of the pancreas is studied by tissue observation and reconstruction using serial sections of 33 human embryo ranging from Carnegie stages 11 to 23. The dorsal pancreas develops from the dorsal wall of the duodenum in stage 12, and the ventral pancreas from the proximal part of the cystic primordium in stage 13 or 14 as a single epithelial thickening, but in one case, as a bilateral thickening which contains some isolated spaces. The rotation of the ventral pancreas starts in stage 15, and completes in stage 17. Surrounding connective tissue differentiates in stage 18.

Human Embryos of Carnegie Stage 13 / 체질인류학회지

Three cases of human embryo of Carnegie stage 13 were described. The CR length of these embryos were 3.0-5.3mm. The authors made a reconstruction model using photograph, photocopy and computer. These embryos were characterized externally by 4 limb buds and 4 pairs of branchial arches, and internally closed otic pits, appearance of venous valves, septum primum and foramen primum in the heart, beginning of the right and left lung buds, appearance of lens disk.