Development of the face

forebrain heart Frontonasal prominence Cardiac promience

Pharyngeal arches begin to develop in the fourth week. The first pharyngeal arch separates into ： Maxillary prominence ( 上颌隆起 ) Mandibular prominence ( 下颌隆起 )

口凹 ). The five facial primordia appear around the large primordial stomodeum ( 口凹 ). Single frontonasal prominence Paired maxillary prominences Paired mandibular promiences Orpharyngeal membrane

（鼻板） nasal placode （鼻板） （鼻窝） nasal pit （鼻窝） median nasal prominence （内侧鼻隆起） （内侧鼻隆起） lateral nasal prominence （外侧鼻隆起） （外侧鼻隆起） frontonasal prominences

口凹 → 原始口腔 → 口裂变小 (1) 内侧鼻隆起 → 人中、上唇正中部 (2) 外侧鼻隆起 → 鼻外侧壁、鼻翼 (3) 下颌隆起 → 下颌、下唇、颊的下部 (4) 上颌隆起 → 上唇的外侧部、颊的上 部、上颌 部、上颌 (5) 额鼻隆起 → 额、鼻梁、鼻尖

► unilateral or bilateral ► results from failure of the maxillary prominence to unite with the merged medial nasal prominences. Cleft Lip （唇裂）

► extremely rare ， associated with a cleft lip 。 ► from the upper lip to the medial margin of the orbit ► result from failure of the maxillary prominences to merge with the lateral and medial nasal prominences.颜面畸形 oblique facial cleft （面斜裂）

Development of the palate

Median palatal process( 正中隆起 ) Lateral palatal process ( 外侧腭突 ) 6th-12th weeks Median palatal process ► formed by merging of the medial nasal prominences ► wedge-shaped Lateral palatal process ► two mesenchymal projections extending from the internal aspects of the maxillary prominences

Median palatal process lateral palatal process

Uvula Hard palate( 硬腭 ) ： bone gradually develops in the primary palate and anterior parts of lateral palatal processes Soft palate( 软腭 ): the posterior parts of lateral palatal processes do not become ossified.

► With or without a cleft lip. ► Result from failure of the lateral palatal processes to meet and fuse with the median palatal process. ► Result from failure of the lateral palatal processes to meet and fuse with each othe.颜面畸形 cleft palate （腭裂）

Development of the digestive system

primitive gut （原始消化管） ► Converting the trilaminar germ disc into an elongated cylinder,during the fourth week as the head, tail, and lateral folds. ► Its cranial end by the oropharyngeal membrane and at its caudal end by cloacal membrane. ► A small amount of yolk sac remains in contact with the primitive gut tube via the vitelline duct foregut （前肠） hindgut （后肠） midgut （中肠）

Derivatives of primitive gut Foregut Hindgut Midgut esophagus, stomach, upper duodenum, lower respiratory system, liver, biliary apparatus, pancreas Lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, half of transverse colon Caudal half of transverse colon, descending colon, rectum, superior part of anal canal

Rotation of the Midgut Loop

) Partitioning of the cloaca( 泄殖腔 ) Cloaca: ► the expanded terminal part of the hindgut. ► In contact with the surface ectoderm at the cloacal membrane. ► Receives the allantois ventrally

6th~7th week Urorectal septum: ► a wedge of mesenchyme ► develops in the angle between the allantois and hindgut. ► divide cloaca into ► divide cloacal memebrane into The rectum and anal canal dorsally The urogenital sinus ventrally Urogenital membrane Ana membrane

The pancreas develops from pancreatic buds that form from the endodermal lining of the foregut. The primordium of the liver, gallbladder, and biliary duct system is an outgrowth of the endodermal epithelial lining of the foregut.

omphalomesenteric fistula( 脐粪瘘 ) an abnormal passageway between the umbilicus and the terminal ileum, formed by persistence of the intraembryonic part of the yolk stalk.

Meckel diverticulum( 梅克尔憩室 ) ► is a small bulge in the small intestine present at birth. It is a vestigal remnant of the yolk stalk. ► is the most frequent malformation of the gastrointestinal tract. ► is present in approximately 2% of the population.

Omphalocoele ( 脐膨出 ) ► failure of loop to return into body cavity after physiological hernation ► at birth intestinal loops clearly seen with transparent sac of amnion ► approximately 50% are stillbirths

Hirschsprung disease ( 先天性巨结肠 ) ► Results from failure of neural crest cells to migrate into the wall of the colon during the fifth to seventh weeks. ► Is the most common cause of neonatal obstruction of the colon and accounts 33% of all neonatal obstructions.

anal atresia or imperforate anus( 肛门闭锁或不通肛 ) The anal membrane does not rupture ate the end of the eighth week.

Development of the respiratory system

Introduction Development of the lungs begins at 4 weeks. The epithelium of the respiratory system develops from endoderm. The connective tissue, cartilage and muscle develop from splanchnic mesoderm and neural crest cells

By the fourth week, a respiratory diverticulum develops from the wall of the foregut

Tracheoesophageal septum divides the foregut into dorsal portion-- the esophagus ventral portion-- the trachea and lung buds

4 th week the lung bud develops. Divides into two lung buds -the right one into three main bronchi -the left one into two main bronchi. The branching continues until the bronchioles begin to form. 17 divisions until 6th fetal month, 24 by early childhood.

tracheoesophageal fistula( 气管食管瘘 ) Results from incomplete division of the foregut into respiratory and esophageal parts.

hyaline membrane disease （透明膜病） Respiratory distress syndrome (RDS) ► Hypoplasia of type Ⅱ alveolar cells → insufficient surfactant → surface tension↑ → alveoli collapse → difficult to breath; ► Usually seen in premature infants and accounts for about 20% of deaths among newborns.