FACIAL CLEFTS

clefts result in a very large mouth—macrostomia. In severe cases, the clefts in the cheeks extend almost to the ears.

Figure 10–30 Infant with unilateral cleft lip and cleft palate.

Clefts of the lip, with or without a cleft palate, occur in approxi- mately 1 in 1000 births; most affected individuals are males.

Figure 10–31 Birth defects of the lip and palate. A, Infant with a left unilateral cleft lip and cleft palate. B, Infant with a bilateral cleft lip and cleft palate.

A B

C H A P T E R 10 PHARYNGEAL APPARATuS, FACE, AND NECk 124.e1

(Courtesy A.E. Chudley, MD, Professor of Paediatrics and Child Health, Children’s Hospital and University of Manitoba, Winnipeg, Manitoba, Canada.)

(Courtesy Dr. Barry H. Grayson and Dr. Bruno L. Vendittelli, Insti- tute of Reconstructive Plastic Surgery, New York University Medical Center, New York, NY.)

C H A P T E R 10 PHARYNGEAL APPARATuS, FACE, AND NECk 125

Figure 10–32 Drawings illustrating the embryologic basis for a complete unilateral cleft lip.

A, 5-week embryo. B, Horizontal section through the head illustrating the grooves between the maxillary prominences and the merging medial nasal prominences. C, 6-week embryo showing a persistent labial groove on the left side. D, Horizontal section through the head showing the groove gradually filling in on the right side after proliferation of the mesenchyme (arrows).

E, 7-week embryo. F, Horizontal section through the head showing that the epithelium on the right has almost been pushed out of the groove between the maxillary and medial nasal prominences. G, 10-week fetus with a complete unilateral cleft lip. H, Horizontal section through the head after stretching of the epithelium and breakdown of the tissues in the floor of the persistent labial groove on the left side, forming complete unilateral cleft lip.

Level of section B

Medial nasal prominences

Maxillary prominence

Groove filling in

Abnormal Normal

Ectoderm Medial nasal

prominences

Groove or furrow

Persistent labial groove

Merging medial nasal prominences

Merged maxillary

and medial nasal prominences Groove almost smoothed out

Mesenchyme

H B

F C

Level of section D

Level of section F

Level of section H

Persistent labial groove

Philtrum of lip

Muscle Complete unilateral cleft lip

Persistent labial groove

Site of subsequent tissue collapse Epithelium

Developing muscle

Separate lateral part of lip

126 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS

CLINICALLY ORIENTED QUESTIONS 1. Do embryos have cleft lips? Does this common facial

defect represent a persistence of such an embryonic condition?

2. Neither Clare nor her husband Jack has a cleft lip or a cleft palate, and no one in either one of their fami- lies is known to have or to have had these anomalies.

What are their chances of having a child with a cleft lip, with or without a cleft palate?

3. Mary’s son has a cleft lip and a cleft palate. Her brother has a similar defect involving his lip and

Figure 10–33 Various types of cleft lip and cleft palate. A, Normal lip and palate. B, Cleft uvula. C, Unilateral cleft of the posterior (secondary) palate. D, Bilat- eral cleft of the posterior palate. E, Com- plete unilateral cleft of the lip and alveolar process of the maxilla with a unilateral cleft of the anterior (primary) palate.

F, Complete bilateral cleft of the lip and the alveolar processes of the maxillae with bilateral cleft of the anterior palate.

G, Complete bilateral cleft of the lip and the alveolar processes of the maxillae with bilateral cleft of the anterior palate and unilateral cleft of the posterior palate.

H, Complete bilateral cleft of the lip and the alveolar processes of the maxillae with complete bilateral cleft of the anterior and posterior palate.

A B

C D

E F

G H

Uvula

Incisive papilla Lip

Hard palate Soft palate

Nasal cavity

Cleft uvula

Nasal septum

Primary palate

Secondary palate

Nasal septum Site of incisive foramen

palate. Although Mary does not plan to have any more children, her husband says that Mary is entirely to blame for their son’s birth defects. Was the defect likely inherited only from Mary’s side of the family?

4. A patient’s son has minor anomalies involving his external ears, but he does not have hearing problems or a facial malformation. Would his ear abnormalities be considered pharyngeal (branchial) arch defects?

The answers to these questions are at the back of this book.

C H A P T E R 10 PHARYNGEAL APPARATuS, FACE, AND NECk 126.e1

Answers to Chapter 10 Clinically Oriented Questions

127

C H A P T E R

Respiratory System

11

Development of Larynx 129 Development of Trachea 129

Development of Bronchi and Lungs 130 Maturation of Lungs 133

Clinically Oriented Questions 135

he lower respiratory organs (larynx, trachea, bronchi, and lungs) begin to form during the fourth week of development. The respiratory system starts as a median outgrowth—

the laryngotracheal groove—that appears in the floor of the caudal end of the primordial pharynx (Fig. 11-1A and B). The primordium of the tracheobronchial tree develops caudal to the fourth pair of pharyngeal pouches. The endodermal lining of the laryngotracheal groove gives rise to the pulmonary epithelium and glands of the larynx, trachea, and bronchi.

The connective tissue, cartilage, and smooth muscle in these structures develop from the splanchnic mesoderm surrounding the foregut (see Fig. 11-4A). Signaling pathways of BMP, Wnt, and FGF control patterning of the expression of Sox2 and Nkx2.1 in the early foregut for the differentiation of the trachea from the esophagus. In the ventral areas, Nkx2.1 is activated while Sox2 is suppressed.

By the end of the fourth week, the laryngotracheal groove has evaginated (protruded) to form a pouch-like laryngotracheal diverticulum (lung bud), which is located ventral to the caudal part of the foregut (see Fig. 11-1A and Fig. 11-2A).

As the diverticulum elongates, its distal end enlarges to form a globular respiratory bud (see Fig. 11-2B). The laryngotracheal diverticulum soon separates from the primordial pharynx, but it maintains communication with it through the primordial laryngeal inlet (see Fig. 11-2A and C). As the diverticulum elongates, it is invested with splanchnic mesoderm (see Fig. 11-2B). Longitudinal tracheoesophageal folds develop in the laryngotracheal diverticulum, approach each other, and fuse to form a partition—the tracheoesophageal septum (see Fig. 11-2D and E).

This septum divides the cranial part of the foregut into a ventral part, the laryngotracheal tube (primordium of the larynx, trachea, bronchi, and lungs), and a dorsal part (primordium of the oropharynx and esophagus) (see Fig. 11-2F). The opening of the laryngotracheal tube into the pharynx becomes the primordial laryngeal inlet (see Fig. 11-2F and Fig.11-3C).

T

128 BEFORE WE ARE BORN ESSENTIALS OF EMBRYOLOGY AND BIRTH DEFECTS

Figure 11–1 A, Sagittal section of the cranial half of a 4-week embryo. B, Horizontal section of the embryo, illustrating the floor of the primordial pharynx and the location of the laryngotracheal groove.

Brain

Openings of pharyngeal pouches into primordial pharynx Site of oropharyngeal

membrane

1st pharyngeal arch

Median lingual swelling Lateral lingual swelling

Foramen cecum of tongue

Hypopharyngeal eminence

4th pharyngeal pouch Laryngotracheal groove Stomodeum

Laryngotracheal

diverticulum Spinal cord

Primordium of esophagus

Site of laryngotracheal groove

1 2

3 4

Figure 11–2 Successive stages in the development of the tracheoesophageal septum during the fourth and fifth weeks of development. A to C, Lateral views of the caudal part of the primordial pharynx, showing the laryngotracheal diverticulum and partitioning of the foregut into the esophagus and the laryngotracheal tube. D to F, Transverse sections, illustrating the formation of the tracheoesophageal septum and how it separates the foregut into the laryngotracheal tube and esophagus. The arrows represent cellular changes resulting from growth.

A B C

D E F

Primordial pharynx Endoderm

(mesoderm removed)

Pharynx Tracheoesophageal fold

Tracheoesophageal septum

Folds fused Splanchnic

mesoderm

Primordial laryngeal inlet

Laryngotracheal tube

Laryngotracheal

diverticulum Esophagus

Esophagus Respiratory bud

Groove

Primordium of laryngotracheal tube

Primary bronchial buds Level of

section D Laryngotracheal

opening

Level of

section E Level of

section F

C H A P T E R 11 RESPIRATORY SYSTEM 129

the larynx and epiglottis is rapid during the first 3 years after birth, by which time the epiglottis has reached its adult form and position.

Dalam dokumen Before We Are Born (Halaman 175-182)