Chapter four pg46-49
17.) How does the primitive pharynx develop?
a. The beginnings of the embryo’s hollow tube are derived from the anterior portion of the foregut and will form the primitive pharynx future oral portion of the throat, or oropharynx. The primitive pharynx widens cranially where it joins the primitive mouth of the stomedum and narrows caudally as it joins the esophagus. The caudal part of the primitive pharynx forms the esophagus, which leads to the stomach.
18.) What is the branchial apparatus:
a. The branchial apparatus consists of the branchial arches, branchial grooves and membrane, and pharyngeal pouches. The name branchial is used because it refers to gill formation in the neck area for respiratory function in lower life forms.
19.) To which tissue does each branchial arch give rise?
a. It is important to note that the fifth branchial arches are so rudimentary that they are absent in humans or are included with the fourth branchial arches. The first pair of arches forms the middle and lower face. The mandibular arch is the first branchial arch.
b. The second branchial arch, or hyoid arch is cartilage similar to the cartilage in the mandibular arch. This cartilage is also called Reichert’s cartilage, and the most of it disappears; however, parts of it are responsible for a middle ear bone, a process of the temporal bone, and portions of the hyoid bone. Additionally the perichondrium surrounding the Reichert’s cartilage gives rise to the ligament of the hyoid bone. The mesoderm of the hyoid arches helps form the muscles of facial expression, the middle ear muscles, and a suprahyoid muscle.
c. The third branchial arch has an unnamed cartilage associated with it. This cartilage will be responsible for the formation of portions of the hyoid bone the only muscle to be derived from the mesoderm of each third arch is a pharyngeal muscle. Each pair of the arches is innervated by the ninth cranial nerve, the glossopharyngeal nerve.
d. Both the forth branchial arch and the sixth branchial arch also unnamed cartilage associated with them. These arches fuse and participate in the formation of most of the laryngeal cartilages. The mesoderm of the arches is associated with the muscles of larynx, and pharynx.
20.) What are the branchial grooves?
a. Between the neighboring branchial arches, external grooves are noted on each side of the embryo. These are the branchial grooves, or pharyngeal grooves. The first branchial groove, which is located between the first and second branchial arches give rise to a definitive mature structure of the head and neck. The first groove forms the external auditory meatus. By the end of the seventh week, the last four branchial grooves are obliterated as a result of a sudden spurt of growth experienced by the pair of hyoid arches, which grow in an inferior direction and eventually form the neck. The obliteration of grooves gives the mature neck a smooth contour.
21.) Name the tissues associated with each pharyngeal pouch.
a. Four well defined pairs of pharyngeal pouches develop as endodermal evaginations from the lateral walls lining the pharynx. The pouches develop as balloon like structures in a craniocaudal sequence between the branchail arch. The fifth pharyngeal pouches are absent or rudimentary. Many tissues of the face and neck are developed from the pharyngeal pouches.
b. The first pharyngeal pouches form between the first and second branchial arches and become the auditory tubes. Palatine tonsillar tissue is derived from the lining of the second pharyngeal pouches and also from the pharyngeal walls. The thymus glad and parathyroid glands appear to be derived from the lining of the third and fourth pharyngeal pouches.
22.) What are cervical cysts, and how can they present?
a. The branchial grooves occasionally do not become obliterated, and thus portions remain as cervical sinuses or cervical cysts. These cysts may drain through sinuses along the neck but may also remain free in the neck tissue just inferior to the angle of the mandible and anywhere along the anterior border of the sternocleidomastiod muscle. These cysts do not become apparent until they produce a slowly enlarging, painless swelling.