T4: Pharyngeal arches and their clinical relevance

Question 1

The 1st pharyngeal arch is composed of (MG)
A. Cervical sinus
B. The maxillary prominence and the mandibular prominence
C. Superior parathyroid bud
D. Thymus

Answer 1

B. The maxillary prominence and the mandibular prominence

Cervical sinus is found between arches 2, 3, and 4 and should obliterate.

Superior parathyroid bud comes from the 4th pouch.

The thymus is from pouch 3.

Question 2

A 3 month old infant is brought into your office. His lateral lower eyelids droop and he has micrognathia as well as an underdeveloped zygoma resulting in a malformed face. What is the cause of this disorder? (MG)
A. Stenosis of the first pouch
B. Agenesis of the first arch
C. Stenosis of the first arch
D. Failure of migration of neural crest cells into first arch

Answer 2

D. Failure of migration of neural crest cells into first arch

This is Treacher Collins Syndrome. Both Treacher Collins and Pierre Robin Sequence are caused by failure of migration of neural crest cells to the first arch, but TC does not result in glossoptosis and only results in cleft palate in 50% of cases.

Question 3

Where can you find the external acoustic meatus? (MG)
A. 2nd pharyngeal pouch
B. 1st pharyngeal groove
C. 1st pharyngeal pouch
D. 2nd pharyngeal groove

Answer 3

B. 1st pharyngeal groove

Grooves 2,3,4 are obliterated by proliferation of the 2nd arch to join the 6th arch

Question 4

A 3 month old infants is brought into your office. He has micrognathia, glossoptosis and cleft lip. What disorder does this child have ?

A. Treacher Collins Sydrome
B. Digeorge Sydrome
C. Down Syndrome
D. Pierre Robin Sequence

RFA.

Answer 4

Ans. D. Pierre Robin Sequence- While both Treacher Collins and Pierre Robins are cause by failure of migration of neural crest cells the Glossoptosis and Cleft lip is the difference

Question 5

A 2 month old boy is taken to the hospital because he has diarrhea and vomiting. Blood test are done and it shows he has hypercalcemia. It is believed that a malformation during development is the route cause. Which is most likely?

A. Malformation of the 1st groove 
B. Malformation of the 2nd groove
C. Malformation of the 3rd groove
D,  Malformation of the 4th groove
E. Malformation of the 1st Pouch
F. Malformation of the 2nd Pouch
G. Malformation of the 3rd Pouch
H. Malformation of the 4th Pouch

RFA

Answer 5

H. Malformation of the left pouch- the patient is suffering from hypercalcemia due to a lack of calcitonin which is secreted by parafollicular cells ( C cell) of the thyroid which are from the ultimopharyngeal body is a derivative of the 4th pouch the 4th pouch also makes the superior parathyroid glands.

A. 1st groove= acoustic meatus

B, C, D. 2nd,3rd,4th-grooves=obliterated

E. 1st pouch= Tubotympanic recess, middle ear cavity, mastoid antrum

F. 2nd Pouch= Palatine tonsils, tonsillar fossa

G. 3rd Pouch= Thymus, inferior parathyroid glands

Question 6

A fetus is being studied in the lab at is is noticed that the 1st Arch was failed to form which of these structures would not be present in the fetus?

A. Anterior Digastric Muscle
B. Stapes
C. Ductus Arteriosus 
D. Stylopharyngeus Muscle
E. Vagus Superior laryngeal Branch
F. Vagus recurrent Laryngeal Branch 
G. Hyoid Bone

RFA

Answer 6

Ans. A. Anterior Digastric Muscle= 1st Arch

B. Stapes= 2nd Arch

C. Ductus Arteriosus= 6th Arch

D. Stylopharyngeus Muscle= 3rd Arch

E. Vagus superior laryngeal branch= 4th Arch

F. Vagus Recurrent laryngeal Branch= 6th Branch

G. Hyoid Bone= 3rd Arch

Question 7

The thyroid gland is derived from which of the following?
(MM)

A) 1st Arch
B) 3rd Arch
C) Floor of Pharynx
D) 3rd Pouch
E) Soft Palate

Answer 7

Answer C

Question 8

An area located in the back of the oropharynx that has cranial nerve nine running and frequently removed in children due to recurrent infection is derived from which of the following? (mm)

A) 1st Arch
B) 2nd Pouch
C) 2nd Groove
D) 3rd Pouch
E) 4th Pouch

Answer 8

Answer C. Your tonsils are removed in kids and has the glossopharyngeal nerve running with them

Question 9

The development of the ear is from 6 auricular hillocks. The posterior portion from the ear is developed from which of the following? (mm)

A) 1st Arch
B) 1st Groove
C) 1st Pouch
D) 2nd Arch
E) 2nd Groove
F) 2nd Pouch
G) 3rd Arch
H) 3rd Groove
I) 3rd Pouch

Answer 9

Answer D

hillocks 1-3 anterior portion from 1st arch

4-6 posterior portion from 2nd arch