Ch. 13 Book Questions Flashcards
Neural crest–derived cells constitute a significant component of which tissue of the eye?
a. Neural retina
b. Lens
c. Optic nerve
d. Cornea
e. None of the above
d. Cornea
The otic placode arises through an inductive message given off by the:
a. Telencephalon
b. Rhombencephalon
c. Infundibulum
d. Diencephalon
e. Mesencephalon
b. Rhombencephalon
What molecule plays a role in guidance of advancing retinal axons through the optic nerve?
a. Pax-2
b. FGF-3
c. BMP-4
d. Pax-6
e. BMP-7
a. Pax-2
Surface ectoderm is induced to become corneal epithelium by an inductive event originating in the:
a. Optic cup
b. Chordamesoderm
c. Optic vesicle
d. Lens vesicle
e. Neural retina
d. Lens vesicle
The second pharyngeal arch contributes to the:
a. Cochlea and earlobe
b. Auditory tube and incus
c. Stapes and earlobe
d. Auditory tube and stapes
e. Otic vesicle and stapes
c. Stapes and earlobe
During a routine physical examination, an infant was found to have a small segment missing from the lower part of one iris. What is the diagnosis, what is the basis for the condition, and why may the infant be sensitive to bright light?
Coloboma of the iris is caused by failure of the choroid fissure to close during the sixth week of pregnancy. Because the area of the defect remains open when the rest of the iris constricts in bright light, excessive unwanted light can enter the eye through the defect.
Why does a person sometimes get a runny nose while crying?
Some of the secretions of the lacrimal glands enter the nasolacrimal ducts, which carry the lacrimal fluid into the nasal cavity.
What extracellular matrix molecule is often associated with migrations of mesenchymal cells, and where does such an event occur in the developing eye?
Hyaluronic acid. Migration of neural crest cells into the developing cornea occurs during a period when large amounts of hyaluronic acid have been secreted into the primary corneal stroma.
Why is the hearing of a newborn often not as acute as it is a few months later?
During the fetal period, the middle ear cavity is filled with a loose connective tissue that dampens the action of the middle ear ossicles. After birth, the connective tissue is resorbed.
Why are malformations or hypoplasia of the lower jaw commonly associated with abnormalities in the shape or position of the ears?
Similar to the lower jaw, much of the external ear arises from tissue of the first arch bordering the first pharyngeal cleft.
A pediatrician is asked to examine a young boy who has arrived from a country with poor access to medical care. The boy has low-set, misshapen ears, an underslung lower jaw, and a severe hearing deficit. The boy’s teeth are also poorly aligned. What is the common denominator for this set of conditions?
The common embryological denominator is a deficit in the neural crest associated with the first pharyngeal arch. The first arch gives rise to the lower jaw, much of the middle ear complex, and a significant part of the external ear.
A pediatrician is asked to examine a young boy who has arrived from a country with poor access to medical care. The boy has low-set, misshapen ears, an underslung lower jaw, and a severe hearing deficit. The boy’s teeth are also poorly aligned. The pediatrician orders an imaging study of the boy’s kidneys and urinary tract. Why does she do that?
Because of the statistical association between abnormalities of the external ear and kidney defects, the physician wants to be sure that there are no underlying abnormalities of the urinary system.
