Embryology of Pharynx and Larynx Flashcards
Which gland is the first endocrine gland to develop int he embryo?
The thyroid gland
Migration of what structure plays a critical role in developing the pharyngeal arches?
Migration of the neural crest
What does each pharyngeal arch consist of?
- Core of mesenchyme
- Covered externally by ectoderm
- Covered internally be endoderm
Every arch also has its own developing cartilage, nerve, vasculature, and muscular components
Pharyngeal (branchial) apparatus?
Note: Branchial means gill
It consist of pharyngeal grooves; clefts, arches, and pouches (CAP) and membranes.
When do the pharyngeal arches begin to develop?
They begin to develop in the fourth week as neural crest cells begin to migrate into the future head an neck regions.
What is different about the 4th 5th and 6th arch?
The 5th arch is rudimentary. The 6th arch becomes incorporated into the 4th arch.
Derivative of the 4 Pharyngeal pouches.
Pouch 1: Tympanic (middle ear) cavity and Auditory (eustachian) tube
Pouch 2: Palatine tonsils and Tonsillar fossa
Pouch 3: Inferior parathyroid gland and Thymus
Pouch 4: Superior parathyroid gland ultimobranchial body (parafollicular [C] cell of the thyroid gland)
What is the fate of the membranes?
Only the first membrane persist and it gives the tympanic membrane.
What are the fates of the clefts?
Cleft 1: External auditory meatus
Cleft 2, 3, 4: are oblitrated by overgrowth of the 2nd and 4th arch toward each other forming a cervical sinus.
C.R. If the cervical sinus persist a Branchial cyst or fistula can be found along the anterior border of the SCM
What effect can the second an fourth arch have on the 2nd 3rd and 4th cleft? Where can it be found?
They can form a cervical sinus around the clefts which turns into a branchial cyst or fistula. This can be found at the anterior border of the SCM muscle
What causes a branchial cyst or fistula?
Overgrowth of the 2nd and 4th arch
What are C-cells? What are they derived from?
C-cells are parafollicular cells that exist in the thyroid gland.
They are derived mainly from the 4th pair of pharyngeal pouches.
What is an ectopic thyroid gland?
It presents as an enlarged painless midline movable mass.
This happens when the thyroid gland does not descend completely from its sight or origin in the tongue.
The thyroglossal duct may persist or remnants of it may give rise to thyroglossal duct cyst.
What are the parts of the tongue?
- The oral part is 2/3
2. The pharyngeal part 1/3
Which cranial nerve provides sensation to the tongue? Which cranial nerve provides taste to the tongue
Sensation = V Taste = VII
Muscles of the tongue arise from migration of what structure?
From migration of the occipital myotomes to the tongue area.
Face: Frontonasal prominence
Forms the forehead and dorsum and apex of the nose
Face: Lateral nasal prominences
Forms the alae (sides) of the nose
Face: Medial nasal prominences
Forms the nasal septum, ethmoid bone, and cribiform plate
Face: Maxillary prominences
form the upper cheek regions and the upper lip
Face: Mandibular prominence
gives rise to the chin, lower lip, and lower cheek regions
Cleft lip vs Cleft palate?
Cleft lip results from failure of mesenchymal masses in the medial nasal and maxillary prominences to merge, whereas cleft palate results from failure of mesenchymal masses in the palatal processes to meet and fuse.
Most cases of cleft lip with or without cleft palate are caused by a combination of genetic and environmental factors.
What is the Pharyngeal arch USMLE mnemonic.
At the restuarante of the golden arches kids ten to CHEW (1st), SMILE (2nd), STYLISH (3rd), SWALLOW (4th), and the SPEAK (6th)
There are two palates. How do they fuse?
Primary palate: arises from the fusion of an unpaired median process
Secondary palate: arises from a paired lateral palatine processes.
What three muscles insert at the posterior of the thyroid cartilage?
- Stylopharynggeus
- Palatopharyngeus
- Salpingopharyngeus
What three muscles attach to the oblique line of the thyroid cartilage?
- Sternohyoid
- Thytohyoid
- A portion of the Inferior Pharyngeal constrictor
What are the names of the paired cartilage that attaches to the Cricoid cartilage in order?
- Arytenoid cartilage
- Corniculate cartilage
- Cuneiform cartilage
The cricoid cartilage has facets for two joints. What are they called? What are they for?
- Cricothyroid- For articulation with the thyroid cartilage
2. Cricoarytenoid- for articulation with the arytenoid cartilage.