10. Development Of The Head And Neck 1 Flashcards
In the 4th week of development, what proportion of the embryo does the head and neck represent?
Half.
What glands develop from modification of the endoderm tube lining the pharynx in the pharyngeal pouches?
Parathyroid, thymus, palatine tonsils, thyroid.
What type of embryological cell are the pharyngeal/brachial arches derived from?
Mesoderm and endoderm.
How many pharyngeal/brachial arches are there?
5, numbered 1-6 as the 5th doesn’t form in humans.
What constitutes the building blocks for the head and neck region in an embryo?
Frontonasal prominence.
Pharyngeal arches.
Which cranial nerves are associated with the pharyngeal arches and supply the derivatives of the arches?
CN V, VII, IX, X.
What muscles are derived from Ph Arch 1?
Muscles of mastication of the face.
What muscles are derived from Ph Arch 2?
Muscles of facial expression.
What muscles are derived from Ph Arch 3?
Stylopharyngeus.
What muscles are derived from Ph Arch 4?
Cricothyroid.
Levator palatine.
Constrictors of the pharynx.
What muscles are derived from Ph Arch 6?
Intrinsic muscles of the larynx.
Each of the pharyngeal arches develops a neural crest-derived cartilage bar. What does each go on to form?
Ph A 1 - meckel’s cartilage, forms the malleus, incus and a template for the formation of the mandible.
Ph A 2 - reicher’s cartilage, forms the stapes plus upper part of the hyoid bone.
Ph A 3 - forms the remainder of the hyoid bone.
Ph A 4 & 6 - forms the cartilages of the larynx.
What cavity does the first pharyngeal pouch become?
Tympanic cavity.
What does the first pharyngeal cleft become, and what happens to the others?
First cleft - becomes the external acoustic meatus.
Others - second arch grows down to cover the others, obliterating all the other clefts.
What can occur if there are remnants of the brachial clefts that should have been obliterated?
Brachial cysts and fistulae can occur on the anterior boarder of sternocleidomastoid.
What drives development of the face?
Expansion of the cranial neural tube, appearance of a complex tissue system with the cranial gut tube and outflow of the developing heart, and development of the sense organs with a need to separate the respiratory tract from the GI tract.
What components form the face embryologically?
Frontonasal prominence.
Stomatodeum with buccopharyngeal membrane at the centre.
1st pharyngeal arch forms the maxillary prominences and mandibular prominences.
What structures does the frontonasal prominence form?
Forehead, bridge of nose, nose, philtrum.
What structures does the maxillary prominence form?
Cheeks.
Lateral upper lip.
Lateral upper jaw.
What structures does the mandibular prominence go on to form?
Lower lip and jaw.
Describe the development of the nose.
Nasal placodes appear on the frontonasal prominence. The maxillary prominences grow medially, pushing the nasal prominences closer together in the midline. These then sink to become the nasal pits, with medial and lateral nasal prominences forming on either side of the pits. Maxillary prominences fuse with the medial nasal prominences, and the medial nasal prominences then fuse in the midline.
Fusion of the medial nasal prominences creates the intermaxillary segment, what does this consist of?
Philtrum, 4 incisors and primary palate.
How is the main part of the definitive palate formed?
Maxillary prominence gives rise to two palatal shelves. These grow vertically downwards into the oral cavity on each side of the developing tongue. The mandible grows large enough to allow the tongue to drop. The palatial shelves then grow towards each other and fuse in the midline. The nasal septum develops as a midline down-growth and ultimately fuses with palatial shelves.
What causes a lateral cleft lip?
Failure of fusion of the medial nasal prominence and maxillary prominence.
