Outline Development of the Branchial Region and Portions of the Head and Neck



Download 53.86 Kb.
Date conversion31.01.2017
Size53.86 Kb.
Outline

Development of the Branchial Region and Portions of the Head and Neck

Dr. Bennett-Clarke



General Information:  All these developmental aspects are happening at the same time (4th – 10th week)

• In the human embryo the primitive mouth (stomodeum) is a shallow depression at the cephalic end of the pharyngeal foregut.

• It is separated from the pharyngeal foregut by the buccopharyngeal membrane.

• During the fourth week of development the buccopharyngeal membrane starts to degenerate, after this the mouth will be open to the amniotic cavity.

-The Pharyngeal arches will wrap around and touch each other and form the pharyngeal apparatus

• At the same time, out-pouchings of the pharyngeal foregut develop just posterior to the degenerating buccopharyngeal membrane (called the pharyngeal pouches).

• Four pairs of grooves develop between the pouches (pharyngeal grooves)

• Interposed between the grooves and the pouches are condensations of mesenchyme called the pharyngeal arches.

• The pharyngeal arches are invaded by neural crest cells from the developing mid- and hindbrain regions of the neural tube.

• The arches continue to develop and grow until they meet in the midline and completely surround of the pharyngeal portion of the foregut.






The pharyngeal apparatus:

The pharyngeal apparatus is made up of the pharyngeal arches, pouches and grooves. The pharyngeal apparatus contributes extensively to the formation of the face, nasal cavities, mouth, larynx, pharynx and viscera of the neck.


Pharyngeal arches- five bars of mesenchymal tissue forming the ventral region of the developing pharyngeal foregut.

Pharyngeal arch components

Initially each arch is composed

1. Outer ectoderm 

2. Core mesoderm  has two types

-Core Mesoderm = from para-axial mesoderm = Muscles & Endothelium of Blood Vessels

- Neural crest cells = skeletal elements & other structures

Failed migration = deformities of the face

3. Inner endoderm  for developing pharynx/ foregut

A typical pharyngeal arch contains

1. Artery – off Dorsal Aorta

2. Cartilaginous Rod

3. Nerve = will be Cranial Nerves

Numbering of the Pharyngeal arches – Develop Sequencially


First arch = Mandibular arch

Second arch = Hyoid Arch

Third arch = No Name

Fourth Arch = No Name

Fifth Arch = Rudimentary

Sixth = Small & Caudal

Fourth and sixth arches- (there is no fifth arch in human and the sixth arch is only rudimentary)-



Derivatives of the pharyngeal arches

Arch

Skeletal

Muscle

Nerve

Blood Vessel

First Arch = Mandibular Arch
-Will turn into Mandibular & Maxillary Process

Meckel's Cartilage-Will completely Regress
Incus, Malleus, & Sphenomandibular Ligament develop here

Temporalis, Masseter, Medial Pterygoid, Lateral Pterygoid, Mylohyoid, Anterior Digastric, Tensor Tympani, & Tensor Veli Palatini 

 CN V = Mandibular Branch

Maxillary artery 

Second arch

Reichert's Cartilage – Mostly Regress
Styloid Process, Stylohyoid Ligament, & Superior part of hyoid

Muscles of facial Expression, Posterior Digastric, Stylohiod, &  Stapedius

CN VII = Facial Nerve

 Stapedial artery

Third arch

Inferior Part of Hyoid, & Small cartilages of the larynx 

Stylopharyngeus 

 CN IX = Glossopharyngeal Nerve

Internal Carotid 

Fourth & Sixth arches

 Large Cartilages of the Larynx

 Muscles of the soft palate, Muscles of the pharynx, & Muscles of the Larynx

CN X = Vagus 

Left = Aortic arch

Right = Subclavian 





Pharyngeal pouches- these are “balloon-like” diverticula that develop between the arches.

• There are four pair of well defined pouches.

• The pouches are lined with endoderm from the developing pharyngeal foregut.
Derivatives for the pharyngeal pouches

1. First pouch (between arch 1 and 2)  Will elongate

2. Second pouch (between arch 2 and 3)  Will be invaded by lymphatic tissue

3. Third pouch (between arch 3 and 4)  Expands into dorsal & ventral diverticula

4. Fourth pouch (between arch 4 and 6)  Expands into dorsal & ventral diverticula

5. Fifth pouch – not well developed





Derivatives for the pharyngeal pouches

Pouch

Derivatives

First pouch (between arch 1 & 2)

Elongates and forms:

  • Tympanic cavity

  • Auditory Tube

  • Internal aspect of tympanic membrane 

Second pouch (between arch 2 & 3)

Forms Tonsilar bed:

Invaded by lymphatic tissue that forms the tonsil 



Third pouch (between arch 3 & 4)

Dorsal Diverticula:

  • Inferior Parathyroids

Ventral Diverticula 



  • Thymus

Fourth pouch (between arch 4 & 5)

Dorsal Diverticula:

  • Superior Parathyroids

Ventral Diverticula 



  • Ultimobranchial Body

  • Invades thyroid & gives rise to parafollicular cells (C-Cells)

Fifth pouch (between arch 5 & 6)

Never Forms 


Pharyngeal grooves (clefts)- depression that separate the arches externally.

Only one pair of grooves exists as an adult structure, the first pharyngeal groove.


Derivatives of the pharyngeal grooves:

1. First groove (between arch 1 and 2)

2. Second through fourth grooves Arches two, three, & four overgrows

 Covers over all the other pharyngeal grooves



    • Makes surface of neck smooth

Forms cervical sinus/cyst & Then Regresses

Derivatives of the pharyngeal grooves

Groove

Derivatives

First groove (between arch 1 & 2)

 Lengthen to form:

External acoustic meatus

External aspect of tympanic membrane


Second through fourth grooves

Forms Cervical Sinus/Cyst

Will then regress




Anomalies of pharyngeal pouches or grooves

1. Branchial sinuses

 Blind pouch/recess on the inside (internal = remnant of pouches) or outside (external = remnant of groove)

-- Usually at 2nd pouch or groove = may find in Tonsilar bed


2. Branchial cysts

 Persistent Cervical sinus/cyst


3. Branchial fistulas

 Opening either onto the skin (External) or into the pharynx (Internal)



Structures that develop in the floor of the pharynx:

Tongue- The tongue develops as a series of swellings in the floor of the pharynx.

1. Median tongue bud (tuberculum impar)

 On the floor of pharynx along 1st arch
2. Lateral lingual swellings/ Distal Tongue Buds

Floor of 1st arch

Increase in size & move midline

Overgrow median bud

forms anterior 2/3rd of tongue
3. Copula

floor of the 2nd arch


4. Hypobranchial/pharyngeal eminence

Posterior to Copula from 3rd, 4th (Mostly), & 6th arches

Overgrows Copula

Forms Posterior 1/3rd of tongue


5. Terminal sulcus

Junction between anterior 2/3rd & Posterior 1/3rd of tongue

Only visible once tongue buds has met
**Muscles of the tongue do not originate in the pharyngeal wall but migrate there from the occipital somites.

Thyroid gland- The thyroid gland is the first endocrine organ to develop in the embryo.


  1. Thyroid diverticulum  pouch in the developing tongue

    1. Migrates anterior to hyoid and thyroid cartilages

  2. Thyroglossal duct

    1. As the diverticulum migrates it drags the duct with it

    2. Will regress (in almost all cases)

  3. Foramen cecum  Spot on the tongue where the thyroid diverticulum is/was

Ectopic Thyroid Tissue- can be anywhere along its course (Tongue, neck, laryngeal cartilages)



  • Can have a pyramidal lobe of the thyroid = from Thyroglossal duct

Thyroglossal duct cysts- These are cysts that form anywhere along the course of the former thyroglossal duct, in the tongue, anterior neck or anterior to the laryngeal cartilages.






Formation of the face- The face develops between the 4th and 8th weeks of development.

There are five faces primordial

1. Frontonasal prominence-

2. Maxillary prominences-

3. Mandibular prominences-
The frontonasal prominence- surrounds the developing forebrain. Develops into the forehead, majority of the nose and a portion of the upper lip.

• Frontonasal prominence develops two lateral thickened areas- the nasal placodes.

• The lateral and medial rims of this enlarge and in the center there is a depression the nasal pit.

• The lateral rim is called the lateral nasal swellings or processes and the medial is the medial nasal swellings or processes.

• The medial nasal swellings meet in the midline to form the intermaxillary segment. This will give rise to the philtrum of the upper lip, and portions of the upper jaw, nasal septum and palate (primary palate).
The maxillary and mandibular prominences develop from the first pharyngeal arch. The prominences are produced by a proliferation of neural crest cells that migrate there from the lower midbrain and hindbrain regions of the developing neural tube.
The maxillary prominences

• Grow toward the lateral nasal swellings and meet at the nasolacrimal groove.

• Result in the formation of the lateral portion of the upper lip, upper cheek, most of the maxilla and the palate.
The mandibular prominences

• Meet the maxillary prominence laterally & the opposite mandibular process in the midline.

• Result in the formation of the adult lower lip, lower cheek, chin and mandible.
The mesenchyme from the second pharyngeal arch invades the areas of these two prominences and forms the muscles of facial expression.




Development of the palate- the palate develops during the 5th week of the embryonic period.

The palate develops from two primordia



The primary palate

The secondary palate
• The primary palate develops from the intermaxillary segment. (remember this came from the frontonasal prominence.) The primary palate forms only the most anterior portion of the adult hard palate, anterior to the incisive foramen.
• The secondary palate develops as two processes from the internal surface of the maxillary prominences. These are the lateral palatine processes. Gradually the processes enlarge and grow to meet in the midline. They also fuse with the developing nasal septum. The anterior portion of these processes contributes to the hard palate and the posterior portion to the soft palate.
• The incisive foramen marks the junction of the primary and secondary palates. The midline raphe marks the junction of the lateral palatal processes.



Cleft palate and lip- These are two of the most common defects of the face. Where intermaxillary segment met the maxillary process
Cleft lip - occurs about 1 in 900 births, more in boys than girls.

Happens just adjacent to the philtrum

1. Unilateral (B) - failure of the fusion of the maxillary and intermaxillary segments to fuse.

2. Bilateral (D) - failure of fusion on both sides


Cleft palate - 1 in 2,500 births, more in girls and than boys.

1. Anterior (primary; C & D)- failure of the primary palate to meet the secondary palate.

2. Posterior (secondary; E))-failure of the lateral palatine processes to fuss together and with the nasal septum.

3. Complete (F)- the most severe clefting combination of both the anterior and posterior





The database is protected by copyright ©dentisty.org 2016
send message

    Main page