Development of pharyngeal apparatus

Bones of the Pelvic GirdleBones of the Pelvic Girdle

And Lower ExtremityAnd Lower Extremity

IntroductionIntroductionAfter folding, the 2ry yolk sac inside the embryo

gives rise to : Fore gut -Mid gut – hind gut.The fore gut The fore gut is divided into :

a. Cranial part : extends from oral membrane to the laryngo-tracheal groove .

It gives rise to : Part of mouth cavity Salivary glands Pharyngeal apparatusPharyngeal apparatus Respiratory system

b. Caudal part : begins distal to the laryngotracheal groove.It gives rise to: esophagus-stomach- part of duodenum-

liver-biliary system –pancreas.

Amniotic cavity

Oral membrane

Gut

Cloacal membrane

Yolk sac

Before folding

Stomodeum

Vitello-intestinal duct

Allantois Cloacal membrane

Hindgut

MidgutForegut

Connecting stalk

Amniotic cavity

After folding

Prof. Mohamed A. AutifiProf. Mohamed A. Autifi

The pharyngeal archesThe pharyngeal arches

They are 6 curved cylindrical mesenchymal 6 curved cylindrical mesenchymal thickening thickening on each side of the primitive pharynx.

They develop in the head & neck similar in origin & structure to gills of the fish.

Gill = Branchia

Each arch consists of :1. Outer ectodermal covering2. Inner endodermal lining3. Mesodermal core


Each pharyngeal arch consists, at first of mesenchyme derived from the lateral plate mesoderm.

Soon, neural crest cells migrate into the pharyngeal arches and surround the central core of mesenchymal cells.

Migration of neural crest cells into the arches produce discrete swelling demarcating each of the pharyngeal arch.

NB. Mesenchyme =connective tissue of embryo The mesenchyme derived from neural crest

cells is called (ectomesenchyme) to differentiate it from mesenchyme derived from mesoderm.


A typical pharyngeal arch A typical pharyngeal arch contains:contains:

1- A cartilaginous rod that forms the skeleton of the arch.

2- A muscular component that differentiates into muscles in the head and neck.

3- An aortic arch , an artery that arises from the truncus arteriosus of the primordial heart.

4- A nerve that supplies the mucosa and muscles derived from the arch.


Nerve supply of the pharyngeal Nerve supply of the pharyngeal archesarches

It is derived from the hindbrain (pons and M.O)

Each arch receives mixed nerve.

Its motor branch supplies muscles derived from the arch.

Its sensory branch supplies skin and mucous membrane of the arch.


Development of Pharyngeal Development of Pharyngeal archesarches


•By the end of the 4th week, 4 well defined pairs of pharyngeal arches are visible externally.•The 5th and 6th arches are small and cannot be seen on the surface of the embryo.



CartilagesCartilages Most of the cartilages that form within the

pharyngeal arches develop from the neural crest of the midbrain and hindbrain regions, although the cartilages of arches 4 and 6 apparently develop from lateral plate mesoderm.

The first pharyngeal arch is remodeled to form a cranial maxillary process (swelling) and a caudal mandibular process (swelling).

Each process contains a central cartilaginous element (the maxillary known as palato-pterygo-quadrate cartilage and the mandibular known as Meckel's cartilage) surrounded by a mesenchymatic tissue.




Prof. Mohamed. A. AutifiProf. Mohamed. A. Autifi

Arch Skeletal Derivatives

Muscular Derivatives

Vascular Element

Nereve

First arch(mandibular arch)Consists of maxillary process andmandibular process

Maxillary process gives rise to:1.Maxilla2.Zygomatic bone3.Squamous part of temporal boneMandibular processdifferentiates into :1.Malleus2.Incus3.Anterior ligament of malleus4.Spheno-mandibular ligament5.Mandible

1.Muscles of

Mastication

2.Tensor palati

3.Tensor tympani

4. Mylohoid

5. Anterior belly of digastric

1. Maxillary artery

Mandibular nerve (V)



Arch Skeletal Derivatives

Muscular Derivatives

Vascular Element

Nereve

Second arch(Hyoid arch)

Reichert’s cartilage:Differentiates into:1.Stapes2.Styloid process3.Stylohyoid ligament4.Lesser horn of the hyoid bone5.Upper part of body of hyoid bone

1. Muscles of

the scalp and face

2. Platysma

3. Stylohyoid

4. Stapedius

5. Posterior belly of digastric

Stapedialartery(carotico-tympanic

br. of ICA)

Facial nerve (VII)


Arch Skeletal derivatives

Muscular derivatives

VascularElement

Nereve

Third arch 1. Greater horn of hyoid bone

2. Lower part ofbody of hyoid

bone

Stylopharyngeus 1. I.C.A1. I.C.A2. C.C.A2. C.C.A

Glossopharyngeal nerve (IX)

Fourth arch

Thyroid cartilage Cricothyroid 1.1. Arch of Arch of aortaaorta

on left side2. Subclavian A 2. Subclavian A

on right side

Superior laryngeal nerve (X)

Sixth arch Rest of Cartilages of the larynx

except epiglottis:

-Cricoid,-Arytenoid,-Corniculate and -Cuneiform.NB. The

epiglottis develops from mesenchyme in hypobrancheal eminence

1. Other intrensicmuscles of larynx

2. Constrectormuscles of

pharynx except

Stylopharyngeus

3. Muscles ofpalate excepttensor palati

1. Pulmonary APulmonary A on each

sides2. DuctusDuctus arteriosusarteriosus on left side

Recurrent laryngeal nerve (X)


Derivatives of Cartilages of Derivatives of Cartilages of FirstFirst Pharyngeal Arch Pharyngeal Arch

The ventral part of the first arch cartilage ( Meckel ( Meckel cartilage ) cartilage ) form primordium of the mandible

The middle part of cartilage forms anterior ligament of malleus and sphenomandibular ligament

The dorsal end of first arch cartilage ossifies to form malleus and incus

More details about More details about cartilagescartilages


Derivatives of Cartilage of Derivatives of Cartilage of secondsecond Pharyngeal Pharyngeal ArchArchThe ventral end of second arch cartilage (Reichert cartilage) ossifies to form the lesser cornu and upper part of the body of the hyoid bone

The dorsal end of second arch cartilage (Reichert cartilage) ossifies to form the stapes, styloid process and stylohyoid ligament


Derivatives of Derivatives of ThirdThird Pharyngeal Arch Cartilage Pharyngeal Arch Cartilage

The third arch cartilage ossifies to form the greater cornu and the lower part of the body of the hyoid bone


• The fourth and sixth arch cartilages fuse to form the laryngeal cartilages except epiglottis which develops from hypobrancheal eminence

• The fifth pharyngeal arch is rudimentary and disappear later and has no derivatives

Derivatives of The fourthfourth and sixthsixth Pharyngeal Arch Cartilages


Muscular component


Pharyngeal Pharyngeal

Pouches Pouches andand clefts clefts

Development of Pharyngeal Development of Pharyngeal pouchespouches and and cleftsclefts


Pharyngeal pouchesPharyngeal pouches The pharyngeal pouches are balloon-like diverticula that

formed on the endodermal side between the pharyngeal arches

The pairs of pouches develop in a craniocaudal sequence between the arches.

The first pair of pouches lies between the first and second pharyngeal arches.

There are four well defined pairs of pharyngeal pouches

The fifth pair is absent or rudimentary

•


First pouchFirst pouch

It gives rise to tubotympanic recess which forms: 1.Tympanic cavity2.Auditory tube. (pharyngotympanic tube or Eustachian tube)


Second pouchSecond pouchGives rise to palatine tonsils-Early in 3rd month, its lining epithelium proliferates ➪ solid tonsillar buds which grow into underlying mesoderm.-Their central cellsdegenerate➪ hollow tonsillar crypts. -Crypts & surrounding mesoderm ➪ palatine tonsils.-Lymphatic tissue infiltrates its mesoderm during 3-5 Month-Tonsillar capsule formed by condensed mesoderm. -Remnants of pouch ➪ intratonsillar cleft


Third pouchThird pouchGives rise to: -inferior parathyroid glands.-thymus gland.At 6th week, they lose connection to pharyngeal wall.

-Thymus gland migrates caudally & medially, pulling the parathyroid. The two thymic rudiments descend into thorax. Gland is large at time of birth, ➚ up to 2nd year, little ➚ until 7th year, rapid growth to 11th year, then ➘ to adult weight (12-15 gm)-Inferior parathyroid glands descends to lower pole of thyroid gland


Fourth pouchFourth pouch

It gives rise to:

1.Superior parathyroid glands.

It migrates with the thyroid gland.

2. Ultimo-branchial body.

It incorporates into the thyroid gland.

It gives parafollicular or C cells of thyroid gland


PHARYNGEAL GROOVES PHARYNGEAL GROOVES (CLEFTS)(CLEFTS)::

In the 5th week: 4 clefts seen. The first cleft gives: external auditory meatus. The epithelium of the bottom forms outer layer of eardrum

NB. Active growth of 2nd arch mesoderm overlaps 3rd & 4th arches.

Temporarily, clefts ➪ectodermal cavity, cervical sinus, which disappears later.


Development of Pharyngeal Development of Pharyngeal pouchespouches and and cleftsclefts




Congenital anomalies Congenital anomalies Lateral cervical cysts and fistulas

(Branchial cyst & Branchial fistula)


1. Branchial Cyst: Sinus persists as cyst along ant border of sternomastoid muscle.

If ruptures ➪ branchial sinus

2. Branchial Sinus:a) External: Cyst opens outside, usually anterior to sternomastoid.b) Internal: Cyst opens

into pharynx,usually in the tonsillar region.

3. Cervical Fistula: Sinus opens externally

& internally, connects pharynx with outside.

Congenital anomalies Congenital anomalies


4. 1st Arch Syndrome (Mandibulofacial dystosis)

Maldevelopment of components of 1st pharyngeal arch results in various congenital malformations of eyes, ears, mandible and palate. This is due to failures of Proper neural crest migration into the 1st branchial arches.

5. DiGeorge Syndrome. Improper migration of neural crest cells into the 3rd and 4th branchial arches.

It is characterized by: 1.Minor deformations of the lower face.2.Thymic and parathyroid aplasia (i.e., no thymus

and no parathyroids). The absence of a thymus has a very deleterious effect on the development of the immune system.

The absence of parathyroids leads to hypocalcemia.3.Problems with aorticopulmonary septation.



6. Ectopic Thymic Tissue: Thymus gland lies in the neck.

7. Ectopic Parathyroid: Inferior parathyroid may present at bifurcation of Common carotid artery.



Thank you Thank you for attentionfor attention


Derivatives of Derivatives of pharyngeal floorpharyngeal floor

The pharyngeal floor is formed by fusion of ventral parts of the arches & pouches: It gives rise to: A. Thyroid gland. B. Tongue.C. Lower respiratory system.


Development of the thyroid Development of the thyroid glandgland

Thyroid primordium appears as a median endodermal proliferation in the floor of the pharynx between tuberculum impar and hypobranchial emenence (the site is indicated by foramen caecum in adult)

This thickening is invaginated to form a bilobed divertaculum which descend ventral to the developing hyoid bone then ventral to the developing larynx.

It remains connected to the dorsum of the tongue by the thyroglossal duct


Development of the thyroid Development of the thyroid glandgland

1

2

3

4


Development of the thyroid glandDevelopment of the thyroid gland

The thyroid gland reaches its final position The thyroid gland reaches its final position by the 7by the 7thth week and week and begins to functionbegins to function at at the end of the 3the end of the 3rdrd month . month .

The endodermal cells of the thyroglossal The endodermal cells of the thyroglossal duct form the thyroid follicles which secrete duct form the thyroid follicles which secrete thyroxine and triiodothyronine hormonesthyroxine and triiodothyronine hormones..

The ultimobranchial body forms The ultimobranchial body forms parafollicular C cells which secrete parafollicular C cells which secrete calcitonin.calcitonin.

The mesoderm forms the true capsule and The mesoderm forms the true capsule and connective tissue septa. connective tissue septa.


Fate of the thyroglossal duct:Fate of the thyroglossal duct:

The part of the duct between hyoid bone and isthmus of the gland gives rise to pyramidal lobe and levator glandulae thyroidae

Above the hyoid bone the duct degenerate completely.


Congenital Congenital AnomaliesAnomalies::

1. Agenesis: 1. Agenesis: congenital congenital hypothyroidismhypothyroidism 2. Ectopic (aberrant) 2. Ectopic (aberrant) thyroid:thyroid: Lingual, Lingual, sublingual, or sublingual, or thoracicthoracic3. Thyroglossal cyst:3. Thyroglossal cyst: In In

midline of neck, midline of neck, common at common at

lingual, lingual, supra-, retro- supra-, retro- or infra-hyoid sitesor infra-hyoid sites4. Thyroglossal sinus:4. Thyroglossal sinus:

Due to rupture of Due to rupture of thyroglossal cystthyroglossal cyst



Thyroglossal cyst

Development of TongueDevelopment of Tongue



A. The mucous membrane

Anterior 2\3: arises from 3 swelling derived from the

ventral parts of both 1st pharyngeal arches as follows:•2 lateral lingual swellings and •1 median swelling “tuberculum impar”

Posteror 1\3: developed from the upper half of hypobranchial eminince” The post.1\3 fuses with the ant.2\3 along a v-shaped sulcus terminalis.



B. The muscles of the tongue

Derived from the occipital myotomesoccipital myotomes that migrate to the developing tongue taking with it their nerve supply (hypoglossal nerve)

Some of the tongue muscles are differentiated in situ.

NB. At first the tongue is fused with the floor of the pharyngeal gut. Later on linguo-gingival groove appears on either side and frees the tongue from the floor of the mouth


Lingual papillae & taste buds:

Vallate & foliate papillae appear first in relation to branches of IX n

Fungiform & filiform papillae appear later near fibers of chorda tympani. -All papillae soon develop taste buds

Lymphoid follicles aggregate under mucosa of post 1/3 of tongue ➪ lingual tonsil


Congenital Anomalies:

1. Ankyloglossia (tongue-tie): Frenulum of tongue extends to its tip. Prevents movements & hinders proper speech

2. Macroglossia: Large tongue, due to lymphangioma or muscular hypertrophy

3. Microglossia

4. Cleft tongue: Incomplete fusion of lingual swellings ➪ median groove/cleft, does not extend to tongue tip

5. Bifid tongue: Cleft extends to tip

6. Congenital cysts & fistulae: Remnants of thyroglossal duct


Tongue tieTongue tie

MicroglossiaMicroglossia

MacroglossiaMacroglossia



Tongue tie

Bifid Tongue


Health & Medicine

Development of pharyngeal apparatus