EMBRYOLOGYBY

Dr. THAAER MOHAMMED DAHER ALSAADSPECIALIST IN GENERAL SURGERY

M.B.Ch.B. (MBBS) F.I.B.M.S. )Ph.D.)SENIOR LECTURER

IMS MSU

TOPICS

• HIGHLIGHTS.

• INTRODUCTION.

• DEVELOPMENT OF THE FACE/ LIPS, NOSE, CHEECHS, EYE, EXTERNAL EAR.

• DEVELOPMENT OF THE PALATE.

• ANOMALIES.

• TIMETABLE.

Age Developmental events

4th week (28th day)

The frontonasal, maxillary and mandibular processes can be identified.Lens and nasal placodes are also present.

5th week (31 to 35 days)

The nasal pits are established.

6th week Tubercles of the development of pinna begins to be formed.On each side, palatal process appears from the maxillary process.

7th week Eyelid established.Maxillary processes fuse with medial nasal process.

8th week Eye shift from lateral to medial position.Bucconasal membrane ruptures.

10th week The palatal processes and nasal septum fuse with each other.

TIMETABLE OF SOME EVENTS DESCRIBED IN THIS CHAPTER

HIGHLIGHTS

• STOMATODIUM = future mouth.

• FRONTONASAL PROCESS + Rt. AND Lt. MANDIBULAR ARCHES.

• THE MANDIBULAR ARCH divides into a maxillary process and a mandibular process.

• The Lt. and Rt. Mandibular processes meet in the midline

and fuse to form the lower and upper jaw.

• The upper lip is formed by fusion of the frontonasal process with the Rt. And Lt. maxillary processes./ hare lip (failure to fuse).

• The cheeks are formed by fusion of the posterior parts of the

maxillary and mandibular processes.

• The nose is derived from the frontonasal process.

• The nasal cavity is formed as follows;

• An ectodermal thickening (nasal placode) appears over the frontonasal process.

• The placode gets depressed below the surface to form the nasal pit.

• The nasal pits enlarged to form the nasal cavity.

• Paranasal sinuses appear as outgrowths from the nasal cavity.

• The palate is formed by fusion of the three components;

• Rt. And Lt. palatal processes (arising from the maxillary process) and

the primitive palate (derived from the frontonasal process).

• Deficiency in fusion leads to various form of cleft palate.

HIGHLIGHTS (continue)

INTRODUCTION

• Brain and heart bulging are separated by the stomatodaeum.

• The floor of the stomatodaeum is formed by the buccopharyngeal membrane.

• Soon, mesoderm covering the developing forebrain proliferates, and forms a downward projection (frontonasal process) that overlaps the upper part of the stomatodaeum.

• Pharyngeal arches are in very close relationship to the stomatodaeum.

• The face is derived from the following structures that lie around the stomatodaeum:

1. The frontonasal process.

2. The 1st pharyngeal arch on each side.

INTRODUCTION

• The mandibular arch forms the lateral wall of the stomatodaeum.

• This arch gives off the maxillary process.

• Maxillary process grows ventro-medially cranial to the main part of the arch (mandibular process).

• The ectoderm of the frontonasal process shows BILATERAL LOCALIZED THICKENINGS (the nasal placodes) that are situated above the stomatodaeum.

• The placodes form nasal pits.

• The pits are continuous with the stomatodaeum below.

• The edges of each pit are raised above the surface as medial and lateral nasal process.

DEVELOPMENT OF THE FACELOWER LIP

• The mandibular processes of the two sides grow toward each other and fuse in the midline.

• They form the lower margin of the

stomatodaeum (mouth).

• The fused mandibular processes give rise to the lower lip, and the lower jaw.

1. The maxillary process fuses with the lateral and then with medial nasal process. The lateral and medial process fuse with each other, forming the external nares (nasal pits) and are cut off from the stomatodaeum.

2. The two external nares come closer together (maxillary process grows and the frontonasal process becomes much narrower).

3. The stomatodaeum is bounded above by the upper lip which derived as follows;

1. Maxillary process forms the mesoderm of the lateral part of the lip. The ectoderm of the maxillary process gives rise to the overlying skin.

2. Mesoderm of the median part (philtrum) is derived from the

frontonasal process. But the ectoderm is derived from the maxillary processes and meet in the midline. Therefore, the skin of entire upper lip is innervated by maxillary nerve.

4. The muscles of the face are derived from the 2nd

branchial arch and are supplied by the facial nerve.

DEVELOPMENT OF THE FACEUPPER LIP

• The nose receives contribution from the frontonasal process, and from the medial and lateral nasal processes of the RT. And Lt. sides.

• Nasal pits – nares --- cut off from the somatodaeum.

• External nares approach each other. (due to the frontonasal process becomes narrower and its deep part forms the nasal septum).

• Mesoderm becomes heaped up in the median plane to form the prominence of the nose.

• Simultaneously, a groove appears between the region of the nose and the bulging forebrain.

• As the nose becomes prominent, the external nares come to open downwards instead of forwards. (the external form of the nose is established).

DEVELOPMENT OF THE FACENOSE

• After the formation of the upper and lower lips, the stomatodaeum is very broad.

• In its lateral part, it is bounded above by the maxillary process and below by the mandibular process.

• These processes undergo progressive fusion with each other to form the cheeks.

• The maxillary process fuses with the lateral nasal process in the region of the lip and extends from the stomatodaeum to the medial angle of the developing eye.

• This line of fusion is called NASO-OPTIC FURROW or NASOLACRIMAL SULCUS.

• A STRIP OF ECTODERM becomes buried along this furrow and gives

rise to the nasolacrimal duct.

DEVELOPMENT OF THE FACECHEEKS

• The region of the eye is first seen as ectodermal thickening, the lens placode.

• Lens placode appears on the ventro-lateral side of the developing forebrain.

• Lens placode is lateral and cranial to the nasal placode.

• LENS PLACODE sinks below the surface and cut off from the surface ectoderm.

• The developing eye produces bulging in this situation. (bulgingsof eyes first directed laterally, and lie in the angles between the maxillary processes and the lateral nasal processes). With the narrowing of the frontonasal process they come to face forwards.

• The eyelids are derived from folds of ectoderm that are formed above and below the eyes, and mesoderm enclosed within the folds.

DEVELOPMENT OF THE FACEEYE

• The external ear is formed around the dorsal part of the 1st

ectodermal cleft.

• A series of mesodermal thickenings appear on the mandibular and hyoid arches where they adjoin this cleft.

• The pinna is formed by fusion of these thickenings.

• When first formed, the pinna lies caudal to the developing jaw.

• It is pushed upwards and backwards to its definitive position due to the great enlargement of the mandibular process.

• If the mandibular process fails to enlarge, the ears remain low down.

DEVELOPMENT OF THE FACEEXTERNAL EAR

1. Hare lip.2. Oblique facial fissure.

3. Macrostomia X Microstpmia // lateral facial cleft.

4. Bifid nose // proboscis +/- cyclops.5. Mandibulofacial dystosis, (1st arch syndrome or Teacher

Collins syndrome).6. Hemiface Underdeveloped/ overdeveloped.7. Retrognathia ??? // Agnathia.8. Congenital tumours.

9. Hypertelorism.

10. Double lip. / congenital pits or fistula.

DEVELOPMENTAL ANOMALIES OF THE FACE (skip)

• The nasal cavities are formed by extension of the nasal pits.• The medial and lateral nasal processes fuse and form a partition

between the nasal pits and the stomatodaeum.• This partition is called the primitive palate. (frontonasal process

derivative).

• Nasal pits deepen to form nasal sacs.• Nasal sac posteriorly is separated from the stomatodaeum by

buccopharyngeal membrane (nasal fin).

• Nasal fin breaks soon.

• Nasal sac has a ventral orifice on the face called the anterior or external nares.

• and a dorsal orifice opens into the stomatodaeum called the primitive posterior nasal aperture.

DEVELOPMENT OF THE FACENASAL CAVITY

• The two nasal sacs are first widely separated from each another by frontonasal process.

• Nasal cavities enlargement + narrowing of the frontonasal

process (=) bring cavities closer together.

• The intervening tissue forms the nasal septum.

• Ventral part of the nasal septum is attached below to the primitive palate.

• Nasal septum posteriorly is at first attached to the

bucconasal membrane, but on disappearance of this membrane it has free lower edge.

DEVELOPMENT OF THE FACENASAL CAVITY (continue)

• The nasal cavity is separated from the mouth by the development of the palate.

• The lateral wall of the nose is derived, on each side, from the lateral nasal process.

• The nasal conchae appear as elevations on the lateral wall of each nasal cavity.

• The original olfactory placodes form the olfactory epithelium that lies in the roof, and adjoining parts of the walls, of the nasal cavity.

DEVELOPMENT OF THE FACENASAL CAVITY (continue)

1) Atresia / uni or bilateral /? Absence.

2) Congenital communication between the cranial cavity and the nose.(cribriform plate defects).

3) Deflected nasal septum. /// absent.

4) Communicates with the mouth.

Anomalies of the Nasal Cavity

In 1961, a twelve man Soviet crew was building a new base in the Antarctic. Mindful that being trapped in sub-zero temperatures for months on end required a medical professional to be on hand, one doctor had been assigned to the team. So what happens when the only man capable of

performing surgery comes down with a severe case of appendicitis?

He does what any reasonably minded person would do.

Performs an appendectomy…on himself

• Paranasal sinuses appear as diverticula from the nasal cavity.

• The diverticula invade the bones after which they are named.

• The maxillary and sphenoidal sinuses begin to develop before birth.

• The other sinuses develop after birth.

• Enlargement of the sinuses associated with the overall enlargement of the facial skeleton including the jaws.

• This provides spaces in the jaws for growth and eruption of teeth.

• Growth of facial skeleton is responsible for the gradual change in looks of a baby.

DEVELOPMENT OF THE FACEPARANASAL SINUSES

DEVELOPMENT OF THE PALATE

• The maxillary process form the upper lip.

• Maxillary process extends backwards on either sides of the stomatodaeum.

• The palatal process grows medially from the maxillary process.

• The palate forms from three components:

1. The two palatal processes, and

2. The primitive palate formed from the frontonasal process.

• The definitive palate is formed by the fusion of three parts as follows:1) Fusion of each palatal process with the posterior margin of the primitive palate.2) Two palatal processes fuse in the midline. (fusion begins anteriorly and

proceeds posteriorly).3) Fusion of the medial edges of the palatal processes with the free lower edge of

the nasal septum. (thus separating nasal cavities from each other and from the mouth).

4) At later stage, the mesoderm in the palate undergoes intramembranous ossification to form the hard palate.

The ossification does not extend to the posterior portion, which remains as the soft palate.

The part of palate derived from the frontonasal process forms the premaxilla, which carries the incisor teeth.

DEVELOPMENT OF THE PALATE (continue)

Cleft Palate

• Defective fusion of the various components of the palate gives rise to clefts in the palate.

• Clefts vary considerably in degree.

• Clefts may be unilateral or bilateral.• Clefts of the palate that extend to its anterior end

are associated with harelip, (as both the upper lip and the palate are formed by fusion of the maxillary processes with the frontonasal process).

• Clefts of the palate result in anomalous communicating between the mouth and the nose.

Age Developmental events

4th week (28th day)

The frontonasal, maxillary and mandibular processes can be identified.Lens and nasal placodes are also present.

5th week (31 to 35 days)

The nasal pits are established.

6th week Tubercles of the development of pinna begins to be formed.On each side, palatal process appears from the maxillary process.

7th week Eyelid established.Maxillary processes fuse with medial nasal process.

8th week Eye shift from lateral to medial position.Bucconasal membrane ruptures.

10th week The palatal processes and nasal septum fuse with each other.

TIMETABLE OF SOME EVENTS DESCRIBED IN THIS CHAPTER

Craniofacial Duplication

Ambrassyndrome or congenital Hypertrichosis or excessive hairgrowth.

The Wolf Girl