Development Of Face And Oral Cavity
Question 1. Describe the development of the face and mention the congenital defects of the orofacial region. (or) Development of palate
Answer:
Developmental of the face:
- The face develops between the 24th and 38th days of gestation.
- The face is derived from the following.
Development of nose:
- The medial nasal processor of both sides together with the frontonasal process gives rise to the nose.
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Upper lip:
- The maxillary processes of both sides grow medially.
- This pushes the medial nasal process medially and merges with that of the opposite side.
- This leads to the formation of the upper lip.
Lower lip:
- The lower lip is formed by merging the mandibular processes.
Primary palate:
- It is formed by the merging of the two medial nasal – processes.
Nasolacrimal duct:
- The lateral nasal processes are separated by the maxillary process by a deep barrow,
- The epithelium in the floor of it forms a solid core.
- It eventually canalizes to form the nasolacrimal duct.
Facial muscles:
- They are derived from the mesenchyme of the second branchial arch.
Cheek:
- It is formed by the fusion of the maxillary and mandibular processes.
Oral cavity:
- Around 4th week of intrauterine life, a prominent bulge develops on the ventral side of the embryo.
- Below it, there is a depression called stomodeum.
- The oral cavity is developed from it.
Congenital defects of the orofacial region:
Question 2. Describe the development of the palate.
Answer:
- The development of the palate initiates between 7- 8 weeks and completes around the third month of gestation.
- The palate develops from.
- Two palatal processes/shelves extending from maxillary processes.
- Fronto nasal process.
- The shelves are directed first downward on each side of the tongue.
- Around the seventh week of development, the tongue is withdrawn from between the shelves.
- The tongue now elevates due to.
- Presence of contractile fibroblasts.
- The growth pattern of the head.
- Both the palatine shelves converge and fuse with each other and with the primary palate.
- The fusion of 2 palatine shelves occurs due to.
- Cessation of DNA synthesis within the epithelium.
- Surface epithelial cells are sloughed off exposing basal epithelial cells.
- These cells permit adhesion and formation of junctions to achieve fusion.
- The fusion of palatal shelves results in separating the primitive oral cavity into nasal and oral cavities.
- Cessation of DNA synthesis within the epithelium.
- Surface epithelial cells are sloughed off exposing basal epithelial cells.
- These cells permit adhesion and formation of functions to achieve fusion.
- The fusion of palatal shelves results in separating the primitive oral cavity into nasal and oral cavities.
Question 3. Name the branchial arches involved in the development of the tongue, and write in detail about the development of the tongue.
Answer:
- The branchial arches that are involved in the development of Longue are:
- 1 arch
- 2 arches and
- 4 arches.
Development of tongue:
1. Development of anterior two-thirds.
- A midline swelling arises from the mandibular process called tuberculum impar.
- The medial most part of the first arch proliferates to form a pair of pulls of lingual swelling
- These lingual swellings enlarge and merge with others and the tuberculum impairs to form large arms.
- This forms the anterior two third of the tongue,
2. Development of posterior one-third,
- Caudal to the median swelling, another midline swelling Called (lie hypobranchial eminence arises from the III and IV arches,
- II In divided Into
- Anterior popular.
- it forms the posterior one-third of the tongue,
- Hypolunnehlal eminence.
- gives rise to the epiglottis,
3. Development of the posterior-most part of the tongue,
- it is derived from IV branchial arch.
4. Development of the musculature of the tongue,
- is derived from Iho occipital myotomes,
- Further development of tongue.
- The longue sopranos from to floor of the mouth by down-growth ol meltdown,
- This degenerates to form the lingual sulcus and gives Iho longue mobility,
- Various papillae of tongue are in the anterior purl,
- Lymphatic tissue develops in the posterior part.
Anomalies:
Question 4. Development of upper lip and lower lip
Answer:
Development of upper lip:
- Each maxillary process grows medially
- It fuses first with the lateral nasal process and then the medial nasal process
- The mesodermal basis of the lateral part of the lip is formed from the maxillary process
- The overlying skin is derived from ectoderm covering the process
- The mesodermal basis of the medial part of the lip is formed from the frontonasal process
- The ectoderm of the maxillary process overgrows the mesoderm to meet the opposite maxillary process in the midline
- This entire upper lip is formed
- Muscles of the upper lip are derived from the mesoderm of the second branchial arch
Development of lower lip:
- The mandibular processes of the two sides grow towards each other and fuse in the midline to form the lower lip
Question 5. Development of mandible
Answer:
In 4th week of IU life, pharyngeal arches are laid down on the lateral and ventral aspects of the foregut.
- Separated by 4 branchial grooves
- The first arch is called the mandibular arch
- The mandibular processes of both sides grow towards each other and fuse in the midline
- Results in the formation of the lower lip and lower jaw.
Meckel’s Cartilage:
- Around the 41st – 45th day of IU life
The first structure to be formed is the bigeminal nerve
↓
Mesenchymal condensation occurs
↓
Activation of neurotrophic factors
↓
Inducbon osteogenesis
↓
Ossification occurs
It starts from the bifurcation of the inferior alveolar nerve in 6th week of IU life
↓
Ossification spreads below and around the nerve
↓
Inbamembranous ossification spreads dorsally and ventrally
↓
Results in the formation of the body and ramus of the mandible
↓
Ossification stops at the site which forms lingula
↓
Remaining Meckel’s carbage which does not undergo ossification forms the following
- Mental ossicles
- Incus and Malleus
- Spine of Sphenoid
- Anterior ligament of malleus
- Spheno mandibular ligament
Condylar process:
In 5th week of IU life
Mesenchymal condensation above the ventral side of the developing mandible
↓
Formation of cartilage at the 10th week
↓
Initiation of ossification in the 14th week
↓
Fusion with mandibular ramus by 4 months
Coronoid process:
The appearance of secondary accessory cartilages at 10-14 weeks of IU life
↓
Incorporation of it into expanding Ramus
Mental Region:
The appearance of Vz small cartilages on either side of the symphysis
↓
Ossification at the 7th month of IU life
↓
Formation of ossicles
↓
incorporation of it into intra-membranous bone
Question 6. Meckel’s cartilage
Answer:
Around the 41st – 45th day of IU life n First structure to be formed is the trigeminal nerve
↓
Mesenchymal condensation occurs
↓
Activation of neurotrophic factors
↓
Induction osteogenesis
↓
Ossification occurs
↓
It starts from the bifurcation of the inferior alveolar nerve in 6th week of IU life
↓
Ossification spreads below and around the nerve
↓
Intramembranous ossification spreads dorsally and ventrally
↓
Results in the formation of the body and ramus of the mandible
↓
Ossification stops at the site which forms lingula
↓
Remaining Meckel’s cartilage which does not undergoes ossification, forms the following
- Mental ossicles
- Incus and Malleus
- Spine of Sphenoid
- Anterior ligament of malleus
- Spheno mandibular ligament
Question 7. Development of tongue.
Answer
- Tuberculum impairs and lingual swellings are derived from the P’branchial arch.
- Hypobranchial eminence is derived from the 3HbranchiaI arch.
- Thus, branchial arches involved are
- 1 branchial arch
- 2 branchial arch
- 4 branchial arch.
Question 8. Development of upper lip.
Answer:
- Ectodermal thickening develops cranial to the stomatodeum.
- These are called olfactory placodes.
- Mesenchymal proliferation occurs resulting in the bulging of placodes
- These convert the placodes into nasal pits.
- The lateral arm of it is called the lateral nasal process and the medial arm is called the medial nasal process
- The maxillary process from both sides grows medially.
- This pushes the medial nasal process towards the midline where it fuses with that of the opposite side
- This leads to the formation of the upper lip
Question 9. Describe the development of the palate.
Answer:
Development of palate:
- The palate develops from.
- Two palatal shelves arising from the maxillary process
- frontonasal process.
- The primary palate is developed from the frontonasal process.
- The palatal shelves are directed first downward on each side of the tongue.
- The tongue is withdrawn from between the shelves, now gels elevated.
- Next, both the palatine shelves converge and fuse with each other and with the primary palate.
- This results in separating the primitive oral easily into oral and nasal cavities.
Question 10. Meckel’s cartilage.
Answer:
- It is the cartilage of the first arch.
- At 6th week of development, this cartilage extends as a solid hyaline cartilaginous rod, surrounded by a fibro cellular capsule, from the developing ear region to the midline of the fused mandibular processes.
- The two cartilages of each side do not meet at the midline but are separated by a thin band of mesenchyme.
- It has a close relationship with the development of the trigeminal nerve beginning at two-thirds of the way along the entire length.
- On the lateral aspect of Meckel’s cartilage, during the sixth week of IU life, a condensation of mesenchyme occurs forming the division of the inferior alveolar nerve.
- At 7 weeks intramembranous ossification begins in this condensation and then spreads anteriorly up to the middle and posteriorly up to the lingula.
- Remaining Meckel’s cartilage forms.
- Mental oscillates.
- Incus and malleus.
- The spine of the sphenoid.
- Anterior ligament of mandible.
- Sphenomandibular ligament.
Question 11. Morula.
Answer:
- After fertilization of the ovum, a series of cell divisions gives rise to an egg cell mass known as the morula.
- It looks like mulberry.
- Fluid seeps into the morula, and the cells realign themselves to form blastocysts,
- Two cell populations are distinguished within the blastocyst.
1. Trophoblast cells.
- Cells lining, the cavity.
- It helps to provide nutrition to the embryo.
- It is associated with the implantation of the embryo and the formation of the placenta.
2. Embryoblast
- They are inner cell mass.
- It forms the embryo proper.
Question 12. Derivatives of first and second branchial arch
Answer:
Derivatives of the first branchial arch:
Skeletal derivatives:
- Dorsal part- gives rise to incus and malleus
- Ventral part – part of it forms the anterior ligament of the malleus and the Sphenomandibular ligament
- Mesenchyme – forms maxilla, mandible, zygomatic bone, palatine bone, and part of the temporal bone
Cartilage:
- Meckel’s cartilage
Muscles:
- Temporalis, masseter, medial and lateral pterygoid n Mylohyoid
- Anterior belly of digastric
- Tensor palatine, tensor tympani
Nerve:
- Mandibular division of trigeminal nerve Derivatives of second branchial arch
Cartilages:
- Stapes of middle ear n Lesser cornua and body of hyoid bone Styloid process of the temporal bone
Stylohyoid ligament Muscles:
- Muscles of facial expression
- Posterior belly of digastric a Stylohyoid
Stapedius Nerve:
Question 13. Neural crest cells
Answer:
- The cells developing from the ectoderm along the lateral margins of the neural plate are called neural crest cells
- They undergo extensive migration and give rise to a variety of different cells
- In the trunk region – forms neural, endocrine, and pigment cells
- In the head and neck region1- forms skeletal and connective tissue cells
- These cells move around the side of the head beneath the surface ectoderm as a sheet of cells
- Towards the completion of migration, the neural crest cells attach themselves to the neural tube
- In trunk region. Schwann cells and all neurons are derived from neural crest cells
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