pharyngeal arches,pouches
TRANSCRIPT
EMBYOLOGY
SUPERVISED BY DR DILABAZ KHAN,DR IMDADULLAH,DR JAMEEL KIFAYATULLAH
PRESENTER HIRA NISARKHYBER COLLEGE OF DENTISTRY
• Bilaminar germ disc • Trilaminar germ disc• Pharangeal apparatus
Presented to : Dr.ImdadDr. Jameel Dr. Dilabaz
Presented by:Hira NisarRoll # 24BDS 2nd year
IN THE NAME OF ALLAH ,THE MOST MERCIFUL ,
THE MOST BENEFICIENT!
CONTENTS:
•Bilaminar Germ disc•Trilaminar Germ disc•Pharangeal Apparatus
Pharangeal Arches Pharangeal Pouches
Pharangeal Clefts Pharangeal Membrane
Bilaminar Germ Disc
Definition:
Formation of epiblast and hypoblast layers in second week of development forms Bilaminar Germ disc.
HOW???
Development Of Trophoblast
1.The trophoblast differentiates into cytotrophoblast & syncytiotrophoblast.
2.Cells of the cytotrophoblast divide and migrate externally.
3.They lose their cell membranes to form the syncytiotrophoblast
Inner cell mass differentiates into two layers
1 :Epiblast layer
2 :Hypoblast layer
Clinical correlates *The syncytiotrophoblast secretes human
chorionic gonadotropin hormone which prevents the degeneration of the corpus luteum.
By the end of the 2nd week, the amount of this hormone will be sufficient to be detected in the maternal blood and urine. This is the basis of pregnancy test.
*occasionally implantation takes place outside the uterus resulting in ectopic or
extra uterine pregnancy.
*In some cases trophoblast develops and forms placental membrane although little or no embryo tissue is present this is known as hydatiform mole.
1.Secondary yolk sac2. Exocoelomic cyst3. Aminotic cavity4. Extra-embryonic coelom5. Epiblast6. Connecting stalk 7. Hypoblast8. Primary villi9. Trophoblastic lacunae10. Extraembryonic somatic mesoderm11. Extraembryonic splanchnic mesoderm
Trilaminar Germ Disc
Definition
Formation of three germinal layers form the trilaminar germ disc
The three layers are1.Ectoderm
2.Endoderm 3.Mesoderm
HOW???
Formation of Trilaminar Germ Disc
1.. Gastrulation- most characteristic feature during 3rd week
2.3 germ layers are established- ectoderm, endoderm and mesoderm
3.Start with formation of PRIMITIVE STREAK
PRIMITIVE STREAK1.Midline groove at epiblast
2.Cephalic end-primitive node
3.Cells of epiblast migrate towards primitive streak
4.This inward movement is known as invagination
5.Invaginated cells displace hypoblast forming endoderm
6 .Some other invaginated cells come to lie between epiblast and newly formed endoderm forming mesoderm
7 .Remaining cells in epiblast form ectoderm
8.These 3 layers form trilaminar germ disc
Clinical Significance*Teratogenesis
For example large doses of alcohol at this stage result in holoprosencephally.
*Caudal dysgenesis(Sirenomelia)Insufficint mesoderm is formed in caudal most region of embryo.
*Situs inversusTransposition of viscera in the thorax and abdomen occurs.
Pharangeal apparatus
Pharangeal apparatus•The head and neck region of The head and neck region of four week human embryo four week human embryo somewhat resemble these somewhat resemble these regions of a fish embryo of regions of a fish embryo of comparable stagecomparable stage
•This explains the former use of This explains the former use of designation branchial apparatusdesignation branchial apparatus
Pharyngeal apparatus consists ofPharyngeal apparatus consists of::
Pharyngeal archesPharyngeal archesPharyngeal pouchesPharyngeal pouchesPharyngeal grooves/cleftsPharyngeal grooves/cleftsPharyngeal membranePharyngeal membrane
Pharyngeal pouchPharyngeal groove
Pharyngeal membrane
Pharyngeal arch
Pharyngeal ArchesPharyngeal Arches
Mesenchymal condensation on either side of the pharynx are known as pharangeal arches.
Definition
•Pharyngeal Pharyngeal arches begin to arches begin to develop early in develop early in the fourth week as the fourth week as neural crest cells neural crest cells migrate into the migrate into the head and neck head and neck regionregion
Pharyngeal ArchesPharyngeal Arches• By the end of the fourth week, four pairs By the end of the fourth week, four pairs
of pharyngeal arches are visible of pharyngeal arches are visible externallyexternally
• The fifth and sixth arches are rudimentary The fifth and sixth arches are rudimentary and are not visible on the surface of the and are not visible on the surface of the embryoembryo
• The pharyngeal arches are separated The pharyngeal arches are separated from each other by fissures called from each other by fissures called pharyngeal groovespharyngeal grooves
• They are numbered in craniocaudal sequenceThey are numbered in craniocaudal sequence
•Each pharyngeal arch consists of a core of Each pharyngeal arch consists of a core of mesenchymemesenchyme
•Is covered externally by ectoderm and Is covered externally by ectoderm and internally by endoderminternally by endoderm
Pharyngeal Arch ComponentsPharyngeal Arch Components
Ist Pharangeal Arch Derivatives
Ist pharangeal arch consists of•Maxillary process•Mandibular process
Skeletal component
Ist pharangeal arch is known as mandibular arch
Maxillaryprocess
Mandibular process
Maxillary process
Maxillary process gives rise to•Maxilla•Premaxilla•Zygomatic bone•Part of temporal bone
Mandibular process
Mandibular process give rise to• Meckle’s cartilage•Mandible•Malleus •Incus•Anterior ligament of malleus•Sphenomandibular ligament
Musculature of ist arch
Musculature of ist pharangeal arch includes•Muscles of mastication•Anterior belly of digastric muscle •mylohyoid•Tensor tympani•Tensor palatini
Nerve supply to the ist arch
•Nerve supply to ist arch is provided by Mandibular branch of trigeminal nerve
Note•Ist arch also contribute to dermis of the face which is innervated by opthalmic ,maxillary and mandibular branch of trigeminal nerve.
as2nd Pharangeal Arch
skeletal component
2nd pharangeal arch gives rise to•Stapes•Styloid process•Stylohyoid ligament•Lesser horn•Upper portion of the body of hyoid bone
2nd pharangeal arch is also known a hyoid arch or rechiert’s cartilage
Musculature of 2nd arch
Musculature of 2nd arch includes•Stapedius muscle•Stylohyoid muscle•Posterior belly of digastric muscle•Auricular muscle•Muscles of facial expression
Nerve supplyNerve supply•2nd arch is innervated by facial nerve
3rd Pharangeal Arch
Skeletal component
3rd arch includes•Lower part of the body•And greater horn of the hyoid bone
MusculatureMusculature is limited to stylopharangeus muscle
Nerve supply
It is innervated by glossopharangeal nerve
4th and 6th Pharangeal Arch
Skeletal component
Cartilage of 4th and 6th arch fuse together to form•Thyroid•Cricoid•Aretenoid• Corniculate• And Cuniform cartilage of larynx
Musculature of 4th Arch
It includes•Cricothyroid•Levator platini•Constrictors of pharynx
Nerve supply of 4th Arch
Innervation is provided bySuperior larangeal branch of vagus
Musculature of 6th arch
•It includes intrinsic muscles of larynx
Nerve supply
•Innervation is by recurrent larangeal branch of vagus
Pharangeal pouches
•The pharyngeal pouches are balloon like diverticula that formed on the endodermal side between the pharyngeal pharyngeal archesarches•The pairs of pouches develop in a craniocaudal sequence between the arches
• There are four well defined pairs of pharyngeal pouches
•The fifth pair is absent or rudimentary
• The first pair of pouches lies between the first and second pharyngeal arches
• The first pharyngeal pouch forms stalk like diverticulum called tubotympanic recess
•The distal portion of diverticulum widens into sac like structure primitive tympanic Or middle ear cavity
•The lining of tympanic cavity later aids in the formation of tympanic membrane or ear drum
Derivatives of Ist Pharangeal Pouch
•While proximal portion forms auditory tube
•The second pharyngeal pouch is largely obliterated ( disappear ) as the palatine tonsils develop
• Part of the cavity of this pouch remains as the tonsillar sinus or fossa
Derivatives of Second Pharyngeal Pouch
Derivatives of 2nd pharangeal pouch
Derivatives of Third Pharyngeal Pouch
Epithelium of dorsal region of 3rd pouch differntiates into inferior thyroid gland
While ventral region differntiates into thymus.
The primordia of thymus and inferior parathyroid glands lose their connections with the pharynx and migrate into the neck Later the inferior parathyroid glands separate from the thymus and lie on the dorsal surface of the thyroid gland
Derivatives of Fourth Pharyngeal PouchDerivatives of Fourth Pharyngeal Pouch
Each dorsal part develops into a Each dorsal part develops into a superior parathyroid glandsuperior parathyroid gland
It lies on the dorsal surface of the thyroid glandIt lies on the dorsal surface of the thyroid gland
Ventral region of 4th pouch forms ultimobranchial body
Ultimobranchial body is later on incorporated into thyroid gland.
Cells of Ultimobranchial body give rise to parafollicular cells Or C cells of thyroid gland which secretes calcitonin.
Derivatives of Fifth Pharyngeal PouchDerivatives of Fifth Pharyngeal Pouch
When this develops, this rudimentary pouch When this develops, this rudimentary pouch becomes part of the fourth pharyngeal becomes part of the fourth pharyngeal pouch and helps to form the pouch and helps to form the ultimopharyngeal bodyultimopharyngeal body
Pharyngeal GroovesPharyngeal Grooves
During the fourth and fifth weeks, head and During the fourth and fifth weeks, head and neck region of the human embryo exhibit neck region of the human embryo exhibit four pharyngeal grooves or clefts on each four pharyngeal grooves or clefts on each side side
These grooves separate the pharyngeal These grooves separate the pharyngeal arches externallyarches externally
Only first pair persists as the external Only first pair persists as the external acoustic meatusacoustic meatus
The other grooves normally obliterated with The other grooves normally obliterated with the cervical sinus as the neck developsthe cervical sinus as the neck develops
Pharyngeal MembranesPharyngeal Membranes
• The connection between the endoderm of the pharyngeal pouchespharyngeal pouches and the ectoderm of the pharyngeal groovespharyngeal grooves form a double layered membrane called the pharyngeal membraneThese membranes form where the epithelia These membranes form where the epithelia of the grooves and pouches approach each of the grooves and pouches approach each otherother
The endoderm of the pouches and ectoderm of The endoderm of the pouches and ectoderm of the grooves are soon separated by the grooves are soon separated by mesenchymemesenchyme
Only first pharyngeal membrane becomes the Only first pharyngeal membrane becomes the tympanic membrane, others obliteratetympanic membrane, others obliterate