This document discusses the development of facial structures, eyes, pharynx, tongue, and teeth in early human embryos. It describes how the face, nasal placodes, lips, and cheeks develop from the 5th to 7th week of gestation. It also summarizes the development of the eyes from the optic field and vesicles, the pharynx from pharyngeal pouches and arches, the tongue from three swellings, and the palate from two palatal processes. Finally, it outlines the development and structure of teeth from the dental lamina, enamel organ, and cells that form dentin, enamel, and cementum.
This document discusses the development of facial structures, eyes, pharynx, tongue, and teeth in early human embryos. It describes how the face, nasal placodes, lips, and cheeks develop from the 5th to 7th week of gestation. It also summarizes the development of the eyes from the optic field and vesicles, the pharynx from pharyngeal pouches and arches, the tongue from three swellings, and the palate from two palatal processes. Finally, it outlines the development and structure of teeth from the dental lamina, enamel organ, and cells that form dentin, enamel, and cementum.
This document discusses the development of facial structures, eyes, pharynx, tongue, and teeth in early human embryos. It describes how the face, nasal placodes, lips, and cheeks develop from the 5th to 7th week of gestation. It also summarizes the development of the eyes from the optic field and vesicles, the pharynx from pharyngeal pouches and arches, the tongue from three swellings, and the palate from two palatal processes. Finally, it outlines the development and structure of teeth from the dental lamina, enamel organ, and cells that form dentin, enamel, and cementum.
This document discusses the development of facial structures, eyes, pharynx, tongue, and teeth in early human embryos. It describes how the face, nasal placodes, lips, and cheeks develop from the 5th to 7th week of gestation. It also summarizes the development of the eyes from the optic field and vesicles, the pharynx from pharyngeal pouches and arches, the tongue from three swellings, and the palate from two palatal processes. Finally, it outlines the development and structure of teeth from the dental lamina, enamel organ, and cells that form dentin, enamel, and cementum.
Associate Professor Department of Morphophysiology and Pharmacology C o l l e g e o f Ve t e r i n a r y S c i e n c e a n d M e d i c i n e Central Luzon State University ▪ 5th wk – the face begins to shape
▪ There are 3 regions of the face are: orbital, nasal
and oral
▪ oral region is marked by the stomodaeum
▪ Nasal placode (primordium) develop bilaterally at
the inferolateral corners of the frontonasal process ▪ Nasal placode invaginates to form the nasal pit
▪ Dev’t of nasal placodes in horse shoe manner lead
to the formation of medial & lateral nasal process
▪ SHH-(sonic hedgehog gene) in the fore brain
signals the normal descent of the fronto nasal prominence ▪ AT 6th & 7th wk- nasal & maxillary process expand and fuse to form upper lip and cheeks
▪ when the mandibular swellings become
continuous with the mandibular depression filled with mesenchyme forms the Lower lip ▪ mandibular process and forms the angle of the mouth
▪ Nasolacrimal groove and duct forms
between the lateral nasal process and maxillary process ▪ When the embryo flex cranially, mesenchymal cells (fr NC) located on the dorsal and rostral surfaces of the prosencephalon migrate to the rostral and ventral surfaces of the head
▪ This group of cells are called frontonasal
mesenchyme that will form the forehead and nasal regions of the face • Nasal septum ▪Fused L & R medial nasal swellings • Alae of the nose ▪ Lateral nasal swellings • External nares/ nostril ▪External opening of olfactory pits • Posterior nares ▪Caudal openings of olfactory pits into oral cavity • Bridge of nose ▪Frontal prominence • Nasolacrimal duct ▪Nasolacrimal groove • Nasal cavity ▪Olfactory pit The Establishment of the Eye
▪ Optic Field is a median area near the rostral margin
of the future prosencephalon (neural tube) • Interaction of this area to the underlying mesoderm of the head causes the single optic field to separate into two lateral eye-forming regions • Failure to separate completely results to a condition called cyclopia, a single eye formed at the center of the head The Establishment of the Eye The Establishment of the Eye
• Optic vesicles grows laterally until they
contact the adjacent surface ectoderm which thickened the ectoderm and form the • Lens placode which subsequently invaginate to form the • Lens vesicles then break away from the surface ectoderm • Latter surface ectoderm becomes the cornea The Establishment of the Eye
▪ What develops from the optic cup
• inner walls of the optic cup becomes the nervous retina
• Outer wall becomes the pigment
epithelium of the retina Congenital Malformation of the Eye
•Anopthalmia/micropthalmia- failure of the optic vesicle to form or
interference with the normal growth of the optic cup;often results from deficiency of vitamin A in dogs, pigs, and cows; hereditary or acquired •Medial/lateral strabismus- medial /lateral deviation of the eyeball •Collie eye- defect in the growth of the optic cup which is usually seen in the retina and choroid as a focal dysplasia ; hereditary defects of the collie dogs •Cataract- loss in the clarity of the lens which maybe hereditary in dogs; appear occasionally in cattle, rarely in horses and cats Establishment of the Pharynx
▪ The pharynx develop as a series of
out pocketings- the pharyngeal pouches which bulges laterally ▪ As pharyngeal pouch approach the overlying ectoderm, pharyngeal clefts formed ▪ In fishes, clefts persists as the gill slits whereas in mammals, only one slit formed and later closes ▪ In each pharyngeal pouches and cleft are pharyngeal arches (visceral/branchial)
▪ There are 5-6 visceral arches in fishes
and 4 in higher vertebrates
▪ Each PP contain precartilage cells (fr NC),
premuscle mesenchyme, blood vessel and cranial nerve PA 1 forms cranial to PP1 precartilage forming cells grows in two directions: ventromedially to form the mandibular swellings and rostrally to form the maxillary swellings In mammals, vestiges persists in the mandibular cartilage as two tiny middle ear ossicles: the incus or anvil and malleus or hammer ▪ Original connection of the pouch to the pharynx persists as the pharyngotympanic tube or eustachian tube which equilibrate the pressure between the middle ear and the outside environment ▪ PC1 gives rise to the external ear or pinna ▪ PP1 fused with PC1 forms the tympanic membrane (ear drum) ▪ Endoderm of PP2 penetrate the adjoining mesenchyme and form the palatine tonsil ▪ PP3 forms the thymus and lower portion of the parathyroid (external ) ▪ PP4 gives rise to the upper portion of the parathyroid (internal ) which also associate with the thyroid ▪ Both the thymus and parathyroid dissociate with the pharynx, move caudally and medially to their adult positions ▪ 4TH WK at Pharyngeal Arches (PA) 1,2,3 4- tongue begins to form
▪ 5th wk , 3 swellings appear : 1 median bud
(tuberculum impar) and 2 lateral lingual buds, rapidly grow and merge each other and form the movable (2/3) part of the tongue ▪ Post 1/3 of the tongue “root of the tongue” is derived from the hypobranchial eminence (PA3)
▪ PA 4 forms the epiglotis
▪ Palate develops from 2 primordia : 1ry and 2ry
▪ 1ry palate arising from the medial nasal
process forms a “wedge shaped mass” composed of mesoderm
▪ eventually extend to the form the floor
of the cavity ▪ 2ry palate develops from 2 lateral palatine processes
▪ As mandible develops, tongue drops and
the palatine processes grow medially and fuse in the midline
▪ Also fuse with the nasal septum and 1ry
palate ▪ Ossification occurs in anteroposterior direction
▪ Posterior portions of the lateral palatine
processes do not become ossified but extend past the nasal septum and fuse to form the soft palate and uvula ▪ midway between the medial and lateral (rostral) margin of the oral cavity thickens to form the labiogingival lamina
▪ extends in the form of an arch along the
inner margins of the mandibular and maxillary processes
▪ Lamina thickens and forms a solid cord of
epithelial cells which invade the underlying mesenchyme ▪ A groove forms in the lamina called labiogingival groovel/sulcus; tissue rostral and lateral to the groove forms the lips and the tissue caudal & medial to the groove forms the gums ▪ Stomodeal ectoderm medial to the labiogingival lamina forms a focal thickenings called dental ledge/ lamina (evident in canine at 25 dys), ▪ invaginates and forms the and forms the dental bud ▪ expands and branches to form the enamel organ- a cup-shaped structure characteristic of the crown of the tooth ▪ Mesenchymal tissue (fr neural crest) inside the cup-shaped enamel organ is called dental papilla ▪ Enamel organ and dental lamina forms the deciduous or milk tooth
▪ Between the enamel organ and surface of the oral
cavity, a tissue bud off that forms the permanent tooth ▪ Epithelial cells near the deeper layer of the enamel organ become the cementoblasts-cementum formers
▪ Inner layer of the enamel organ differentiates into
ameloblasts- enamel forming cells
▪ Mesenchymal cells next to the ameloblasts
differentiate into odontoblasts –dentine formers ▪ Dentine is the primary matrix component of the tooth, surrounds the dental pulp- the sensitive part of the tooth
▪ Odontoblasts draw their raw materials from the
blood vessels in the dental pulp and secrete their products towards the enamel organ
▪ As the odontoblasts secrete, they back out from the
material previously formed ▪ Like the odontoblasts, the ameloblasts pushed back as they secrete the enamel towards the dentine and upon eruption of the tooth, the ameloblasts degenerate ▪ Formation of the dentine and enamel start at the tip of the crown towards the root of the tooth ▪ When the tooth acquire its full growth and definitive position in the alveolus of the jaw, the cementoblasts begin to secrete the cementum the same way in the formation of the bone ▪ Sharpey’s fibers ( fibrous c.t.) located in periodontal memb. attached tooth to the bones of the jaw Crown – part of the tooth visible, composed of dentine and enamel Root – the part embedded in the alveolus made of the dentine, enamel and cementum Neck – region between the crown and root of the tooth Dental pulp- tissue inside the root containing blood vessels and nerves, thus is the most sensitive part of the tooth ▪ Bone, dentine and enamel have similar organic and inorganic components, though bone has 45%, dentine- 30% and enamel has 5% organic substrate
▪ Microscopic structure, bone, dentine and enamel are dissimilar as
bone are formed in lamellation and has cells scattered through it while the dentine and enamel are not formed in lamellation and there are no cells scattered in their matrix as the cells back away after they secrete their finished products