GIT I

2010

Development of GIT Primitive gut – from oropharyngeal to cloacal

membrane, connected with yolk sac by means of ductus omphaloentericus

Development from endoderm, ectoderm of stomodeum and proctodeum, and from splanchnopleura (visceral layerof mesoderm)

Segmentation of endoderm – expressed Hox genes: Foregut – truncus coeliacus Midgut - a. mesenterica superior Hindgut – a. mesenterica inferior

Foregut Primitive pharynx and organs, which

develop from it: aditory (eustachian) tube and tympanic cavity, tonsilla palatina, parathyroid glands, thymus)

Respiratory system Oesophagus and stomach Duodenum Liver, gallbladder, bile ducts and

pancreas

Development of face

4.week - reagion surrounding stomodeum – under control of induction from prosencephalic organisating centre – (mesoderm rostral to notochord) and rhombencephalic organisating centre (ventral to hindbrain)

Derived from pharyngeal arches

Face Stomodeum and bucopharyngeal

membrane Frontonasal prominence

Nasal (olphactory) placodes Medial nasal processes Lateral nasal processes

1. pharyngeal arch Maxillary swellings (prominences) Mandibulary swellings (prominences)

Face

Mandibular swellings fuse - mandible Medial nasal processes grow and fuse in

midline (intermaxillary process), later they fuse with maxillary swellings – upper jaw – maxilla

Lateral nasal processes are separated by nasolacrimal groove – during 6th week they fuse with maxilla - nasolacrimal duct and sac.

Summary

FNP forms forehead, tip and dorsum of the nose

Lateral nasal processes – lateral part of the nose (alae)

Medial nasal processes – intermaxillary segment - nasal septum, philtrum, premaxilla and primary palate

Maxillary swellings – upper part of cheeks, upper lip, maxilla and secondary palate

Development of the nasal cavities

Nasal placodes - nasal pits – primordium of nasal vesicles – in front of the brain

Nasal vesicles are separated from oral cavity by nasal fin (keel) – after rupture of nasal vesicles – oral and nasal cavities fuse – primitive choana – dorsally from primary palate

Development of palate

Primary palate – intermaxillary process (6.week) - medial nasal processes

Secondary palate - laterally – palatine shelves – paralel to the tongue – in medio-caudal direction

Growth of mandible moves tongue down – palatine shelves rotate upward into a horizontal position and fuse with each other, with primary palate and nasal septum

Finished during 12th week

Malformations:

Cleft lip and cleft palate: Disturbed proliferative activity in mesenchymal tissue – shelves fail to meet in midline and to fuse – multifactorial heredity, trisomia 13

Oblique facial clefts – nasolacrimal groove persistency

Macrostomia, microstomia

Tongue development

Floor of the primitive pharynx Distal lingual buds - lateral lingual

swellings Tuberculum impar – medial lingual bud Median groove – lingual septum Copula (2nd arch) Hypopharyngeal eminence (3rd + 4th

arches) Entrance into the larynx

Hypopharyngeal eminence expands and overlaps copula

Lateral lingual swellling fuse - septum Border between dorsum and root – terminal

sulcus – transverse groove Foramen coecum

Development of the tongue

Muscles – occipital myotomes Motoric inervation – hypoglossal

nerve Sensoric inervation – trigeminus,

glossopharyngeal and vagus nerves Taste buds - VII, IX. nerves (Thyroid gland - thyroglossal ducts –

foramen caecum)

Tongue - structure

Intrinsic muscles: skeletel muscle (3 directions) covered by mucosa

Lingual septum and fascia – dense collagen connective tissue

Surface of dorsum and apex – papillae Root of tongue - lingual tonsilla Lower part – submucosa, dorsal - mucosa fused

with fascia

Extrinsic muscles of the tongue

Genioglossal – symphysis of mandible-body of hyoid bone and tongue – forward

Hyoglossal – major horns of hyoid bone - tongue - down

Styloglossal -processus styloideus – tongue – upward and backward

Palatoglossal – soft palate

Development of teeth

Maxilla and mandible – labiogingival groove – lip and jaw

Oral ectoderm - epithelium – dental lamina – tooth buds

Mesenchyme from neural crest Dental papilla Bud stage Cap stage Bell stage

Bud stage

Dental papilla – 10 proliferative centres – decidual teeth

Permanent teeth – deep in dental lamina – lingually from decidual teeth or in dorsal region

Activin (FGF) and BMP4 (TGFβ)

Cap stage

Tooth bud Epithelial cells proliferate and

invaginate into mesenchyme - enamel knot

Ectoderm – enamel organ – outer enamel epithelium, inner enamel epithelium, enamel (stellate) reticulum

Mesenchyme – dental papilla

Bell stage

Mesenchyme differentiates into odontoblasts – production of predentin-dentin

Inner enamel epithelium – ameloblast – enamel

Root of tooth – development is postponed - dental sac – cement and periodontal ligaments

Epithelial root sheath – induces development of root

Inner epithelial cells induce - development of

cementoblasts

Eruption

Growing root pushes crown – mucosa around differenciates into gingiva (bony socket and ligaments)

Decidual teeth – from 6.month (medial lower incisivi ) till the end of 2nd year

Permanent teeth – rooth of decidual tooth id resorbed – teeth are replaced

Permanent teeth from 6th year till adult

(1st molar)

Tooth

Crown – enamel Neck Root – cement

Dentin Dental pulp, root canal

apical foramen

Enamel

96% anorganic compounds (crystals of hydroxyapatite)

1% organic - proteins (amelogenin and enamelin) Amelogenin controls mineralization (linear calcification); enamelin – protease – necessary for reassembly of enamel

Enamel: rods and interrod region, produced by ameloblasts

After eruption covered by the membrane of Nasmyth - cuticle

Ameloblast

Columnar cell, narrow and toll - ectoderm Reversal orientation - mito and terminal web

under nucleus, apical region - GER,GC, secretory granules – glycoproteins of enamel matrix

Apical process – Tomes´ process - extends into enamel

Enames is produced between cell and basal lamina

Dentin

Similar to bone: organic – 20% - collagen I., glycosaminoglycans; hydroxyapatite (70%), water (10%)

Predentin – nonmineralized After mineralization – dentin Mineralization front – demarcation of

dentin and predentin Dentin stays well-established even after

necrosis of odontoblasts

Odontoblast

Neural crest cells – surround dental papilla Nuclei in basal part of cell, polarized cell GER, GC, secretory granules Apical process in dentinal tube – canaliculi

dentis, extends to enamel Cells connected by intercellular junctiones

Pulp

Loose collagen connective tissue Mesenchyme-like elements Vessels, nerves, lymphatics Bodies of odontoblasts

Auxilliary structures

Cement – similar to woven bone (cementocytes in lacunae ), fibers of Sharpey – attachment of ligaments

Periodontal ligaments (attachment of tooth , periost of alveolar bone): gingival, transeptal, apical, horizontal, oblique, crestal

Alveolar bone – woven bone Gingiva: stratified squamous epithelium,

epithelial tentacle of Gottlieb (BL), gingival sulcus

Lamina propria fuses with periost

Teeth

Decidual teeth Permanent teeth

Incisor – dens incisivum Incisor – dens incisivum

Incisor – dens incisivum Incisor – dens incisivum

Caninus – dens caninus Caninus – dens caninus

Molar Premolar

Molar Premolar

Molar

Molar

Molar

Malformations:

Numerical abnormalities (supernumerary teeth, partial or total anodontia)

Amelogenesis imperfecta – X linked – affected gene for amelogenin

Autosomal dominant – affected enamelin

Dentinogenesis imperfecta Discolored teeth - tetracyclines