FOREGUT
PRELARYNGEAL PART OF FOREGUT
- cephalic or pharyngeal part of foregut
- funnel shaped expansion compressed dorsoventrally
- dorsal wall or roof
- notochord
- hindbrain
- pair of dorsal aorta
- ventral wall or floor
- ectodermal stomodaeum
- forward bulging of pericardial sac
- developing heart
- septum transversum
- two lateral walls
- separated from overlying surface ectoderm by
- splanchnic mesoderm
- undergoes segmentation
- mesodermal bars / branchial or visceral arches
- Each arch contains
- surface ectoderm
- core of mesoderm
- inner lining of pharyngeal endoderm
- extends ventrally and medially
- along floor or ventral wall of pharynx
- meets the corresponding arch of opposite side
- Between each arch
- closely approximated membranes
- in fishes they rupture
- in terrestrial
- series of ectodermal grooves called branchial or visceral cleft / ectodermal cleft
- same on inner side endodermal pouches / pharyngeal pouches are formed
- FIRST POUCH
- dorsal part extends in to mesenchyme outwards
- medial part of this recess persists as auditory tube
- lateral part forms primitive tympanic cavity
- mucous lining of tympanic cavity
- mastoid antrum , mastoid air cells
- mucous layer of tympanic membrane
- the thin layer of mesoderm between First pouch and first cleft
- this region forms tympanic membrane ( tridermal in nature )
- SECOND POUCH
- THIRD POUCH
- FOURTH POUCH
- Floor of primitive pharynx
- developing tongue
- thyroid diverticulum
- laryngo-tracheal groove
- FIFTH POUCH
- FIRST ARCH ( श - स - ष ) ectoderm - mesoderm - endoderm
- श -
- forms skin over the
- upper jaw , lower jaw and tragus of auricle
- स -
- Artery - first aortic arch which disappears
- Nerve -
- pre trematic accompanies caudal border or preceeding arch
- Chorda Tympani nerve
- post trematic follows cephalic border of succeeding arch
- Mandibular nerve
- Muscle
- Tensor tympani , tensor veli palatini
- Muscles of Mastication , Mylohyoid
- Anterior belly of digastric
- Skeletal -
- central axis of mesodermal core is chondrified
- cartilaginous bar is enveloped by perichondrium
- dorsal maxillary process
- Ventral Mandibular process ( called as meckel's cartilage )
- dorsal part ossified to form
- malleus and incus
- ascending part regresses
- fibrous part persists as
- anterior ligament of malleus
- sphenomandibular ligament
- fibrous part is ossified to form
- body of mandible
- from mandibular foramen to mental foramen
- SECOND ARCH
- S -
- Muscle -
- Stapedius , stylohyoid ,
- Platysma , posterior belly of digastric
- Auricular , epicranius
- Skeletal -
- Cartilaginous bar is called as reichert's cartilage
- dorsal part of cartilage ossified to form
- stapes
- succeeding part forms
- styloid process of temporal bone , stylohyoid ligament
- Ventral part is converted
- lesser cornu
- upper part of body of hyoid bone
- THIRD ARCH
- S
- muscle
- stylopharyngeus
- skeletal -
- cartilaginous bar
- dorsal part dissapears
- ventral part is ossified
- greater cornu of hyoid bone and lower part of hyoid bone
- FOURTH ARCH
- S
- muscle
- cricothyroid
- Skeletal
- cartilaginous bar
- dorsal part dissapears
- Ventral part forms lamina of thyroid cartilage
- FIFTH ARCH
- DISSAPEARS
- SIXTH ARCH
- S
- muscle
- all intrinsic muscles except cricothyroid
- Skeletal
- Cartilaginous bar
- Dorsal part dissappears
- Ventral part forms cricoid and arytenoid cartilage
POST LARYNGEAL PART OF FOREGUT
- Oesophageal segment
- extending from laryngeal diverticulum to fusiform dilation stomach
- buds
- lung buds
- Gastric segment
- dorsal border grows more rapidly than ventral border
- greater curvature and lesser curvature
- ventral border
- suspended from anterior body wall by
- ventral mesogastrium
- by hepatic bud gets divided to form
- lesser omentum
- falciform and coronary ligaments of liver
- dorsal border
- attached to posterior body wall
- dorsal mesogastrium
- spleen develops
- it undergoes rotation vertical axis - 90 degrees
- left surface —> ventral
- left vagus supplies anterosuperior surface
- right surface —> dorsal
- right vagus supplies postero inferior
- Duodenal Segment
- Two off shoots
- liver
- pancreas