Anatomy & Embryology - GIS - Weebly

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Anatomy & Embryology - GISDone ByWaad BarghouthiCorrected ByRaha Al Zoubi

Gi tract embryology 1

Development of the oral cavity The mouth has 2 sources ofdevelopment: 1. depression in the stomodeum(lined with ectoderm) (Ectodermal origin) 2. cephalic(upper) end of theforegut(lined with endoderm)(Endodermal origin) These two points are separated by thebuccopharyngeal membrane During the 3rd week of developmentthe membrane disappearsHence the oral cavities become onecavityOral cavity

BuccopharyngealmembraneCephalic endof the foregutStomodeum

To differentiate between structures ofthe ectoderm and endoderm( theirorigin) we create an imaginary line If the membrane persists (we create animaginary line), it will extend to: Body of sphenoidSoft palateInner surface of the mandible, inferior tothe incisor teeth Structures that are anterior to this planeare ectodermic in origin(epithelium) like: Hard palateSides of the mouthLipsEnamel of the teeth

Structures situated posterior to this plane arederived from endoderm: TongueSoft palatePalatoglossus and palatopharyngeal foldsFloor of the mouth

Note on previous slides:We already know that the mucosa of theoral cavity is composed of epithelialtissue adding to what was discussednow this epithelium is either ectodermalin origin or endodermal in origin

Development of the salivary glands During the 7th week it arises as asolid outgrowth of cells from thewalls(endoderm or epithelialtissue ) of the developing mouth(Epithelial tissue inside, connective tissueoutside(mesenchymal tissue)) These cells will grow into theunderlying mesenchyme(throughthe connective tissue) The epithelial buds will go throughrepeated branching to form solidducts(filled with cells) The ends of these ducts will formthe secretory acini, and they willboth go through canalization thusopening the ducts (by theremoval of cells)Glands that open in the oral cavity like;parotid,submandibular,sublingual

The surrounding mesenchyme will condense to form: The capsule of the gland Septa that divide the gland into different lobes andlobules The ducts and acini of the parotid gland are bothderived from the ectoderm Submandibular and sublingual glands are derived fromthe endoderm

Tongue The tongue appears in embryos of approximately 4 weeks in the form of two laterallingual swellings and one medial swelling, the tuberculum impar(these three willform the anterior two third of the tongue) These three swellings originate from the first pharyngeal arch. A second median swelling, the copula, or hypobranchial eminence, is formed bymesoderm of the second, third, and part of the fourth arch ( will form the posteriorthird of the tongue) Finally, a third median swelling, formed by the posterior part of the fourth arch,marks development of the epiglottis.

PharyngealarchesEach arch from theoutside isectodermal whilefrom the inside isendodermal andbetween theectoderm and theendoderm itcontainsmesenchyme

Immediately behind this swelling is thelaryngeal orifice(connect the pharynxwith the larynx)which is flanked by thearytenoids swellings As the lateral lingual swellings increase insize, they overgrow the tuberculum imparand merge, forming the anterior twothirds, or body, of the tongue Since the mucosa covering the body ofthe tongue originates from the firstpharyngeal arch, sensory innervation tothis area is by the mandibularbranch(lingual branch) of the trigeminalnerve since the trigeminal branchoriginate from the first arch The body of the tongue is separated fromthe posterior third by a V-shaped groove,the terminal sulcus since two parts havedifferent origin

The posterior part, or root, of thetongue originates from the second,third, and part of the fourthpharyngeal arch. The fact that sensory innervation tothis part of the tongue is supplied bythe glossopharyngeal nerveindicates that tissue of the third archovergrows that of the second (thethird arch overlies the second arch). The epiglottis and the extremeposterior part of the tongue areinnervated by the superior laryngealnerve( from the vagus nerve since itoriginate in the fourth arch),reflecting their development fromthe fourth arch.

Some of the tongue muscles probably differentiate insitu, but most are derived from myoblasts originatingin occipital somites.(formed by myotome migratingfrom the occipital somites to the tongue) Thus, tongue musculature is innervated by thehypoglossal nerve. Special sensory innervation (taste) to the anterior twothirds of the tongue is provided by the chorda tympani branch of the facial nerve, while the posterior third issupplied by the glossopharyngeal nerve.

Development of the pharynx The pharynx develops in the neck from theendoderm of the foregut The endoderm is separate from the surfaceectoderm by mesenchyme The mesenchyme in each side splits up to 5-6arches Each arch forms a swelling on the surface ofthe walls of the foregut As a result of these swellings a series of cleftsare seen between the arches .pharyngealclefts Similar grooves are found on the lateral wallsof the foregut .pharyngeal pouches The foregut on this level is known as thepharynx

Development of the anteriorabdominal wall Following the segmentation of the mesoderm, the lateralmesoderm divides into:Somatic (on the wall) layer related to ectodermSplanchic(on the viscera) layer related to endodermBoth lined by endo and ectoderm The ant. Abdominal wall is derived from the somatopluericmesoderm(muscles) and they retain their innervation from the ventral ramiof the thoracic spinal nerves The somatoplueric mesoderm then tangentially divides into three layers:Ext. obliqueInt. obliqueTrans. abdominus

Differentiate intothe skin and thenervous systemImportant for the connectivetissue and structures likebones,cartilages and musclesDifferentiate tothe GI tract

The rectus abdominus muscleretains the indications of thesegmental origin due to themyotome positioning in therectus sheath and thepresence of tendinousintersections Finally the abd. Wall right andleft sides of mesenchymefuses together at 3 monthsinto the midline to form thelinea alpa. On either side of the lina alpathe rectus muscles lies withintheir rectus sheaths

Development of the umblicus andthe umblical cord The amnion(gives the amniotic sac filled with the amniotic fluid)and the chorion (gives the placenta)fuse together The amnion encloses the body stalk and the yolk sac with their blood vessels to form the tubularumbilical cord( kept after birth these days due to being rich with mesenchymal stem cells) The mesenchyme core of the cord (whartons jelly ( mucoid tissue))form a loose connective tissuewhich embed the following:Remains of yolk sacVittelline duct (connection between the umbilicus and midgut/ need to be obliterated and obstructionif not it’ll form a fistula where fecal material will come out from the umbilicus)Remains of allantois ( connection between the urinary bladder and umbilicus/ also needs obliteration ifnot it’ll form a tract or fistula between the urinary bladder and umbilicus)Umbilical blood vessels We have 2 arteries that carries deoxygenated blood from the fetus to the chorion (placenta) 2 veins carry oxygenated blood from thePlacenta to the fetus , but the right vein will soon disappear

Vitelline Duct Abnormalities In 2 to 4% of people, a smallportion of the vitelline ductpersists, forming anoutpocketing of the ileum,Meckel’s diverticulum or ilealdiverticulum In the adult, thisdiverticulum(2 in pouch),approximately 40 to 60 cmfrom the ileocecal valve on theantimesenteric border of theileum, does not usually causeany symptoms. However, when it containsheterotopic pancreatic tissueor gastric mucosa, it may causeulceration, bleeding, or evenperforation.

Sometimes both ends of the vitelline ducttransform into fibrous cords, and the middleportion forms a large cyst, an enterocystoma,or vitelline cyst

Formation of the Lung Buds When the embryo is approximately 4weeks old, the respiratorydiverticulum (lung bud) appears as anoutgrowth from the ventral wall of theforegut The location of the bud along the guttube is determined by signals from thesurrounding mesenchyme, includingfibroblast growth factors (FGFs) that“instruct”the endoderm. Hence epithelium of the internal liningof the larynx, trachea, and bronchi, aswell as that of the lungs, is entirely ofendodermal origin. The cartilaginous, muscular, andconnective tissue components of thetrachea and lungs are derived fromsplanchnic mesoderm surrounding theforegutBeginning of theforegut are theesophagus andthe pharynx

Initially the lung bud is in opencommunication with the foregut When the diverticulum expands caudally,however, two longitudinal ridges, thetracheoesophageal ridges, separate itfrom the foregut Subsequently, when these ridges fuse toform the tracheoesophageal septum,the foregut is divided into a dorsalportion, the esophagus, and a ventralportion, the trachea and lung buds (that will give origin to the respiratorytract) The respiratory primordium maintains itscommunication with the pharynxthrough the laryngeal orifice

Anatomy & Embryology - GIS Done By Waad Barghouthi Corrected By Raha Al Zoubi. Gi tract embryology 1. . nervous system Important for the connective tissue and structures like bones,cartilages and muscles . that will give origin to the respiratory tract) The respiratory primordium maintains its

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