UNIT8 EMBRYOLOGY ORGANOGENESIS OF ALIMENTARY SYSTEM Date of

UNIT-8 EMBRYOLOGY ORGANOGENESIS OF ALIMENTARY SYSTEM Date of Lecture 20. 06. 2020 Course Instructor – Dr. Manoj Kumar Sinha Asst. professor-cum-Jr. scientist Department of veterinary Anatomy

ALIMENTARY SYSTEM ØDevelops from endoderm, endodermal layer forms mucus lining of gut and structure derived from gut ØMouth, anal canal are derived from ectoderm ØThe musculature, fibrous stroma and serous coat derived from the splanchnopleuric layer of mesoderm ØPrimitive gut tube extends along the mid line from cephalic end (bucco-phararyngeal) to the caudal end (cloacal membrane) ØThe primitive gut tube is derived from the dorsal part of the yolk sac ØPrimitive gut tube is divided into three section : Fore gut, Mid gut and Hind gut

YOLK SAC

FORE GUT Ø It is cranial part of the gut tube and separated from the stomatodaeum (primitive mouth cavity) from buccopharyngeal membrane at early stage Ø Later at 4 th week of development this bilaminar membrane disappears Ø Caudally fore gut extends upto 2 nd part of duodenum at the level of openinig of bile duct Ø Fore gut divided into two parts : pre-laryngeal Part and postlaryngeal parts give rise to following parts: Pre-pharyngeal part Part of mouth cavity, Pharynx, tongue, glands, plaatine tonsils, respiratory passage Post-pharyngeal part Esophagus, stomach , liver pancreas, proximal part of duodenum

MID GUT �This is middle part of primitive gut tube which extends from duodenum to transverse colon in adults �Mid gut connected with the extraembryonic part of the yolk sac by vitello-intestinal tube �Mid gut divided into two parts: pre-cecal part and post-cecal part Pre-cecal Post-cecal Distal part of duodenum cecum, colon Jejunam, Ileum (ascending and transverse)

HIND GUT Ø It is the caudal part of the primitive gut tube, and separated from the ectoderm by clocal membrane (bilaminar membrane) Ø Hind gut is divided into two parts: pre-allantoic part and post allantoic part pre-allantoic part Descending colon post allantoic part Primitive urogenital sinus Rectum Ø The splanchnopleuric layer of the mesoderm after enclosing the gut with its muscular, fibrous and serous layer forms primitive dorsal mesentery Ø The dorsal mesentery suspends the gut from the dorsal wall and gives passage to blood vessels Ø Celiac artery supplies the abdominal part of the fore gut, cranial mesenteric artery supplies the mid gut and caudal mysentric artery supplies the hind gut

PRE-LARYNGEAL PART OF THE FORE GUT Ø Cephalic part of fore gut separated from stomatodaeum by buccopharyngeal membrane and after rupture of this membrane cephalic part of foregut opens to the exterior through stomadodaeum Ø Then primitive pharynx is formed and is composed of three layer: Ectoderm, Mesoderm and Endoderm Ø Mesoderm of the lateral wall of fore gut undergoes thickening at intervals and form a series of bars (6 pairs) k/a Branchial or Pharyngeal arches , each of these bars grow and take the shape of arch k/a Pharyngeal Arches Ø The grooves which develop outside between the bars are k/a Branchial clefts and those develop outside between the bars are k/a Pharyngeal pouches Ø Branchial arches + Branchial clefts + Pharyngeal pouches together called Branchial Apparatus Ø Branchial Apparatus resposible for development of face, neck, mouth, pharynx and larynx

c ni Ty ty c i av pa m l i ns To Branchial Apparatus

BRANCHIAL CLEFTS AND PHARYNGEAL POUCH BRANCHIAL CLEFTS Ø First cleft gives rise to the lining membrane of External acoustic meatus Ø 1 st 2 nd and 4 th clefts invaginate into mesenchyme and form placodal vesicles Ø These vesicles associated with the development of ganglia of 7 th 9 th and 10 th cranial nerves PHARYNGEAL POUCH: 1 st pouch and part of 2 nd Forms Auditary tube and tympanic cavity 2 nd pouch (part) Forms Tonsil 3 rd pouch Forms Inferior Parathyroid and Thymus 4 th pouch Forms superior parathyroid and thyroid gland 5 th pouch Forms Uitimobronchial body that gives rise to parafollicular part of the thyroid gland

BRANCHIAL ARCHES Derivatives of Branchial Arches ARCHES ARTERIES 1 st (Mandibular Arch) Part of Maxillary artery 2 nd (Hyoid Arch) SKELETON MUSCLES Mandibular, chorda tympani Maxillaryprocess, mandible, malleus, incus Muscles of mastication, Tensor tympani - Facial Body of hyoid bone, Stapes Stapedius, stylohyoid and facial muscles 2 rd Arch Commomn carotid Glossopharryn geal Great cornu of hyoid arch Stylophryngious 3 rd Arch of Aorta Superior Laryngeal Thyoid cartilage Cricothyoid 4 th Arch 5 th Arch NERVES Disappear early Pulmonary artery, Ductus arteriosus Recurrent laryngeal Cricoid arytenoid cartilage and Intrinsic muscles of larynx execpt Crico-thyroid