PHARYNGEAL ARCHES , POUCHES , MEMBRANE AND CLEFT

pharyngeal arches ppt

1. PHARYNGEAL APPARATUS Dr. Mayura Setiya Associate professor

2. INTRODUCTION On formation of embryonic folds - foregut develops from the part of yolk sac that lies within the head fold. At the cephalic end ,it is separated from the stomodeum or the primitive mouth cavity by a bilaminar membrane called the Buccopharyngeal membrane. This membrane ruptures at about 4 th week of development

3. Thus ,the foregut communicates with the exterior through the stomodeum. Caudally the foregut is continuous with the mid-gut at the junction called Anterior intestinal portal.

4. Ventrally ,at the future pharyngo-esophageal junction of the foregut presents a median laryngo-tracheal groove bulges forwards and downwards to form the lower respiratory passage including the lung buds.

5. Foregut is divided into the Pre-laryngeal part or the cephalic part. Post- laryngeal part or the caudal part. The cephalic part develops into pharynx the floor of the definitive mouth cavity

6. Cephalic part or Pharyngeal part of foregut Pharynx is a part of the throat behind the mouth and nose. The cephalic or the pharyngeal part of foregut presents a funnel shaped tubular structure which is compressed dorso-ventrally.

7. Cephalic part or Pharyngeal part of foregut The pharyngeal part of the foregut has a Ventral wall or floor Dorsal wall or roof Two lateral walls Ventral wall is formed cranio-caudally by Ectodermal stomodeum Pericardial sac and developing heart Septum transversum

8. Subsequently the mesenchyme undergoes segmentation in cranio -caudal sequence to form six pairs of mesodermal bars known as the Branchial or Visceral arches. 5 th arch is rudimentary and disappears Each branchial arch consists of an outer covering of surface ectoderm Central core of mesoderm Inner lining of pharyngeal endoderm .

9. In the interval between the branchial arches the ectoderm and the endodermal layers are closely approximated to form closing membranes. In fishes these closing membranes rupture to form gill slits. In man these closing membranes do not rupture ; a thin layer of mesenchyme appears within the closing membrane and forms the fibro-areolar tissue of the neck

10. Thus, a human embryo shows ectodermal clefts , 4 in number called branchial or visceral clefts. The endoderm of the primitive pharynx shows depressions between the adjacent pharyngeal arches called Pharyngeal pouches. Pharyngeal arches appear in the 4 th and 5 th week of development

11. Each branchial arch extend ventrally and medially along the floor or the ventral wall of the primitive pharynx and meets the corresponding arch of the opposite side in the mid-ventral line. The cephalic end of the pharyngeal gut is initially separated from the stomodeum or the primitive mouth by the Buccopharyngeal membrane which ruptures at about 4 th week.

12. PHARYNGEAL APPARATUS

13. PHARYNGEAL APPARATUS It consist of Pharyngeal arches Pharyngeal pouches (Endodermal) Pharyngeal clefts (Ectodermal) Fifth arch disappears . The branchial apparatus is responsible for the development of Face , Neck Definitive mouth, Pharynx and larynx

14. Pharyngeal arches Thickened mesodermal bars covered externally by ectoderm and lined internally by endoderm Present in the floor and lateral wall of the primitive pharynx are called pharyngeal arches. Pharyngeal clefts Depressions (grooves) on the surface ectoderm in between adjacent arches are called pharyngeal clefts. Pharyngeal pouches Endodermal depressions between adjacent pharyngeal arches in the floor and lateral wall of the primitive pharynx are called pharyngeal pouches Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

15. Pharyngeal Arches Horse-shoe shaped thickened mesodermal bars in the lateral wall and the floor of the primitive pharynx is called pharyngeal arch Number Six pharyngeal arches Fifth pharyngeal arch is rudimentary (small and disappears) Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

16. Components Each arch consist of splanchnopleuric mesoderm with invaded neural crest cells Invading neural crest cells form skeletal elements and connective tissue of the head and neck region It consist of four components Arteries Nerves Skeletal tissue Muscle masses

17. Skeletal Elements Neural crest cells form the cartilaginous rod in the substance of the pharyngeal arch Fate of cartilages of the pharyngeal arches: Some part of the cartilage persists Some part disappears Some part is converted into bone Some part of perichondrium persists as ligament Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

18. First arch First arch is differentiated into dorsal maxillary process ventral mandibular process Maxillary process forms part of the upper lip, upper jaw and palate Cartilage of mandibular part the first arch is called Meckel’s Cartilage Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

19. Meckel’s Cartilage - Malleus from dorsal part - Incus from dorsal part - Anterior ligament of malleus - Sphenomandibular ligament Body of the mandible is formed by the fibrous membrane surrounding of the Meckel’s cartilage Meckel’s cartilage does not form mandible

20. Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

21. Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

22. Second arch cartilage Cartilage of second (hyoid)arch is called Reichert’s cartilage Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

23. Reichert’s cartilage forms: Stapes (ear ossicle) from dorsal part Styloid process of the temporal bone from dorsal part Smaller (lesser) cornua of the hyoid bone from ventral part Superior (upper) part of the body of hyoid bone from ventral part Stylohyoid ligament from perichondrium of disappearing cartilage between styloid process and hyoid bone

24. Third arch cartilage Dorsal part of the third arch cartilage disappears Ventral part of the third arch cartilage forms Greater cornua of the hyoid bone Lower part of the body of the hyoid bone

25. Fourth and sixth arch Dorsal part of the fourth and sixth arch cartilage disappears Ventral part of the fourth and sixth arch forms cartilages of larynx (except epiglottis) such as Thyroid cartilage Cricoid cartilage Arytenoid cartilage Corniculate cartilage Cuneiform cartilage

26. Muscles derived from arches

27. First arch Second arch Muscles derived are Muscles of mastication: temporalis, masseter, lateral pterygoid and medial pterygoid Tensor tympani Tensor veli palatini Anterior belly of digastric Mylohyoid muscle Nerve supply: Mandibular nerve Muscles derived from the second arch Muscles of facial expression Posterior belly of digastric Stapedius Stylohyoid Platysma Auricular muscles E picranius Nerve supply : Facial nerve

28. Third arch Stylopharyngeus Nerve supply: G lossopharyngeal nerve Fourth arch Cricothyroid Constrictor muscles of pharynx Muscles of palate except tensor veli palatini Nerve supply : S uperior laryngeal branch of the vagus nerve Sixth arch All the intrinsic muscles of the larynx except cricothyroid Nerve supply: Recurrent laryngeal branch of vagus nerve Human Embryology/Yogesh Sontakke/2nd edn /CBS Publishers

29. Nerves of Pharyngeal Arches

30. Nerves of Pharyngeal Arches Pharyngeal arches receive nerve supply from hindbrain vesicle Each nerve appears at the dorsal end of the cleft and divides into pre- trematic and post- trematic branches Pre- trematic branch supplies the arch cranial to the cleft, whereas post- trematic branch supplies caudal to the cleft Human Embryology/Yogesh Sontakke/2nd edn /CBS Publishers

31. Pre- trematic nerve of all arches degenerate except the first arch Pre- trematic nerve of the first arch forms chorda tympani nerve MCQ

32. Nerves of arches : First arch: Mandibular nerve (post-trematic ) and Chorda tympani branch of facial nerve (pre-trematic) Second arch : Facial nerve Third arch : Glossopharyngeal nerve Fourth arch : Superior laryngeal nerve Sixth arch : Recurrent laryngeal nerve

33. Arteries of Arches

34. Arteries of Arches Each arch contains one arch artery These arch arteries connect dorsal aorta with aortic sac (that lies ventrally) First aortic arch artery : part of maxillary artery Second aortic arch artery : stapedial artery , hyoid artery Third aortic arch artery : a. Common carotid artery from the ventral part of third aortic arch b. The stem of the internal carotid artery from the dorsal part of the third aortic arch Human Embryology/Yogesh Sontakke/2nd edn /CBS Publishers

35. Fourth aortic arch artery a. On the right side – proximal part of the right subclavian artery b. On the left side – arch of the aorta Fifth aortic arch artery – disappears completely Sixth aortic arch artery – a. On the right side – right pulmonary artery b. On the left side – left pulmonary artery and ductus arteriosus ( foetus ) (after birth-ligamentum arteriosum) Human Embryology/Yogesh Sontakke/2nd edn /CBS Publishers

36. First Arch Syndromes First arch syndromes occur due to the failure of the migration of neural crest cells into the first arch These neural crest cells form skeletal elements and connective tissue in the first arch The first arch syndrome includes Treacher Collins syndrome and Pierre Robin syndrome Human Embryology/Yogesh Sontakke/2 nd edn /CBS Publishers

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