1. DEVELOPMENT of BODY CAVITY.pptx

embryological development of body cavities

1. THE DEVELOPMENT OF THE BODY CAVITIES 1

2. THE DEVELOPMENT OF THE BODY CAVITIES The intraembryonic coelom begins to develop near the end of the 3 rd week. By the 4th week it appears as a horseshoe-shaped cavity in the cardiogenic and lateral mesoderm. 2

3. Drawing of a dorsal view of a 22-day embryo showing the outline of the horseshoe-shaped intraembryonic coelom. The amnion has been removed, and the coelom is shown as if the embryo were translucent. The continuity of the intraembryonic coelom, as well as the communication of its right and left limbs with the extraembryonic coelom, is indicated by arrows. B, Transverse section through the embryo at the level shown in A 3

4. 2 Midsagittal sections of embryos at various stages of development showing cephalocaudal folding and its effects upon position of the heart, septum transversum, yolk sac, and amnion. Note that, as folding progresses, the opening of the gut tube into the yolk sac narrows until it forms a thin connection, the vitelline (yolk sac) duct, between the midgut and the yolk sac (D). Simultaneously, the amnion is pulled ventrally until the amniotic cavity nearly surrounds the embryo. A. 17 days. B. 22 days. C. 24 days. D. 28 days. 4

5. THE EMBRYONIC BODY CAVITY The intraembryonic coelom becomes the embryonic body cavity, which is divided into three well-defined cavities during the fourth week which are: A pericardial cavity Two pericardioperitoneal canals A peritoneal cavity 5

6. Figure 8-3 Illustrations of the mesenteries and body cavities at the beginning of the fifth week. A, Schematic sagittal section. Note that the dorsal mesentery serves as a pathway for the arteries supplying the developing gut. Nerves and lymphatics also pass between the layers of this mesentery. B to E, Transverse sections through the embryo at the levels indicated in A . The ventral mesentery disappears, except in the region of the terminal esophagus, stomach, and first part of the duodenum. Note that the right and left parts of the peritoneal cavity, separate in C, are continuous in E 6

7. Body Cavities Thoracic cavity contains: One pericardial & Two pleural cavities Abdominopelvic cavity contains: One large peritoneal cavity 7

8. Body Cavities These body cavities have a parietal wall lined by mesothelium (future parietal layer of peritoneum) derived from somatic mesoderm and a visceral wall covered by mesothelium (future visceral layer of peritoneum) derived from splanchnic mesoderm. The peritoneal cavity (the major part of intraembryonic coelom) is connected with the extraembryonic coelom at the umbilicus. The peritoneal cavity loses its connection with the extraembryonic coelom during the 10th week as the intestines return to the abdomen from the umbilical cord. 8

9. Intraembryonic Coelom Appears as a horseshoe-shaped cavity in the cardiogenic area and lateral mesoderm by the 4 th week The bend in this cavity indicates the future pericardial cavity & the limbs indicate the future pleural and peritoneal cavities The greater part of each limb opens laterally into the extra-embryonic celom (EEC) EEC 9

10. The curve of the cavity represents the future pericardial cavity and its lateral extensions represent the future pleural and peritoneal cavities 10

11. Folding of embryo In the 4 th week also the embryonic disc will fold. Lateral parts of the intraembryonic coelom move together on the ventral aspect of the embryo. When the caudal part of the ventral mesentery disappears, the right and left parts of the intraembryonic coelom merge to form the peritoneal cavity 11

12. Folding of embryo During cranial folding of embryo, the pericardial cavity comes to lie ventral to the foregut The pericardioperitoneal canals: arise from the dorsal wall of the pericardial cavity pass on each side of the foregut (future esophagus) lie dorsal to septum transversum open into the peritoneal cavity 12

13. During horizontal folding, the limbs of the coelom are brought together on the ventral aspect of the embryo The coelom is lined by mesothelium derived from the somatic mesoderm (parietal layer) and the splanchnic mesoderm (visceral layer) The peritoneal cavity looses its connection with the extraembryonic coelom during the 10 th week Parietal layer Visceral layer 13

14. THE DEVELOPMENT OF THE BODY CAVITIES Until the 7 th week, the embryonic pericardial cavity communicates with the peritoneal cavity through paired pericardioperitoneal canals. During the 5 th and 6 th weeks, folds (later membranes) form near the cranial and caudal ends of these canals. 14

15. Division of Embryonic Coelom Partitions appear to separate the pericardioperitoneal canals from the pericardial cavity and the peritoneal cavity 15

16. As the lung buds grow into the pericardioperitoneal canals, a pair of membranous ridges is produced in the lateral wall of each canal: The pleuropericardial folds cranial to the developing lungs The pleuroperitoneal folds caudal to the developing lungs 16

17. Pleuropericardial Membranes The bronchial buds grow laterally from the caudal end of the trachea into the pericardioperitoneal canals (future pleural cavities) As the pleural cavities expand ventrally, they grow into the body wall in the angle between the body wall and a ridge raised by the common cardinal vein and the phrenic nerve 17

18. This results in splitting the mesenchyme into: An outer layer that forms the thoracic wall An inner layer that forms the pleuro-pericardial membrane 18

19. With the growth and descent of the heart and expansion of the pleural cavities, the pleuro -pericardial membranes expand and move medially 19

20. By 7 th week, the membranes fuse with the mesenchyme ventral to the esophagus forming the primordial mediastinum , thus closing the pleuropericardial openings . 20

21. The right pleuropericardial opening closes slightly earlier than the left (right common cardinal vein is larger than the left and so raises a bigger fold) Phrenic nerve 21

22. Pleuroperitoneal Membranes Develop from the pleuroperitoneal folds that are attached dorsolaterally to the body wall and their free edges project into the caudal part of the pericardioperitoneal canals As the developing lung enlarges cranially and liver expands caudally, these folds become more prominent and gradually become membranous which will be invaded by the myoblasts (primitive muscle cells). 22

23. During 6 th week, the pleuroperitoneal membranes extend ventromedially and fuse with the dorsal mesentery of the esophagus and the septum transversum This results in closure of the pericardioperitoneal openings. The right opening closes slightly earlier than the left 23

24. Primitive Mesenteries 24

25. After embryonic folding…….. 25

26. What is a mesentery? Double layer of peritoneum enclosing a mass of mesoderm Connects the organ to the body wall Carries vessels, nerves & lymphatics for the organ Is the site where the visceral peritoneum continues as parietal peritoneum 26

27. After embryonic folding …….. 27

28. The caudal part of the foregut is connected to the anterior and posterior abdominal walls by the ventral & dorsal mesentery respectively 28

29. The midgut and the hindgut are suspended in the peritoneal cavity from the posterior abdominal wall by the dorsal mesentery 29

30. The ventral mesentery degenerates in the region of the future peritoneal cavity, extending from the heart to the pelvic region 30

31. Development of the Diaphragm 31

32. The diaphragm develops from four embryonic components: Septum transversum Pleuroperitoneal membranes Dorsal mesentery of esophagus Muscular ingrowth from lateral body walls 1 3 2 4 32

33. Septum Transversum A thick plate of mesodermal tissue Lies: Between the pericardial cavity and the yolk sac Ventral to the foregut and the pleuro -peritoneal canals Grows dorsally from the ventrolateral body wall 33

34. Forms an incomplete partition between the thoracic cavity and the abdominal cavity Expands and fuses with the pleuroperitoneal membranes and the mesenchyme ventral to the esophagus Septum transversum is the primordium of the central tendon of the diaphragm 34

35. During 6 th week , the three basic components: Pleuroperitoneal membranes Mesoesphagus Septum transversum 1 1 3 2 fuse with each other and form a complete partition between the thoracic and abdominal cavities 35

36. During 9 th – 12 th weeks the lungs and pleural cavities enlarge, burrowing into the body wall, splitting it into: External layer that becomes part of the body wall Internal layer that contributes muscles to peripheral portions of diaphragm, extending to the parts derived from the pleuroperitoneal membranes 36

37. Body wall: peripheral muscular part Pleuroperitoneal membranes: form large portion of fetal diaphragm but represent a smaller portion in infants Septum transversum : Central tendon Dorsal mesentery of esophagus: Crura 37

38. Positional Changes & Innervation of the Diaphragm During the 4 th week , the septum transversum lies opposite the 3 rd – 5 th cervical somites During 5 th week , myoblasts from these somites move to the developing diaphragm bringing their nerve fibers with them 38

39. Rapid growth of the body of embryo result in further descent of diaphragm By the 6 th week , the diaphragm lies at the level of the thoracic somites By the end of 8 th week the dorsal end of diaphragm lies at the level of first lumbar vertebra 39

40. When the 4 parts of the diaphragm fuse, the mesenchymal cells from the septum transversum extend into the other three parts, change into myoblasts, and give rise to the muscles of the diaphragm. Thus phrenic nerve supplies all the muscles of diaphragm The phrenic nerve also supplies sensory fibers to diaphram except in the peripheral region which is derived from the body wall and brings its nerve supply (lower intercostal nerves) with it 40

41. Gastroschisis and Congenital Epigastric Hernia This uncommon hernia occurs in the median plane between the xiphoid process and umbilicus. Gastroschisis and epigastric hernias result from failure of the lateral body folds to fuse completely when forming the anterior abdominal wall during folding in the fourth week. The small intestine herniates into the amniotic cavity, which can be detected prenatally by ultrasonography. 41

42. Congenital Hiatal Hernia There may be herniation of part of the foetal stomach through an excessively large oesophageal hiatus -the opening in the diaphragm through which the oesophagus and vagus nerves pass; however, thi . Although hiatal hernia is usually an acquired lesion occurring during adult life, a congenitally enlarged esophageal hiatus may be the predisposing factor in some cases 42

43. Congenital Pericardial Defects Defective Fusion of the pleuropericardial membranes separating the pericardial and pleural cavities results in a congenital defect of the pericardium. 43