• Coelom and body cavities • Skull and axial skeleton Why it is quite good to have a body cavity COELOM ? Why it is quite good to have a body cavity ? COELOM COELOM • „Coelom is a „true body cavity“ = body cavity within non-segmented lateral plate mesoderm • Significant evolutionary innovation • Lined by coelomic epithelium • Filled with coelomic fluid FLUID IN BODY CAVITIES • normally only a small amount of fluid (50 mL) • plasma ultrafiltrate • Proteins (3.0 g/mL) • Leukocytes (PMN, lymphocytes, macrophages) • Erythrocytes & Volume: important indicator of many diseases ParacentesisAscites COELOMIC FLUID • 3rd week of development • intraembryonic mesoderm • paraxial → somites (sclerotomes, dermomyotomes) • intermediate → nephrotomes • lateral → IE and EE somatopleure a splanchnopleure → IE and EE coelom COELOM DEFINITION: A CAVITY IN MESODERM COELOM IN EARLY EMBRYOGENESIS • Bilaminar → trilaminar germ disc 1 Primitive streak 2 Neural folds 3 Amnion 25. den 1,5-2,5 mm Carnegie stage 9 1 Yolk sac 2 Primitive streak 3 Primitive node 4 Germ disc 19. den 0,4 mm Carnegie stage 7 28. den 2-3,5 mm Carnegie stage 10 1 Amnion 2a Neural groove 2b Neural tube 2c Caudal neuropor 2d Rostral neuropor 3 Neural folds 4 Somites 5 Yolk sac http://www.embryology.ch/anglais/iperiodembry/carnegie03.html#st710 Dorsálně Ventrálně COELOM IN EARLY EMBRYOGENESIS COELOM FORMS A COMMON INTRAEMBRYONIC CAVITY COELOM IN EARLY EMBRYOGENESIS • Dehiscence of cardiogenic and lateral plate mesoderm • IE and EE coelom connected until cephalocaudal flexion (except for region within d. omphaloentericus) • Ventral mesogastrium disappears → common intraembryonic cavity that further separates to pericardial, pleural and peritoneal cavities COELOM IN EARLY EMBRYOGENESIS • 5mm embryo, Carnegie Stage 13, from ectopic pregnancy. • Ectoderm: Neural tube continues to close, caudal neuropore closes, forebrain • Mesoderm: continued segmentation of paraxial mesoderm (21 - 29 somite pairs), heart prominence • Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of otic placode, stomodeum • Body: heart, liver, umbilical, early upper limb bulge • Week 4-5, 26 - 30 days, 3 - 5 mm, Somite Number 21 - 29 COELOM IN EARLY EMBRYOGENESIS Day 33 (Carnegie stage 14) COELOM IN EARLY EMBRYOGENESIS 1. Arm buds 2. Pleuropericardial membrane 3. Development of the pleural cavity in the pericardioperitoneal canal 4. Esophago-tracheal septum 5. Esophagus 6. Trachea 7. Lung buds 8. Bulbus cordis 9. Heart 10. Pericardial cavity Common coelom cavity is divided into • pericardial cavity • peritoneal cavity • pericardioperitoneal canals http://www.embryology.ch/anglais /rrespiratory/korperhohlen01.html SEPARATION OF COMMON INTRAEMBRYONIC CAVITY COELOM IN EARLY EMBRYOGENESIS pleural pericardial peritoneal PLEUROPERITONEAL MEMBRANES • separate the pleural and peritoneal cavities • by week 6 - ventromedial dilatation and fusion with dorsal mesentery of oesophagus and septum transversum PLEUROPERICARDIAL MEMBRANES • separate the pleural and pericardial cavities • by week 7- fusion with mesenchyme located ventrally to esophagus and primitive mediastinum (c.t) - divide the thoracic cavity to pericardial cavity and 2 pleural cavities FORMATION OF DEFINITIVE BODY CAVITIES FORMATION OF DEFINITIVE BODY CAVITIES DEVELOPMENT OF DIAPHRAGM 1. Septum transversum (centrum tendineum) 2. Pleuroperitoneal membranes 3. Dorsal mesentery of esophagus 4. Mesenchyme of body wall + myoblasts cervical somites (crura diaphragmatis) COELOM IN EARLY EMBRYOGENESIS DEVELOPMENT OF DIAPHRAGM 1. Septum transversum (centrum tendineum) 2. Pleuroperitoneal membranes 3. Dorsal mesentery of esophagus 4. Mesenchyme of body wall + myoblasts cervical somites (crura diaphragmatis) COELOM IN EARLY EMBRYOGENESIS • mesodermal plate separating thoracic and abdominal cavities - level of yolk sac stalk → centrum tendineum • separation incomplete → pericardioperitoneal canals → pleuropericardial and pleuroperitoneal folds n. phrenicus (C3-C5 spinal segment) • descent of septum transversum due to growth of embryo DEVELOPMENT OF DIAPHRAGM SEPTUM TRANSVERSUM • CEDC - biologically very active and plastic stem (progenitor) cell population lining coelomic cavity • essential for visceral morphogenesis • provide cells capable of production of ECM, differentiation to vessels or other specialized cells Epicardium Spleen Urogenital system Adrenal cortex Mesothelium Liver COELOMIC EPITHELIUM & CE-DERIVED CELLS (advanced, not required) G2-GATA4 Liver Body wall Aorta Adrenal cortex Plica genitalis Oesophagus Plica mesonephridica E13.5 = human Day 44 E16.5 (human day 58) newborn CEDC CONTRIBUTE TO VISCERAL MORPHOGENESIS (advanced, not required) • Body wall defects 19. den 20. den ABNORMALITIES IN DEVELOPMENT OF BODY WALL • CLEFT STERNUM / STERNAL FORAMEN - failed midline fusion of the sternum - supraumbilical - ECTOPIA CORDIS - PENTALOGY OF CANTRELL (or thoraco-abdominal syndrome) - cleft sternum, ectopia cordis, omphalocele, diaphragmatic hernia, CVS disorders - polyhydramnion - craniofacial defects, urogenital malformations, limb abnormalities... ABNORMALITIES IN DEVELOPMENT OF BODY WALL • OMFALOCELE (EXOMPHALOS) - begins in week 6 - failed intestinal rotation and closure of physiological umbilical hernia in week 10 (1:4000) - intestines, liver, stomach, spleen, urinary bladder - lined by amniotic ectoderm - associated defects (CVS, NTD) - chromosomal aberrations - -fetoprotein  (analogue to serum albinun, elevated in structural body defects) ABNORMALITIES IN DEVELOPMENT OF BODY WALL • GASTROSCHISIS (laparoschisis) - 1:10000 - organs (intestines) released to amniotic cavity → volvulus - laterally to umbilicus - no lining by amniotic ectoderm → maceration - -fetoprotein  ABNORMALITIES IN DEVELOPMENT OF BODY WALL • BLADDER EXSTROPHY • ectopia vesicae • 1:10 000-50 000 • exstrophy-epispadias complex ABNORMALITIES IN DEVELOPMENT OF BODY WALL • CONGENITAL DIAPHRAGMATIC HERNIA - 1:2000 - pleuroperitoneal membranes fail to close pleuroperitoneal canal(s) - pleural and peritoneal cavities communicate - herniation of intestinal loops, liver, spleen, stomach to pleural cavities - hypoplasia of lungs → respiratory distress → high mortality ABNORMALITIES IN DEVELOPMENT OF BODY WALL • ACCESSORY DIAPHRAGM - very rare - hypoplasia of lungs - fibromuscular membrane on top of normally formed diaphragm dividing the hemithorax into two compartments trapping part of the pulmonary parenchyma • EVENTRATION OF DIAPHRAGM • diaphragm intact, but with defective muscular component - similar to other posterolateral defects (hernia) Case reports: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4091454/ ABNORMALITIES IN DEVELOPMENT OF BODY WALL • PARASTERNAL HERNIA - sternocostal area (foramen singulare Morgagni) - herniation of intestines to pericardial cavity - other abnormalities (omphalocele) • CONGENITAL HIATAL HERNIA - short oesophagus - often asymptomatic ABNORMALITIES IN DEVELOPMENT OF DIAPHRAGM DEVELOPMENT OF SKULL DEVELOPMENT OF SKULL SKULL DEVELOPMENT • Unique anatomy (complexity of morphology, rigidity, flexibility) • Unique embryonic origin (mesenchyma, neural crest) • Unique way of ossification (intramembranous, endochondral) HISTOGENETIC PERIODS IN SKULL DEVELOPMENT • Blastemal : all bones of skull • Chondrogenous : only basis cranii • Bone : calva – intramembranous ossification basis cranii – endochondral File:Mouse head E9-neural crest GFP.jpg Neural crest cells • neurocranium (brain and sensory organs) • splanchnocranium (viscerocranium) – face, jaws, palate, hyoids • cranial mesenchyme (including ectomesenchyme) DEVELOPMENT OF SKULL • chondrocranium (cranial base) - inductive role of chorda dorsalis - chondrification centers in mesenchyme blastema of cranial base and cartilaginous capsules around sensory organs • desmocranium (calva) NEUROCRANIUM CHONDROCRANIUM DESMOCRANIUM ENDOCHONDRAL vs. INTRAMEMBRANOUS OSSIFICATION https://www.youtube.com/watch?v=p-3PuLXp9Wg&feature=emb_logo how ossification works? see the video • paired cartilage plates (parachordalia) parachordal plate, • paired cartilage trabecules (prior chorda), trabeculae cranii - trabecular plate • between trabecular and parachordal plates - paired hypophyseal cartilages around pituitary primordium • all cartilages fuse into a single basal plate (→ origin of occipital and sphenoid bone) • basal plate growths anteriorly - forms processus ethmoidalis • laterally around otic vesicels - capsulae oticae, form majority of temporal bone • chondrification goes anteriorly towards nasal region - capsula nasalis (septum nasi from trabecular plate) CHONDROCRANIUM FISH MAMMAL • paired cartilage plates (parachordalia) parachordal plate, • paired cartilage trabecules (prior chorda), trabeculae cranii - trabecular plate • between trabecular and parachordal plates - paired hypophyseal cartilages around pituitary primordium • all cartilages fuse into a single basal plate (→ origin of occipital and sphenoid bone) • basal plate growths anteriorly - forms processus ethmoidalis • laterally around otic vesicels - capsulae oticae, form majority of temporal bone • chondrification goes anteriorly towards nasal region - capsula nasalis (septum nasi from trabecular plate) CHONDROCRANIUM • regio occipitalis - from basal plate - paired processes surrounding brain stem (joining to tectum posterius and lamina parietali) - the only parts of calva that ossify through cartilage • foramen occipitale magnum between base and tectum posterius • regio otica - capsula otica - base for pars petrosa ossis temporalis • orbitotemporal region - development of sphenoid bone (fossa hypophysealis and sella turcica, allae) - cartialge model • ethmoid region - septum interorbitale and septum nasi, paranasal plates laterally fuse with nasal septum → capsula nasi CHONDROCRANIUM • Viscerocranium • Membranous ossification of mesenchymal blastema of branchial arches - maxilla, partly mandible, zygomatic) • Chondrogenic ossification - cartilages within branchial arches - 1st arch - three cartilages: incus, maleus, cartilago Meckeli (neck, head, processus condylaris and processus coronoideus of mandible) - 2nd arch - stapes, cartilago Reicherti (processus styloideus, cornu minus and upper part of body of hyoid) SPLANCHNOCRANIUM SKULL FLEXIBILITY • During ossification, skull bones remain separated • Basis cranii - synchondrosis (after birth synostosis) • Calva - sutures develop late in development (allow growth of brain). • C.t. membranes : • Fontanela major, minor • Paired fonticulus mastoideus a sphenoidalis • Ossify around the end of the 1st year of life IMPORTANT SIZES Diameter suboccipitobregmatica 9.5 cm Circumferentia suboccipitobregmatica 32 cm Diameter mentooccipitalis 13.5 cm Circumferentia mentooccipitalis 36 cm Diameter frontooccipitalis 12 cm Circumferentia frontooocipitalis 34 cm IMPORTANT SIZES Diameter bitemporalis 8 cm Diameter biparietalis 9.5 cm IMPORTANT SIZES • Paraxial mesoderm • Left and right sclerotome surrounds chorda • Sclerotomes are not homogeneous (loose and dense regions) • Intersegmental arteries • caudal (dense) regions fuse with adjacent cranial (loose) region of neighbor sclerotome - future vertebral body • Muscles derived from myotomes attach to adjacent vertebrae • Anulus fibrosus • Chorda dorsalis - nucleus pulposus DEVELOPMENT OF THE BACKBONE • Development of vertebrae • From vertebral body – dorsally: processus neurales (neurapophysis) -arcus vertebrae and ventrolaterally: processus costales (pleurapophysis). • Chondrification by the week 4: 3 pairs of chondrification centres (1 pair in vertebral bodies, 1 pair in neurapophysis, 1 pair in pleurapophysis) • Chorda dorsalis replaced by cartilage • On arcus vertebrae – processus transversus, p. articularis superior and inferior, p. laminaris - p. spinosus. • Morphogenesis of the first two cervical vertebrae is different DEVELOPMENT OF THE BACKBONE • Processus costales of thoracic vertebrae grow ventrally and form anlage for ribs • Ventral ends fuse and form the sternal bars (paired basis for body of sternum). Manubrium sterni from interclavicular blastema • Processus costales of cervical and lumbar vertebrae are short, fuse with processus transversi. In sacral region, processus costales fuse with vertebral bodies and processus transversi - ala sacralis. Processus articulares also fuse. DEVELOPMENT OF THE RIBS AND STERNUM ABNORMAL DEVELOPMENT OF STERNUM https://www.youtube.com/watch?v=TcVJdMSGPX8 Thank you for attention Petr Vaňhara Department of Histology and Embryology pvanhara@med.muni.cz http://www.histology.med.muni.cz