The endoderm folds to become the gut tube

The endoderm folds to become the gut tube and the body sides form to enclose body cavities 8 day mouse, transverse N So S Sp E N Neural tube S Somite So Lateral mesoderm (somatopleure) Sp Lateral mesoderm (splanchnopleure) E Gut tube 9 day mouse, transverse A A G C So Sp A Split aorta G Gut tube So Somatopleure, parietal mesoderm* Sp Splanchnopleure, visceral mesoderm* C Cavity * Collectively a serous membrane around the body cavity http: //www. med. unc. edu/embryo_images/

The pleuropericardial cavity divides and the cavities are lined by parietal and visceral surfaces Aorta Oesophagus Lungs Peripleural cavity Heart Pericardial cavity Parietal surface of pleural and pericardial cavities Visceral surface of pleural and pericardial cavities Form a single serous membrane sac around the cavity

The peritoneal cavity is subdivided laterally at the rostral end but is a single cavity at the caudal end Aorta Pancreas Dorsal mesentery Stomach Small intestine Liver Ventral mesentery Parietal surface of peritoneal cavity Visceral surface of peritoneal cavity Form a single serous membrane sac around the cavity

DEVELOPMENT OF THE HEART AND GREAT BLOOD VESSELS LEARNING OUTCOMES 1. explain the early development of the heart from splanchnic mesoderm ahead of the neural plate which is then folded beneath the pharynx of the head fold. 2. outline the fusion of the endocardial tubes to form the simple linear heart with atrium, ventricle and valvular flaps pumping blood into the aortic arches. 3. define three circulatory arcs of the heart supplying the body tissues, the yolk sac (vitelline) and the allantois and describe their functions 4. describe the role of the yolk sac splanchnopleure in early haematopoiesis 5. Understand the developmental process by which the aortic arches and truncus arteriosis are adapted to give the aortic and pulmonary trunks and the carotids 6. Show septum formation in the primitive linear heart allows separate pumping of blood into the aorta and the pulmonary trunk 7. describe the congenital abnormalities of septal defects, patent ductus arteriosus, and persistent aortic arch

FORMATION OF THE MAMMALIAN GASTRULA - 9 MESODERM TYPE INTERMEDIATE STRUCTURE HEAD CHORDA- MESODERM DERIVATIVE HEAD MUSCLES, SKULL, CARTILAGE NOTOCHORD LIMB MUSCLES AXIAL SKELETON PARAXIAL ICM EPIBLAST SOMITES MESODERM TRUNK MUSCLES DERMIS INTERMEDIATE PARTS OF KIDNEY AND REPRODUCTIVE TRACT LIMB SKELETON LATERAL HEART BODY CAVITY DIVIDERS BLOOD CELLS AMNION CHORION YOLK SAC ALLANTOIS

* epithelial part only of organ Thyroid* Lungs* Pharynx Pharyngeal pouches Pancreas* Middle Ear* Tonsils* Gut tube* Liver* Gonads* EPIBLAST MESODERM Bladder* Parathyroid* Sclerotome Paraxial mesoderm Lateral mesoderm Intermediate mesoderm Hair, nails Anal canal Olfactory epithelium Mammary glands Surface epithelium ENDODERM Allantois* ECTODERM Head mesoderm Notochord Stomodeal epithelium Neural tube Skull Branchial cartilage Oral epithelium THE MAP OF ORIGINS Teeth enamel Anterior pituitary Brain Spinal cord Eye Somatic mesoderm Extraembryonic Kidney and Neural Parietal pleura, mesoderm of yolk reproductive Axial crest pericardium, sac and allantois tracts skeleton Dermatome peritoneum Extraembryonic Blood mesoderm of Visceral pleura Dermis cells amnion and chorion Visceral peritoneum Trunk Splanchnic Mesenteries Muscles mesoderm Teeth Appendicular dentine muscles Connective tissue, Heart Sympathetic smooth muscle ganglia of viscera and Vascular blood vessels endothelium Melanocytes Myotome Primary germ cells INNER CELL MASS Extraembryonic endoderm of yolk sac and allantois Sweat glands Cranial motor nerves Spinal motor nerves Cranial sensory nerves Adrenal medulla Spinal sensory nerves

The cardiac tube folds under the gut tube…… THE EARLY DEVELOPMENT OF THE HEART - 1 B A DORSAL AORTA GUT TUBE ENDODERM CARDIAC TUBE PERICARDIAL CAVITY VITELLINE VEINS CARDIAC PRIMORDIUM (SPLANCHNIC MESODERM) The cardiac primordia are established in the early gastrula as regions of splanchnic mesoderm ahead of the embryo itself. As a result of the head fold, this region ends up beneath the pharynx. The heart is a U-shaped tube at this stage and the forming blood vessels are initially unconnected

……and connects bilaterally with the dorsal aorta via the aortic arches C FUSED DORSAL AORTA 1 ST AORTIC ARCH (R) VENTRICLE ORAL PLATE The sides of the U-tube then fuse to produce the atrial and ventricle regions with valvular flaps to prevent back flow so that the heart can function as a simple peristaltic pump. ATRIUM VENOUS RETURN FROM CARDINAL VEINS, VITELLINE VEIN AND ALLANTOIC (UMBILICAL) VEIN The dorsal aorta form independently and then grow to meet the ventral output from the heart in the aortic arches

This pattern of mammalian development is a good example of recapitulation The diagram shows 6 aortic arches but, in mammals, 1 and 2 are regressing while the later arches are forming and arches 5 never form

REMINDER: The branchial arches and clefts and the juxtaposed pharyngeal pouches are a recapitulation of the respiratory anatomy of fish

Mouse, 8 day, sagittal Mouse, 9 day, frontal Mouse, 10 day, frontal The heart twists so that the atrium is rostral to the ventricle Mouse, 8 day, frontal The heart folds under the pharynx Mouse, 9 day, side http: //www. med. unc. edu/embryo_images/

The embryonic circulation has three circulatory arcs through which blood is pumped by a simple linear heart Dorsal aorta Cardinal veins Mesonephros Aortic arches Vitelline vein Vitelline artery Allantoic vein Deoxygenated blood Mixed blood Oxygenated blood Yolk sac Chorio-allantoic placenta

THE CIRCULATORY ARCS OF THE EMBRYONIC BLOOD SUPPLY 1. BODY CIRCULATION TRANSPORT OF O 2 /FOOD MATERIALS TO TISSUES TRANSPORT OF WASTE MATERIALS AWAY 2. VITELLINE CIRCULATION CARRIES MOBILISED FOOD MATERIALS FROM THE YOLK SAC LOST FUNCTION IN MAMMALS BECAUSE SAC EMPTY CARRIES FIRST BLOOD CELLS FROM YOLK SAC SPLANCHNOPLEURE 3. ALLANTOIC CIRCULATION IN MAMMALS TAKES OVER THE FUNCTIONS OF THE VITELLINE ARC IN BIRDS SUPPLIES FOOD MATERIALS FROM MATERNAL CIRCULATION RETAINS AVIAN FUNCTION OF REMOVAL OF WASTE AND GAS EXCHANGE

MESENCHYME IN SPLANCHNOPLEURE OF YOLK SAC Haematopoiesis begins in the splanchnopleure of the yolk sac before transferring to the embryo itself later in development CELL CLUSTERS ENDOTHELIAL CELLS HAEMATOPOIETIC CELLS FORMATION OF BLOOD VESSEL AGGREGATION OF FURTHER MESENCHYME TO FORM MUSCULAR AND CONNECTIVE TISSUE WALL

The simple tubular heart twists to prepare for septum formation and the creation of a fourchambered organ. The aortic arches are selectively modifed to give rise to the great arteries THE HEART AND THE AORTIC ARCHES - FORMATION OF THE GREAT BLOOD VESSELS CAROTIDS (from L and RIII) AORTA (from LIV) I II IV V VI III IV VI TA A RIGHT SUBCLAVIAN (from RIV) DUCTUS ARTERIOSUS (LVI to LIV) RA LA PULMONARY TRUNK (from LVI) SEPTA A V V RV VENOUS RETURN NOTES: 1. View from ventral surface 2. RA - Right atrium, LA - Left atrium, RV - right ventricle, LV - left ventricle, TA = truncus arteriosus LV After birth venous return is from vena cava (blue arrows) and pulmonary veins (red arrows)

The separation between atria and between ventricles and between atria and ventricles occurs by means of septum formation

A Mouse, 12 days, section of truncus arteriosus Mouse, 10 days, frontal section Blood from the atrium passes to the ventricle by means of a channel. The beginnings of interatrial septum formation can be seen (A) Cushions form within the truncus arteriosus and will fuse to form the aortico-pulmonary septum separating the aortic and pulmonary flows http: //www. med. unc. edu/embryo_images/

FOETAL CIRCULATION 25 Brachycephalic vessels 14 To lungs 19 DA From lungs FO 25 19 25 14 Liver 30 22 Trunk Placenta Hindlimb There is a split between deoxygenated blood returning from the rostral end of the foetus and oxygenated blood returning from the placenta. This spit is achieved by directed flow through the foramen ovale

CHANGES IN THE CIRCULATION AT BIRTH • Contraction of allantoic artery and veins to force placental blood into main circulation. Rupture of umbilical cord • Contraction of Ductus arteriosus and closure of Foramen ovale so that right side blood is directed to lungs

DEFECTIVE SEPTUM FORMATION INTER-ATRIAL SEPTAL DEFECT (persistent Foramen ovale) INTER-VENTRICULAR SEPTAL DEFECT (Tetralogy of Fallot is variation on this)

PERSISTENCE OF AORTIC ARCHES AND VASCULAR RING ANOMALIES Right 4 Left 6 Oesophagus PATENT DUCTUS ARTERIOSUS PERSISTENT RIGHT AORTIC ARCH IV

REFERENCES Carlson BM (2003) Patten's Foundations of Embryology Noden DM, de Lahunta (1985) A Embryology of domestic animals Mc. Geady TA, Quinn PJ, Fitzpatrick ES, Ryan MT (2006) Veterinary embryology University of North Carolina web site: http: //www. med. unc. edu/embryo_images/