1. 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 the 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 how 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 DEVELOPMENT OF THE HEART AND GREAT BLOOD VESSELS

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

3. PERICARDIAL CAVITY CARDIAC PRIMORDIUM (SPLANCHNIC MESODERM) DORSAL AORTA ENDODERM A THE EARLY DEVELOPMENT OF THE HEART - 1 The cardiac tube folds under the gut tube…… 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. VITELLINE VEINS GUT TUBE CARDIAC TUBE B The heart is a U-shaped tube at this stage and the forming blood vessels are initially unconnected

4. ……and connects bilaterally with the dorsal aorta via the aortic arches 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. The dorsal aorta form independently and then grow to meet the ventral output from the heart in the aortic arches FUSED DORSAL AORTA 1 ST AORTIC ARCH (R) ORAL PLATE ATRIUM VENTRICLE VENOUS RETURN FROM CARDINAL VEINS, VITELLINE VEIN AND ALLANTOIC (UMBILICAL) VEIN C

5. 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 This pattern of mammalian development is a good example of recapitulation

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

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

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

9. 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

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

11. The simple tubular heart twists to prepare for septum formation and the creation of a four- chambered 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 NOTES: 1. View from ventral surface 2. RA - Right atrium, LA - Left atrium, RV - right ventricle, LV - left ventricle, TA = truncus arteriosus A V I II III IV V VI VENOUS RETURN V A III IV VI TA After birth venous return is from vena cava (blue arrows) and pulmonary veins (red arrows) LA RA LV RV CAROTIDS (from L and RIII) AORTA (from LIV) DUCTUS ARTERIOSUS (LVI to LIV) SEPTA RIGHT SUBCLAVIAN (from RIV) PULMONARY TRUNK (from LVI)

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

13. Mouse, 10 days, frontal section Mouse, 12 days, section of truncus arteriosus A 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/

14. DA FO Trunk Hindlimb Placenta Liver From lungs To lungs Brachycephalic vessels 14 30 14 25 22 19 FOETAL CIRCULATION 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

15. 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

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

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

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