EMBROYOLOGY OF CARDIOVASCULAR SYSTEM

LEARNING OBJECTIVES Outline the steps in normal development of heart chambers and relate to congenital heart diseases Outline the steps of the development of aortic arch

The heart has for centuries been the fascination of anatomists, biologists and physicians. As the organ most essential for life, the heart is the first organ formed in an embryo

Introduction Pair of valved muscular pumps combined in a single organ Each pump is physiologically separate and interposed in series at different points in double circulation

Introduction Primodial heart and vascular system appears in the middle of the third week Heart starts function in the beginning of 4 th week Need for an efficient method of Acquiring oxygen and nutrients from the maternal blood Disposing of the carbon dioxide and waste products

Cells that give rise to the heart Splanchnic layer of lateral plate mesoderm – Myoepicardial mantle-myocardium, epicardium (visceral layer of pericardium) & conducting tissue – Angioblastic mesenchyme- endocardium Somatic layer of lateral plate mesoderm- – Parietal layer of pericardium

Extracardiac contributions to heart development Neural crest cells: – Aortic- pulmonary septum – Tunica media of the great vessels

ESTABLISHMENT OF CARDIOGENIC FIELD Cardiac progenitor cells-epiblast

Signals from the node induces to form heart field Cardiac progenitor cells migrate craniolaterally and reside in the splanchnic layer of the mesoderm

Once these progenitor reside in the splanchnic layer of mesoderm, The underlying endoderm induces these heart field to develop endocardial tube, myoepicardial mantle and other blood vessels.

EARLY DEVELOPMENT OF CARDIOVASCULAR SYSTEM Vasculogenesis- process of new blood vessel formation during embryonic development of the cardiovascular system Angiogenesis- the process by which new blood vessels take shape from existing blood vessels by "sprouting" of endothelial cells thus expanding the vascular tree.

Angioblasts (vessel forming cells) Differentiation of mesenchymal cells Blood islands (isolated angiogenic clusters)

Primordial cardiovascular system 1.Angioblastic mesenchyme aggregate to form epithelium (endocardium) 2.Encloses small cavities (blood islands) 3.They coalesce in the vicinity of developing foregut 4.Establish bilateral hollow endocardial tubes

THE PRIMORDIAL CARDIOVASCULAR SYSTEM

Cephalocaudal folding Ventral region Dorsal region Myoepicardial mantle

Formation of folding at fourth week

Septum transversum Lengthening of septum transversum will occur It is a plate of mesoderm Initially at cranial most aspect Give contribution in development of: – Diaphragm – Ventral mesentery in GIT system – Fibrous pericardium

Pericardium Outer fibrous pericardium - (septum transversum) Inner serous pericardium – Has 2 layers- parietal (somatic layer of lateral plate mesoderm) & visceral layer (splanchnic layer of lateral mesoderm) – Within the serous pericardium there is serous cavity called pericardial cavity – With these layers is serous fluid

Summary Layers of heartDerived from EndodermAngioblastic mesenchyme of splanchnic mesoderm Myocardium & EpicardiumMyoepicardial mantle of Splanchnic mesoderm Parietal pericardiumSomatopleuric layer of lateral plate mesoderm Fibrous pericardiumMesothelial cells arise from the external surface of the septum transversun and spread over the myocardium

Formation of primitive heart Arterial end Venous end

Formation of primitive heart tube

MAIN SUB DIVISIONS OF THE HEART TUBE AND THEIR FATE

FORMATION OF CARDIAC LOOP

Because the bulbus cordis and ventricles grow faster than other regions, the heart bends to the right, forming a U-shaped bulbo ventricle loop. Bulbo-ventricle sulcus- junction between ventricle and bulbur cordis As the primordial heart bends, the atrium and the sinus venosus come to lie dorsal to the truncal arteriosus, bulbus cordis and ventricles. Dorso-cranial looping Cranial part-moves towards R side Caudal part – moves toward L side

CLINICAL APPLICATION DEXTROCARDIA Heart lies to the right side of the thorax instead of left. Heart loops to left instead of right It may coincide with situs inversus

SITUS INVERSUS

DEVELOPMENT OF SINUS VENOSUS Middle of the fourth week- receives venous blood from the right and left sinus Receives blood from three important veins: – Vitelline (omphalo- mesenteric) vein – Umbilical vein – Common Cardinal vein

4 th week- receives blood from left and right sinus horns 5 th week- obliteration of: – Right umbilical vein – Left vitelline vein 10 th week- obliteration of left common cardinal vein- complete obliteration of left horn

Left horn loses its importance and sinuatrial oriface slowly sifts towards right side

5 th week- obliteration of: – Right umbilical vein – Left vitelline vein Left sinus loses its importance

Tenth week- obliteration of left common cardinal vein All that remains of the left sinus horn will give rise to oblique vein of the left atrium Coronary sinus

Right sinus horn and veins enlarge greatly Sinus venosus is incorporated into right atrium- smooth-walled part of the right atrium

DEVELOPMENT OF RIGHT ATRIUM Right half of the primitive atrium- forms the rough part of the atrium Body and right horn of the sinus venosus- forms the smooth part of the atrium Right half of the AV canal- forms the right AV orifice

Sinuatrial orifice Left venous valve and right venous valve fuse dorso-cranially to form septum spurium With further development, septum sporium and left venous valve incorporated in the formation of inter-atrial septum Superior part of right venous valve gets obliterated Inferior valve of right venous valve mainly contributes in the formation of inferior venacava and valve of coronary sinus

FORMATION OF LEFT ARIUM Left half of the primitive atrium- forms the rough part of the atrium Absorbed pulmonary veins- forms the smooth part of the atrium left half of the AV canal- forms the left AV orifice