Development of the cardiovascular system Begins to function by end of the 3rd week Necessary in order to meet nutrient needs of rapidly growing embryo Angioblasts arise from: mesoderm Splanchnic & chorionic mesenchyme yolk sac & umbilical cord Give rise to blood & blood vessels

Angioblasts AKA hemopoietic mesenchyme differentiates into the blood islands Central cells of blood islands differentiate into blood and blood cells Lined with endothelium

Formation of blood cells Yolk sac-4th week Body mesenchyme & blood vessels-5th week Liver-6th week Spleen, thymus, lymph glands-2-3 months Bone marrow- 4th month There is overlap in production sites

Development of Main Blood Vessels First indication of paired blood vessels 3 week old embryo Embryonic period (4-8 weeks) By end of embryonic period the main organ systems have been established Appear as solid cell clusters which acquire a lumen & form a pair of longitudinal vessels Dorsal aorta Aortic arches Continue anteriorly and run ventrally Heart primordia Continue posteriorly

Venous system at 4 weeks 3 systems of paired veins drain into heart Vitelline veins Returning blood from yolk sac Umbilical veins Bring blood from the chorion and placenta Cardinal veins Returning blood from various parts of the body vascular system

Arterial system at end of 4 weeks Four pairs of aortic arches have appeared Dorsal aorta have fused throughout much of their length  descending aorta

Development of the heart Starts as two thin walled endocardial tubes Caudal continuation of the first aortic arches Endocardial heart tubes Begin to fuse to form a single tube As heart tube fuses Surrounding mesenchyme thickens to form Myocardium Epicardium Tubular heart elongates and develops dilations or sacculations Primordia of Truncus, Bulbus, Ventricle, Atrium, Sinus (SI) heart development (adam) development of the heart actual mouse embryo

Primitive heart Primordia (SI) (Cranially Caudally) (A V) Truncus Continuous cranially with first pair of aortic arches Bulbus Ventricle Both bulbus and ventricle grow faster than other parts which causes S shape bend animation Atrium Sinus Receives venous return from Umbilical, Vitelline & Common cardinal veins

Primitive heart As primitive heart bends the atrium and sinus come to lie dorsal to the bulbus & ventricle Reversal of original cranio-caudal relationship Atrial portion being paired becomes one Atrioventricular junction remains narrow Form an atrioventricular canal Connecting atrium with the ventricle

Primitive heart (cont) At the end of loop formation, the smooth inner heart surface begins to form the primitive trabecullae in the ventricle Atrium & bulbus remain temporarily smooth Sinus maintains it’s paired condition longer than any other portion of heart tube Contraction begins by day 22 Initially ebb & flow  unidirectional flow By end of 4th week, rhythmic contraction

Formation of cardiac septa Begins around middle of 4th week & completed by end of 6th week Two methods Tissue growth Two of more actively growing masses of tissue which approach each other in the same plane, fuse to divide a single chamber into two Overgrowth Involves growth of a chamber at all points except for a narrow strip which fails to grow Leaves a small canal connecting the two chambers

Cardiac Septum Atrioventricular septum (during 4th week) Bulges form on dorsal & ventral walls of AV canal AKA endocardial cushion septum Atrial septa (end of 4th week) Sickle-shaped crest grows from roof of common atrium in the direction of the endocardial cushion Septum primum As right atrium grows & incorporates part of the sinus Septum secundum associated with foramin ovale (oval foramin) Ostium primum Opening between septum and endocardial cushion which closes by growth of endocardial cushion Ostium secundum superior in septum primum

Foramin ovale (FO) Shunts blood from Right to left atria via ostium secudum Mostly blood returning via inferior vena cava Bypasses lungs in fetus Associtated with septum secundum At birth FO pressed against septum primum which seals the opening

Septal formation Ventricular septum (starts by end of 4th week) Expansive growth of ventricle laterally & ultimate fusion of the medial walls starts the formation of the Muscular Interventricular Septum near apex Communication btw ventricles below cushion Closed by membranous IV septum at end of 7th week Septum of the truncus & bulbus Continous paired ridges fuse Form a spiral septum (aorticopulmonary septum) Cavum aorticum  LV Cavum pulmonare  RV Two cava eventually separate forming acending aorta & pulmonary trunk image

Congential malformations Acardia Absence of heart Only occurs in conjoined monozygotic twins 1:35,000 Ectopic Cordis Heart is located through a sternal fissure into: Into the neck Down through a diaphragmatic hernia into a exomphalocoele Protruding outside chest Dextra thoracic ectopia Limited life expectancy

Congenital Malformations Dextracardia Heart is located in right hemithorax Most cases associated with situs inversus Heart, great vessels, other thoracic & abdominal organs may present a mirror image of the norm. 1:10,000 Known to occur with other anomolies Duodenal atresia Agenesis of spleen Spina bifida Isolated cases rare (1:900,000)

Septal Defects Atrial Septal Defect Well tolerated into adult life Problem in old age May be combined with rarity of other cardiac anomalies Prenatal Closure of the interatrial shunt Enlargement of right atrium & ventricle Causes hypoplastic left side Death soon after birth Ventricular Septal Defect About ½ of all cases of congestive heart failure show a VSD Uncomplicated form considered harmless Harsh systolic murmur with no cyanosis 6:10,000

Tetralogy of Fallot Pulmonary stenosis VSD Overriding Aorta Right Ventricular hypertrophy Life expectancy 12 years Major symptom is cyanosis Paroxysmal dyspnea on exertion is common Above symptoms may lead to unconsciousness & paralysis

Trilogy of Fallot Pulmonary Stenosis ASD Right ventricular hypertrophy

Development of the arterial system Branchial/pharyngeal arches develop during 4th & 5th week Each arch receives its own artery & nerve Arteries called aortic arches Arise from the truncus Terminate in dorsal aorta 6 pairs of aortic arches develop By the time the 6th pair has formed, the first two pairs have disappeared

Aortic Arches 1st pair  largely disappears, small ventral portion persists to form maxillary artery 2nd pair  largely disappears, dorsal portion remains to form parts of the hyoid & stapedial arteries 3rd pair  forms the beginning of internal carotid artery 4th pair  right arch becomes proximal portion of right subclavian artery left arch forms part of arch of aorta 5th pair  rudimentary (50%) or never develops (50%) 6th pair  Proximal part of each pair becomes a pulmonary artery Distal part of left persists as ductus arteriosis, distal right regresses diagram

Development of Venous System In 5th week of development 3 major pairs Vitelline veins  Portal vein and superior mesenteric from right VV Umbilical veins  Left umbilical vein connects to right hepatocardiac channel via ductus venosus (bypass liver sinusoids) After birth Ductus venosus closes  ligamentum venosus Left umbilical vein is obliterated  ligamentum teres hepatis Cardinal veins  main venous drainage of fetus

Cardinal veins (CV) Ant. cardinal veins drain anterior region Anatomose btw ant CV  left brachiocephalic V Post. cardinal V drain rest During 5th – 7th weeks more veins formed Subcardinal V Mainly drains the kidneys Anatomose  left renal vein Supracardinal V Drains the body wall by way of intercostal veins Superior vena cava From rt. common & proximal part of rt. ant. CV

Vena Cava, Azygous, Hemizygous Superior vena cava Formed by the right common CV & proximal part of right common CV Inferior vena cava Formed from right subcardinal vein Azygous Formed from right supracardinal veins Hemizygous Formed from part of left supracardinal veins