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 (SI)– heart development (adam)– development of the heart– actual mouse embryo

Primitive heart

• Primordia (SI) (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