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Development of Cardiovascular System

Primordia of cardiovascular system from which the heart, blood vessels and blood cells develop is mesoderm. Cardiovascular system begins to develop in the middle of 3rd week.

Development of Heart

Heart develops from splanchnic mesoderm forming the cardiogenic area. Primordial heart develops as two endothelial heart tubes which fuse in cranio-caudal direction to form a single tubular heart. Endothelial heart tube is surrounded by a layer of mesoderm known as myo-epicardial mantle, which gives rise to myocardium and visceral pericardium (epicardium). Myoepicardium then secretes a thick layer of extracellular matrix called cardiac jelly that separates it from tubular heart. Thus developing heart consistsofthree layers:
  1. endocardium,
  2. myocardium and
  3. epicardium (serous pericardium).

Tubular heart has following components, cranio-caudally:

  1. Bulbus cardis: It is the cranial most part and is subdivided into:-
    1. Truncus arteriosus (distal part): It is the most cephalic part of endothelial heart tube (tubular heart). It later forms ascending aorta and pulmonary trunk. Distal end of truncus arteriosus dilates to form aortic sac which divides into right and left limbs. Each limb is connected with the corresponding dorsal aorta through six aortic arches.
    2. Conus cordis (mid portion): Later forms the outflow tract of both ventricles.
    3. Proximal part: It forms the trabeculated part of right ventricle.
  2. Primitive ventricle: Along with conus cordis it forms the right and left ventricles.
  3. Primitive atrium: Primitive atrium will later form right and left atria. Primitive atrium is connected to primitive
    Ventricle by atrioventricular canaL
  4. Sinus venosus: It is the caudal most part of tubular heart. At its lower end it presents right and left horns. Each horn receives blood from following three veins:
    1. Vitelline vein from yolk sac. Right vitelline vein forms terminal part of interior vena cava.
    2. Umbilical vein from placenta.
    3. Common cardinal vein from body wall. Right common cardinal vein forms superior vena cava.

Truncus arteriosus is the arterial end and sinus venosus is venous end of heart tube (tubular heart).

Formation of atria

Formation of atria involves following processes:-
  1. Septation of atrioventricular canal (AV canal): AV canal is the passage through which primitive atrium is connected to primitive ventricle. AV canal is divided into right and left canal by endocardial cushions (atrioventricular cushions or AV cushions). The fused cushions form septum intermedium.
  2. Septation of primitive atrium: The primitive atrium is divided into left and right atria by interatrial septum which is formed by fusion of septum primum and septum secundum. The sequence of events are as follows:-
    1. Septum primum arises from the roof of common atrium (primitive atrium) and grows caudally towards septum intermedium (fused AV cushions).
    2. Foramen primum is formed between free border of growing septum primum and fused AV cushions (septum intermedium).
    3. Shortly afterwards the septum primum fuses with septum intermedium (fused AV cushions), obliterating foramen primum
    4. Foramen secundum is formed by degeneration of cranial part of septum primum.
    5. Septum secundum grows caudally to the right of septum primum and overlaps the foramen secundum. The passage between septum primum and septum secundum is called foramen ovale. After birth, foramen ovale closes by fusion of septum primum with septum secundum. Failure of fusion of these two septa results in patent foramen ovale.
  3. Incorporation of sinus venosus into right atrium: Right horn of sinus venosus is incorporated to form posterior smooth part of right atrium. Left horn of sinus venosus forms the coronary sinus.
  4. Incorporation of pulmonary veins into left atrium: Right and left tributaries and their first bifurcations, are incorporated to form posterior smooth part of left atrium.


Summary of development of atrium
Right atrium develops from Left atrium develops from
  1. Rough anterior (pectinate) part - Primitive atrium (right half).
  2. Smooth posterior part - Absorption of right horn of sinus venosus
  3. Right atrioventricular canal is also absorbed to some extent into right atrium
  1. Rough anterior part - Primitive atrium (left half). 
  2. Smooth posterior part - Absorption of pulmonary veins  
  3. Left atrioventricular canal is also absorbed to some extent into left atrium


  • Interatrial septum separates right atrium from left atrium and is formed by fusion of septum primum with septum secundum.
  • Fossa ovalis is the remnant of septum primum.
  • Limbus fossa ovalis (annulus ovalis) is the remnant of septum secundum.


Formation of ventricles


Development of ventricles is as follows:-

  1. Right ventricle: Right ventricle develops from;
    1. Rough part: from proximal part of bulbar cordis and right half of primitive ventricle.
    2. Smooth part (infundibulum): from caudal part of bulbus cordis (conus cordis).
  2. Left ventricle: Left ventricle develops from;
    1. Rough part: from left half of primitive ventricle.
    2. Smooth part (vestibule): from caudal part of bulbus cordis (conus cordis).


Development of major arteries
Blood vessel Development components
Ascending aorta Truncus arteriosus
Arch of aorta
  1. Left horn of aortic sac
  2. Left 4th arch artery
  3. Left dorsal aorta
Descending aorta
  1. Left dorsal aorta beyond 7th cervical intersegmental artery
  2. Fused dorsal aortae
Brachiocephalic artery Right horn of aortic sac in which right 3rd and 4th arch arteries are opening
Common carotid 3rd arch artery distal to external carotid bud
Internal carotid artery
  1. 3rd arch artery distal to external carotid bud
  2. Dorsal aorta cranial to attachment of 3rd arch artery
External carotid artery New sprout (bud) from 3rd arch artery
Right Subclavian artery Right 4th arch artery and Right 7th cervical intersegmental artery
Left Subclavian artery Left 7th cervical intersegmental artery
Pulmonary trunk Truncus arteriosus
Pulmonary artery 6th arch artery (proximal part)
Ductus arteriosus Distal part of left 6th arch artery between pulmonary artery and descending aorta.

Dorsal aortae and their branches

The dorsal aorta is a paired vessel in the early human embryo. The two aortae fuse caudal to T4, forming a single aorta. Each dorsal aorta, even before the stage of fusion gives numerous branches which arise at right angles to the long axis (right and left branches) and are arranged in three groups:-
  1. Intersegmental arteries
    About 30 somatic intersegmental arteries supply blood to developing somites and their derivatives. They form following arteries:-
    1. In neck (cervical intersegmental arteries) they form vertebral arteries, 7th cervical intersegmental artery forms complete subclavian artery on left side and part of subclavian artery on right side.
    2. In the thorax (thoracic intersegmental arteries) they persist as intercostal arteries. Their ventral divisions anastomose with ventral division of 7th cervical intersegmental artery to form internal thoracic artery.
    3. In abdomen (lumbar intersegmental arteries) they form lumbar arteries, but 5th pair of lumbar intersegmental arteries remains as common iliac arteries.
    4. In the sacral region they form the lateral sacral arteries.
  2. Lateral splanchnic branches
    1. These supply the mesonephros (including adult kidney) and genital ridge (testis or ovary), and part of adrenal gland.
  3. Ventral splanchnic branches (vitelline arteries)
    1. These form coeliac trunk (for foregut), superior mesenteric artery (for midgut) and inferior mesenteric artery (for hindgut).

Developmental anomalies of aortic arches

Important abnormalities in the development of aortic arch are:-
  1. Double aortic arch results when right dorsal aorta also persists distal to the origin of the right 7th cervical intersegmental artery.
  2. Right aortic arch results when right dorsal aorta persists and corresponding portion of left dorsal aorta disappears.
  3. Interrupted aortic arch, i.e. absence of a segment of aortic arch results due to obliteration of 4th aortic arch on the left side which normally forms the segment of aorta which lies between left common carotid and left subclavian arteries. Thus the part of arch of aorta between left common carotid artery and left subclavian artery is absent and the ascending aorta ends by supplying the artery arises from distal segment and receives blood through patent ductus arteriosus.
  4. Abnormal origin of subclavian artery: Normally right subclavian artery is formed from right 4th arch artery. However, sometimes the right 4th arch and proximal part of right dorsal aorta obliterate and right 7th cervical intersegment artery and right dorsal caudal to it are continued as right subclavian artery.
  5. Left common carotid artery mostly arise from arch of aorta but in 30% cases it may arise from brachiocephalic trunk which is most common variation of branching pattern of arch of aorta.

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