1. 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

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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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)

17. 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

18. 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

19. Trilogy of Fallot
Pulmonary Stenosis
ASD
Right ventricular hypertrophy

20. 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

21. 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

22. 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

23. 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

24. 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