development of the cardiovascular system begins to function by end of the 3 rd week –necessary in...
TRANSCRIPT
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
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