Download DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM The Heart

DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM
The Heart: It starts as 2 Endothelial longitudinal tubes side by side in the floor of the
pericardial cavity, after folding of the embryo the tubes lies in the roof of
pericardium.Later on they becomes fused to form a single tube which is surrounded by
myoepithelial mantle ( myocardium & epicardium).
At this stage it shows 5 swellings & constrictions in between them as :
1-Sinus Venosus(caudal ).
2-Common Atrium.
3-Common Ventricle.
4-Bulbus Cordis .
5-Truncus Arteriosus.
This tube with its swellings & constrictions has U Shaped and then S shaped.
The Sinus Venosus: Consists of body & 2 horns.Each horn receives 3 veins.
1-Umbilical vein .
2-Vitelline vein from the yolk sac.
3-Common cardinal vein from body wall.
The sinus venosus opens into the dorsum of the common atrium by Sino-atrial orifice.
The fate of Sinus venosus:
1-Left horn becomes coronary sinus.
2-Left common cardinal vein becomes oblique vein of left atrium.
3-Right common cardinal vein becomes lower half of superior vena cava.
4-The right horn & body of sinus venosus becomes absorbed in to the right atrium.
5-The right edge of Sinu-atrial orifice gives .
a-Crista terminalis.
b-Valve of the inferior vena cava.
c-Valve of coronary sinus.
The Right Atrium : It consists of Smooth & Rough parts as follows.
A-The smooth part is derived from 2 sources .
1-Sinus Venosus.
2-Right half of atrio-ventricular canal
B- Rough Part. It forms right half of Common Atrium.
Left Atrium is formed as follows :
A-Smooth part from .
1-Pulmonary veins.
2-Left half of Atrio-Ventricular Canal.
B-Rough part from left half of Common Atrium.
The inteatrial septum formation passes in 3 stages.
1-Septum intermedium develops in the Atrioventricualr canal by fusion of dorsal &
ventral endocardial cushions,This septum divides the A-V canal in to R.& L. orifices
2- Septum Primum starts from the roof of common atrium ,it is sickle shaped with 2
Horns with a foramen in between the 2 horns known as Ostium primum.
The Ostium Primum gradually closes & is replaced by Ostium Secundum.
3- Ostium Secundum.It starts on the R. Side of septum primum & is sickle shaped
With 2 horns.The foramen ovale forms as a gap between the cephalic margin of septum
primum & caudal margin of Septum Secundum.In a dult caudal margin of septum
secundum forms the Limbus Fossa Ovale,while Septum primum forms fossa ovale it self.
THE VENTRICLES
Develops from: 1- The Common Ventricle.
2-The Bulbus Cordis.
A-Conus Arteriosus & Aortic Vestibule.
B-Absorbed in to the Common Ventricle to form the Common
Bulbo-Ventricular part.
The Interventricular Septum ; Derives as :
1-Muscular part of Septum from muscular tissue of apex ,having 2 horns with
Interventricular foramen.
2-Membranous part of septum from endocardial tissue which fills the I.V foramen
TRUNCUS ARTERIOSUS
Is the most cranial part of the heart tube.It is divided in to Ascending Aorta &
Pulmonary trunk by Aortico-pulmonary septum.
CONGENITAL HEART DEFECTS
1-Ectopia of the heart(with bifid apex),it is very rare a normally ,but fatal where the
Heart is in an abnormal position being located out side the chest wall.
2-Dextrocardia, here the apex of the heart is directed to the right & there is transposition
It is usually associated with transposition & abdominal viscera as SINUS INVERSUS.
3-Septal defects as :
A-Atrial Septal Defect:
1-Patent foramen ovale.
2-Patent Ostium Primum.
3-Complete absence of the septum.
B-Ventricular Septal Defect:
1-Patent interventricular foramen.
2-Presence of foramen in the muscular part of the septum.
4-Defect in the Aortico-pulmonary septum ( Defects in Truncus Arteriosus)
A-Transposition of Aorta & pulmonary trunk.
B- Aortico-pulmonary window ( a foramen in the septum).
C- Complete absence of septum ,here the trunk arises from the heart
Branches to give the Aorta & Pulmonary trunk.In this case a single trunk
Arises from the heart to supply the systemic,pulmonary & coronary circulation.
5-Transposition of the grat blood arteries is the most common cause of cyanotic
Heart disease.Here the Aorta lies anterior to the right of the pulmonary trunk
& arises from R.V where as pulmonary trunk will arise from L. V.
6-Anomalies of Heart Orifices as :
A-Stenosis of A-V orifices ( more common right ).
B-Abnormally wide A-V Orifice.
C- Stenosis of Pulmonary Orifice.
7-Tetrallogy of Fallot( multiple anomalies ) with 4 cardiac defects as :
A-Stenosis of Pulmonary Trunk.
B- Overriding of the Aorta.
C-Patent interventricular foramen.
D-Hypertrophy of the Right Ventricle.
BLOOD VESSELS
At first 2 primitive Aorta lies on each side of the Notochord,they join the Placenta
caudally & the Heart tube cranially on folding of the Embryonic disc each one is divided in
1-Dorsal Aorta located dorsal to the Gut.
2-Ventral Aorta located ventral to the Gut.
3-Connecting segment for both Aorta.
The 2 Ventral Aorta fuse to form the Aortic Sac.The sac has a stem & 2 horns.The sac is
connected to the Dorsal Aorta by 6 Aortic Arches.The 2 Dorsal Aorta fuse together to
form a single Dorsal Aorta which has the following branches.
1-Three Ventral Splanchnic Arteries to the Gut.
2-Lateral Splanchnic Arteries to the Urogenital Organs.
3-Intersegmental ( Somatic ) Arteries to the body wall & limbs.
4-Umbilical Arteries to the Placenta.
The Fate of The Aortic Arches
A-The first & second disappear completely leaving no important trace.
B- The third Arch will form the External carotid A,the beginning of the Internal carotid A
& the Common Carotid A.
C-The fourth Arch will form the proximal part of the R.Subclavia A on the right side & on
the left side will form part of the Arch of the Aorta extending from left common carotid to
the left subclavian arteries.
D-The fifth Arch will disappear completely.
E-The six Arch gives a pulmonary branch which enters the lung bud and part of the 6th
Will form the Ductus Arteriosus.
Congenital Anomalies of The Aortic Arches
1-Coarctation of the Aorta
2-Patent Ductus Arteriosus.
3-Right Aortic Arch ,where the Aortic Arch is directed towards the right side.
4-Abnormal origin of the right Subclavian artery.
THE FETAL CIRCULATION
The oxygenated blood is carried from Placenta to the Fetus by the left Umbilical
Vein which goes to the Liver.In the Liver it is distributed by 2 pathways as follows:
1-Most of it Bypass the liver to reach the Inferior Veina Cava via DUCTUS ARTERIOSUS.
In the I.V.C it mixes with the Non-Oxygenated blood.
2-Little amount passes through the Liver Sinusoids to reach then to the I.V.C via
The hepatic veins.
From the I.V.C it goes to the Right Atrium which contains mixture of blood
A-Most of the Blood goes to Left Atrium via Foramen Ovale.From left atrium it goes to
Left Ventricle then to Aorta to supply the Head & Neck region ( Oxygenated).
B-Little from Right Atrium goes to the Right Ventricle,then passes in to the Pulmonary
Trunk.As the lungs are Not-Functioning in the Fetus,so the blood will pass to the dorsle
Aorta via the Ductus Arteriosus.
The Dorsal Aorta distal to the attachment of Ductus Arteriosus contains mixture blood:
A-Part coming from the Right Ventricle coming via Ductus Arteriosus
B-Blood coming from the Left Ventricle through the Arch of Aorta.
The blood supplies the Trunks & Lower Limbs ,and what remains as Non-Oxygenated
Blood goes to the Placenta via 2 Umbilical Arteries.
The Changes After Birth
1-Immediate changes is closure of Foramen Ovale due to the following reasons:
A-Occlusion of the Left Umbilical Vein.
B-Inflation of the Lungs & start of Respiration by the new borne baby.
2-Late changes which includes the following:
A-Ductus Venosus converts in to Ligamentum Venosus.
B-Ductus Arteriosus converts in to Ligamentus Arteriosus.
C-Left Umbilical Vein converts in to Ligamentum Teres.
D-The Umbilical Arteries converts in to Lateral Umbilical Ligament