Development of cardiovascular system. Dr. Lubna Nazli

Objectives Primitive heart tube formation Sinus venosus Primitive atrium Primitive ventricle Bulbus cordis Truncus arteriosus Anomalies Fetal circulation & changes after birth

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

Development of Main Blood Vessels First indication of paired blood vessels 3 week old embryo

The endocardial tube

The heart tube invaginates the percardial sac(dorsal mesocardium)

Cranial end is an arterial end & caudal end is a venous end

Germ layer for Cardiovascular system The mesodermal germ layer gives rise to the entire cardiovascular system (heart, blood vessels and blood cells). The heart develops from  two simple epithelial tubes which fuse to form a single chambered heart that is efficiently pumping blood by the fourth week of embryonic development.

The first heart beat By day 21/22 of gestation , the primitive heart starts the first beat. By 29th day of gestation the circulation begins in the blood vessels. The primitive heart has 5 chambers. Truncus arteriosus. Bulbus cordis. Primitive ventricle. Primitive atrium. Sinus venosus.

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

Development of atria The primitive atrium divides into right and left atria by the partitioning and forming of interatrial septa. The smooth part of right atrium is derived from the absorbed part of right horn of sinus venosus. The rough part of right atrium is derived from the primitive atrium. The smooth part of left atrium is from the absorbed part of pulmonary veins. The rough part is from the primitive atrium.

Foramen ovale Permanent anatomical closure of the foramen ovale occurs with time in normal infants. Inappropriate closure of the foramen ovale results in patent foramen ovale.

Development of ventricles The primitive ventricle, after bending of the heart tube, gets partitioned into two, by the developing of the interventricular septum. The right ventricle is formed by the primitive ventricle as well as the bulbus cordis. The left ventricle is formed by the primitive ventricle. The truncus arteriosus get absorbed into the aorta and pulmonary trunk.

Interventricular septum The primitive ventricle is partitioned by the septum growing as muscular /membranous part of interventricular septum. The membranous part is arising from the endocardial cushions. The failure to fuse between muscular and membranous part results in interventricular septal defect. (V.S.D.)

Normal R&L ventricles Ventricular septal defect

Congenital Malformations Dextrocardia Heart is located in right hemithorax Most cases associated with situs inversus Atrial Septal Defect Ventricular Septal Defect About ½ of all cases of congestive heart failure show a VSD

Fallot’s Tetralogy The tetralogy is comprised of the following four defects:- 1.Pulmonary artery/valve stenosis 2.Ventricular septal defect 3.Overriding aorta 4. Right ventricular hypertrophy

Transposition of great vessels

Flow of blood in the chambers of fetal heart Both venae cava drains blood into right atrium. The inferior vena caval blood is directed in to the left atrium through the foramen ovale. The superior vena caval blood is directed into the right ventricle passing through the tricuspid valve.

The left atrium Receives four pulmonary veins from the fetal lungs. Fetal lungs are non functional during fetal life, no oxygenation occurs as lungs are still glandular. Through the foramen ovale, the blood enters into left atrium. From left atrium the blood enters the left ventricle, passing through mitral valve.

Both ventricles When contract pushes the blood into the aorta and pulmonary trunk. There is a shunt between pulmonary trunk and under surface of arch of aorta. This connection is called as ductus arteriosus. The blood circulates through out the body by branches of aorta.

The umbilical arteries Arise from the internal iliac arteries and carry blood to the placenta for oxygenation. The umbilical cord has 2 umbilical arteries and one umbilical vein.

Fetal circulation just after birth When the child is born, the pulmonary circulation is opened up. The first cry of life, opens up the lungs and air enters in to the lung alveoli. The pulmonary trunk carries the deoxygenated blood by means of pulmonary arteries. The pulmonary veins drain from lungs into the left atrium.

Changes after birth The umbilical vein stops flow of blood. The umbilical arteries also stops flow of blood. The foramen ovale get closed. The ductus venosus closes, when there is no flow of blood. The ductus arteriosus also get cicatrized and flow stops.

Embryological remains Foramen ovale = fossa ovalis Umbilical arteries = medial umbilical ligaments. Umbilical vein = ligamentum teres hepatis (round ligament of liver). Ductus venosus = ligamentum venosum. Ductus arteriosus = ligamentum arteriosum.