the Cardiovascular System Development of the Cardiovascular System

Contents Establishment of the primordial cardio-vascular system Development of the heart Blood circulation of fetus and circulatory changes after birth Congenital defects of the cardiovascular system

Establishment of the Primordial Cardiovascular System

Yolk sac mesenchyme cells blood islands Central C Peripheral C Primitive Blood cell Endothelial C Blood C Endothelial tubule Endothelial tube meshwork

Endothelial tube network appears in chorion and body stalk, and connect to vitelline circulation. By the 18-20th days, endothelial tube network appears in intraembry-onic mesenchyma to form intraembryonic endothe-lial tube network.

By the end of 3rd week, intraembryonic and extra-embryonic endothelial tube networks connect to each other. Endothelial tube networks fuse or disappear to form primordial cardiovas-cular system.

① cardiac tube:2 tubes1 tubeprimitive heart ② arteries ③ veins cardiac tubes 20d 4w End of 4w ① cardiac tube:2 tubes1 tubeprimitive heart ② arteries ③ veins

① cardiac tube ② arteries ③ veins 2 dorsal A  1 ,many branches Aortic arches Dorsal aorta 20d 4w End of 4w Vitelline A Umbilical A ① cardiac tube ② arteries ③ veins 2 dorsal A  1 ,many branches Few pairs of vitelline A 1 pair of umbilical A 6 pairs of aortic arches

① cardiac tube ② arteries ③ veins 1 pair of anterior cardinal V Posterior cardinal V Vitelline V Common cardinal V Umbilical V 20d 4w End of 4w ① cardiac tube ② arteries ③ veins 1 pair of anterior cardinal V 1 pair of posterior cardinal V 1 pair of vitelline V 1 pair of umbilical V Common cardinal V

vitelline, umbilical and embryonic circulation.

Development of the Heart Development of the cardiac tube Morphogenesis of the heart Partitioning of heart chambers

Development of the cardiac tube Cardiogenic area Oropharyngeal membrane Cardiogenic area is anterior to the oropharyngeal membrane.

A cavity appears in the cardiogenic area --pericardial cavity cardiaogenic plate 18~19th day A cavity appears in the cardiogenic area --pericardial cavity B. Ventral of the cavity is cardiaogenic cords --cardiaogenic plate

C. cardiaogenic plate becomes hollow --cardiac tube Pericardial cavity cardiac tube 20th day C. cardiaogenic plate becomes hollow --cardiac tube

Pericardial cavity: dorsal → ventral Cardiac tube: ventral → dorsal 22nd day D. Cephalic folding: Pericardial cavity: dorsal → ventral Cardiac tube: ventral → dorsal

E. Lateral folding: 2 cardiac tubes → single cardiac tube. F. The tube remains attached to the dorsal side of the pericardial cavity by the dorsal mesocardium.

G. The dorsal mesocardium breaks down to form the Transverse sinus Pericardial cavity cardiac tube Cephalic end Caudal end G. The dorsal mesocardium breaks down to form the transverse sinus, which connects both sides of the pericardial cavity. Cephalic end  Arteries，Caudal end  Veins

Morphogenesis of the heart Vein end Cardiac tube Artery end The 21st d Part of the cardiac tubes merged Cephalic end  A Caudal end  V

Cardiac tubes almost merged atrium ventricle bulbus cordis Cardiac tubes almost merged Three expansions Bulbus cordis Ventricle Atrium The 22nd d

The 4th expansion, the sinus venosus appears The truncus arteriosus appears The bulbus cordis and ventricle grow faster than other regions, the cardiac tube starts to bend. The 23rd d atrium bulbus cordis truncus arteriosus sinus venosus ventricle bulboventricular portion of heart tube grows rapidly, bends forming a loop

Form a ‘U’ like structure, the cardiac loop--bulboventricular loop. The 24th d sinus venosus truncus arteriosus Form a ‘U’ like structure, the cardiac loop--bulboventricular loop.

The bulboventricular loop continues to grow and bend: Atrium shifts in dorso-cranial direction and bulges laterally on each side of bulbus. Sinus venousus located at caudal portion of atrium The 35th d atrium Aortic arches ventricle

Primary ventricle develop into the left ventricle. The bulbus cordis proximal portion develops into the right ventricle. Atrioventricular canal: atrioventricular junction remains narrow. The 35th d atrium Aortic arches ventricle The normal heart shape was established, but partitioning has not completed.

Partitioning of Heart Chambers (from 27th day to 37th day) Partitioning of atrioventricular canal Partitioning of the primitive atrium Partitioning of the primitive ventricle Division of truncus arteriosus and bulbus cordis

Partitioning of atrioventricular canal Endocardiac cushion: The endocardial cushions grow toward each other and fuse

Lateral atrioventricular cushion: form atrioventricular valve. Left → bicuspid, right → tricuspid Bicuspid Ttricuspid Endocardiac cushion

Partitioning of the primitive atrium Septum primum: a thin sickle-shaped crest appearing from dorso-cranial wall of atrium. Foramen primum: septum primum grows toward the endocardial cushions, leaving an opening between its lower edge and the endocardial cushions Foramen primum Septum Endocardiac cushion End of the 4th w

Early 5th w Small holes Foramen primum

End of the 5th w Septum primum Foramen secundum Foramen secundum Small holes fuse to form the foramen se-cundum,The foramen primum closed. Septum secundum： another membrane appears on the right of the septum primum.

The septum primum covers the foramen ovale, serves as a valve. secundum primum Foramen ovale : septum secundum extends downward to cover the foramen secundum, but leaving an opening. The septum primum covers the foramen ovale, serves as a valve. Early 6th w

Before birth, blood can flow from right atrium toward the left atrium After birth, two septums fuse , the foramen ovale closed complete, and atrium is separated into R and L atria.

Partitioning of the primitive ventricle The muscular Interventricular septum grows up from the floor of the ventricle. EC LV RV Inter-ventricular septum The 4th w

Interventricular foramen the muscular interven- tricular septum keeps growing toward endo- cardial cushions, but left an opening, called inter- ventricular foramen. EC Inter- ventricular foramen IV septum End of the 5th w

Membranous interventricular septum: Derived from right bulbar ridge, left bulbar ridge and the endocardial cushion,closes the interventricular foramen Membranous interventricular septum endocardial cushions End of the 7th w

Left ventricle Pulmonary artery Right ventricle Aorta The interventricular septum: muscular partion + membranous portion Left ventricle Pulmonary artery Right ventricle Aorta

Division of truncus arteriosus and bulbus cordis Truncal ridge Bulbar ridge The 5th w Two spiral truncal ridges/ bulbar ridges grow from the inner walls of the truncus arteriosus and bulbus cordis.

Pulmonary artery Aortico- pulmonary septum Aorta These ridges twist around each other and fuse to form a spiral aorticopulmonary septum.

The ridges spiral neatly down the truncus until they reach the ventricles.

As the same time, the division of the ventricle is completed. Aorticopulmonary septum divides truncus arteriosus and bulbus cordis into two channels: pulmonary trunk connecting to the right ventricle; aorta connecting to the left ventricle.

Blood circulation of fetus and circulatory changes after birth

Before birth Placental circulation: umbilical A. & V.

Blood circulation of fetus

Circulatory changes after birth a.Umbilical A: distal parts becomes into medial umbilical ligament, but proximal portions persist as superior vesical arteries. b. Umbilical V and ducts venousus: constrict and becomes into ligamen-tum teres hepatis and ligamentum venosus c. Ductus arteriosus: constrict and become ligamentum arteriosum d. Foramen ovale closed

Congenital defects of the cardiovascular system

Atrial septal defect An atrial septal defect (ASD) is a common congenital heart anomaly. The most common form of ASD is patent oval foramen. Consequently there is a mixing of oxygenated and deoxygenated blood.

Atrial septal defect Perforation of valve of ovale foramen Excessive resorption of the septum primum Inadequate development of the septum secundum. B+C Endocardial cushion defect with septum primum defect

Ventricular septal defect Muscular part of the ventricular septum: sparsely Membranous part of the ventricular septum defect:commonly Unfused endocardial cushion,bulbar ridge and muscular septum or over absorption of membranous septum

Patent ductus arteriosus Ductus arteriosus fails to be closed after birth. Isolated or combined with other defects. Blood will be shunted from the aorta to the lungs, eventually causing irreversible pulmonary hypertension.

Persistent truncus arteriosus Aorticopulmonary septal ridges fail to fuse and descend; Truncus overrides both ventricles; Accompanied by ventricular septal defect; Resulting in cyanotic defect.

Transposition of great vessels Aorticopulmonary septum failing to follow its spiral course and descending straight downward Aorta originates from right ventricle, pulmonary artery from left Usually combined with patent ductus arteriosus

Tetralogy of Fallot Unequal division of the truncus and bulbus A complex of 4 defects: Pulmonary stenosis Overriding aorta Ventricular septal defect Hypertrophy of the right ventricle

Key points Morphogenesis of the heart Partitioning of atrioventricular canal, autrium, ventricle, and truncus arteriosus and bulbus cordis Congenital defects of the cardiovascular system（ Tetralogy of Fallot ）

Prepare for Development of Urogenital System