Development of the Circulatory System Development of cardiovascular system Development of lymphatic vascular system

overview The cardiovascular system is derived from the mesoderm. It appears in the middle of the 3rd week. Blood circulation starts by the end of the 3rd week. Some changes take place at birth and in the 1st postnatal month.

Key points Development of primitive cardiovascular system Development of Heart Formation and modification of aortic arches Circulation before and after birth Congenital Malformations ※

Primitive Cardiovascular System Oropharyngeal membrane Cardiogenic area

Primitive cardiovascular system Yolk sac mesenchyme cells blood islands Central C Peripheral C Primitive Blood cell Endothelia C Blood C Vessels Endothelial tubes of intraembryo and extraembryo are connected with each other by body stalk.

primitive cardiovascular system Yolk sac mesenchyme cells blood islands Central C Peripheral C Primitive Blood cell Endothelia C Blood C Vessels Vessels net primitive cardiovascular system

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

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

① heart tube ② arteries ③ veins 1 pair of anterior cardinal V A cardinal V Posterior Vitelline V Common cardinal V Umbilical V 20d 4w End of 4w ① heart 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 heart

Three separate circulations vitelline, umbilical and embryonic circulation.

Development of the Heart ►Development of the heart tube ► Morphogenesis of the heart ► Partitioning of Heart Chambers ► Development of sinus venosus and differentiation of veins

Development of the heart tube Cardiogenic area Oropharyngeal membrane Cardiogenic area is anterior to the oropharyngeal membrane and the neural plate.

Development of the heart tube Pericardial cavity Buccopharyngeal M cardiaogenic plate About 18~19d, a cavity appears in the cardiogenic area --pericardiac cavity B. Ventral of the cavity is cardiaogenic cords --cardiaogenic plate

Development of the heart tube Pericardial cavity cardiac tube The 20th d C. cardiaogenic plate becomes hollow--cardiac tube

Development of the heart tube Pericardial cavity cardiac tube The 22nd d D. As the embryo folds cephalocaudally, the developing heart tube bulges more and more into the pericardial cavity.

Development of the heart tube Pericardial cavity cardiac tube The 28th d E. The paired heart tubes merge except at their caudalmost ends. F. The tube remains attached to the dorsal side of the pericardial cavity by the dorsal mesocardium.

Development of the heart tube Caudal end Cephalic end Heart tube Pericardial cavity G. Cephalic end  Arteries，Caudal end  Veins

Pericardial cavity

Wall of primitive heart tube Endocardial heart tube → endocardium Myoepicardial mantle → myocardium, epicardium Cardiac jelly → subendocardial tissue

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

Morphogenesis of the heart atrium ventricle bulbus cordis C. Heart tubes almost merged D. Three expansions bulbus cordis(心球) Ventricle(心室) Atrium(心房) The 22nd d

Morphogenesis of the heart truncus arteriosus E. The 4th expansion, the sinus venosus(静脉窦) appears F. The truncus arteriosus(动脉干)appears G. The heart tube starts to bend bulbus cordis ventricle atrium sinus venosus The 23rd d

Morphogenesis of the heart The cephalic portion bends ventrally, caudally, and to the right. The caudal part shifts dorsocranially and to the left. Form a ‘U’ like structure, the cardiac loop (bulboventricular loop). truncus arteriosus Bulboventricular loop Sinus venosus The 24th d

Morphogenesis of the heart I. The bulboventricular loop keeps turning, the atrium shifts to the cephalodorsal of the ventricle G. Two atria and two ventricles Aortic arches atrium ventricle The 35th d The normal heart shape was established, but partitioning has not completed

Development of the Heart ►Development of the heart tube ► Morphogenesis of the heart ► Partitioning of Heart Chambers ► Development of sinus venosus and differentiation of veins

Partitioning of Heart Chambers ►Division of atrioventricular canal ► Partitiioning of the primitive atrium ► Partitioning of the primitive ventricle ► Division of truncus and bulbus

Subendocardial tissue → dorsal and ventral endocardial cushions → fuse → right and left canals

Septum formation in part arises from development of endocardial cushion. Many malformations are related to abnormal cushion morphogenesis. atria Endocardiac cushion ventricle The 4th w

The 5th w Fusion of the opposing superior and inferior cushions divides the orifice into R and L aterioventricular canals. Endocardiac cushion L AV orifice R AV orifice The 5th w

The 4th month Left biscuspid Right tricuspid bicuspid tricuspid Endocardiac cushion Left Right biscuspid tricuspid bicuspid tricuspid The 4th month

Partitioning of Heart Chambers ►Division of atrioventricular canal ► Partitiioning of the primitive atrium ► Partitioning of the primitive ventricle ► Division of truncus and bulbus

A. Septum primum(原发隔/第一房间隔) grows down and fuses with the EC. B. There is a small opening between the two chambers, foramen primum (原发孔) Septum primum foramen primum Endocardiac cushion The 4th w

Early 5th w C. The foramen primum hasn’t closed. D. There are few small holes on the septum primum. Small holes foramen primum Early 5th w

Septum secundum E. Septum secundum (继发隔/第二房间隔)appears on the right of the septum primum. F. Small holes fuse to form the foramen secundum(继发孔/第二房间孔). G. The foramen primum closed. Foramen secundum Septum primum End of the 5th w

Septum secundum Foramen secundum H. Septum secundum extends downward to cover the foramen secundum, but leaving an opening, foramen ovale(卵圆孔) I. The septum primum covers the foramen ovale, serves as a valve. Septum primum Foramen ovale Early 6th w

G. Blood L atrium R R L atrium K. After birth, the foramen ovale closed complete, and atrium is separated into R and L atria.

Partitiioning of the primitive atrium

Partitioning of Heart Chambers ►Division of atrioventricular canal ► Partitiioning of the primitive atrium ► Partitioning of the primitive ventricle ► Division of truncus and bulbus

The muscular Interventricular septum(室间隔肌部) grows up from the floor of the ventricle. EC LV RV Inter-ventricular septum The 4th w

B. The muscular interventricular septum keeps growing up, an interventricular foramen(室间孔) remains. EC Inter- ventricular foramen IV septum End of the 5th w

C. Membranous interventricular septum(室间隔膜部) derived from the EC, closes the interventricular foramen. EC Membranous IV septum IV septum End of the 7th w

Left ventricle Pulmonary artery Right ventricle Aorta The interventricular septum=muscular part + membranous portion Left ventricle Pulmonary artery Right ventricle Aorta

Partitioning of Heart Chambers ►Division of atrioventricular canal ► Partitiioning of the primitive atrium ► Partitioning of the primitive ventricle ► Division of truncus and bulbus

truncal ridge Truncus arteriosus bulbar ridge Bulbus cordis The 5th w truncal ridge Truncus arteriosus bulbar ridge Bulbus cordis A. Two spiral truncal ridges(动脉干嵴)/ bulbar ridges(心球嵴) grow from the inner walls of the truncus arteriosus and bulbus cordis.

C. Truncal ridges + Bulbar ridges → aorticopulmonary septum Aorta pulmonary Aortico- pulmonary septum B. These ridges grow into the truncus from either side and fuse in the middle. C. Truncal ridges + Bulbar ridges → aorticopulmonary septum

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

E. Aorticopulmonary septum divides the bulbus and truncus into two channels: pulmonary trunk connecting to the right ventricle; aorta connecting to the left ventricle.

F. As the same time, the division of the ventricle is completed.

Development of the Heart ►Development of the heart tube ► Morphogenesis of the heart ► Partitioning of Heart Chambers ► Development of sinus venosus and differentiation of veins

Three separate circulations vitelline, umbilical and embryonic circulation.

卵黄静脉 Ductus venosus （肝血窦） 门静脉

Primitive plumary vein

Formation and modification of aortic arches

Circulation before and after birth

Before birth Placental circulation: umbilical A. & V.

80% O2 saturation 58%

After birth Umbilical arteries→ lateral umbilical ligaments Umbilical vein → ligamentum teres hepatis Ductus venosus → venous ligament Ductus arteriosus → arterial ligament Foramen ovale → oval fossa

胎儿出生后血液循环的变化 胎盘血循环中断→下腔静脉和右心房的血压下降 肺开始呼吸（肺充气）→肺血管阻力显著下降→肺血流量明显增加 →左心房的血压高于右心房 脐动脉：大部分→脐侧韧带； 近侧段→膀胱上动脉 脐静脉→肝圆韧带 静脉导管→静脉韧带 动脉导管→动脉韧带 (生后 3 个月左右) 卵圆孔→卵圆窝 (生后 1 年左右)

Atrial septal defect(房间隔缺损 ) Primum type involves the endocardial cushions. Secundum type involves septum primum or septum secundum. There is communication between the right and left atria which causes a left to right shunting of blood due to the lower pressure in the pulmonary circulatory system. Consequently there is a mixing of oxygenated (systemic) and deoxygenated (pulmonary) blood.

Ventricular septal defect(室间隔缺损 ) Defect of the membranous septum, isolated or associated with other abnormalities. There is a massive left to right shunting of blood and pulmonary hypertension.

Tetralogy of Fallot(法洛四联症) Unequal division of truncus and bulbus : a large aorta a smaller pulmonary trunk (1) Pulmonary stenosis (2) Overriding aorta (the aorta straddles the VSD) (3) Ventricular septal defect (VSD) of the membranous portion (4) The walls of the right ventricle to expand. right ventricular hypertrophy due to the shunting of blood from left to right.

Patent ductus arteriosus(动脉导管未闭) Ductus arteriosus fails to be closed after birth. Blood will be shunted from the aorta to the lungs, eventually causing irreversible pulmonary hypertension.

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