(Shrinked) Dev Of Heart I 2007

Heart Development I

Dr. J.K. Brueckner

Anatomy and Neurobiology

jbrueck@uky.edu

The cardiovascular system is the first body system to function in the embryo. Formation of the primitive heart and vascular system begins during week 3 and the heart starts beating by the beginning of week 4. This precocious cardiac development is necessary because diffusion becomes insufficient to satisfy the rapidly growing embryo by week 4. Functionally, the embryonic heart must act as a single pump that maintains blood flow through the body into the placenta where fetal wastes are exchanged for oxygen and nutrients. It must be prepared, however, for the radical changes that occurs at birth when the placental circulation is abruptly cut off and breathing is initiated.

Heart Development

Heart Development

Heart development: Construction of the primitive heart tube

Heart development begins during week 3. At the rostral end of the embryonic body in an area called the cardiogenic region, mesodermal cells aggregate to form longitudinal cellular strands termed angioblastic cords. These cords are located ventral to the pericardial coelom. The angioblastic cords canalize (hollow out) to form two parallel endocardial heart tubes.

Heart Development

Heart development: Construction of the primitive heart tube

Heart development begins during week 3. At the rostral end of the embryonic body in an area called the cardiogenic region, mesodermal cells aggregate to form longitudinal cellular strands termed angioblastic cords. These cords are located ventral to the pericardial coelom. The angioblastic cords canalize (hollow out) to form two parallel endocardial heart tubes.

Heart Development

Heart development: Construction of the primitive heart tube

Heart development begins during week 3. At the rostral end of the embryonic body in an area called the cardiogenic region, mesodermal cells aggregate to form longitudinal cellular strands termed angioblastic cords. These cords are located ventral to the pericardial coelom. The angioblastic cords canalize (hollow out) to form two parallel endocardial heart tubes.

Heart Development

Heart development: Construction of the primitive heart tube

Heart development begins during week 3. At the rostral end of the embryonic body in an area called the cardiogenic region, mesodermal cells aggregate to form longitudinal cellular strands termed angioblastic cords. These cords are located ventral to the pericardial coelom. The angioblastic cords canalize (hollow out) to form two parallel endocardial heart tubes.

Heart Development

Heart development: Construction of the primitive heart tube

Heart development begins during week 3. At the rostral end of the embryonic body in an area called the cardiogenic region, mesodermal cells aggregate to form longitudinal cellular strands termed angioblastic cords. These cords are located ventral to the pericardial coelom. The angioblastic cords canalize (hollow out) to form two parallel endocardial heart tubes.

Heart Development

Heart development: Construction of the primitive heart tube

Heart development begins during week 3. At the rostral end of the embryonic body in an area called the cardiogenic region, mesodermal cells aggregate to form longitudinal cellular strands termed angioblastic cords. These cords are located ventral to the pericardial coelom. The angioblastic cords canalize (hollow out) to form two parallel endocardial heart tubes.

Heart Development

Embryonic folding brings the two endocardial tubes into the thorax where they meet along midline and fuse to form a single tube. Fusion of the endocardial tubes begins at the cranial end of the heart and proceeds caudally. Impact of Lateral Folding on Early Heart Development

Angioblastic cords

Heart Development

Embryonic folding brings the two endocardial tubes into the thorax where they meet along midline and fuse to form a single tube. Fusion of the endocardial tubes begins at the cranial end of the heart and proceeds caudally. Impact of Lateral Folding on Early Heart Development

Endocardial tubesAngioblastic cords

Heart Development

Embryonic folding brings the two endocardial tubes into the thorax where they meet along midline and fuse to form a single tube. Fusion of the endocardial tubes begins at the cranial end of the heart and proceeds caudally. Impact of Lateral Folding on Early Heart Development

Angioblastic cords Endocardial tubes

Heart Development

Embryonic folding brings the two endocardial tubes into the thorax where they meet along midline and fuse to form a single tube. Fusion of the endocardial tubes begins at the cranial end of the heart and proceeds caudally. Impact of Lateral Folding on Early Heart Development

Angioblastic cords Endocardial tubes

Heart Development

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium).

Angioblastic cords Endocardial tubes

Heart Development

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium).

Angioblastic cords Endocardial tubes

Heart Development

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium).

Angioblastic cords Endocardial tubes

Heart Development

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium).

Angioblastic cords Endocardial tubes

Splanchnic mesoderm

Heart Development

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium).

Angioblastic cords Endocardial tubes

Splanchnic mesoderm

Somatic mesoderm

Heart Development

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium). Also forms visceral pericardium

Angioblastic cords Endocardial tubes

Splanchnic mesoderm

Somatic mesoderm

Heart Development

Angioblastic cords Endocardial tubes

Splanchnic mesoderm

Somatic mesoderm

Parietal pericardium

The fused endocardial tubes form the inner lining of the heart (endocardium). As the heart tubes fuse, the mesoderm surrounding the pericardial coelom forms two layers: a thick, inner gelatinous matrix (cardiac jelly) and an outer muscular layer (myocardium). Also forms visceral pericardium

As the heart elongates and bends it gradually invaginates into the pericardial cavity. It is initially suspended from the dorsal wall by dorsal mesocardium, but this degenerates, forming a communication (transverse pericardial sinus) between left and right sides of the pericardial cavity. As a result, the heart is anchored only at its cranial and caudal ends.

Heart Development

Angioblastic cords Endocardial tubes

Splanchnic mesoderm

Somatic mesoderm

Parietal pericardium

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Concurrent with embryonic folding, the tubular heart elongates and develops dilations and series of constrictions that subdivide the primitive heart.

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Concurrent with embryonic folding, the tubular heart elongates and develops dilations and series of constrictions that subdivide the primitive heart.

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood enters the caudal end of the tube, the sinus venosus (which receives blood from 1. the body via the common cardinal veins 2. the placenta via the umbilical veins 3. the yolk sac via the vitelline veins).

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood enters the caudal end of the tube, the sinus venosus (which receives blood from 1. the body via the common cardinal veins 2. the placenta via the umbilical veins 3. the yolk sac via the vitelline veins).

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood enters the caudal end of the tube, the sinus venosus (which receives blood from 1. the body via the common cardinal veins 2. the placenta via the umbilical veins 3. the yolk sac via the vitelline veins).

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v. Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood enters the caudal end of the tube, the sinus venosus (which receives blood from 1. the body via the common cardinal veins 2. the placenta via the umbilical veins 3. the yolk sac via the vitelline veins).

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v. Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood enters the caudal end of the tube, the sinus venosus (which receives blood from 1. the body via the common cardinal veins 2. the placenta via the umbilical veins 3. the yolk sac via the vitelline veins).

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

From the sinus venosus, blood flows cranially into the primitive atrium. From the atrium, blood enters the primitive ventricle.

Post. Cardinal v.

Umbilical v. Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

From the sinus venosus, blood flows cranially into the primitive atrium. From the atrium, blood enters the primitive ventricle.

Post. Cardinal v.

Umbilical v. Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Post. Cardinal v.

Umbilical v. Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

From the ventricle, blood is pumped to the bulbis cordis which drains into truncus arteriosus. The truncus is continuous cranially with the expanded aortic sac from which the aortic arches arise.

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Post. Cardinal v.

Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood flows from the aortic arches into the dorsal aortae in order to reach the embryonic body, the placenta and the yolk sac.

Heart DevelopmentDorsal aorta

Ant. Cardinal v.

Post. Cardinal v.

Umbilical v.Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Post. Cardinal v.

Umbilical a.

Vitelline v.

Vitelline a.

Aortic arches

Cranial capillaries

Sinus venosus

Atrium

Ventricle

Bulbis cordis

Truncus arteriosus

Aortic arches

Blood flows from the aortic arches into the dorsal aortae in order to reach the embryonic body, the placenta and the yolk sac.

• Folding of the primitive heart tube brings the four putative chambers of the adult heart into the correct spatial relationship with one another.

Heart Development

Heart Development

•As the heart tube begins to lengthen, it bulges and bends to the right within the pericardial cavity.

•The bulbis cordis and ventricle grow faster than other regions, initiating folding of the tubular heart.

•Bulbis cordis moves inferiorly, ventrally, and to the right.

•Primitive ventricle moves to the left, while the primitive atrium moves posteriorly and superiorly.

•Bending of the heart tube also partitions the sinus venosus into right and left horns and it gradually shifts to the right to empty into the right atrium.

Heart Development

• In isolated dextrocardia, the heart is abnormally positioned on the right side of the thorax and is associated with other severe cardiac anomalies.

• Dextrocardia with situs inversus accompanies inversion of other viscera such as the liver and is not associated with other cardiac anomalies.

Heart Development

Atrial Wall Remodeling

Right atrial wall: The right side of the sinus venosus is incorporated into the right posterior wall of the primitive atrium, displacing the original right half ventrally and to the right. The portion of the atrium that consists of the incorporated sinus venosus is called the sinus venarum, while the original right side of the primitive atrium becomes the right auricle.

Heart Development

Primitive atrium

Atrial Wall Remodeling

Right atrial wall: The right side of the sinus venosus is incorporated into the right posterior wall of the primitive atrium, displacing the original right half ventrally and to the right. The portion of the atrium that consists of the incorporated sinus venosus is called the sinus venarum, while the original right side of the primitive atrium becomes the right auricle.

Heart Development

Primitive atrium

Left atrial wall: During week 4, the primitive atrium sprouts a pulmonary vein that divides to produce a total of 4 pulmonary veins that grow toward the lungs where they anastomose with veins developing in the mesoderm around the bronchial buds. Much of the left atrial wall is formed by the incorporation of the primitive pulmonary vein and its branches, giving it a smooth appearance. The trabeculated left side of the primitive atrium is displaced to the left where it becomes the left auricle.

Heart Development

Primitive atrium

Left atrial wall: During week 4, the primitive atrium sprouts a pulmonary vein that divides to produce a total of 4 pulmonary veins that grow toward the lungs where they anastomose with veins developing in the mesoderm around the bronchial buds. Much of the left atrial wall is formed by the incorporation of the primitive pulmonary vein and its branches, giving it a smooth appearance. The trabeculated left side of the primitive atrium is displaced to the left where it becomes the left auricle.

Heart Development

Primitive atrium

Heart Development

Embryonic structure

Adult Derivative/s

Primitive atria Auricles of right and left atria

Right horn of sinus venosus

Smooth part of the right atrium (sinus venarum)

Left horn of sinus venosus

Coronary sinus

Primitive pulmonary veins

Smooth part of left atrium

Conus cordis (upper bulbis cordis)

Outflow tract for both ventricles: conus arteriosus (infundibulum) for right ventricle and aortic vestibule just below aortic valve for left ventricle

Bulbis cordis Trabeculated right ventricle

Primitive ventricle

Trabeculated left ventricle

Truncus arteriosus

Ascending aorta and pulmonary trunk

Heart Development

Partitioning the primitive heart

As the heart is bending and enlarging, its original single chamber begins to be partitioned in order to separate the systemic and pulmonary circulations. Four sets of partitions form simultaneously in the atrium and the ventricle during weeks 4-5. These partitions will separate:

1) the atria from the ventricles 2) the right and left atria 3) the right and left ventricles 4) the pulmonary trunk and ascending aorta

Heart DevelopmentPartitioning atria from ventricles

There is a large single passageway between the primitive atrium and the primitive ventricle (atrioventricular canal). During week 4, swellings (endocardial cushions) develop on the walls of the primitive heart at the level of the atrioventricular canal.

Atrioventricular septum

Rt. AV orifice

Lt. AV orifice

RA LA

RV LV

Sagittal sections Coronal section

Atrioventricular septum

A

V

BC

Endocardial cushion

A

Ventricle

BC

Primitive AV canal

Endocardial cushions

Heart DevelopmentPartitioning atria from ventricles

There is a large single passageway between the primitive atrium and the primitive ventricle (atrioventricular canal). During week 4, swellings (endocardial cushions) develop on the walls of the primitive heart at the level of the atrioventricular canal.

Atrioventricular septum

Rt. AV orifice

Lt. AV orifice

RA LA

RV LV

Sagittal sections Coronal section

Atrioventricular septum

A

V

BC

Endocardial cushion

A

Ventricle

BC

Primitive AV canal

Endocardial cushions

Heart DevelopmentPartitioning atria from ventricles

There is a large single passageway between the primitive atrium and the primitive ventricle (atrioventricular canal). During week 4, swellings (endocardial cushions) develop on the walls of the primitive heart at the level of the atrioventricular canal.

Atrioventricular septum

Rt. AV orifice

Lt. AV orifice

RA LA

RV LV

Sagittal sections Coronal section

Atrioventricular septum

A

V

BC

Endocardial cushion

A

Ventricle

BC

Primitive AV canal

Endocardial cushions

Heart Development

Atrioventricular septum

Rt. AV orifice

Lt. AV orifice

RA LA

RV LV

Sagittal sections Coronal section

Atrioventricular septum

A

V

BC

Endocardial cushion

A

Ventricle

BC

Primitive AV canal

Endocardial cushions

The endocardial cushions grow toward one another and fuse medially, dividing the AV canal into a right and left atrioventricular openings. The endocardial cushions do not run the entire length of the heart. The atrioventricular valves (left bicuspid/mitral valve and right tricuspid valve) are formed later by fibrosis and thinning of the endocardial cushion tissue.

Heart Development

Atrioventricular septum

Rt. AV orifice

Lt. AV orifice

RA LA

RV LV

Sagittal sections Coronal section

Atrioventricular septum

A

V

BC

Endocardial cushion

A

Ventricle

BC

Primitive AV canal

Endocardial cushions

The endocardial cushions grow toward one another and fuse medially, dividing the AV canal into a right and left atrioventricular openings. The endocardial cushions do not run the entire length of the heart. The atrioventricular valves (left bicuspid/mitral valve and right tricuspid valve) are formed later by fibrosis and thinning of the endocardial cushion tissue.

Heart Development

Endocardialcushion

Endocardialcushion

Atrioventricular canal

Heart Development

The endocardial cushions also participate in formation of the membranous portion of the interventricular septum and in closure of foramen primum. In ultrasonography, this region appears as a cross, with the atrial and ventricular septa forming the post and the endocardial cushions forming the horizontal cross bar. The integrity of this cross is an important sign in cardiac ultrasounds. If the cushions fail to fuse, the result is persistent atrioventricular canal.

Heart Development

Heart Development