1. HEART TUBE & PERICARDIUM
Dr. Mujahid Khan

2. Early Development of Heart
The earliest sign of heart is the appearance of paired endothelial strands called angioblastic cords
They develop in the cardiogenic mesoderm during the third week
These cords canalize to form heart tubes
These cords fuse together to form the tubular heart late in the third week

3. Early Development of Heart
Primordium of heart is first evident at 18 days in the cardiogenic area
The heart begins to beat at days
Blood flow begins during the fourth week and can be visualized by Doppler ultrasonography

5. Development of Heart
The endocardial heart tubes approach each other and fuse to form a single heart tube after lateral folding
Fusion of tubes begins at the cranial end of the developing heart and extends caudally

6. Primordial Myocardium
As the heart tubes fuse, an external layer of the embryonic heart, the primordial myocardium is formed from splanchnic mesoderm around pericardial coelom
At this stage the developing heart is composed of a thin endothelial tube, separated from thick muscular tube by gelatinous connective tissue, cardiac jelly

7. Endocardium
The endothelial tube becomes the internal endothelial lining of the heart, called endocardium
The primordial myocardium becomes the muscular wall of the heart or myocardium
The visceral pericardium or epicardium is derived from mesothelial cells and spread over the myocardium

8. After Folding As folding of head region occurs
The heart and pericardial cavity come to lie ventral to the foregut and caudal to the oropharyngeal membrane

10. Fate of Heart Tubes
The tubular heart elongates and develops alternate dilations and constrictions:
Truncus Arteriosus
Bulbus Cordis
Ventricle
Atrium
Sinus venosus

12. Fate of Heart Tubes
As the developing heart elongates and bends, it gradually invaginates into the pericardial cavity
Initially suspended from the dorsal wall by a mesentery, the dorsal mesocardium
Central part of this mesentery soon degenerates
Heart is now attached only at its cranial and caudal ends

13. Truncus Arteriosus
Is continuous cranially with the aortic sac, from which the aortic arches arise
The sinus venosus receives umbilical, vitelline, and common cardinal veins from the chorion, yolk sac, and embryo respectively
Bulbus cordis and ventricle grow faster than other regions, the heart bends upon itself, forming bulboventricular loop

15. Truncus Arteriosus
As the primordial heart bends, the atrium and sinus venosus come to lie dorsal to the truncus arteriosus, bulbus cordis, and ventricle
By this stage the sinus venosus has developed lateral expansions, the right and left horns of the sinus venosus

17. Pericardial Cavity
As the heart elongates and bends, it gradually invaginates into the pericardial cavity
The heart is initially suspended from the dorsal wall by a mesentery, the dorsal mesocardium
The central part of the mesentery soon degenerates
Forms a communication, the transverse pericardial sinus between the right and left sides of the pericardial cavity

20. Pericardial Cavity
During the fourth week three well defined body cavities are formed:
Pericardial cavity
2 pericardioperitoneal canals
Peritoneal cavity

21. Pleuropericardial Membranes
As the pleuropericardial folds enlarge, they form partitions that separate the pericardial cavity from the pleural cavities
As the primordial pleural cavities expand ventrally around the heart, they extend into the body wall, splitting the mesenchyme into:
An outer layer that becomes the thoracic wall
An inner layer becomes the fibrous pericardium, the outer layer of the pericardial sac enclosing the heart