Development of the heart
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Development of the heart. Dr Rania Gabr. oBJECTIVES. Describe the formation and position of the heart tube. Explain the mechanism of formation of the cardiac loop. Discuss the development of sinus venosus . Explain how cardiac septa are formed.

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Objectives
oBJECTIVES

  • Describe the formation and position of the heart tube.

  • Explain the mechanism of formation of the cardiac loop.

  • Discuss the development of sinus venosus.

  • Explain how cardiac septa are formed.

  • Describe the septum formation in the common atrium.

  • Discuss the septum formation in the Atrioventricular canal.

  • Discuss the septum formation in the Truncusarteriosus and BulbusCordis

  • Describe the septum formation in the ventricles.


Angiogenesis
Angiogenesis

  • The vascular system as well as the blood elements are Mesodermal in origin.

  • The splanchnic mesodermal cells proliferate and form cell clusters called “angiogenic clusters” or “blood islands” which lie in front and on either side of the anterior part of the embryonic disc.


Formation of the Cardiogenic field

Clusters of angiogenetic cells form a "horseshoe-shaped" cluster anterior and lateral to the brain plate.


- The clusters form endothelial vessels which fuse to form the right and left endocardial heart tubes

- As a result of folding of embryo in transverse direction the two endocardial heart tubes come close to each other and fuse to form single endocardial tube


Origin of the heart tube
Origin of the heart tube:

Mesoderm of the cardiogenic plate at the 3rd week.



Development:

  • It starts by the formation of 2 heart tubes each has a cranial end and a caudal end.

  • The cranial end is the arterialend and is connected to the aortic sac then to dorsal aorta,

  • and the caudal end which is the venous end, (embedded in the septum transversum).


  • This venous end (caudal end) receives 3 veins for each tube; they are:

    1- umbilical,

    2- vitellineand

    3- common cardinal veins.

  • - Fusion of the 2 heart tubes occurs. This fusion occurred in a cranio-caudal direction leads to the formation of single heart tube.


Lateral folding

Lateral folding results in fusion of the caudal portion of the paired endocardial tubes


Pericardial cavity

Dorsal mesocardium


  • The heart tube continues to elongate forming the cardiac loop.

  • -The cardiac loop invaginates in the pericardial cavity.

  • -Hence the heart is covered by 2 layers of the pericardium: visceral layer internally and parietal one externally and in between lies the pericardial cavity.

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Parts of the heart tube

1 into st aortic arch

Parts of the Heart Tube

Chambers of the heart tube:

  • Three grooves are formed in the tube will form four chambers:

  • Sinus venosus, Primitive atrium, Primitive ventricle and Bulbuscordis.


  • - At the into venous end another groove appears and separates the atrial part from the sinus venosus. This groove is called

  • 3-sino-atrial groove..


Truncus arteriosus
Truncus into arteriosus

  • Cranial to the bulbuscordis appears the Truncusarteriosus,

  • Its cranial part dilates to form the aortic sac

  • This sac is connected to the dorsal aorta by the six aortic arches on each side


--- into “S”-shaped heart:

The heart tube continues to grow and bend, atrium shifts in the dorso-cranial direction; sinus venoususlocated at caudal portion of atrium.


Development of the sinus venosus
Development into of the sinus venosus

  • The sinus venosus receives venous blood from the right and the left horns.

  • Again each horn receives 3 veins: umbilical-vitelline and common cardinal veins.

  • The sinus is widely connected to the primitive atrium. through the Sino-atrial orifice.

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  • Venous blood drainage into shifts from left to the right side.

  • The communication between the sinus and the atrium is shifted to the right.

  • The right umbilical vein and the left vitelline vein are obliterated during 5thweek

  • Left common cardinal vein is obliterated at 10th week.

  • The left sinus horn regresses, and what remains only oblique vein of left atrium and coronary sinus.

  • Right sinus horn is enlarged and incorporated into the right atrium, to form the smooth-walled part of right atrium.


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