Difference between revisions of "Intermediate - Primordial Heart Tube"

From Embryology
Line 8: Line 8:
  
  
The heart primordium arises predominantly from '''splanchnic mesoderm''' in the '''cardiogenic region''' of the trilaminar embryo.  The cardiogenic region can be thought of as ''bilateral fields that merge cranially'' to form a horseshoe shaped field.  During the third week of development (approximately day 18), '''angioblastic cords''' develop in this cardiogenic mesoderm and canalise to form bilateral '''endocardial heart tubes'''.
+
The heart primordium arises predominantly from '''splanchnic mesoderm''' in the '''cardiogenic region''' of the trilaminar embryo.  The cardiogenic region can be thought of as ''bilateral fields that merge cranially'' to form a horseshoe-shaped field.  During the third week of development (approximately day 18) '''angioblastic cords''' develop in this cardiogenic mesoderm and canalise to form bilateral '''endocardial heart tubes'''.
  
 
{|align=center
 
{|align=center
Line 16: Line 16:
 
|}
 
|}
  
Lateral folding of the embryo brings the heart tubes into the ventral midline allowing them to fuse to form a single primordial heart tube.  Fusion of the heart tubes begins cranially and extends caudally and is facilitated by '''apoptosis'''.  The animation below shows a cross section of the embryo, the development of the endocardial heart tubes as well as their migration and fusion in the midline.
+
Lateral folding of the embryo brings the heart tubes into the ventral midline, allowing them to fuse to form a single primordial heart tube.  Fusion of the heart tubes begins cranially and extends caudally and is facilitated by '''apoptosis'''.  The animation below shows a cross section of the embryo and the development of the endocardial heart tubes as well as their migration and fusion in the midline.
  
  
Line 29: Line 29:
  
  
After fusion ''constrictions and dilations'' appear in the heart tube forming the following divisions (listed from cranial to caudal position):
+
After fusion, ''constrictions and dilations'' appear in the heart tube, forming the following divisions (listed from cranial to caudal position):
  
 
* '''Truncus arteriosus'''
 
* '''Truncus arteriosus'''
Line 43: Line 43:
  
  
In the previous animation, you saw that the '''dorsal aortae''' developed concurrently with the endocardial heart tubes and form a cranial connection with the endocardial heart tubes prior to folding.  As the embryo folds the cranial ends of the dorsal aortae are pulled ventrally until they form a dorsoventral loop, the first '''aortic arch arteries'''.  The embryonic vascular system is discussed in further detail [[Intermediate_-_Vascular_Overview|here]].
+
In the previous animation you saw that the '''dorsal aortae''' develop concurrently with the endocardial heart tubes and form a cranial connection with the endocardial heart tubes prior to folding.  As the embryo folds, the cranial ends of the dorsal aortae are pulled ventrally until they form a dorsoventral loop: the first '''aortic arch arteries'''.  The embryonic vascular system is discussed in further detail [[Intermediate_-_Vascular_Overview|here]].
  
 
==Heart Layers==
 
==Heart Layers==

Revision as of 13:27, 6 November 2009

Intermediateicon.jpg
Begin Intermediate: Primordial Heart Tube  Heart Tube Looping  Atrial Ventricular Septation  Outflow Tract  Heart Valves  Cardiac Abnormalities  Vascular Overview


Cardiac Embryology     Begin Basic     Begin Intermediate     Begin Advanced  


HeartILP draft itimeline.jpg


The heart primordium arises predominantly from splanchnic mesoderm in the cardiogenic region of the trilaminar embryo. The cardiogenic region can be thought of as bilateral fields that merge cranially to form a horseshoe-shaped field. During the third week of development (approximately day 18) angioblastic cords develop in this cardiogenic mesoderm and canalise to form bilateral endocardial heart tubes.

Dorsal view of 18 day embryo
File:HeartILP draft HeartTubeLateral.jpg
Lateral view of 18 day embryo

Lateral folding of the embryo brings the heart tubes into the ventral midline, allowing them to fuse to form a single primordial heart tube. Fusion of the heart tubes begins cranially and extends caudally and is facilitated by apoptosis. The animation below shows a cross section of the embryo and the development of the endocardial heart tubes as well as their migration and fusion in the midline.


<Flowplayer height="564" width="720" autoplay="false">Heart folding 003.flv</Flowplayer>


File:HeartILP draft brightfieldtubefusion.jpg
Brightfield images showing fusion of the heart tubes and the earliest appearance of segments of the fused heart tube
Early divisions of the heart tube


After fusion, constrictions and dilations appear in the heart tube, forming the following divisions (listed from cranial to caudal position):

  • Truncus arteriosus
  • Bulbus cordis
  • Primordial ventricle
  • Primordial atrium
  • Sinus venosus

The sinus venosus is also divided into two parts: the right horn of the sinus venosus and the left horn of the sinus venosus.


By day 22, coordinated contractions of the heart tube are present and push blood cranially from the sinus venosus.


In the previous animation you saw that the dorsal aortae develop concurrently with the endocardial heart tubes and form a cranial connection with the endocardial heart tubes prior to folding. As the embryo folds, the cranial ends of the dorsal aortae are pulled ventrally until they form a dorsoventral loop: the first aortic arch arteries. The embryonic vascular system is discussed in further detail here.

Heart Layers

Myocardium: forms from splanchnic mesoderm surrounding the pericardial coelom. Additional myocardial cells are added to the outflow tract during heart looping.

Cardiac Jelly: gelatinous connective tissue separating the myocardium and heart tube endothelium.

Endocardium: forms from the endothelium of the heart tube.

Epicardium: develops from mesothelial cells arising from the sinus venosus which spread cranially over the myocardium.


File:HeartILP draft heartlayers.jpg
Cross-section through the ventricular section of the heart tube


Back to the intermediate homepage Next: Looping of the Heart Tube
Go to this section in the basic level Go to this section in the advanced level