40 Questions
What is the result of the partitioning and septation of the heart tubes?
Formation of the separate 4 chambers of the heart
During which days of development do the major septa of the heart form?
Between 27th and 37th days
What is the result of the proximal part of the bulbus cordis becoming incorporated into the right ventricle?
Formation of the infundibulum
What is the result of the partitioning of the atrioventricular canal?
Separation of the atria and ventricles
What is the function of the endocardial cushions?
To partition the atrioventricular canal
What is the term for the open tube in which both atria and both ventricles are open to each other?
Developing heart tube
What is the term for the part of the bulbus cordis that becomes incorporated into the left ventricle?
Aortic vestibule
How many steps are involved in the process of septation and partitioning of the heart?
4 simultaneous steps
What develops from the left half of the primitive atrium?
Anterior rough part of the left atrium and left auricle
What is the origin of the ventral smooth part of the left atrium?
Left half of atrioventricular canal
What is the process shown in Figure 12.16?
Absorption of pulmonary veins
What is the origin of the rough part of the left ventricle?
Corresponding primitive ventricle
What develops from the conus cordis and the proximal part of the bulbus cordis?
Smooth part of each ventricle
What is the significance of Figure 12.18?
Shows the development of the ventricles from day 21 to day 50
What is shown in Figure 12.17?
The parts of the left atrium in relation to their origins from the fetal left atrium
What is the developmental origin of the posterior smooth part of the left atrium?
Absorption of pulmonary veins
What is the origin of the two endocardial cushions in the heart tube?
From the extracellular matrix of the cardiac jelly
Where do the two endocardial cushions appear in the AV canal?
On the dorsal and ventral walls
What is the result of the fusion of the two endocardial cushions?
Formation of the septum intermedium
What type of transformation do the cells from the endocardium undergo to become mesenchymal cells?
Epithelial-mesenchymal transformation
What is the layer of tissue that separates the myocardium and endocardium?
Cardiac jelly
What is the name of the structure that is formed by the fusion of the two endocardial cushions?
Septum intermedium
During which week of development do the endocardial cushions approach and fuse?
Fifth week
What is the result of the fusion of the endocardial cushions on the AV canal?
Division of the AV canal into right and left halves
From which tissue does the sinoatrial node develop during the 5th week of IUL?
Mesodermal tissue
What is the final location of the sinoatrial node after the incorporation of sinus venosus into the right atrium?
In the wall of the right atrium near the opening of the SVC
What is the origin of the AV node and AV bundle?
Cells in the left wall of the sinus venosus and AV canal
What is the origin of the fibrous pericardium?
Somatopleuric mesoderm and septum transversum
What is the other name for the visceral pericardium?
Epicardium
What are the three layers of the heart tube?
Endocardium, myocardium, and visceral pericardium
What is the name of the fold of mesodermal tissue that initially attaches the heart tube to the dorsal side of the pericardial cavity?
Dorsal mesocardium
What structure connects both sides of the pericardial cavity after the middle section of the dorsal mesocardium disappears?
Transverse pericardial sinus
What happens to the pressure in the left atrium immediately after birth?
It increases
What is the result of the valve of the oval foramen being pressed against the septum secundum?
Physiological closure of the foramen ovale
What is the name of the opening between the free edge of the IV septum and the fused endocardial cushions?
IV foramen
By what week does the IV foramen usually close?
Seventh week
What are the three parts of the interventricular septum?
Muscular, bulbar, and membranous parts
What develops from the proliferation of AV cushion?
Membranous part of the interventricular septum
What is the shape of the upper free margin of the muscular part of the interventricular septum?
Concave
What is the result of the active proliferation of mesenchymal cells in the walls of the bulbus cordis?
Formation of the bulbar ridges
Study Notes
Development of the Left Atrium
- The anterior rough part of the left atrium and left auricle develop from the left half of the primitive atrium.
- The posterior smooth part (between the openings of the pulmonary veins) develops from the absorption of pulmonary veins.
- The ventral smooth part develops from the left half of the atrioventricular canal.
Development of the Ventricles
- Each ventricle develops from two parts:
- A rough part from the corresponding primitive ventricle.
- A smooth part (the outflow portion of each ventricle), derived from the conus cordis and the proximal part of the bulbus cordis.
Partitioning and Septation of the Primordial Heart
- Septation and partitioning of the heart tubes result in the formation of the separate 4 chambers of the heart and septation of the outflow.
- The major septa of the heart are formed between the 27th and 37th days of development.
Partitioning of the Atrioventricular Canal
- Partitioning of the atrioventricular canal begins with the formation of the two atrioventricular cushions, also called the endocardial cushions.
- The two cushions grow towards each other and fuse together to form the atrioventricular septum (AV septum).
Partitioning of the Primitive Ventricle
- Partitioning of the common ventricle is achieved by the formation of the interventricular septum, also called the IV septum.
- The interventricular septum develops from three parts:
- Muscular part: develops from a muscular ridge arising on the floor of the primitive ventricle.
- Bulbar part: develops from right and left bulbar ridges arising from conus cordis.
- Membranous part: develops from proliferation of AV cushion that fills the gap between muscular and bulbar parts.
Development of the Conducting System of the Heart
- The sinoatrial node develops during the 5th week of IUL and is initially located in the right wall of the sinus venosus.
- The AV node and AV bundle (bundle of His) are derived from cells in the left wall of the sinus venosus and AV canal.
Development of the Pericardium
- The pericardium develops from two layers:
- Fibrous pericardium derived from somatopleuric mesoderm and septum transversum.
- Serous pericardium:
- Parietal pericardium derived from somatic mesoderm.
- Visceral pericardium derived from visceral splanchnic mesoderm (also called epicardium).
Dorsal Mesocardium and Transverse Pericardial Sinus
- The dorsal mesocardium is a fold of mesodermal tissue that attaches the developing heart tube to the dorsal side of the pericardial cavity.
- The middle section of the dorsal mesocardium disappears, creating the transverse pericardial sinus, which connects both sides of the pericardial cavity.
Learn about the formation of the left atrium, including the development of the anterior rough part, posterior smooth part, and ventral smooth part. Understand the process of absorption of pulmonary veins and how they relate to the fetal left atrium.
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