Detailed Cardiac - Pulmonary Vein
|Embryology - 29 Oct 2020 Expand to Translate|
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|Detailed Cardiac: Systemic Venous Sinus | Pulmonary Vein | Superior Interatrial Fold | Atrioventricular Cushions | Atrioventricular Canal | Interventricular Communication | Subpulmonary Infundibulum | Arterial Roots | Intrapericardial Arterial Trunks | Extrapericardial Arterial Channels | Sinus Node | Atrioventricular Conduction Axis|
Formation of the Pulmonary Vein, and its Subsequent Incorporation into the Left Atrium
Some Recent Findings
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Search term: Pulmonary Vein Development
<pubmed limit=5>Pulmonary Vein Development</pubmed>
<pubmed limit=5>Pulmonary Vein Embryology</pubmed>
Remodelling of the Venous Tributaries
Further development of the atrial chambers, which occurs concomitant with the process of ballooning, requires remodeling of the venous channels which bring the blood back to the heart. There are three such sets of venous tributaries.They bring blood from the embryo, the yolk sac, and the placenta, respectively. The three sets unify to form the so-called sinus horns, which then drain to the initial atrial part of the heart tube. At the initial stages, when the blood enters the atrial component of the heart on each side through the so-called sinus horns, there is minimal formation of the lungs, so there are no pulmonary veins. It is the systemic venous return, therefore, which enters both sides of the atrial part of the tube. This part of the tube, moreover, remains connected to the body of the embryo through a stalk, known as the dorsal mesocardium. The dorsal mesocardium is bordered by two prominences known as the pulmonary ridges. The connection with the pharyngeal mesenchyme through the heart stalk will eventually, subsequent to the development of vascular channels within the lung buds, function as the portal of entry for the pulmonary vein (Figure 4).
Fig. 4. The section is from another mouse embryo early at E10.5. It shows the continuity of the atrial component of the heart tube with the pharyngeal mesenchyme through the connection known as the dorsal mesocardium, or heart stalk. This connects the heart with the body of the embryo, producing raised flanges known as the pulmonary ridges. These flank the pulmonary pit (white stars with black borders). Note the presence of a midline strand within the pharyngeal mesenchyme. This will eventually canalize to form the pulmonary vein.
Prior to canalization of the pulmonary vein, however, there is a shift of the blood entering the heart through the systemic venous tributaries. As already emphasized, the channels bringing the blood from the embryo back to the heart initially enter the atrial component of the heart tube in symmetrical fashion (Figure 5).
Fig. 5. The image is a scanning electron micrograph through the dorsal mesocardium prepared from a mouse embryo at E8.5, earlier than the specimen shown in Figure 4. The lungs have yet to develop at this early stage. The venous tributaries open in relatively symmetrical fashion to the atrial component of the heart tube through the channels known as the horn of the systemic venous sinus.
At the earlier stage, as shown in Figure 5, there are no obvious boundaries between the atrial chamber and the systemic venous channels, with the lungs not yet having been formed. With ongoing development, the venous channels move rightwards so that, eventually, they open only to the right side of the initially common atrial chamber. As the channels move rightwards, so flaps of myocardium are formed at their junction with the atrial chamber, producing the structures known as the venous valves. It is at this stage, furthermore, during the early part of E10.5 in the mouse, that the first sign is seen of atrial septation (Figure 6).
Fig. 6. The image is prepared from the same dataset as Figure 4. It shows a cut through the junction between the venous tributaries and the atrial component of the heart tube, with the boundary between the two now marked by the venous valves. As can be seen, the junction is to the right side of the common atrial chamber. Note the pulmonary pit between the pulmonary ridges, which mark the site of the dorsal mesicardium. Note also the appearance of the atrial septum in the roof of the common atrial chamber.
It is subsequent to the rightward shift of the systemic venous tributaries, as shown in Figure 6, that the lung buds grow and develop their own vasculature. The intraparenchymal pulmonary veins initially form a plexus that has connections with the adjacent systemic venous channels developing within the body of the embryo itself. With normal development, however, the pulmonary veins unite in the midline, with formation of a common pulmonary vein. This canalizes from the mid-pharyngeal strand, which was recognizable even before the establishment of the intraparenchymal plexuses (Figure 4). The common pulmonary vein then opens to the heart through the pulmonary pit, itself adjacent to the left sinus horn in the left atrioventricular junction (Figure 7).
Fig. 7. The images are from different human embryos at Carnegie stage 14, at the end of the fourth week of development. The left hand panel, which is a sagittal section, shows the entrance of the pulmonary vein adjacent to the left sinus horn and the atrioventricular junction. The right hand panel, sectioned in frontal fashion, shows how the vein enters the atrial component of the heart tube between the pulmonary ridges, confirming its adjacency to the atrioventricular canal.
- <pubmed>21779373</pubmed> PLoS One
Cite this page: Hill, M.A. (2020, October 29) Embryology Detailed Cardiac - Pulmonary Vein. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Detailed_Cardiac_-_Pulmonary_Vein
- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G