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Cardiovascular system

The pulmonary veins

The pulmonary veins are not assigned to any of the three systems just mentioned because they develop independently. There is no consensus about whether the pulmonary vein as a branch from the left atrium obtains a connection to the lung plexus or the pulmonary vein forms as a solitary vessel in the dorsal mesocardium and is only secondarily incorporated into the atrium. In either case, with the further development of the heart, more and more of the pulmonary veins are incorporated into the left atrium, so that at the end of the embryonic period 4 independent pulmonary veins empty into the atrium.

Fig. 24 - Formation of the pulmonary veins; Stage 12 (ca. the 30 day)
media/module16/p6c1_Pulm12.gif

  1. Septum spurium
  2. Inlet of the sinus venosus
  3. Dorsal septum atrio-ventriculare
  4. Sulcus atrio-ventricularis
  5. Atrium
  6. Ventricle

Fig. 25 - Formation of the pulmonary veins; Stage 13 (ca. the 32 day)
media/module16/p6c2_Pulm13.gif

  1. Incorporation of the sinus venosus into the right atrium
  2. Pulmonary veins
  3. Incorporation of the pulmonary veins into the left atrium

Legend
Fig. 24

Initially, only one pulmonary vein empties into the left atrium.

Fig. 25

More and more of the sinus venosus and the pulmonary vein become incorporated into the atrium.

 
Fig. 26 - Formation of the pulmonary veins; Stage 14 (ca. the 33 day)
media/module16/p6c3_Pulm14.gif

  1. Incorporation of the sinus venosus into the right atrium
  2. Pulmonary veins
  3. Incorporation of the pulmonary veins into the left atrium

Fig. 27 - Formation of the pulmonary veins; Stage 15 (ca. the 36 day)
media/module16/p6c4_Pulm15.gif

  1. Incorporation of the sinus venosus into the right atrium
  2. Pulmonary veins
  3. Incorporation of the four pulmonary veins into the left atrium

Legend
Fig. 26

With time the two pulmonary veins empty separately into the left atrium-

Fig. 27

In stage 15 the 4 pulmonary veins empty into the left atrium.

 
More info

The latest research shows that the pulmonary veins arise as solitary vessels in the mesenchyma of the mediasatinum and canalize the blood of the pulmonary vein plexus into the heart. The individual pulmonary veins that have been engendered become incorporated into the left atrium and finally 4 independent pulmonary veins empty into the heart