Sinus Venosus Embryology > Cardiorespiratory System > Cardiorespiratory System

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NOTES

Key points

• Between days 24-56 (approximately), asymmetrical heart and vascular remodeling ensures that all systemic blood flows into the right atrium.

• Ultimately:

- The left sinus horn becomes coronary sinus and oblique vein of the left atrium

- The right horn is incorporated into right atrium, forms venous valves.

FEATURES ON DAY 24:

• Primitive left and right atria and ventricles

• Outflow tract arises ventrally, and the singular orifice of the pulmonary vein drains into the area of the left atrium.

The sinus venosus bilaterally drains the following veins:

• Common cardinal veins

- Common drainage vessels for the anterior and posterior cardinal veins.

• Umbilical vein

- Drains blood from the placenta

• Vitelline vein

- Drains the developing gut

FEATURES ON DAY 50:

• Outcroppings of the atria, called auricles, are forming.

• The outflow tract has separated and formed the pulmonary trunk and arteries, which delivers blood to the pulmonary

1 / 3 circulation.

• The aorta sends blood into the systemic circulation.

• The orifice of the pulmonary vein now comprises four separate entrances; recall that two right and two left pulmonary veins return blood to the adult heart.

Sinus venosus and tributaries:

• The left vitelline and proximal portions of both umbilical veins are obliterated (the distal portion of the left umbilical veins persists and anastomoses with the ductus venosus to bypass the liver).

• Both posterior cardinal veins, and the left anterior cardinal vein are in the process of obliterating.

• As the left anterior cardinal vein degenerates, its branches (the thymic and thyroid veins) form anastomoses with those of the right anterior cardinal vein.

FEATURES ON DAY 56:

• Left horn becomes the coronary sinus and oblique vein of the left atrium.

• Inferior vena cava comprises remnants of the right vitelline vein; for reference, sub- and supra-cardinal veins also contribute to this section of the inferior vena cava.

• The right anterior cardinal vein gives rise to the superior vena cava, and, via anastomoses with the left anterior cardinal vein, the left brachiocephalic vein.

- Each brachiocephalic vein drains blood from the jugular veins, which are also derived from the anterior cardinal veins, and, the subclavian veins, which drain the upper extremities.

SUMMARY OF EMBRYONIC VEINS AND THEIR ADULT DERIVATIVES.&NBSP;

• Sinus venosus is incorporated into the heart as the sinus venarum of the right heart; in the adult, it is identified by its smooth surface.

• Right vitelline vein gives rise to a portion of the inferior vena cava, and the left vitelline vein has no adult derivatives.

• Right umbilical vein degenerates.

• After birth, the portion of the of the left umbilical vein that connected with the ductus venosus degenerates to form the ligamentum teres hepatis.

• Via anastomoses, the anterior cardinal veins give rise to the superior vena cava, left brachiocephalic vein, and the jugular veins.

• The posterior cardinal veins have no adult derivatives.

Bear in mind that the venous circulation is even more variable than the arteries:

• A common variation in the sidedness or number of superior vena cavae results when the left anterior cardinal vein persists:

2 / 3 - If the right anterior cardinal vein also persists, double superior vena cava result;

- If the right anterior cardinal vein degenerates, the superior vena cava will form on the left from the left anterior cardinal vein.

FULL-LENGTH TEXT

Here we will learn about the development of the sinus venous and its incorporation into adult cardiac features. To begin, start a table, and denote the following key points: Between days 24-56 (approximately), asymmetrical heart and vascular remodeling ensures that all systemic blood flows into the right atrium. Ultimately, the left sinus horn becomes coronary sinus and oblique vein of the left atrium; the right horn is incorporated into right atrium, forms venous valves. Now, let's show the venous return to the heart on day 24. In dorsal view, draw the primitive left and right atria and ventricles. Indicate right/left orientation, and, show that the outflow tract arises ventrally, and the singular orifice of the pulmonary vein drains into the area of the left atrium. Next, show that the sinus venosus bilaterally drains the following veins: Common cardinal veins, which, as their name implies, are common drainage vessels for the anterior and posterior cardinal veins. Medial to the posterior cardinal veins, label the umbilical vein, then, the vitelline vein. Recall that the umbilical vein drains blood from the placenta, and the vitelline vein drains the developing gut. Over the next few weeks, venous blood flow shifts to the right. To show this, we'll draw the heart on day 50. First, re-draw the atria and ventricles. Indicate that outcroppings of the atria, called auricles, are forming. Next, show that the outflow tract has separated and formed the pulmonary trunk and arteries, which delivers blood to the pulmonary circulation, and, the aorta, which sends blood into the systemic circulation. Also, indicate that the orifice of the pulmonary vein now comprises four separate entrances; recall that two right and two left pulmonary veins return blood to the adult heart. Next, let's show what happens to the sinus venosus and its tributaries as venous blood return shifts to the right: The left vitelline and proximal portions of both umbilical veins are obliterated (the distal portion of the left umbilical veins persists and anastomoses with the ductus venosus to bypass the liver). Both posterior cardinal veins, and the left anterior cardinal vein are in the process of obliterating. As the left anterior cardinal vein degenerates, its branches (the thymic and thyroid veins) form anastomoses with those of the right anterior cardinal vein. Next, let's see how reorganization of venous return gives rise to the adult form. Re-draw the atria, auricles, ventricles, openings of the pulmonary veins, pulmonary arteries, and aorta. Then, show that the left horn has become the coronary sinus and oblique vein of the left atrium. Indicate the inferior vena cava, which comprises remnants of the right vitelline vein; for reference, write that sub- and supra-cardinal veins also contribute to this section of the inferior vena cava. The right anterior cardinal vein gives rise to the superior vena cava, and, via anastomoses with the left anterior cardinal vein, the left brachiocephalic vein. For completeness, show that each brachiocephalic vein drains blood from the jugular veins, which are also derived from the anterior cardinal veins, and, the subclavian veins, which drain the upper extremities. Finally, let's make a summary table of embryonic veins and their adult derivatives. First, write that the sinus venosus is incorporated into the heart as the sinus venarum of the right heart; in the adult, it is identified by its smooth surface. Next, the right vitelline vein gives rise to a portion of the inferior vena cava, and the left vitelline vein has no adult derivatives. Similarly, the right umbilical vein degenerates. After birth, the portion of the of the left umbilical vein that connected with the ductus venosus degenerates to form the ligamentum teres hepatis. Via anastomoses, the anterior cardinal veins give rise to the superior vena cava, left brachiocephalic vein, and the jugular veins; the posterior cardinal veins have no adult derivatives. Lastly, bear in mind that the venous circulation is even more variable than the arteries. For example, a common variation in the sidedness or number of superior vena cavae results when the left anterior cardinal vein persists: If the right anterior cardinal vein also persists, double superior vena cava result; If the right anterior cardinal vein degenerates, the superior vena cava will form on the left from the left anterior cardinal vein.