The SA node develops during the fifth week of embryology and is located in the right wall of the sinus venosus; into which heart chamber is it later incorporated?

The SA node develops during the fifth week of embryology and is located in the right wall of the sinus venosus; into which heart chamber is it later incorporated?

• A. Right atrium
• B. Left atrium
• C. Right ventricle
• D. Left ventricle

Answer: (A)

The pacemaker tissue comes from the sinus venosus during early heart development. As the heart forms, the sinus venosus is absorbed into the right atrium, creating the smooth-walled portion called the sinus venarum. The SA node remains in this region, so its adult location is in the right atrial wall near where the superior vena cava enters. It isn’t found in the left atrium or the ventricles because those chambers arise from other cardiac regions, while the sinus venosus ultimately becomes part of the right atrium.

The pacemaker tissue comes from the sinus venosus during early heart development. As the heart forms, the sinus venosus is absorbed into the right atrium, creating the smooth-walled portion called the sinus venarum. The SA node remains in this region, so its adult location is in the right atrial wall near where the superior vena cava enters. It isn’t found in the left atrium or the ventricles because those chambers arise from other cardiac regions, while the sinus venosus ultimately becomes part of the right atrium.