Question

which of the following statements concerning the embryonic cardiovascular system is true?
multiple choice
18
the bulbus cordis becomes the sinoatrial node (the adult pacemaker).
an opening in the interatrial septum is called the sinus venosus.
there is an opening in the interventricular septum.
the heart develops from four endothelial tubes.
blood vessels form from blood islands.

Explanation:

• The bulbus cordis does not become the sinoatrial node. The sinoatrial node has a different origin.
• An opening in the interatrial septum is the foramen ovale, not the sinus venosus. The sinus venosus is a different structure in embryonic development.
• In embryonic development, there is an opening in the interventricular septum (the interventricular foramen) which later closes.
• The heart develops from two endothelial tubes (not four) that fuse.
• Blood vessels form from blood islands. Blood islands consist of angioblasts which differentiate to form the endothelial lining of blood vessels.

Answer:

• The statement “There is an opening in the interventricular septum” is true.
• The statement “Blood vessels form from blood islands” is also a correct embryological fact.

If this is a single - answer multiple - choice (assuming only one correct answer is expected in the original full - context exam question, and based on common embryonic cardiovascular system exam questions), the more likely focus is on the interventricular septum opening. But strictly based on the provided explanations, both “There is an opening in the interventricular septum” and “Blood vessels form from blood islands” are correct embryological statements. If forced to choose one (as per some textbook emphasis on heart septation for this type of question), “There is an opening in the interventricular septum” might be the answer expected in a basic embryonic cardiovascular system exam question.