Question

Expended cardiac tube portion of developing heart contains following structures craniocaudally after truncus arteriosus
(A) Atrium
(B) Ventricle
(C) Bulbus cordis
(D) Sinus venosus
Choose the correct answer from the options given below:

• A. (A), (B), (C), (D).
• B. (A), (C), (B), (D).
• C. (C), (B), (A), (D).
• D. (C), (B), (D), (A).

Hint:

To memorize the primitive heart tube sequence from inflow (caudal) to outflow (cranial):
\[ \text{Sinus Venosus} \rightarrow \text{Atrium} \rightarrow \text{Ventricle} \rightarrow \text{Bulbus Cordis} \rightarrow \text{Truncus Arteriosus} \]
Reversing this sequence gives the craniocaudal outflow path.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The embryonic heart develops from a simple, straight cardiac tube that undergoes rapid focal expansions and looping to form the definitive chambers of the heart.

Step 2: Detailed Explanation:
The primitive heart tube receives blood at its caudal end and pumps it out of its cranial end.
From cranial (outflow tract) to caudal (inflow tract), the heart tube exhibits five distinct, sequential dilations:
1. Truncus arteriosus (the most cranial portion, which divides to form the ascending aorta and pulmonary trunk).
Following the truncus arteriosus, the sequential structures in a cranial-to-caudal (craniocaudal) direction are:
2. Bulbus cordis (C): Situated immediately caudal to the truncus arteriosus. It eventually forms the smooth parts of the left and right ventricles.
3. Primitive Ventricle (B): Situated caudal to the bulbus cordis, giving rise to the trabeculated parts of the left and right ventricles.
4. Primitive Atrium (A): Situated caudal to the ventricle, giving rise to the pectinate parts of the left and right atria (auricles).
5. Sinus venosus (D): The most caudal portion, receiving systemic and vitelline veins. It eventually incorporates into the right atrium (sinus venarum) and forms the coronary sinus.
Therefore, the craniocaudal sequence after the truncus arteriosus is:
Bulbus cordis (C) $\rightarrow$ Ventricle (B) $\rightarrow$ Atrium (A) $\rightarrow$ Sinus venosus (D).

Step 3: Final Answer:
The correct option is (C), representing (C), (B), (A), (D).