What is the first structure that contracts in a fish heart?Multiple choice question.The conus arteriosusThe ventricleThe sinus venosusThe atrium

Answer to the Question

In a fish heart, the first structure that contracts is the sinus venosus.

Explanation

The fish heart has a unique structure composed of several chambers. Here’s how the contraction occurs:

1. Sinus Venosus: This is a thin-walled structure that collects deoxygenated blood returning from the body. It serves as the pacemaker of the fish heart and is the first to contract, initiating the heart cycle.

2. Atrium: After the sinus venosus contracts, blood flows into the atrium, which is the second chamber to contract.

3. Ventricle: Following the atrium, the ventricle contracts next, pushing blood into the conus arteriosus.

4. Conus Arteriosus: Finally, this structure directs blood out of the heart to the gills for oxygenation.

Thus, the correct answer to the question regarding the first structure that contracts in a fish heart is the sinus venosus.