I think the first one is right
1st-degree AV heart block can occur with any rhythm originating in the SA node, such as sinus rhythm, bradycardia, or tachycardia.......
Genes are located in chromosomes
The respiratory system mainly consists of the lungs. The lungs give oxygen to the body, when you inhale air. They are responsible for removing carbon dioxide from the body. The circulatory system mainly consists of the heart. The heart pumps blood through the body, giving us oxygen. The heart is responsible for pumping blood and creating new blood cells. If we did not have a heart then there would be no blood, therefore, no oxygen. If you think about it, the body's oxygen transport system takes oxygen to the working muscles, through the circulatory and respiratory systems working together. The main workers are the heart, blood and lungs. The whole oxygen transport system works in a cycle.
