1. 42.1- Circulatory systems link exchange surfaces with cells throughout the body Circulatory Systems Three Basic Components- circulatory fluid, a set of interconnecting tubes, and a muscular pump. Open Circulatory Systems- circulatory fluid bathes the organs directly. Closed C.S.- blood is confined to vessels.

2. Single Circulation- blood passes through the heart once in each complete circuit. Bony fishes, Rays, Sharks, and Fish all have a single circulation circuit.

3. Double Circulation- separate pulmonary and systemic circuits, blood passes through the heart after completing each circuit. Amphibians, Reptiles, and Mammals all have this.

4. 42.2- Coordinated cycles of heart contraction drive double circulation in mammals. The heart produces it's own electrical impulses through the sinoatrial node, also known as the pacemaker. These impulses are then sent through the rest of heart, forming contractions that pump blood through the heart and body.