How is a dogfish circulatory different from humans?

1. Number of hearts:

- Humans: 4-chambered heart (2 atria, 2 ventricles)

- Dogfish: 2-chambered heart (1 atrium, 1 ventricle)

2. Blood flow pattern:

- Humans: Double circulation (separate pulmonary and systemic circuits)

- Dogfish: Single circulation (blood passes through the heart once per circuit)

3. Oxygenation of blood:

- Humans: Blood is oxygenated in the lungs

- Dogfish: Blood is oxygenated in the gills

4. Structure of the heart:

- Humans: The heart is divided into four chambers by septa

- Dogfish: The heart has only one atrium and one ventricle and lacks septa

5. Presence of valves:

- Humans: Heart valves ensure proper blood flow and prevent backflow

- Dogfish: Heart valves are absent; instead, muscular sphincters control blood flow