Identify major differences between fish and reptilian hearts.

1. Number of chambers: Fish have a two-chambered heart, consisting of one atrium and one ventricle, while reptiles have a three-chambered heart, consisting of two atria and one ventricle.

2. Oxygenation: Fish have a single circulation system, where blood is pumped from the heart to the gills to pick up oxygen and then circulated to the rest of the body. Reptiles have a double circulation system, where oxygenated and deoxygenated blood are kept separate, with the heart pumping blood to the lungs and body separately.

3. Efficiency: The three-chambered heart of reptiles allows for more efficient separation of oxygenated and deoxygenated blood, resulting in better oxygen delivery to the body compared to the two-chambered heart of fish.

4. Size and structure: Reptilian hearts are generally larger and more complex in structure compared to fish hearts, reflecting the greater metabolic demands of reptiles.

Fish Hearts:

- Two-chambered: Consists of an atrium and a ventricle.
- Single circuit circulation: Blood flows from the heart to the gills for oxygenation, then back to the heart.
- Sprial valve in the conus arteriosus: Increases the blood pressure for circulation.
- Low pressure system: Blood is pumped at a relatively low pressure due to the single circuit circulation.
- Specialized cells called pillar cells: Line the ventricle and help regulate the heartbeat.

Reptilian Hearts:

- Three-chambered: Consists of two atria and a ventricle, with a partial septum dividing the ventricle.
- Double circuit circulation: Blood flows from the heart to the lungs for oxygenation, back to the heart, then to the body.
- Incomplete separation of the ventricles: The ventricular septum is incomplete, allowing some mixing of oxygenated and deoxygenated blood.
- Higher pressure system: Blood is pumped at a higher pressure due to the double circuit circulation.
- наличието на stinger: A muscular tube that helps propel blood from the heart.