Fish possess a single-loop circulatory system that efficiently moves blood through their bodies in a continuous loop. This system comprises a heart with two main chambers—one ventricle and one atrium—that pumps deoxygenated blood to the gills for oxygenation. From the gills, the oxygen-rich blood is distributed to the rest of the body, returning to the heart to complete the circuit.
- Fish have a two-chambered heart (one atrium, one ventricle).
- Blood flows in a single loop: heart → gills → body → heart.
- Efficiently delivers oxygen and nutrients while removing waste.
Gills: The Oxygen Exchange
Gills are specialized organs that extract oxygen from water as it flows over them. In fish, water enters the mouth, passes over the gills, and exits through the gill slits. As water flows, oxygen diffuses into the blood, while carbon dioxide diffuses out, making gills essential for both respiration and circulation.
- Water enters through the mouth and exits via gill slits.
- Oxygen diffuses into the blood from the water.
- Carbon dioxide diffuses out of the blood into the water.
Blood Flow Pathway
The pathway of blood in a fish’s single-loop system is straightforward. Deoxygenated blood from the body enters the heart’s atrium, flows into the ventricle, and is pumped to the gills for oxygenation. From the gills, the oxygenated blood travels to the body, delivers nutrients, and returns to the heart to start the cycle again.
- Deoxygenated blood enters the heart's atrium.
- Blood is pumped from the ventricle to the gills.
- Oxygenated blood travels to the body and returns to the heart.
Nutrient and Waste Exchange
As blood circulates through the body, it delivers oxygen and essential nutrients to tissues and organs. Cells use these nutrients for metabolism, producing waste products like carbon dioxide and urea. Blood then collects these wastes and returns to the heart, completing the cycle and preparing for re-oxygenation in the gills.
- Blood delivers oxygen and nutrients to body cells.
- Cells produce waste products, including carbon dioxide.
- Blood carries waste back to the heart for removal.