A heart is a muscular organ that functions as a pump, circulating blood throughout an organism’s body to deliver oxygen and nutrients while removing waste products. Like all vertebrates, sharks possess a heart that drives their circulatory system. This organ is uniquely adapted to their aquatic environment and plays a central role in their survival as ocean predators.
Location and Basic Anatomy
A shark’s heart is located in the anterior ventral region of its body, positioned behind the gills. This organ is housed within a protective structure called the pericardial cavity, which is found anterior to the transverse septum. The pericardial cavity is a relatively small, upper portion of the shark’s body cavity. The heart itself is an S-shaped tube, proportionally small in relation to the shark’s overall body size.
The shark heart consists of two primary chambers: an atrium and a ventricle. The atrium is a thin-walled chamber, while the ventricle is a thick, muscular-walled cavity. These two chambers form the core of the shark’s circulatory pump.
How a Shark’s Heart Functions
Sharks utilize a single-circuit circulatory system, meaning blood passes through the heart only once during each complete circuit around the body. Deoxygenated blood from the shark’s body first enters a collection sac known as the sinus venosus, which then drains into the atrium. From the atrium, blood is pumped into the muscular ventricle.
The ventricle then forcefully pumps this deoxygenated blood through a muscular outflow tract, the conus arteriosus, towards the gills. At the gills, the blood releases carbon dioxide and absorbs oxygen from the surrounding water. Once oxygenated, the blood circulates directly from the gills to the rest of the body, delivering oxygen and nutrients to tissues and organs. Following this systemic circulation, the deoxygenated blood returns to the sinus venosus to complete the cycle. The conus arteriosus contains a series of semilunar valves that help direct blood flow and maintain pressure as blood exits the heart.
Unique Adaptations and Efficiency
The shark’s heart possesses specific adaptations that enhance its function within their aquatic environment. The pericardial cavity, which encases the heart, is notably rigid or semi-rigid. This rigid structure creates a negative pressure, or suction, within the pericardium as the ventricle contracts and ejects blood. This negative pressure aids in drawing deoxygenated blood back into the heart, compensating for the relatively low blood pressure inherent in their single-circuit system.
The continuous swimming motions of many shark species also contribute to blood circulation, helping to return blood to the heart. Some active predatory sharks, such as Great Whites and Makos, have evolved a specialized circulatory modification called the rete mirabile. This network of blood vessels allows these sharks to retain metabolic heat generated by their muscles, warming the blood returning to the heart and enabling them to operate effectively in colder waters.