3. Circulatory and Respiratory System
A shark’s heart is a two-chambered S-shaped tube, small in proportion to body size located in the head region. Has an atrium and ventricle. The blood is pumped by the heart through the afferent branchial arteries to capillaries in the gills, where the blood is oxygenated). The blood then flows through efferent branchial arteries, through the tissues of the body, and back to the heart in veins. Sharks have low blood pressures; the walls of the pericardium are rigid, creating suction within the pericardium to maintain the flow of blood. To circulate blood throughout their bodies, many sharks must swim continuously. The blood flow is similar to humans because blood is pumped by the heart to the rest of the body by arteries and returned to the heart by veins. A difference is that humans have 4-chambered hearts while sharks only have 2 chambers. Humans also don’t need to constantly move to circulate their blood, as we have higher blood pressures and we can maintain our body temperatures with food energy. Humans are warm blooded creatures, while most sharks are cold blooded which requires them to constantly move and use external heat sources to maintain body temperature.
Sharks can respire by pumping water over their gills by opening and closing their mouths. From the mouth, water enters the gill chambers and exits through the gill slits. Blood in the gill filaments absorbs oxygen from the incoming water. Gill rakers, which are cartilaginous projections on the gill support structure, protect the delicate gill filaments from particles in the water that might damage them. Because sharks have low blood pressure, most must swim continuously because muscular contractions are needed to circulate the blood. The respiratory system of a shark is very different from a humans because sharks do not have a trachea, lungs, and a diaphragm for gas exchange. Instead of alveoli, the oxygen is absorbed by gills. Sharks also absorb oxygen from water rather than the air like humans do.
All about sharks. (1998, January 1). Enchanted Learning. Retrieved November 20, 2011, from http://www.enchantedlearning.com/subjects/sharks/
Sharks & rays. (n.d.). SeaWorld/Busch Gardens animals . Retrieved November 20, 2011, from http://www.seaworld.org/animal-info/info-books/sharks-&-rays/index.htm
[Untitled diagram of the shark’s respiratory and circulatory system] Retrieved November 20, 2011 from: http://www.shark-info.com/shark-anatomy/respiration/shark-respiration.htm