With reference to fish and mammals compare single and double circulatory systems
The circulatory system is how blood moves throughout living organisms. Some creatures, such as fish, have a single circulatory system, some have a double, such as mammals, and some have a partial, such as amphibians.
Fish are cold blooded and so rely on the water temperature around them to keep them warm or cool enough. They have gills for breathing, or gaseous exchange, whereas mammals have lungs. The main advantage of having gills is probably that it’s impossible for a fish to choke. Some fish such as gourami and betta have a labyrinth organ which also allows them to breath air from the surface of water. In a fish blood is pumped first to the gills where it is oxygenized, then it is taken around the entire body, before returning to the heart, where it then goes back to the lungs gills. The hearts main purpose is to act as a pump so that the blood have enough pressure to make it’s journey through the entire body without loosing too much pressure like when it goes through capillaries. Fish have a single circulatory system, so the blood only goes through their heart (The ‘pump’) once on it’s journey, this means that there is less momentum for the blood especially once it has gone through capillaries. The distances that the blood needs to travel can be great and so the demands are high. This system is seen to be less efficient than a double circulatory system.
Mammals such as monkeys, felines, canines and humans are all warm blooded, meaning they are able to maintain their own body temperature (Generally kept at least 10°C above air temperature.) Mammals have a very high demand on energy and nutrients. The specialist exchange surfaces used for gaseous exchange (Or, respiration) in mammals are known as the lungs. In the mammal circulatory system blood travels first through the right atrium, at this point is contains no oxygen and so would be blue in colour, it then travels through the right ventricle where it travels to the lung. In the lung the blood becomes oxygenated, now it would appear red. Next the blood travels via the pulmonary veins through to the left atrium. After that the blood goes through the left venticle, leaves the heart by the aorta and begins travelling around the body. The ventricles act as pumps and so because the blood has gone trhough wo of these ‘pumps’ it has much more momentum to use in it’s journey around the body. The most energy is require when the blood reaches the feet, and needs to travel back up to the heart, this is why when people have low blood pressure, they faint. This is the bodies way of making it easier for the blood to get back to the heart. The double pump system, aka double circulatory system is much more effective than a single circulatory system because of the increased pressure that allows a more effective blood transport system.
