Circulatory system picture
The circulatory system is an organ system that moves nutrients,
gases, and wastes to and from cells, helps fight diseases and helps
stabilize body temperature and pH to maintain homeostasis. This system
may be seen strictly as a blood distribution network, but some consider
the circulatory system as composed of the cardiovascular system, which
distributes blood, and the lymphatic system, which distributes lymph.
While humans, as well as other vertebrates, have a closed cardiovascular
system (meaning that the blood never leaves the network of arteries,
veins and capillaries), some invertebrate groups have an open
cardiovascular system. The most primitive animal phyla lack circulatory
systems. The lymphatic system, on the other hand, is an open system.
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