The Circulatory System


The circulatory system is an organ system that passes nutrients (such as amino acids and electrolytes), gases, hormones, bloodcells, , etc. to and from cells in the body to help fight diseases and help 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 thecardiovascular system, which distributes blood, and thelymphatic 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 a circulatory system. The lymphatic system, on the other hand, is an open system.

The main components of the human circulatory system are the heart, the blood, and the blood vessels. The circulatory system includes: the pulmonary circulation, a “loop” through the lungswhere blood is oxygenated; and the systemic circulation, a “loop” through the rest of the body to provide oxygenated blood. An average adult contains about a gallon and a half of blood, which consists of plasma, red blood cells, white blood cells, and platelets.

Also, the digestive system works with the circulatory system to provide nutrients the system needs to keep the heart pumping.

Two types of fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the cardiovascular system. The lymph, lymph nodes, and lymph vessels form the lymphatic system. The cardiovascular system and the lymphatic system collectively make up the circulatory system.





   1. Lacking a backbone or spinal column; not vertebrate.

   2. Of or relating to invertebrates: invertebrate zoology.

An animal, such as an insect or mollusk, that lacks a backbone or spinal column.

invertebrate , any animal lacking a backbone. The invertebrates include thetunicates and lancelets of phylum Chordata, as well as all animal phyla other than Chordata. The major invertebrate phyla include: the sponges (Porifera), coelenterates (Cnidaria), echinoderms (Echinodermata), flatworms (Platyhelminthes), roundworms (Nematoda), segmented worms (Annelida), mollusks (Mollusca), and arthropods (Arthropoda). Invertebrates are tremendously diverse, ranging from microscopic wormlike mezozoans (see Mezozoa) to very large animals such as the giantsquid. Approximately 95% of all the earth’s animal species are invertebrates; of these the vast majority are insects and other arthropods. Invertebrates are important as parasites and are essential elements of all ecological communities