circulatory system
Meaning of circulatory system: The heart and its network of vessels, a closed loop delivering oxygen and fuel to tissue and carrying waste away.
Definition of circulatory system
The circulatory system is the heart together with the network of vessels that carries blood around the body. Two loops run from it: one sends blood to the lungs to collect oxygen, the other sends it out to every tissue, where oxygen and nutrients are handed over and waste is picked up. Lymphatic vessels drain fluid that escapes this network and return it.
What are the two circuits?
The heart is really two pumps side by side. The right side receives oxygen poor blood returning from the body and pushes it to the lungs, where carbon dioxide leaves and oxygen enters. That short trip is the pulmonary circuit. Blood then arrives at the left side, which pumps it out under much higher pressure to the brain, gut, kidneys, muscle and skin. That longer trip is the systemic circuit. The two run in series, so every drop passes through the lungs before it reaches the body again.
What does each kind of vessel do?
| Vessel | Job |
|---|---|
| Artery | Thick muscular wall, carries blood away from the heart under pressure |
| Arteriole | Small and adjustable, decides which tissue receives more flow |
| Capillary | One cell thick, the only place where exchange with tissue happens |
| Vein | Thin walled, holds most of the body's blood, valves stop backflow |
How does the lymph system fit in?
Capillaries leak. A little fluid escapes into the tissue with every heartbeat, and if it stayed there the limbs would swell. A separate set of thin vessels collects it, filters it through nodes on the way, and empties it back into a large vein near the collarbone. That returned fluid is lymph. Blocking or removing those channels, as happens after some cancer surgery, produces persistent swelling in the limb they drained.
What goes wrong with it?
Most common problems are problems of flow. Fatty plaque narrows an artery until the tissue beyond it runs short. A clot lodges in a blood vessel and stops flow abruptly. Valves in leg veins fail, so blood pools and the veins bulge. When the pump itself weakens, fluid backs up behind it into the lungs and the legs, the pattern named congestive heart failure.
Also known as
Used in a sentence
Fluid overload places extra demand on the circulatory system and can worsen breathlessness.
Good to know
Arteries are defined by carrying blood away from the heart rather than by carrying oxygen, which is why the pulmonary artery holds oxygen poor blood and the pulmonary veins hold oxygen rich blood.
Word origin
Where “circulatory system” comes from
Circulatory comes from the Latin circulare, meaning to move in a circle, from circulus, a small ring.