The circulatory system is an organ system

Organ (anatomy)

In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

 that passes nutrients (such as amino acids, electrolytes and lymph

Lymph

Lymph is considered a part of the interstitial fluid, the fluid which lies in the interstices of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary...

), gases, hormones, blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 cells, etc. to and from cells in the body to help fight diseases and help stabilize body temperature

Thermoregulation

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...

 and pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 to maintain homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

.

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

Lymphatic system

The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...

, which distributes lymph

Lymph

Lymph is considered a part of the interstitial fluid, the fluid which lies in the interstices of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary...

.