They are part of the cardiovascular system.
Veins are the part of the circulatory system that carry blood back to the heart.
The circulatory system
Circulation
Because it contains numerous organs (heart, lungs, veins etc).
It contains numerous organs (heart, lungs, veins etc.)
The circulatory system
Veins belong to the circulatory system, because they transport blood there for they belong to the circulatory system.
The genitourinary system.
The digestive system contains the liver.
Circulatory System
The circulatory system contains your heart your blood cells and your veins
The circulatory system is an example of an organ system in the human body. The circulatory system is made up of the heart, arteries, veins, and capillaries.
skeletal system
Digestive system.
the digestive system