The most important part of the Circulatory Sytem is the capillaries.
There isn't one - one part fails and it's all useless.
It is the heart
The heart
Capillaries
cardiovascular system
The Circulatory System
It affects virtually all organ systems. The most significantly affeccted are the cardiovascular system and the Central Nervous System.
The brain is the most important organ of the nervous system. The spinal cord and the brain are the main parts of the nervous system but the spinal cord is not considered to be an organ.
The lungs.
lungs
Ovaries
The Kidneys
skin!
the skull because it protects the brain
blood
organ system