Large multicellular organisms such as humans require circulatory systems for the distribution and collection of substances.

Substances carried by circulatory systems include oxygen, nutrients, waste products and hormones.

Circulatory systems in the human body include the cardiovascular system, the lymphatic system and the cerebrospinal fluid system.

The components of any circulatory system include the vehicle, conduits and motive forces.
The cardiovascular system comprises the blood, the blood vessels (arteries and veins) and the heart.

The cardiovascular system provides transport and protection for the body.

Generally, arteries carry blood from the heart to the body tissues, while veins carry blood from the body tissues to the heart.

Blood circulation is also a two cycle system. It involves both the pulmonary cycle and the systemic cycle.

Blood is the vehicle of the cardiovascular system

Blood is composed of plasma, red blood cells, white blood cells and platelets.

The red blood cells carry oxygen.

The white blood cells play a role in protecting the body from infection.

The blood transports oxygen, carbon dioxide, nutrients, waste products and hormones.

The response of the vascular system to hemorrhaging involves vascular contraction, clumping of platelets and the blood clotting process.
The cardiovascular system enables energy mobilization by:

carrying the oxygen required to make ATP
carrying hormones needed to mobilize energy
carrying fats needed for energy
increasing blood supply to particular areas when they most need it

Recipient and donor blood types must be matched for blood transfusions.

Blood plays an important role in temperature control in the body.