The cardiovascular system is the primary circulatory system of the human body.

It includes:

• a heart

• blood

• blood vessels

Cardiovascular System
Brief description of the human cardiovascular system.

General Functions of the Cardiovascular System
One function of the cardiovascular system is transport.

Some substances carried by the cardiovascular system are dissolved or suspended in the fluid portion of
the blood.

Others are bound up in special cellular elements (RBCs).

The cardiovascular system also provides protection against foreign substances.

This function involves active attack by white blood cells as well as more subtle processes of the immune system.

Direction of Flow of Arteries and Veins
Blood vessels make up a closed system, since there is no place in the system where whole blood can leave.

Arteries carry blood from the chambers of the heart to the tissue of the body.

Veins carry blood from the tissues to the chambers of the heart.

(Coronary arteries carry blood from the chambers of the heart inside to the walls of the heart outside.)

Two Cycle System
See graphic – Cardiovascular circulatory pattern.
Blood circulation is also a two cycle system.

It involves both the pulmonary cycle and the systemic cycle. Blood circulates through two circuits.

In the pulmonary cycle, blood circulates from the heart to the lungs and back to the heart.

In the systemic cycle, blood circulates from the heart to the rest of the body and back to the heart.

Fetal Circulation
Since the fetus is located within the uterus, its lungs do not take in air.

Therefore, the pulmonary cycle does not function in the fetus.

Essentially, fetal blood flows to and from the placenta.

There are certain bypasses in the heart to avoid the pulmonary cycle.
At the time of birth, the fetal circulation is changed to the normal pattern.