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 called red blood cells (RBCs).

Erythrocytes (RBC) and Leukocytes (WBC)

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 are the conduits of the cardiovascular system. They make up a closed system, since there is no place in the system where whole blood can leave.

Arteries and Veins

Arteries generally 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.)

The Circulatory System

The Circulatory System

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.

Materials Carried through the Circulatory System:

Oxygen

Oxygen is obtained by the blood through the process of external respiration in the lungs. Oxygen is then transported to the individual body cells, where it is used in metabolic oxidation.  This provides energy for production of ATP (adenosine triphosphate), which is necessary for carrying on the life processes of the body.

Nutrients

Some of the substances distributed to the body cells are products of the digestive system.  These materials meet individual cell requirements for energy, growth, repair, synthesis of new materials, and storage for later use.

Waste Substances

Some substances are collected from the body cells for elimination.  These include carbon dioxide, nitrogenous wastes, and other potentially harmful substances that are carried to organs like the lungs, liver, or kidneys for elimination from the body.

Hormones

Hormones are the products of endocrine glands.  Hormones and other control substances are distributed throughout the body by circulatory systems. The tissues or organs affected by these substances are usually called target organs. In turn, substances released by the target organs often affect the original endocrine gland. This results in a feedback system.

Components of Any Circulatory System

Any circulatory system has three general components as follows:

• Vehicle

• Conduits

• Motive forces

Vehicle:

The vehicle is a fluid (flowing) medium. The materials being carried are dissolved or suspended in this fluid.  Examples of this include blood, lymph, or cerebrospinal fluid.

Conduits:

Conduits are like pipes.  They contain the fluids in which materials are transported to and from the various parts of the body. The blood vessels or lymph vessels are examples of these.

Motive Parts:

Motive forces act upon the vehicle to make it flow through the conduits. In the cardiovascular system these are provided by the heart.