The Human circulatory system reference article from the English Wikipedia on 24-Apr-2004
(provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Human circulatory system

For thoughtful child sponsors
The human circulatory system is composed of the blood, vascular system, and heart of the human.

Table of contents
1 Functions
2 Anatomy

Functions

Following are some basic functions of the human circulatory system:
  1. Delivery of oxygen and nutrients to all parts of the body and removal of waste.
  2. Role in the immune system of defence against infection.
  3. Transport of hormones.

Anatomy

The human circulatory system consists of the heart which acts as a pump, and the blood vessels in which the blood flows. We distinguish between arteries in which blood flows away from the heart, veins in which blood flows back to the heart, and capillaries which are very thin vessels where the actual oxygen and nutrient exchange takes place and which form the interface between arteries and veins.
Image:Blood circulation (human).png
The double circulation system in humans. In the first circuit, the blood is pumped to the lungs, where it acquires oxygen. It then returns to the heart and enters the second circuit, going to the rest of the body, eventually returning to the heart. Blood circulates through the body two to three times every minute. In one day, the blood travels a total of 19,000 km (12,000 miles)--that's four times the distance across the US from coast to coast.

The double circulatory system

The "double circulation" system of blood flow in the human body is divided into the pulmonary circulation and the systemic circulation.

The adult human heart consists of two separated pumps, the right side with the right atrium and ventricle, and the left side with the left atrium and ventricle (seen from the perspective of the heart's owner).