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The purpose of the cardiovascular system (=CVS) is for the blood to flow through all the organs and tissues of the body.
This blood flow is necessary to provide all the organs and tissues with oxygen and nutrients and to remove waste products from them.
3.
The CVS consists of the following major parts:
The arteries run from the heart to all the organs. These are really tubes that transports the blood to these organs and tissues. In other words, the blood flows though the arteries from the heart to the organs.
The capillaries are located in all the organs and receive the blood from the arteries. Inside the capillaries, the blood exchanges the oxygen and nutrients with the fluid inside the organs and collects all the waste from these organs.
The veins collect the blood from the capillaries in the organs and transport it back to the heart.
In other words, the CVS system is one big circle with the heart (= the pump) at one end of the circle, and the organs (the receiving part), at the other side of the circle.
However, there are actually, two circulations in the body; the large (also called ‘systemic’) circulation and a smaller circulation.
The smaller circulation transports the blood to the lungs (= pulmones). This is why this circulation is called ‘the pulmonary circulation’.
The function of the pulmonary circulation is to transport de-oxygenated blood to the lungs where it is re-oxygenated (‘filled with oxygen’).
In other words, there are actually two hearts; one heart that pumps the oxygenated blood into the systemic circulation and a second heart that pumps de-oxygenated blood to the lungs.
Note that the blood vessels coming from the heart to the organs are called ‘arteries’ and the vessels that go from the organs to the heart are called ‘veins’!
This is crucial stuff!
In the systemic circulation, the arteries transport oxygenated blood and the veins transport de-oxygenated blood back to the heart.
In the pulmonary circulation, it is the other way around: the pulmonary arteries transport de-oxygenated blood to the lungs and the pulmonary veins transport oxygenated blood back to the heart.
So, as you have seen above, there are actually two hearts, the right and the left heart.
The left heart receives the oxygenated blood from the pulmonary veins and pumps it to the arteries of the systemic circulation.
4.
When the heart contracts (=pumps), this phase is called the systole. After each contraction (=systole), the heart then relaxes. This is called the diastole.
More information is available about the function of the heart on page B3. The Electrical Heart and B.4. The contracting Heart
Both the arterial and the venous vessels are built like a ‘tree’.
This tree starts as a ‘trunk’; which is a major artery or vein. This vessel then splits into smaller and small branches thereby developing into a tree.
The major difference between the arterial and the venous tree is that the arterial system splits up into smaller and smaller arteries while in the venous system, the reverse occurs. That is, smaller veins merge gradually into bigger ones.
4.
Finally, (!), the capillaries. These are vessels that are very small and very thin.
These vessels are so thin that fluid can easily leave the vessel and flow into the organ that they supply.
Because fluid, actually water, can easily flow into the tissue of an organ, it also carries the oxygen and other nutrients, which are dissolved in the water, into the organ.
5. More Information:B.5.3. The Capillaries
