The Circulatory System

A Conceptual Model of the Circulatory System

It may be useful to have a conceptual model of the circulatory system both in order to understand how it works and how it may fail.

I have used an analogy with a simple industrial system. Let us suppose that we have a factory that uses oxygen in order to produce it's goods. This factory is supplied by an oxygen producing plant some miles away. In order for the oxygen to get from the plant to the factory it has to be sent in a sealed pipeline dissolved in an inert fluid. In between the two there are two pumps attached to the pipelines in order to ensure a continuous flow from the Oxygen Plant to the Factory. At it's inlet valve Pump 1 receives oxygen rich fluid from the Oxygen Plant and pumps it through it's outlet valve under pressure to the Factory.

At the Factory the oxygen is extracted from the pipeline and the remaining fluid, now at a lower pressure is sent on through the pipeline to the inlet valve of Pump 2

Pump 2 sends the fluid through it's outlet valve into a pipeline which goes to the Oxygen Plant where it is replenished with dissolved oxygen and sent to the inlet valve of pump 1 and the whole process begins again.

Think about things that can go wrong with the system that would cause loss of production at the factory.

The conceptual model outlined above is obviously a simplification but it can help to get an idea about the circulatory system. The Oxygen Plant represents the lungs. The pipelines the major blood vessels. Pump 1 represents the left side of the heart with it's valves whereas Pump 2 represents the right side of the heart and it's corresponding valves. The factory represents the metabolic processes going on in the body.

Simplified human circulatory system

The picture on the left shows a simplified animation of the human circulatory system.

Unfortunately it has 28 frames so can take a little time to download depending on your connection speed and you computer so please be patient.

It follows the path taken by a red blood cell leaving the ascending aorta of the heart. From here it goes into the capillary network of the systemic circulation where it loses it's oxygen so that it can be used in metabolic activities.

The deoxygenated blood is eventually taken to the right auricle of the heart via the inferior or superior vena cava (depending where in the body it went to).

From here it passes into the right ventricle of the heart which contracts and sends it towards the lungs via the pulmonary arteries.

In the capillary bed of the lungs the red blood cell is recharged with oxygen and sent back to the heart via the pulmonary veins. It re-enters the heart at the left auricle and passes into the left ventricle. The left ventricle contracts to send it into the ascending aorta and the cycle starts again.

Did you come up with any ideas on what can go wrong with my conceptual model of the factory?

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This page last updated on Monday, 07 June 1999 12:14 +0100

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