School Biology notes: Human circulatory system: Part 1. Heart and lungs
The human double circulatory system 1. Explaining the double circulatory system involving the heart and lungs and its advantages
Doc Brown's GCSE level Biology exam study revision notes
There are various sections to work through, after 1 they can be read and studied in any order.
1. A double circulatory system - advantages
Oxygen is needed to produce energy from respiration chemistry to power the cells of any organism. Carbon dioxide is the waste product from respiration. So, a gas exchange system is required - this takes place in the alveoli of the lungs.
This is described on the Gas exchange in the lungs by diffusion page, so here we concentrate on the double circulatory system and how the heart works.
The circulatory system transports substances around the body
In the second circuit, the left ventricle of the heart pumps oxygenated blood from the lungs to all the organs and associated structures (the rest of the body except for the lungs) and returns it to the heart (left diagram).
After circulating round the body discharging its oxygen to all the cells of the body, the heart pumps the blood back to the lungs to be re-oxygenated.
Blood is pumped out of the heart under high pressure into the arteries.
The blood flows through the arteries to the capillaries and then the veins, in doing so , the pressure decreases.
The whole double circulation system is pretty complicated (right diagram).
The diagram is a simplified diagram of the double circulatory system of the human body as an example of the mammalian circulation structure.
Apart from the lungs, the blood vessel system must pass near all the rest of the exchange surfaces too e.g.
The advantages of the mammalian double circulatory system
Note on fish:
Summary of learning objectives and key words or phrases
Be able to interpret diagrams explaining the double circulatory system of the heart and lungs in humans and other mammals and be able to explain the advantages of a double circulatory system.
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