THE HEART/ CIRCULATORY SYSTEM
- Created by: dav09
- Created on: 09-10-21 06:58
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- The Heart
- The heart and circulation have one primary purpose
– to move substances around the body.
- such as oxygen, carbon dioxide and digestive products are moved around the organism by diffusion.
- Many complex organism have a circulatory system as they too bigger to rely on only diffusion. Circulation allows substances to be move quickly /efficiently.
- Open circulatory system
- In insects and some other animal groups, blood circulates in large open spaces. A simple heart pumps blood out into cavities surrounding the animal’s organs.
- Substances can diffuse between the blood and cells. When the heart muscle relaxes, blood is drawn from the cavity back into the heart, through small valved openings along its length.
- Closed circulatory system
- Many animals, including all vertebrates, have a closed circulatory system in which the blood is enclosed within tubes
- This generates higher blood pressures as the blood is forced along fairly narrow channels instead of flowing into large cavities.
- This means the blood travels faster and so the blood system is more efficient at delivering substances around the body
- Animals with closed circulatory systems are generally larger in size, and often more active than those with open systems.
- Single circulatory systems
- Animals with a closed circulatory system have either single circulation or double circulation. Single circulation is found, for example, in fish
- Double circulatory systems
- This means that the blood flows through the heart twice
for each complete circuit of the body.
- The heart gives the blood returning from the lungs an extra ‘boost’, which reduces the time it takes for the blood to circulate round the whole body.
- This allows birds and mammals to have a high metabolic rate, because oxygen and food substances required for metabolic processes can be delivered more rapidly to cells.
- This means that the blood flows through the heart twice
for each complete circuit of the body.
- The heart and circulation have one primary purpose
– to move substances around the body.
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