Transport in animals

Circulatory system in mammals

• The circulatory system is a system of blood vessels with a pump and valves to ensure one-way flow of blood.
• Blood flows twice through the heart during one circuit of the body:
• The right side of the heart pumps blood to the lungs and back to the heart again. The pressure required to force blood to the lungs is not very high since there is little resistance to flow.
• The left side of the heart pumps blood to the rest of the body and back to the heart again. The pressure here is greater because there is much more resistance to flow.
• This completes one circuit.
• Advantages of a double circulation:
• Higher blood pressure
• Greater flow of blood to the tissues.
• No mixing of oxygenated and deoxygenated blood.
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Single circulation in fish

• The blood travels from the heart to the gills, where it absorbs oxygen and releases carbon dioxide.
• It then flows from the gills to the organs and tissues in the rest of the body, and back to the heart. There is just one circuit from the heart.
• Blood is under low pressure.
• In the circulatory system of a fish, the blood travels from the heart to the gills, where it absorbs oxygen and releases carbon dioxide. It then flows from the gills to the organs and tissues in the rest of the body, and back to the heart. There is just one circuit from the heart.
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