B9.1 Circulatory system

What is the circulatory system?

• A network made up of the heart, blood vessels (arteries, veins and capillaries), and valves that ensure the blood flows in 1 direction only

• Supplies oxygen and nutrients to different parts of the body and removes carbon dioxide and other waste material

Describe the single circulation of a fish

• Fishes have a simple circulatory system where blood flows from the heart to the gills for oxygenation and from the gills to the rest of the body

• Heart → Gills → Rest of the body → Heart

Describe the double circulation of a mammal

• In double circulation the blood follows 2 circuits:

  • First circuit: the blood flows from the heart to the lungs for oxygenation and then back to the heart

  • Second circuit: blood flows from the heart to the rest of the body then back to the heart

• Heart → Lungs → Heart → Rest of the body → Heart

Advantages of double circulation

• In double circulation, blood is pressurized twice (before going into the lungs and again before going into the body) which allows efficient gas exchange and a faster delivery of oxygen nutrients

• Oxygen and glucose are supplied quickly to cells in the body, waste and carbon dioxide are removed quickly

• Blood can be supplied to distant parts of large animals

• Allows sufficient flow of warm blood around the body