The Great Transportation Network Inside Animals

What is the Circulatory System?

The circulatory system is like a highway inside an animal’s body. Instead of cars, it moves important fluids around. It uses a pump (imagine a strong engine) and special tubes that make sure everything flows in one direction.

The circulatory system is made up of:

• blood vessels
• the heart (a pump)
• one way valve system for blood flow

 

Single vs. Double Circulation

Single Circulation (e.g., in a fish):

• Imagine a simple loop. Fluid goes from the pump, around the body, and back to the pump once. It’s like riding a bike around one big circle.
• Fish have single circulation and a two-chambered heart
• This structure means that as the blood goes round the body it only passes the heart once per trip

 

 

Double Circulation (e.g., in a mammal):

• Now imagine two loops linked together, like a figure-eight track. The fluid goes from the pump to the body and back, and also from the pump to the lungs and back. Two loops mean more efficient delivery of what the body needs
• This is mammals double circulation system. Due to this mammals have four-chambered hearts
• This structure means that as the blood goes round the body it only passes the heart twice per trip
• The hearts left side takes in oxygenated blood from the lungs and pumps it to the body (systemic circulation)
• The hearts right side takes in deoxygenated blood from the body and pumps it to the lungs to recieve oxygen (pulmonary circulation)

 

Why Double Circulation is Handy

• Having two loops can help deliver what the body needs faster and more effectively. It’s like having two delivery routes instead of just one, making sure everyone gets their packages quicker.
• The blood travelling through the capillaries loses most of the pressure it recieved from the heart meaning it can't travel fast
• Allowing the blood to return to the heart after going to the lungs allows the pressure to be increased again. This means the cells can recieve the oxygen and glucose needed for respiration at a faster rate