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Animal Systems

Circulation is the Key

The circulatory is a system of vessels that pass through your entire body. You may read about two types of circulatory systems in animals. There are open circulatory systems in primitive organisms where you will find a heart that pumps fluids through the creature, but no complete system of vessels. More advanced organisms, including you, have closed circulatory systems where the heart is connected to a complete system of vessels. The fluids of a closed circulatory system never leave the vessels.

What Does This System Do?

How does a circulatory system help you? It is the transportation system for your body. The circulatory system carries chemicals to all points in your body. The fluids also carry waste products and dissolved gases for your cells.

Think of the chemical compounds as cars and the circulatory system as a network of freeways, main streets, and side streets. The cars can pass from one building to another using these streets in the same way that a compound might be created in the brain and sent to the kidneys.

Interacting with Other Systems

The circulatory system touches every organ and system in your body. The system is connected to all of your body's cells so that it can transport oxygen efficiently. When you breathe, the circulatory system carries oxygen to your cells and carries dissolved carbon dioxide back to the lungs.

Every cell that needs oxygen needs access to the fluids in your circulatory system. The circulatory system and its fluids are super important to your digestive system that has absorbed nutrients from your food. Guess what? Hormones created by your endocrine system are sent through the body by the circulatory system.

Basic Parts of the Circulatory System

The core components of your circulatory system are the heart and vessels. You happen to have a four-chambered heart while other organisms may have one, two, or three chambers. The heart is the pump for the system. As blood is pumped from the heart, it passes through a system of arteries, arterioles, and then capillaries. The capillaries are the vessels that allow for most of the transfer of compounds and dissolved gases. Capillaries are very small and have thin walls to allow easier passage of compounds including nutrients, glucose, carbon dioxide, and waste products. After the capillaries, your blood passes through venules and veins. The veins lead the circulatory fluids back to the heart. That's it, the system is complete (and closed).

Next Page on Animal Systems
- Overview
- Regulation
- Skeletal
- Muscular
> Circulatory
- Respiratory
- Digestive
- Excretory
- Nervous
- Endocrine
- Integumentary
- Immune
- Lymphatic


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Animal Systems Quiz

Circulatory System Quiz

Useful Reference Materials
Encyclopædia Britannica:
Books on
- Modern Biology (Rinehart and Holt)
- Campbell Biology: Concepts and Connections (Reese, Taylor, Simon, and Dickey)
- Prentice Hall: Biology (Miller and Levine)
- Principles of Human Physiology (Silverthorn)
- Principles of Human Physiology (Stanfield)

- Chem4Kids: Metabolism
- Chem4Kids: Enzymes
- Geography4Kids: Populations
- Geography4Kids: Carbon Cycle
- Geography4Kids: Oxygen Cycle
- Geography4Kids: Nitrogen Cycle

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