Many different things can happen to you during the course of a day. You might have to race for the bus, locate materials when you arrive at school, or review for a science test. Did you know that the environment inside your body is constantly changing too? For instance, during stressful situations, your body will react by producing hormones that supply you with energy right away and cause your heart to speed up. This reaction to stress helps you perform well during tests or emergencies. Your body is constantly responding to changes that occur in the environment around you. In this activity, you will learn how your body adjusts to these changes. 

A change in the outside environment generates a response from your body’s internal environment. Your body must maintain the proper internal conditions while responding to changes in the outside environment. This ability of your body to maintain an internal balance is called homeostasis (pronounced: hoh-mee-o-STAY-sis).

In L10 — A1, you learned that all living organisms have special structures that carry out life processes or life functions. You can review these life functions below.

In other parts of this course, you have also learned about some of the systems of the human body, including the digestive system, the circulatory system, and the immune system.

The life functions and all the body systems work together to maintain homeostasis.

Here are just some examples of how your body maintains homeostasis:

• In the circulatory system, during times of high activity or stress, your heart rate increases to help circulate more blood to deliver the necessary nutrients and oxygen to the cells.

• Every time you exhale, your respiratory system eliminates waste as carbon dioxide.

• Your body gets rid of toxic materials by filtering the blood through the kidneys.

• If you eat a meal high in sugar, the concentration of glucose in the blood vessels rises. In response, the pancreas releases a hormone called insulin. Insulin moves glucose from the blood to body tissues. This returns glucose concentrations to normal levels.