Unit 2 Lesson 8 PDF

LESSON 8 Why do changes happen in the body when we’re sick? Sick with symptoms In addition to fever, we often feel a variety of other symptoms when we’re sick. In particular pain, heat, redness, swelling, and loss of function are all symptoms of inflammation. Inflammation is the body’s response to...

LESSON 8 Why do changes happen in the body when we’re sick? Sick with symptoms In addition to fever, we often feel a variety of other symptoms when we’re sick. In particular pain, heat, redness, swelling, and loss of function are all symptoms of inflammation. Inflammation is the body’s response to injury, irritants, or infection. A look under the hood Medical professionals may suspect harmful bacteria have entered and begun growing in the body, even if they cannot see outward symptoms of inflammation. They may collect a small sample of blood and run tests for cells and molecules that indicate inflammation. The table below provides an overview of three common tests. Test C-reactive protein (CRP) Description • C-reactive protein is one of the first types of proteins produced in response to inflammation in the body. • It stimulates increased production of white blood cells. • CRP rises dramatically when there is inflammation. Complete blood count (CBC) • A complete blood count determines the number of red and white blood cells in the bloodstream. • The number of white blood cells is of particular interest because they are immune system cells. • This number rises dramatically when there is inflammation. • White blood cells destroy and remove bacteria and damaged body cells. • The white blood cells also alert other immune system cells to the presence of infectious agents. Erythrocyte sedimentation rate (ESR) • Erythrocytes are red blood cells that circulate in the bloodstream and transport oxygen to cells and carbon dioxide away from cells. • The ESR test measures the amount of time it takes for red blood cells to settle to the bottom of a test tube. • When there is inflammation, there is an increase in the amount of clotting factors in the bloodstream. Fibrinogen is one type of clotting factor. • When clotting factors increase in the blood, red blood cells tend to clump together more. Then they settle faster in the test tube. Tests for cell responses to inflammation. If the CRP, CBC, or ESR tests are elevated, indicating an increase in the levels of CRP, white blood cells, or fibrinogen, doctors know that the body is experiencing inflammation, and could be being attacked by an infectious agent if no other injury or irritant is present. How do these cells and molecules fight bacteria? Just as on a battlefield, immune cells enact stages of defense. These stages include (1) detecting the invaders and the damage created, (2) destroying the invaders and removing them, and (3) mobilizing action, which includes using signals to alert others that may be further away to come and help, creating barriers to block the invaders, and aid in repairing damages. White blood cells can detect molecules that are specific to bacteria as well as molecules that are released when our own body cells are damaged or killed. Some types of white blood cells can destroy bacteria by engulfing or “eating” them—digesting them and shredding them apart. Many white blood cells also mobilize action by sending signals to other immune cells and other parts of the body to assist with the immune response. The white blood cell in the middle has released signal molecules (which we can’t see here) and it has attracted other white blood cells. So why do we feel bad when our immune system is saving the day? In order to create conditions that are conducive to immune system activity and a hostile environment for the bacteria, immune cells send signals to the brain that trigger fever, they increase blood flow to the site of infection, and they increase blood clotting. As you can see, some of the things your body does to fight the infection are responsible for making you feel bad. Benefit vs. cost A common symptom of a disease is fatigue. You may describe yourself as having no energy. You may have noticed that you often lose weight when you are sick, especially if the illness lasts several days or weeks. This is only partly due to eating less when you don’t feel well. It takes a lot of energy for your body to produce the extra immune system cells and proteins that fight infection in your body. In addition, body cells that are destroyed in the infection must be replaced. In addition to the energy cost of maintaining the immune response, the ongoing inflammation caused by immune cells and molecules is harmful to the body. For example, people who have inflammatory bowel disease (IBD) experience ongoing inflammation that makes them more likely to develop other diseases as well. Thus, it is important that the body turn off the immune response once it has destroyed disease-causing bacteria.