The Impact of Viruses & Microorganisms on Homeostasis

Instructor: Erika Steele

Erika has taught college Biology, Microbiology, and Environmental Science. She has a PhD in Science Education.

Viruses and bacteria are so tiny that you can't even see them without a microscope. Even though they are extremely small, both can have a huge impact on how good or how bad you feel. Keep reading to find out more about how a bacteria can make the difference between having a bellyache or not!

What Are Viruses and Bacteria?

Maybe you've heard of viruses like the flu and bacteria like 'E coli' making people sick, but what exactly are viruses and bacteria? Bacteria are living organism just like you! Just like humans, bacteria are made of cells, need food or an energy source and healthy environments to live, grow, and reproduce. Bacteria (bacterium if it's just one) are extremely tiny organisms that are made of only one cell. The cell has a membrane, called a plasma membrane, surrounding its nucleic acid. Nucleic acids are pieces of DNA and RNA which are the instructions to make the bacteria a bacterium or you a human.

Viruses are even smaller than bacteria. However, unlike bacteria, viruses are not alive; they aren't even cells, which is an important characteristic of life. They also do not have a plasma membrane or take in nutrients to sustain themselves. A virus is a set of RNA or DNA (nucleic acid), surrounded by a protein coat called a capsid. Viral particles must 'hijack' or infect cells and force them to make more viruses instead of reproducing on their own. Without other cells they can't do anything. Viruses are parasites that depend on the living to exist.

Figure 1: Bacteria are living organisms, while viruses are not alive
Bacteria and viruses

Did you know that your skin is completely covered with bacteria even after you take a bath? There are thousands of viruses hiding in the genes of your cells. Although you are covered in bacteria and your cells are always infected with a virus or two, you are not always sick. How can this be?

Homeostasis: Working as a System

Homeostasis is the scientific word to describe how your body works to stay stable and healthy. The organs of your body work together as a system to keep your body in the same state even if your environment changes. Each organ has a role in keeping things in balance. For example, some organs act as receptors that detect signals from the environment. Your nerves are great examples of receptors. Equally important are organs called effectors that cause a change in the body in response to signals received from receptors in order to maintain balance.

Finally, in order for effectors and receptors to work together, there has to be something to help them communicate. Organs called integrators take the signals from the receivers and pass them along to the effectors. If you are thinking that the brain is the integrator in your body, you are correct! Your brain receives signals from your nerves and conveys those signals to other organs that can make adjustments in order to maintain your body's balance.

Here's an example of homeostasis in your body. Think about what happens if you go outside; your body doesn't heat up or cool down to the temperature of the environment. Instead, it reacts to stay at a steady state. First, your nerves act as receptors that detect the temperature. From there your brain receives the signals and relays the message causing your muscles to shiver if it is cold, or causing you to sweat if it is hot. These actions keep your body at an even temperature despite the temperature outside. Ultimately, homeostasis is the process of the organs in your body working together as a system to keep you healthy.

Figure 2:1) Nerves sense temperature, 2) the brain receives the signal and convey the message, 3) the appropriate effector acts to adjust body temperature; sweat glands sweat and muscles shiver.

Homeostasis works in other living organisms as well; this includes animals and plants. Animals have organ systems very similar to ours, thus homeostasis works similarly in animals as it does in humans. Have you ever noticed that dogs pant when it is hot out or they've been playing a lot? Well dogs don't sweat like we do, instead their brain tells them to pant. Did you know that even plants sweat when it is hot? It is technically called transpiration. Plants regulate their temperature using specialized openings in their leaves called stomata. When it is hot, the stomata open, allowing water to escape and cool the plant down in the same way our sweat cools us down.

Viruses and Bacteria: Friends or Foes?

Bacteria and viruses make us sick by growing uncontrollably, growing in places they don't belong or by producing toxins that harm us. Whenever anything happens to make your body out of balance- like when viruses and bacteria invade, your organs will work as a system to maintain homeostasis. Your immune system, a special group of cells in the body, has the task of getting rid of anything foreign that gets into your body. Animals and plants have to fight against bacteria and viruses as well. Animals have immune systems just like we do, but plants are different. Even though they don't fight off bacteria and viruses exactly like us, they are still able to do it.

Once your immune system detects a foreign invader, it is destroyed by the immune system. How does this work? Your immune system recognizes foreign invaders and sends signals that cause your body to respond to the intruders. For instance, these cells produce chemicals called cytokines that tell your brain to increase body temperature in an attempt to kill any bacteria or cells infected with a virus. Other cytokines lead to inflammation or swelling in an attempt to keep the infection in one area of your body. For these reasons, in addition to producing toxins, bacteria and viruses make us sick because our immune system is recognizing and destroying foreign invaders. In doing so, our cells are affected. However, we usually out survive bacteria and viruses, our body will return to normal, and homeostasis is maintained.

Figure 3:Our immune cells release cytokines to help get rid of viruses and bacteria, but these make us feel sick, too.
why we get sick

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