Homeostasis is the process in which the body maintains normal, healthy ranges for factors such as temperature, energy intake and growth. The immune response contributes to homeostasis by preparing the body to fight off infection and to help the healing process in case harm occurs. During infection, the immune system will cause the body to develop a fever. The immune system also causes an increase in blood flow to bring oxygen and other immune cells to sites of infection. In addition, the immune system helps in wound healing, so that proper barriers in organs can be reformed such that those organs can correctly participate in homeostasis.
TL;DR (Too Long; Didn't Read)
Homeostasis is the body’s process for maintaining even ranges of body systems such as temperature, hydration and energy intake. Homeostasis is essential for healthy bodies. The immune response contributes to homeostasis by helping to fight off infection and heal after infection or trauma. During an infection, molecules called pyrogens are released, which alert the brain to increase the temperature of the body, causing a fever. The fever inhibits the movement of bacteria and viruses, buying more time for the immune cells to find and eliminate the invaders.
At the site of a bruise or cut, immune cells called mast cells release chemicals that enlarge the blood vessels, increasing blood flow and bringing more oxygen and immune cells to the injury site. Dead or broken cells at the wound site are eaten by immune cells called macrophages. In damaged skeletal muscle, macrophages accumulate at the site of injury and release a protein that causes muscle cells to regrow. In damaged skin, macrophages fill up the wound and release chemicals that cause new blood vessels to form.
Immune cells called T and B lymphocytes recognize proteins captured from infectious invaders, and learn how to attack the invader. They make a copy of themselves so that one cell becomes the effector cell, fighting the invader, and the other copy becomes a memory cell, waiting in the body for long periods in case the same invader returns again, so it can fight it off more quickly.
The Fever Fight
When a body is infected by bacteria or viruses, the body must invest a lot of energy to fight off the invaders. There is no point in maintaining homeostasis of hydration levels and the many other systems the body regulates if the whole organism is going to die from infection. Pyrogens are molecules that are released by infected cells or infectious agents. Their presence alerts the brain to increase body temperature, which it does by ordering the body to retain heat. This results in a fever. Fevers’ function is to slow down bacteria and viruses, which do not like high temperatures. This buys more time for the immune cells to find and eliminate the invaders.
Increased Blood Flow
The site of an injury or infection will turn red, swell, and feel tender and warm. These are the symptoms of what is called inflammation. Immune cells rush to the site and release chemicals that cause these symptoms. In particular, mast cells are immune cells which release chemicals that enlarge, or dilate, the blood vessels at the site of a bruise or a cut. This dilation brings more blood to the site of injury, including more oxygen to sustain the burst of repair activity, and more immune cells to help. Increased blood flow means faster repair. Faster repair means the body can get back to normal faster.
Wound healing is the process in which a damaged tissue is repaired. At the site of damage, dead or broken cells are eaten by immune cells called macrophages. In damaged skeletal muscle, macrophages accumulate at the site of injury and release a protein that causes muscle cells to regrow. In damaged skin, macrophages fill up the wound and release chemicals that cause new blood vessels to form. These blood vessels will be necessary to bring nutrients to and remove wastes from the new skin cells that will form. Until the wound is repaired, the body is at higher risk of infection and homeostasis cannot be fully attained.
Immune cells called T or B lymphocytes become activated for battle after they encounter foreign proteins that were captured from invading organisms. After finding a protein molecule from a particular type of foreign invader, T and B cells train themselves to fight against this invader. T and B cells can undergo what is called clonal selection, which is the process in which they divide to make two different types of copies of themselves. One type of copied cell is called the effector cells, which go right into battle fighting invaders. The other type of copied cell is called memory cells, which stay inactive in the body for a long time, waiting to encounter the same invader in the future so that they can mount a faster attack the second time around. Memory cells make the body better prepared for future invasions, which makes it easier to maintain homeostasis in the future.
- Scientific American: What Causes a Fever?
- Medical News Today: What Is Inflammation? What Causes Inflammation?
- American Society of Hematology: Blood: Mast Cell Modulation of the Vascular and Lymphatic Endothelium
- Medical News Today: Inflammation Helps To Heal Wounds - Surprise Discovery
- National Health Institute: International Journal of Clinical and Experimental Pathology: Skin Wound Healing Modulation by Macrophages
About the Author
David H. Nguyen holds a PhD and is a cancer biologist and science writer. His specialty is tumor biology. He also has a strong interest in the deep intersections between social injustice and cancer health disparities, which particularly affect ethnic minorities and enslaved peoples. He is author of the Kindle eBook "Tips of Surviving Graduate & Professional School."