The truth about being "sick"
Many disease symptoms that befall us are actually caused by the immune system's response to invading pathogenic microbes, rather than something the microbes are doing, specifically. Take, for instance, the common cold.
When the rhinovirus gets into your upper respiratory tract and invades epithelial cells (those that line the cavities in the body), it triggers inflammatory and immune responses. Certain cells release histamines, which dilate your blood vessels and increase their permeability, allowing white blood cells and some proteins to get to the infected tissues.
You often experience nasal congestion because your inflamed blood vessels are now so large that they stuff you up. But histamines also affect the amount of mucus your body produces, as well as its viscosity — this altered mucus production, along with the increased fluid leakage from now-permeable capillaries, can cause a runny nose.
Similar immune system reactions take place when you develop pneumonia, which is most often caused by bacteria and viruses (especially the bacterium Streptococcus pneumonia). Your body has pretty decent defenses to keep microbes out of the lungs, including nose hairs that filter air and certain reflexes (coughing and sneezing) that shoot microorganisms that enter your body back out. But sometimes that's just not enough.
If bacteria get inside the alveoli (tiny air sacs in the lungs), they can invade the spaces between cells and even travel to adjacent alveoli. Your immune system responds by once again inflaming your blood vessels and making them permeable, allowing white blood cells and proteins to come to the rescue. But this permeability allows fluids to seep into the alveoli, taking up space that's needed for the oxygen-carbon dioxide exchange. You become somewhat oxygen deprived and exhibit the shortness of breath and fatigue, both of which are a common symptom of pneumonia. Moreover, your respirations increase as you try to bring more oxygen in and blow more carbon dioxide out.
Pneumonia and the common cold are also marked by fever, something that also arises because of our immune system. When white blood cells called macrophages encounter bacteria or viruses in your system, they produce cell-signaling proteins called interleukin-1 (IL-1). These proteins do two things: They call in helper T-cells and they bind to certain hypothalamus receptors in your brain, causing a rise in your body temperature, which is thought to help kill some pathogenic microbes. Substances that induce fevers, such as IL-1, are called pyrogens; some bacteria can induce fevers with pyrogens, too.
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When the rhinovirus gets into your upper respiratory tract and invades epithelial cells (those that line the cavities in the body), it triggers inflammatory and immune responses. Certain cells release histamines, which dilate your blood vessels and increase their permeability, allowing white blood cells and some proteins to get to the infected tissues.
You often experience nasal congestion because your inflamed blood vessels are now so large that they stuff you up. But histamines also affect the amount of mucus your body produces, as well as its viscosity — this altered mucus production, along with the increased fluid leakage from now-permeable capillaries, can cause a runny nose.
Similar immune system reactions take place when you develop pneumonia, which is most often caused by bacteria and viruses (especially the bacterium Streptococcus pneumonia). Your body has pretty decent defenses to keep microbes out of the lungs, including nose hairs that filter air and certain reflexes (coughing and sneezing) that shoot microorganisms that enter your body back out. But sometimes that's just not enough.
If bacteria get inside the alveoli (tiny air sacs in the lungs), they can invade the spaces between cells and even travel to adjacent alveoli. Your immune system responds by once again inflaming your blood vessels and making them permeable, allowing white blood cells and proteins to come to the rescue. But this permeability allows fluids to seep into the alveoli, taking up space that's needed for the oxygen-carbon dioxide exchange. You become somewhat oxygen deprived and exhibit the shortness of breath and fatigue, both of which are a common symptom of pneumonia. Moreover, your respirations increase as you try to bring more oxygen in and blow more carbon dioxide out.
Pneumonia and the common cold are also marked by fever, something that also arises because of our immune system. When white blood cells called macrophages encounter bacteria or viruses in your system, they produce cell-signaling proteins called interleukin-1 (IL-1). These proteins do two things: They call in helper T-cells and they bind to certain hypothalamus receptors in your brain, causing a rise in your body temperature, which is thought to help kill some pathogenic microbes. Substances that induce fevers, such as IL-1, are called pyrogens; some bacteria can induce fevers with pyrogens, too.
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