COVID-19 and Loss of Smell Explained

Hi everyone, Dr. Mike, you've probably heard that some people with Covert 19 lose their sense of

smell

. We call this

loss

of

smell

anosmea, and interestingly, it is a relatively common symptom of Covert 19. Up to 55 percent of people who have Covert 19 experience it. Fortunately, a nosmia is now called transient, meaning that the sense of smell smell should return. Most people regain that sense of smell within a couple of weeks; However, there is a subset of people, about 10 percent, who still haven't regained that sense of smell in a month. Now how does this happen and why does it happen?

So I've drawn here the nasal cavity deep in the nose and what you'll find is obviously that we breathe in air and as we breathe in air we bring in chemicals and smells and what happens is Sensory neurons that project from our central nervous system, specifically in an area called the olfactory bulb. They project neurons through a bony plate in the nose. Now, if you were to stick your finger in your nose, you wouldn't be able to reach this area. At the top, which we call the olfactory epithelium, the neurons that project through this bone plate can actually be damaged by a blow and what happens is that the bone plate cuts these neurons.

This is not what is happening on deck 19. The neurons that The project will pick up these chemicals known as odors and send the signal directly to the olfactory bulb and then to the central nervous system and brain so that we are aware of what we have smelled. Okay, now that this olfactory epithelium is no longer done. From these olfactory neurons or olfactory sensory neurons, there are actually a bunch of other cells present called supporting cells. These support cells can include microvilli cells, sustainacular cells, globular basal cells, olfactory and lining cells, there are a lot of different cells that support the role of olfactory sensory neurons now when I say support what they do is provide products metabolic, they remove metabolic waste, they support the cytoskeletal architecture around the area and they also make sure that if any of the cells die, they phagocytose them, so they eat them and recycle them.

They ensure that homeostasis is maintained in this microenvironment so that the olfactory neurons can do their job and capture the sense of smell. Now, when we breathe in, for example, particles containing the sars cov2 virus, we know that the virus is surrounded by proteins. called s proteins now what needs to happen is that the cells or tissues need to express two particular receptors ace2 and tmprss2 ace2 is angiotensin converting enzyme 2 and tmpr ss2 is a serine protease basically they are scissors that cut the proteins what happens is that the virus needs to bind to the ace2 receptors and this little serine protease needs to cut some of the proteins on the outer surface of the virus which then activates the proteins so it can embed itself in the cell membrane and you can release your virus again or should That is, it can release its DNA into the cell itself for replication, so what scientists have done recently is look at all the tissues within the body and they had to look at the expression of these particular receptors to see in which tissues they are highly expressed. . because that means they will probably be more susceptible to infection by the sars cov2 virus, what they found is that the heart has high levels of expression, the kidneys, the blood vessels, the brain, so aspects of the nervous system, the respiratory and lungs.

Also, this is one of the reasons we have multiple organ dysfunction in covert 19. What a more recent article did in August 2020 is that they looked at the cells of the olfactory epithelium and the expression levels of these two particular receptors. What they found were the olfactory sensory neurons, those that capture odors for the sense of smell, in They don't actually express those two, however, the supporting cells do or at least a subset of those supporting cells do too, for example. microvillar cells, sustainacular cells and globular basal cells tend to express ace2 and t and pr ss2 relatively high compared to others now what this highlights is that the sars cov2 virus tends to infect the supporting cells and damage their ability to maintain homeostasis during The olfactory sensory neurons, therefore, over time, the olfactory sensory neurons cannot do their job and the sense of smell is lost and is transient because once the virus has run its course, the supporting cells They can regenerate and then can support the old factory neurons.

I like to think of this as a racing driver, now the racing driver seems to do all the work. The racing driver is the sensory neurons of the old factory, however, without his support team, without people there to refuel the car and repair it when it is damaged. to tell the driver where to go in a short period of time, the car will simply stop and the driver will stop working, but once he replenishes, rejuvenates or regenerates that support equipment, the driver will be able to start putting it into gear. so to speak and be able to do its job so this seems to be what happens when the virus says cov2 is infecting the olfactory epithelia and people are losing their sense of smell covert 19.