Often times, the connection between patient symptoms and cellular problems is difficult to either define or appreciate. If you are in pain, the answer is Advil (or Tylenol, Motrin, YourFavoritePainRevliever, etc). Very few people pause to ask how YFPR actually takes care of pain; they just want the discomfort gone. Typically, the answer is quite straightforward (and I’ll explain it in another post!) Unfortunately, some problems are multi-variable situations where you can’t easily say “This Issue” leads to “These Symptoms.”
Interestingly, in the case of HPV infection, we are partially able to explain the relationship. I say partially only because different experiments have shown conflicting results as to exactly what pressures will lead to faster or slower cancer growth, but they all agree how HPV sets the cell up to become cancerous. (Scientists also use the term “transform” or “transformation” to define a cell that has changed from healthy to cancerous.)
So, let’s transition from clinical symptoms (covered in HPV & Personal Reasons Post) to proteins/viruses inside cells by first looking closer at stratified epithelium, which is the type of tissue that comprises a cervix.
Figure 18.1 shows a cross-section of stratified epithelium. It contains all different kinds of cells that are represented here as purple, white, and beige rectangles. The very top white/beige cells are the outermost layer of the tissue and are exposed to the environment outside the body. The lower cells are what you would find if you removed the outer layer and went deeper into the tissue.
Let’s ignore the green cells for right now and focus on the purple, beige and white cells to the far right. I’m going to use this section to explain how stratified epithelium works.
First, compare the bottom purple cells to the upper-most beige/white cells. They look very different, yes? This is because, while they are similar cells, they have two very different jobs.
The upper-most beige/white cells are forming a layer between the outside world and the inside body. Their job is to protect the cells underneath. In the course of their job, these cells will come off and be shed to the environment. This means that the body will need to have more protective cells on hand to ensure proper protection from the outside environment. Unfortunately, these upper-most beige/white cells cannot replicate themselves anymore. So, how does the body ensure that it will have plenty of replacements?
The bottom purple cells (known as basal cells) serve this function. They are actively dividing and constantly providing new cells for the epithelium.
Interestingly, when a basal cell replicates, it does not spit out a cell that is immediately ready to serve and protect. The cell must be properly prepared and trained. All the cells between the bottom purple ones and the upper-most beige/white ones are in the process of changing from an actively dividing basal cell to protective cell. This process is called differentiation.
Think for a moment about old-school battle practices where the infantry used to line up in rows and rows of men. The first row of men would be in battle. They’d fire, some men would go down, and then the next row of men would move up to take their place. Way back behind all this, the lines of men were constantly being prepared from soldiers in the camp. Think of epithelium in the same way. The camp serves as the basal cells and the front line of men are the upper-most beige/white cells facing the elements. All the soldiers in between are preparing to fight.
Now let’s focus on the green cells. What are they?
They are cells infected with HPV, my friend. They look different because they aren’t like the cells around them. They aren’t changing from basal cells into upper-most beige/white cells; they are completely doing their own thing. More disturbingly, you have actively dividing cells on the surface of your cervix, meaning they aren’t protecting the cells underneath at all. Morphologically, they look and behave so differently that if you look at the surface of a cervix containing these cells, you can visibly pick out the diseased cells.
A Pap smear removes some cervical cells and places them on a slide. Looking under a microscope, a pathologist can see if the cells look like they normally should or not. A colposcopy allows for a doctor to view the cervix under magnification and look for patches of cells that do not look like the others. They spray acetic acid on the cells to enhance the differences and more easily define infected cells from healthy cells. These HPV infected cells that can be visibly seen are referred to as lesions.
HPV can only infect (“get inside,” see Spanish Influence, Part 2 post) basal cells. The virus comes from the environment. How does the virus get down to the basal cells if these upper-most beige/white cells are protecting them? Just like a skinned knee, the cervix can get microabrasions. This is depicted as the long break on the right side of Figure 18.1. HPV can travel down the abrasion and reach the basal cells. You may think those upper-most beige/white cells aren’t doing their job, but remember that we all get cuts and scrapes during life that sometimes get infected. This is no different.
We are getting deeper into how an HPV infection leads to cancer. What I’ve shown here is how a healthy epithelium works, how HPV can infect it, and how that can damage the tissue. The cancer actually arises from these green cells that are actively dividing all over the epithelium.
Transform: when a cell has a changed from healthy to malignant/cancerous
Differentiation: the process a cell undergoes to change from type of cell to another
Lesions: a localized abnormal or diseased spot in the body
REFERENCES
Doorbar, J. Journal of Clinical Virology (2005) 32, pgs S7 – S15
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