Back To CoursePathophysiology Textbook
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I once had a car that was so poorly made that everything seemed to go wrong with it from day one. The mirrors would fall off, but I'd glue them back on. The stereo buttons wouldn't work, so I had to use the little tune button to find my favorite stations. Premature rusting occurred, so I had to paint over it. All those little injuries to my car were reversible, or a workaround could be found.
But after many years, the damage to more serious structures like the wheel bearings, electrical system, and transmission began to occur to the point of being irreversible - meaning, I just had to let the car go, and it sort of died on me.
In a congruous fashion, sometimes your body's cells are so damaged by potentially so many different ways that the injury may be irreversible, and the cell may even die. This lesson will explore some of these different types of cell death.
Other lessons mentioned the wide variety of injuries that can cause a cell to die, such as radiation that may cause lipid peroxidation, or the breakdown of lipid-based cellular structures due to oxidation. Other causes for injury to a cell may include intracellular accumulations of carbohydrates, such as in the lysosomal storage disease known as mannosidosis. Furthermore, oxygen deficiency due to anemia, blunt force trauma, toxins, and drugs can all cause either reversible or irreversible injury to a cell and even an entire organ or tissue.
One type of end result of cell injury is known as apoptosis, where a cell decides to die in a quiet fashion that doesn't induce inflammation and results in the ordered and structured shrinking of a cell without releasing its intracellular contents into the outside world. This last point is important to note since the release of those contents could trigger inflammation, which doesn't occur in apoptosis.
However, inflammation does occur in a process of cell death known as necrosis, which occurs as a result of an injurious event. Once an irreversible injury to a cell occurs, then necrosis will result. However, there are different types of necrosis that may occur, and that's what we'll focus in on from now on.
One form of cell death is known as coagulation necrosis. Coagulation necrosis is a type of cell death that preserves the core outlines of dead cells and results in a gel-like appearance as a result of protein denaturation. The major reason that coagulation necrosis occurs is due to a lack of blood or oxygen supply to a part of the body. The coagulation of proteins that occurs in coagulation necrosis can be likened to cooking liquid egg whites into semi-solid-like structures.
Again, the defining feature here is that the morphology of the cells is maintained during their death and can be readily identified under the microscope. It's like when you cook those egg whites - at first, the clear liquid spreads about the pan, but then sort of freezes or maintains its structure as it's cooked and doesn't fall apart thereafter. That way, you'll remember that coagulation necrosis preserves cell and tissue architecture more so than the other types of necrosis we'll talk about. One famous subtype of coagulation necrosis that you have certainly heard of is called 'gangrene.'
Another form of cell death as a result of irreversible injury is known as liquefactive necrosis. This type of cell death is characterized by rapid enzymatic degradation of cells into a liquid form. Here, as you can tell, the cells are completely destroyed, don't maintain their outlines or architecture, and basically melt into this gooey, wet, liquid mess. It's the exact opposite of coagulation necrosis. To me, it's the equivalent of taking an ice cube out of the fridge and letting it melt into a big mess. That's what happens in liquefactive necrosis.
This type of cell death is most common in the central nervous system, such as the brain, or due to a bacterial infection. In the case of the latter, the inflammatory response initiated by the bacteria causes a lot of destructive enzymes to be released by cells called neutrophils, resulting in the death of bacteria, cells, and tissues. This causes a yellow-white mixture of dead debris to accumulate. In fact, an abscess, which is a pus-filled structure, is a more commonly known type of liquefactive necrosis.
A third type of necrosis is known as caseous necrosis and is a type of necrosis associated with a longstanding initiator of cellular injury that cannot be destroyed or broken down, which causes the dead surrounding tissue to resemble cottage cheese.
Caseous necrosis can be thought of as a middle ground between the more structured coagulation necrosis and the utterly destroyed mess of liquefactive necrosis. If you were to take a piece of tissue undergoing caseous necrosis, it would crumble in your hands like cottage cheese and in longstanding cases may feel a bit gritty as well as a result of tissue calcification. Longstanding bacterial infection such as by tuberculosis or fungal infections are common causes for this type of necrosis.
There are two other types of necrosis that may occur in your body. One of these is known as fat necrosis. In this type of cell death specific to fat in the body, enzymes that digest fat may escape the pancreas when it is inflamed, thereby causing the fat to saponify, or turn into soap. One final type of necrosis is known as fibrinoid necrosis and mainly occurs during immune reactions that target the blood vessels.
As a final note, each type of necrosis may occur simultaneously due to a similar injurious event or may occur sequentially, such as when liquefactive necrosis may follow coagulation necrosis in the long run.
Furthermore, tissues may be simultaneously undergoing necrotic and apoptotic events all depending on how injured a cell may be as well as the duration and cause of the injury. This lesson has been a generalization of what occurs, but do keep in mind that the real world is a bit more complicated.
Well, with those disgusting examples of cell death finally over with, let's quickly glance over them one last time, and hopefully you'll never have to see any of them in real life, because one thing I cannot tell or show you accurately enough through these videos are all of the delicious smells associated with cell death.
The different ways by which irreversible cell injury may occur are many. One such example is radiation that causes lipid peroxidation, or the breakdown of lipid-based cellular structures due to oxidation.
Regardless of cause, cells may undergo necrosis, or cell death, as a result of an irreversible injury.
There are many different types of necrosis. They are:
Studying this video lesson might help you to:
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Back To CoursePathophysiology Textbook
20 chapters | 274 lessons