Back To CoursePathophysiology Textbook
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Oceans can swell, bruises can swell, and even people can swell. The reasons for swelling can run the gamut from global warming to inflammation to a diet full of sweets, in each case respectively. It all depends on what is actually swelling.
In our case, we're not going to deal with the giant, or macroscopic, world at large. We will actually look at the microscopic or cellular details of why cells may swell and whether it's reversible or not.
Cell swelling, also known as hydropic degeneration, is the earliest and most universal indicator of potentially reversible cellular injury. Cell swelling, to put this lesson briefly, occurs as a result of too much water moving into the cells as a result of some injury.
This must be contrasted to a term we learned in another lesson, called hypertrophy. If you watched that lesson, you should remember that hypertrophy also occurs when there's an increase in cell size. But, the increase in cell size in hypertrophy is not due to an increase in water, but due to an increase of normal organelles within the cell.
With that small, but important, tidbit out of the way, we can go over how a cell can become injured. Since we also did this in another lesson, I won't harp on these generalities as much, since we need to deal with the nitty-gritty of cell swelling this time around.
Cells are nothing more than microscopic components of who you are. I am certain you can think of many ways that you, your entire self, can become injured. If you can do that, then you can surely understand that the injury you see and feel also injures your cells, which cause you pain and inflammation. Cellular injury, therefore, can occur from something like a fall, a bad drug or poison, radiation, infectious causes such as a viral invasion, or an autoimmune disease such as myasthenia gravis.
Regardless of the cause of the injury to a cell that results in cell swelling, if it's caught early enough, the cell may compensate for the injury and survive, resulting in a potentially reversible injury. Other times, if the damage is too severe or it's not dealt with medically soon enough, the cell swelling becomes irreversible and leads to necrosis, or the death of cells and tissues.
Okay, now that we've gotten the really easy stuff out of the way, it's important for you to understand how it is that a cell begins to swell as a result of injury.
Let's say that in our particular case, the injury is a result of something like a blocked artery. When an artery is blocked, it cannot deliver enough blood to an area of the body. If not enough blood comes into the area, not enough oxygen can be carried through by the red blood cells. If there's not enough oxygen, a state of hypoxia results.
This is a big deal. It's not that hard to understand why. If you were to hold your breath for a few minutes, you would die. If your cells don't get enough oxygen, they can die as well.
The reason for this is because oxygen is extremely important for the production of the body's energy currency, known as ATP. If a cell doesn't have ATP, which is produced in large quantities, thanks to oxygen, then it basically has no money in its pocket to pay the bills. These bills must be paid to cellular organelles that produce proteins that run important chemical processes to channels in the cell membrane that block or allow important or bad things from getting into or out of the cell, and for the upkeep of the protective cell membrane itself. If the cell can't pay its bills to these utility-like structures and companies, they begin to shut down their services.
Well, some of the most important structures that shut down are the ion pumps of the cells that normally move sodium out of the cell and potassium into the cell. The ion pumps can be compared to something like the crossing point commonly known as Checkpoint Charlie that divided East Berlin and West Berlin during the Cold War. If the guards at the checkpoint weren't paid, they would leave, allowing anything and anyone to go between the two sides freely. If, however, they are paid enough, they stay there and check everyone's credentials and only allow what needs to pass through to do so.
In a normal cell, these channels, like Checkpoint Charlie, move sodium out of the cell and move potassium into the cell. As soon as our hypoxic injury causes the energy currency to be depleted out of the cell, the sodium-potassium pumps stop working. Since there's more sodium on the outside of the cell than on the inside, sodium rushes into the cell in great quantities, and that's a big, big, problem.
That's because water follows sodium. Remember that: water follows sodium in your body. If you've ever eaten a lot of salt, of which sodium is a part, then you most assuredly wanted to drink a lot of water as a follow-up.
As soon as the sodium rushes into the cell, water rushes in and causes the cell to swell.
Now, as I mentioned before, the causes of cell injury aren't always about oxygen deficiency. If anything damages the cell membranes or membranes of internal organelles, such as a crushing blow or free radical damage, then the ion pumps critical to a cell's survival located in the membranes or the membranes themselves will break apart, causing sodium and other ions to rush into the cell. The end result will be the same: cell swelling and degradation of internal cellular structures.
If the injury is slow enough in onset or isn't severe enough, the cell may compensate for all of this water coming into the cell, whose accumulation may disrupt important chemical reactions by pumping the excess water into organelles such as the endoplasmic reticulum, Golgi apparatus, and mitochondrion. This action will result in the formation of vacuoles, which are membrane-bound organelles filled with water, fat, or glycogen. That's why hydropic degeneration is sometimes also called vacuolar degeneration.
In the case of cell swelling, the vacuoles can be likened to temporary overflow tanks where excess water leaking into the cell can be stored until the cell can repair itself and pump the excess water out. If the cell can't repair itself in time, it won't be able to sustain this overflow for long and will eventually die.
Now, normal cells under a microscope will have a certain color to them, like a red or pink color, thanks to special stains. If cell swelling occurs, then the cells will look cloudy or pale under the microscope, instead, as everything becomes diluted internally due to the accumulation of water. Similarly, the organs where the cell swelling occurs will also look more pale and swollen than usual due to all of that intracellular accumulation.
This type of cloudy swelling must be differentiated with special stains from the other types of vacuolar degeneration I hinted at, including accumulation of lipids (fat) or glycogen. It must be noted that like cell swelling due to water, another potentially reversible signal of cellular injury is called fatty change or fatty degeneration, which is a type of vacuolar degeneration. When a cell is injured, it is unable to utilize fat for energy purposes appropriately, resulting in the accumulation of fat within the cell. So, again, the two changes that are usually associated with potentially reversible cellular injury are cell swelling and fatty change.
Okay, I know there was a lot of crazy detail in this lesson that by no means covered everything that actually occurs. But, at least you can appreciate why cells swell when they're injured.
Let's summarize why this occurs one more time. When something injures a cell, two main signs of potentially reversible cellular injury may occur. These are known as cell swelling, also known as hydropic degeneration, which is the earliest and most universal indicator of potentially reversible cellular injury, and fatty degeneration. Both fatty change and cell swelling are a type of vacuolar degeneration where vacuoles, which are membrane-bound organelles filled with water, fat, or glycogen, will form.
The main reason for cell swelling, or cloudy swelling of the cell under the microscope, is water. Water rushes into the cell as a result of sodium influx into the cell when the cellular membrane is damaged or the ion pumps are either damaged or have no more ATP, the body's energy currency, left to power their work.
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Back To CoursePathophysiology Textbook
20 chapters | 274 lessons