Yes, in one of my many previous lives I studied pathology at university. My lecturer was the then semi-famous Nick Vardaxis. Whilst it was never my best subject at uni, it turned out to be one of my favourite. That was 20 years ago, but amazingly I still can remember some details. I hope you enjoy the puzzle.
Medically, injury can be defined as when an external stress is placed upon a normal healthy living cell. Ultimately the injury to the cell caused by this stress, can be defined as reversible or irreversible.
When a cell is injured it goes through a series of changes, which if not stopped will ultimately reach what is known as a “point of no return”. These processes may take milliseconds or they may take several hours, days or even weeks to occur. Once a cell reaches the “point of no return” the injury is deemed to be irreversible and the cell is doomed to die and will undergo necrosis.
Necrosis refers to the death of cells whilst they are still part of a living body. Some common causes of necrosis are..
Anoxia is defined as a deficiency of oxygen to a cell and is most commonly caused by ischaemia, which is a reduced blood supply to the cell. Different cells react in different ways to ischaemia and thus have different survival rates. For example neurons (brain cells), myocardium (heart muscle cells) and fibroblasts (connective tissue cells) all have differing survival rates to ischaemia ranging from 3 to 5 minutes to 30 to 40 minutes and up to many hours.
Not all cells that are undergoing anoxia though are necessarily ischaemic. Sometimes anoxic cells are receiving more than adequate blood supply, but are not receiving adequate amounts of oxygen, for example during carbon monoxide poisoning and strangulation.
Some bacteria, plants and animals produce various toxins which can cause cell damage, resulting in necrosis. Common toxins include lipopolysaccharide, latrotoxin and oxalic acid.
Some infections cause an immune response which leads to the immune system attacking, harming and even killing healthy tissue surrounding the infection. In many autoimmune diseases, the immune system stops recognizing the tissue as being from the body and reacts against it causing large amounts of tissue damage and necrosis.
Some viruses and bacteria that live within some cells may end up killing the host cell, for example in AIDs and Chlamydia.
Many chemicals will injure and kill living cells, especially around organs that are involved with the secretion of the chemical or the metabolism of the chemical, such as the liver and the kidneys where the concentration of the chemical is usually the highest. The usual cause of death in most cases of poisoning from chemicals is renal (kidney) or hepatic (liver) failure.
Physical agents such as temperature (extreme heat or cold), radiation or direct trauma will damage cells and can ultimately also cause their death.
Types of Necrosis.
Different cells undergo necrosis in different ways and it can depend not only on the type of cell, but also the cause of the injury and whether an infection is present or not.
- Coagulative Necrosis results in the necrotic area becoming swollen and firm, the cells outlines are usually still visible under a microscope but all detail inside the cell is lost.
- Colliquative Necrosis is when the necrotic cells become softened due to their lipid nature and ultimately become a liquid.
- Caseous Necrosis is named because the resultant necrotic cells have a dry, crumbly appearance that resembles cheese, the remaining necrotic tissue in no way resembles the original normal tissue.
- Gangrenous Necrosis results in the necrotic cells taking on a black, or sometimes brown or green colour and frequently produces a foul smelling gas.
- Gummatous Necrosis is similar to coagulative necrosis but the resultant tissue is usually yellower in colour and has a firmer consistency to it.
- Fat Necrosis is obviously necrosis of fat (or adipose) tissue, which results usually in fatty acids being released and combining with calcium ions to form a type of “soap” which gives the entire area a bluish colour that may later calcify completely into a hard mass.
These differing types of necrosis may be seen in various different parts of the body such as the skin and bowels, the brain, the heart or the area surrounding the pancreas during pancreatitis. Or it may be seen following diseases such as tuberculosis or syphilis.
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