Apoptosis is an active biochemical process associated with limited inflammation and disruption of tissues of the body. Programmed cell death was introduced as early as 1964 through a proposal that the death of cells during development is not accidental but rather through a sequential controlled steps that lead to the local and temporary defined self-destruction.
Apoptosis is a process that takes place in the body of a living organism resulting in the natural death of cells. It is a genetically controlled mechanism of the cell involved in the regulation of tissue homeostasis involving two major pathways namely the extrinsic and intrinsic all found in the cytoplasm.
The term of apoptosis has been used to describe the morphological processes thatlead to the controlled cellular self-destruction.This process is also important in the regulation of cell population in tissues whenever there is pathological conditions.
As apoptosis destroys unwanted cells, mitosis (cell division) makes new cells. While they may seem to be at odds, apoptosis and mitosis work together to keep us healthy. For example, our skin and hair cells are renewed via a continuous cycle of apoptosis and mitosis.
Cells that undergo apoptosis go through a different and much more orderly process. They shrink and develop bubble-like protrusions (technical name: “blebs”) on their surface. The DNA in the nucleus gets chopped up into small pieces, and some organelles of the cell, such as the endoplasmic reticulum, break down into fragments.
In the end, the entire cell splits up into small chunks, each neatly enclosed in a package of membrane. What happens to the chunks? They release signals that attract debris-eating (phagocytic) immune cells, such as macrophages.
Also, the fragments of the dying cell display a lipid molecule called phosphatidylserine on their surface. Phosphatidylserine is usually hidden on the inside of the membrane, and when it is on the outside, it lets the phagocytes bind and “eat” the cell fragment.
Apoptosis also plays a key role in human development. For instance, as we saw in the introduction, your hand started out as a paddle-like block of tissue when you were an embryo. The block was “carved” into fingers by apoptosis of the cells in between the developing fingers.
This process occurs in all sorts of vertebrate species that have finger- or toe-like digits, and less apoptosis results in more webbing between the digits. Sometimes, if a small mistake happens during finger or toe development, apoptosis may be incomplete (leading, for instance, to fused toes).
Other examples of apoptosis during normal development include the loss of a tadpole’s tail as it turns into a frog, and the removal of unneeded neurons in as neural circuits in the brain are “wired.”
Many cells in the human body have the built-in ability to undergo apoptosis (in the same waycthat they have the built-in ability to copy their DNA or break down fuels). Basically, apoptosis is a general and convenient way to remove cells that should no longer be part of the organism.
● Some cells need to be “deleted” during development – for instance, to whittle an intricate
structure like a hand out of a larger block of tissue.
● Some cells are abnormal and could hurt the rest of the organism if they survive, such as
cells with viral infections or DNA damage.
● Cells in an adult organism may be eliminated to maintain balance – to make way for new
cells or remove cells needed only for temporary tasks.
Apoptosis also plays an essential role in the development and maintenance of a healthy immune system. When B and T cells (immune cells that bind specific molecules) are first produced, they’re tested to see if they react against any of the body’s own “self” components.
Cells that do are eliminated right away by apoptosis. If this process fails, self-reactive cells may be released into the body, where they can attack tissues and cause autoimmune conditions.
Apoptosis also plays an important role in allowing the immune system to turn off its response to a pathogen. When a pathogen is detected, the immune cells that recognize the pathogen divide extensively, undergoing a huge increase in numbers with the purpose of destroying the pathogen.
Once the pathogen is cleared from the body, the large numbers of pathogen-specific immune cells are no longer needed and must be removed by apoptosis to maintain homeostasis (balance) in the immune system.
In some cases, a cell can pose a threat to the rest of the body if it survives. For instance, this may be the case for cells with DNA damage, pre-cancerous cells, and cells infected by viruses.
If these cells undergo apoptosis, the threat to the rest of the organism (such as cancer or spread of a viral infection) is removed. When a cell’s DNA is damaged, it will typically detect the damage and try to repair it.
If the damage is beyond repair, the cell will normally send itself into apoptosis, ensuring that it will not pass on its damaged DNA.
When cells have DNA damage but fail to undergo apoptosis, they may be on the road to cancer Sometimes, pre-cancerous cells that have avoided internal apoptosis cues are detected by immune cells, which try to trigger apoptosis through an external signaling pathway.
Successful cancer cells, however, manage to duck both internal and external cues that would normally trigger apoptosis. This allows them to divide out of control and accumulate mutations (changes in their DNA)
Apoptosis is a form of programmed cell death, or “cellular suicide.” It is different from necrosis, in which cells die due to injury. Apoptosis is not the only form of programmed cell death, but it is the form we understand best.
Apoptosis is an orderly process in which the cell’s contents break down and are packaged into small packets of membrane for “garbage collection” by immune cells. It contrasts with necrosis (death by injury), in which the dying cell’s contents spill out and cause inflammation