Why Apoptosis Matters: Role in Health, Disease & Development
Apoptosis can be defined as a form of cell death in which a programmed sequence of cells dies without releasing harmful substances into the surrounding area. It is also known as programmed cell death or cellular suicide. This is the best-understood form of programmed cell death. It involves the death of a cell but benefits the organism as a whole. This is an orderly process in which the cell's contents are packaged into small packets of membrane for garbage collection by the immune cells. It helps to maintain the balance in the body by removing cells during development and by eliminating potentially cancerous and virus-infected cells.
Apoptosis Pathway
There are two types of apoptosis pathways
Intrinsic Pathway - This is also known as the mitochondrial pathway. In this, the cell receives a signal to destroy itself from one of its own genes or proteins due to the detection of DNA damage.
Extrinsic Pathway - This is also known as the death receptor pathway. In this, a cell receives a signal to start apoptosis from other cells in the organism. This is triggered when a cell has outlived its usefulness or is no longer a good investment for the organism to support.
Apoptosis Examples
Development From Tadpole to Frog - The best and spectacular example of apoptosis is found in frog tadpoles, which destroy and reabsorb the entire body structures as they undergo their transformation into frogs. The cells in the tadpole gills, fins, and tail tend to die by apoptosis signals as the tadpole matures. For new growing limbs the raw material of the destroyed cells becomes an important material and also supplements as food.
Mouse Feet - At the time of embryonic development, the feet of mice start out as flat, spade-shaped things. As development proceeds, the feet separate into five distinct toes by the process of apoptosis. To create distinct gaps between them the cells get connected.
Apoptosis Steps
Cell Shrinks - It is observed in all the examples of apoptosis in which the loss of cell volume is a ubiquitous characteristic of programmed cell death.
Cell Fragments - In this step, the DNA in the nucleus of the cell condenses and breaks into evenly sized fragments.
Cytoskeleton Collapses - At this stage, the immature organism's cytoskeleton gets collapsed.
Nuclear Envelope Disassembles - At this step nuclear covering gets disassembled.
Cells Release Apoptotic Bodies - At this step, cells undergo morphological changes including membrane blebbing, thin membrane protrusion formation, and generation of distinct apoptotic bodies.
Significance of Apoptosis
This contributes to the sculpturing of many organs and tissues during the development of cells that are produced in excess and eventually undergo programmed cell death.
In the human body, nearly one lakh cells are dying by apoptosis in every single second and a similar number are produced by mitosis.
In average children of ages 8 to 14, about 29 to 30 billion cells die in a day.
Full epithelial lining in our body changes every 23 days due to apoptosis.
Role of Apoptosis
Adverse Ventricular Remodeling - cardiac remodeling is a process in which heart chamber dilation and wall thinning occur in association with systolic and diastolic dysfunction.
Pathology of Pancreatic Cancer - pancreatic tumors resist apoptotic cell death which would lead to new molecular strategies to treat pancreatic cancer.
Morphogenesis - Thisapoptosis acts as a stone sculpture, eliminates the material, and reveals new shape.
Cancer - Apoptosis evolves a rapid and irreversible process to efficiently eliminate dysfunctional cells
Pathogenesis and Treatment in Bone - Related Diseases - In malignant transformation defective apoptosis may participate as the dysregulation of cells. The death mechanism is involved in the pathogenesis of increasing bone disease.
Relationship Between Apoptosis and Cancer
Cancer is also known as carcinogenesis. It is the result of the succession of genetic changes during which a normal cell is transformed into a malignant one while the evasion of cell death is one of the necessary changes in a cell that causes this malignant transformation. As in apoptosis, a large number of cells die which reduces the risk of cancer in an individual. If a cancer person's body undergoes apoptosis it becomes easier for the diagnosis without any risk factor.
FAQs on Apoptosis Explained: Definition, Process & Importance
1. What is apoptosis in simple terms?
Apoptosis is the process of programmed cell death, a highly regulated mechanism the body uses to eliminate cells that are no longer needed, are damaged, or have become abnormal. Unlike messy cell death from injury, apoptosis is a neat, orderly process that prevents inflammation and ensures the safe removal and recycling of cellular components.
2. What are the main stages of the apoptosis process?
The process of apoptosis generally unfolds in a few key stages:
- Signalling Phase: The cell receives internal or external signals that trigger the death program. This could be due to DNA damage or signals from other immune cells.
- Execution Phase: Special enzymes called caspases are activated. These enzymes act like molecular scissors, breaking down essential proteins within the cell's cytoplasm and nucleus.
- Blebbing and Apoptotic Bodies: The cell shrinks and its membrane begins to bulge outwards, a process called blebbing. The cell then breaks apart into smaller, membrane-enclosed fragments known as apoptotic bodies.
- Phagocytosis: These apoptotic bodies are quickly engulfed and digested by specialised immune cells called phagocytes, ensuring a clean removal without triggering an inflammatory response.
3. Why is apoptosis so important for the human body?
Apoptosis is crucial for several reasons. It is essential for normal embryonic development, such as removing the webbing between fingers and toes. In adults, it maintains tissue homeostasis by removing old or damaged cells to make way for new ones. Crucially, it serves as a defence mechanism by eliminating cells with viral infections or cells with significant DNA damage that could otherwise become cancerous.
4. What is the primary difference between apoptosis and necrosis?
The primary difference lies in how the cell dies. Apoptosis is a controlled, programmed process that is non-inflammatory. The cell shrinks, breaks into neat apoptotic bodies, and is cleared away by phagocytes. In contrast, necrosis is an uncontrolled cell death, typically caused by injury, toxins, or infection. In necrosis, the cell swells and bursts, releasing its contents into the surrounding tissue and causing a significant inflammatory response and potential damage to neighbouring cells.
5. What are the key molecular triggers for apoptosis?
Apoptosis is initiated by two main pathways. The intrinsic pathway (or mitochondrial pathway) is triggered by internal cell stress, such as severe DNA damage or withdrawal of growth factors. This leads to the release of cytochrome c from the mitochondria, which activates a cascade of caspases. The extrinsic pathway is triggered by external signals, where molecules from other cells (like immune cells) bind to 'death receptors' on the cell surface, directly activating the caspase cascade to execute cell death.
6. What can happen if the process of apoptosis fails?
Failure of apoptosis can lead to serious diseases. If damaged or mutated cells are not eliminated, they can continue to divide uncontrollably, which is a hallmark of cancer. Conversely, excessive apoptosis can also cause problems, leading to tissue damage and contributing to neurodegenerative diseases like Alzheimer's or Parkinson's, as well as autoimmune disorders where the body mistakenly attacks its own healthy cells.
7. Can you give some real-world examples of apoptosis in action?
Certainly. Apoptosis occurs constantly in our bodies. Some common examples include:
- The shedding of the uterine lining (endometrium) during the menstrual cycle.
- The removal of a tadpole's tail during its metamorphosis into a frog.
- The elimination of self-reactive immune cells to prevent autoimmune diseases.
- The programmed death of skin cells as they move towards the surface, eventually becoming the protective outer layer that we shed.
