Apoptosis, otherwise known as Programmed Cell Death (PCD), is a process which allows cells to commit suicide to help aid organisms in growth and to avoid any possibilities of acquiring diseases. It eradicates cells which are no longer needed in the organism. Although there are many types of PCD, it tends to be compared to Necrosis, but they’re used under different conditions, each having a separate, different process for PCD. The process and the reason for apoptosis within development have been researched in numerous organisms like in mice and the C. elegans worm. It plays a vital part in the immune system to keep an organism healthy. If there’s unnecessary or not enough apoptosis occurring within humans, then it can lead to many different severe disorders or diseases.
Apoptosis neatly makes cells suicide without causing any damage to the surrounding cells. On the other hand, necrosis often damages and harms the nearby tissue which tends to result in the area to become inflamed. In the first stages of apoptosis, the cells would begin to shrink which therefore results in the cells to become smaller with a denser cytoplasm. Thus, the organelles within the cell become more compact and firmly packed together. After that, chromatin condensation occurs so the surfaces of the chromatin clusters and clumps together into many different shapes. It then develops blebs because the cytoplasm blebs out, which are like bubbly-shaped lumps, onto the plasma membrane. When the blebs disconnect and buds off from the plasma membrane, they become apoptotic bodies with organelles inside. This divides the entire cell into smaller chunks.
Furthermore, the organelles are the cell fragments that can be recycled through phagocytosis very quickly. The macrophages are attracted towards the apoptotic bodies, when the signals are released, to engulf them by using its pseudopodia to surround it. While the phagocytes engulf the apoptotic bodies, the pseudopodia don’t take up any solutes. It when starts to digest the apoptotic bodies which would be inside the phagocytic vacuole that fuses together with a lysosome to make a phagosome. The apoptotic bodies will break down after the lysozymes get released from the lysosomes. As soon as the apoptotic bodies are digested, the macrophages become tingible body macrophages which can be stained.
There are several pathways in which apoptosis can be activated: the intrinsic pathway, the extrinsic pathway and the perforin/granzyme pathway. Caspases (cysteine proteases) activates apoptosis and they start off as procaspases, which is an inactive form of caspase, until they’re initialised to start killing cells. In addition, caspases can also activate other caspases by using a cascading effect.
Firstly, the intrinsic pathway is also called the mitochondrial pathway because the mitochondria releases Cytochrome C to activate the caspase. It has two different types of signals in which it can be activated by. These are the positive and negative signals; the signals are sent from within the cell itself. Therefore, the signals are sent due to stress on the cell. Examples of positive signals would be ‘radiation, toxins, hypoxia, hyperthermia, viral infections, and free radicals’. Examples of negative signals would be ‘the absence of certain growth factors, hormones and cytokines’. The negative signals stop any restrictions that there may be of apoptosis later by destroying the cell earlier.