Cell injury and Adaptation

Play an AI-generated podcast conversation about this lesson

What are the causes of cell injury?

The causes of cell injury would be:-

Oxygen deprivation
Physical damage (trauma)
Microbial
Immunological
Chemical

What are the ways in which a cell can be damaged?

There are six categories by which damage to cells can be characterised:-

ATP depletion/reduced synthesis
Mitochondrial damage
Intracellular calcium
Free radical damage
Defective membrane permeability
Protein misfolding

What is hypoxia?

Hypoxia is the low oxygen circulation in the body tissues. This leads to an interference with the aerobic oxidative respiration.

What causes hypoxia?

Hypoxia is caused by:- <ol> <li>Ischaemia- reduction of blood flow to specific body tissues</li> <li>Reducing in oxygen carrying capacity of the blood e.g. anaemia, CO poisoning.</li> <li>Inadequate blood oxygenation (pneumonia- lung disease)</li> </ol> Signup and view all the answers

What is the result of a hypoxic injury?

There is a reduction in intracellular generation of ATP therefore it causes:- <ol> <li>Sodium pump activity reduction- sodium accumulates in the cell and causes isoosmotic gain of water and cellular swelling.</li> <li>Increase in anaerobic glycolysis- rapid depletion in glycogen stores</li> <li>Ribosomes also detach from the RER and polysomes dissociate causing a reduction in protein synthesis.</li> </ol> Signup and view all the answers

What are results of a persistent hypoxia condition?

The cytoskeleton breaks down and there is a loss of ultrastructural features. After a point where it remains reversible, it undergoes an irreversible injury causing cell death. Signup and view all the answers

What is the ischaemia reperfusion injury?

While in some instances, restoration of blood flow can result in cellular recovery, it can also paradoxically cause further injury. Reperfusion can cause calcium overload and ROS production which can cause apoptosis and necrosis. Signup and view all the answers

What is free radical?

A free radical is an atom, molecule or ion with one or more unpaired valence electron. Signup and view all the answers

What is a reactive oxygen species?

Reactive oxygen species (ROS) are natural byproducts of cellular oxidative metabolism and play important roles in the modulation of cell survival, cell death, differentiation, cell signaling, and inflammation-related factor production. They are associated with free radicals. Signup and view all the answers

What is the result of high ROS levels?

High ROS levels can cause membrane damage and promote mitochondrial permeability transition. Signup and view all the answers

What are some ways of mechanical injury for cells?

<ol> <li>Direct mechanical damage- cell membrane rupture and cytoplasm spills out.</li> <li>Freezing- Intracellular and cell membranes perforated by ice crystals.</li> <li>Osmotic imbalance- Rupture as a result of rapid change in osmotic pressure.</li> </ol> Signup and view all the answers

How can microbial injury damage cells?

There are various mechanisms by which microbes can harm cells:- <ol> <li>Bacteria- metabolic products/ secretions which harm the host cells. Host inflammatory response causes further damage.</li> <li>Viruses- Can cause physical rupture of host cells and host inflammatory response can cause further damage.</li> </ol> Signup and view all the answers

How can chemicals damage cells?

Certain drugs and poisons have the capacity to inflict a local or systemic toxicity. For example, caustic substances can cause rapid local cell death from extreme alkalinity or acidity. It also has a corrosive effect on tissue. Signup and view all the answers

How can cells respond to injury?

The cellular homeostatic response allows the cells to experience stress and it has the opportunity to undergo adaptation. If it is unable to adapt, it results in injury and eventually cell death. Signup and view all the answers

What are the mechanisms in which a cell can respond to stress?

Following a cell stress response, it may go through an adaptation phase where it can undergo atrophy, hypertrophy, hyperplasia, metaplasia and dysplasia. If it is unable to respond to stress, it can lead to reversible or irreversible cell injury. Reversible cell injury would allow for an adaptation and rehabilitation period, however, beyond a certain point, it can only cause necrosis. Signup and view all the answers

What is atrophy?

Atrophy is the shrinkage in the size of a cell by the loss of cell substance. Signup and view all the answers

What is hypertrophy?

Hypertrophy is the increase in the size of cells and consequently an increase in the size of an organ. Signup and view all the answers

What is hyperplasia?

Hyperplasia is the increase in number of cells in an organ or tissue. Signup and view all the answers

What is metaplasia?

Metaplasia is the reversible change in which one adult cell type is replaced by another adult cell type. e.g. Following an injury or inflammation in the oesophagus, the normal squamous epithelium may be replaced by metaplastic columnar tissue. Signup and view all the answers

What are the two forms of cell death following irreversible cell damage?

The 2 forms of cell death are apoptosis and necrosis. Signup and view all the answers

What is the difference between apoptosis and necrosis?

In apoptosis, cell contents are contained and there is no surrounding damage. In necrosis, cell contents spill out and there is tissue damage. Signup and view all the answers

What are the types of necrosis?

<ol> <li>Coagulative necrosis</li> <li>Colliquative necrosis</li> <li>Caseous necrosis</li> <li>Gangrenous necrosis</li> <li>Fat necrosis</li> </ol> Signup and view all the answers

What is coagulative necrosis and what causes it?

Coagulative necrosis is a condition where ischaemia results in decreased ATP. increased cytosolic calcium ions and free radicals which cause membrane damage. It results in a localised area of ischemic necrosis. Signup and view all the answers

What is caseous necrosis?

It is a distinct form of coagulative necrosis where the coagulated tissue does not resemble the cells but presents in the form of chunks of debris. It is a giant cell and granulamtous reaction. E.g. Tuberculosis Signup and view all the answers

What is colliquative necrosis?

Colliquative necrosis often occurs in the brain because of a lack of supporting stroma which predisposes it to liquefaction when necrotic. It is usually caused by focal bacterial infection because they attract neutrophils. The enzymes in the neutrophils dissolve the tissues nearby causing pus accumulation and liquefaction of the tissue. Signup and view all the answers

What is fat necrosis?

Fat necrosis is the release of enzymes from the pancreas or gut. These enzymes (lipases) release free fatty acids which with calcium produce soapy deposits in tissues. Signup and view all the answers

What is gangrenous necrosis?

Gangrene is a clinical condition of ischemic and necrotic tissue, often circumferential around a digit or extremity. It is identified by discolored or black tissue and associated sloughing of natural tissue planes. Signup and view all the answers

What are the types of gangrenous necrosis?

The three types of gangrenous necrosis are:- <ol> <li>Wet- gastrointestinal tract and it is bacterial</li> <li>Dry- limbs (diabetic)</li> <li>Gas- Clostridium bacteria and release of gas.</li> </ol> Signup and view all the answers

What is autolysis?

Autolysis is a term for the rotting of the tissue. Following the death of the organism, there is lysis of the tissues by their own enzymes but with no vital reaction (inflammation). Signup and view all the answers

What is necrosis?

Necrosis results in the loss of cell membrane integrity and an uncontrolled release of products of cell death into the extracellular space. Necrosis includes autolysis of cells supplemented with inflammation and leukocyte action. Signup and view all the answers

What is apoptosis?

Apoptosis is a process of programmed cell death which removes unwanted cells without damaging surrounding tissues. Signup and view all the answers

What is the physiological importance of apoptosis in embryogenesis?

As cells rapidly proliferate during development, some of them undergo apoptosis, which is necessary for many stages in development, including neural development, reduction in egg cells (oocytes) at birth, as well as the shaping of fingers and vestigial organs in humans and other animals. Signup and view all the answers

What is the physiological importance of apoptosis in the menstrual cycle?

Apoptosis helps to maintain cellular homeostasis during the menstrual cycle by eliminating senescent cells from the functional layer of the uterine endometrium during the late secretory and menstrual phase of the cycle. Signup and view all the answers

What is the physiological importance of apoptosis in the immune system?

It is important in the death of post inflammatory neutrophils, removal of self reactive lymphocytes and death of virally infected cells. Signup and view all the answers

What is the clinical diagnosis of cell death?

<ol> <li>In the case of myocardial infarction, there is myocyte necrosis in which enzymes like troponin, CK-MB and LDH) are released.</li> <li>In the case of pancreatitis, there is pancreatic cell necrosis in which amylase enzyme is released.</li> </ol> Signup and view all the answers

What are the ways of healing and repair?

The two ways of healing and repair are:- <ol> <li>Healing by primary intention- Restitution with no- or minimal- residual defect</li> <li>Healing by secondary intention- Organisation and repair where there is tissue loss and granulation tissue</li> </ol> Signup and view all the answers

What are the factors in regeneration of cells?

The outcome of an injury often depends on cell type and their characteristics like:- <ol> <li>Replicative capabilities</li> <li>Ability to replace complex architectural structures</li> </ol> Signup and view all the answers

How can we classify cells in terms of their capacity of regeneration? Also provide examples.

There are three ways to classify them:- <ol> <li>Labile- Good capacity to regenerate (e.g. surface epithelial cells)</li> <li>Stable- Divide at a slow rate but can regenerate if needed (e.g. hepatocytes in liver)</li> <li>Permanent- no means of effective regeneration (e.g. nerve cells, striated muscle cells)</li> </ol> Signup and view all the answers