how the cells respond to injury

Question 1

What are the four main types of tissue?

Answer 1

The four main types of tissue are epithelial, muscle, nervous, and connective. Each type of tissue has specific functions and characteristics.

Question 2

What are the mechanisms of tissue growth?

Answer 2

The tissue growth mechanisms include multiplicative, auxetic, and accretionary growth. Multiplicative growth involves an increase in cell numbers during embryonic development. Auxetic growth refers to increased cell size, muscle tissue growth, and accretionary change.

Question 3

What are labile cells?

Answer 3

Labile cells are cells with regenerative ability that have a short lifespan and continuously proliferate. They exhibit rapid cell turnover. Examples of labile cells include surface epithelial cells.

Question 4

What are stable cells?

Answer 4

Stable cells are cells that have regenerative capacity and the ability to proliferate, but they divide at a slow rate. These cells have a slower turnover compared to labile cells. Examples of stable cells include quiescent tissues such as hepatocytes (liver cells) and renal tubular cells.

Question 5

What are permanent cells?

Answer 5

Permanent cells do not have regenerative capacity. They are terminally differentiated and cannot proliferate. Examples of permanent cells include red blood cells, keratinocytes (skin cells), neurons, and cardiac and skeletal muscle cells.

Question 6

What are the phases of the cell cycle?

Answer 6

The cell cycle consists of the following phases: G1 phase (gap phase 1), DNA synthesis (S) phase, G2 phase (gap phase 2), and mitosis. These phases occur sequentially to ensure proper cell division and replication.

Question 7

What happens during the G1 phase of the cell cycle?

Answer 7

During the G1 phase, the cell grows, carries out its normal functions, and prepares for DNA synthesis. Multiple checkpoints within the G1 phase ensure the cell is ready to progress to the next phase.

Question 8

What occurs during the DNA synthesis (S) phase?

Answer 8

During the DNA synthesis (S) phase, the cell duplicates its DNA, ensuring each daughter cell receives a complete set of genetic material.

Question 9

What happens during the G2 phase of the cell cycle?

Answer 9

The G2 phase follows DNA synthesis, and during this phase, the cell continues to grow, prepares for cell division, and checks for any errors or damage in the replicated DNA.

Question 10

What is mitosis?

Answer 10

Mitosis is the cell cycle phase where the cell divides into two daughter cells, each with the same number of chromosomes as the parent cell. Mitosis ensures the distribution of genetic material to each daughter cell.

Question 11

What is the G0 phase in the cell cycle?

Answer 11

Terminally differentiated cells, which do not actively divide, remain in a resting phase called G0. In G0, these cells do not progress through the cell cycle and typically perform their specialised functions.

Question 12

What triggers cell proliferation?

Answer 12

Cell proliferation is triggered by specific stimuli, such as mitogens (molecules that induce mitosis), growth, and survival proteins. These signals initiate cell division and promote cell growth.

Question 13

How does cell proliferation vary in adult tissues?

Answer 13

In adult tissues, cell proliferation varies depending on the cell type and tissue function. Some tissues have a higher turnover rate and more active cell proliferation, while others have slower proliferation rates.

Question 14

When does cell proliferation occur after an injury?

Answer 14

Cell proliferation can occur after injury when tissues need to repair themselves. In response to the injury, cells are stimulated to proliferate and replace damaged or lost cells.

Question 15

What is the difference between stem/progenitor cells and differentiated cells regarding proliferation?

Answer 15

Stem and progenitor cells retain their ability to proliferate and divide, allowing them to replenish and regenerate tissues. In contrast, differentiated cells have lost their ability to proliferate and remain non-dividing, carrying out their specialised functions.

Question 16

What is cell differentiation?

Answer 16

Cell differentiation refers to the process by which stem or progenitor cells acquire specialised characteristics and functions. It is tightly controlled and often coupled with cell proliferation.

Question 17

What is the importance of cell differentiation?

Answer 17

Cell differentiation is crucial for tissue self-renewal and repair following damage or injury. It allows stem or progenitor cells to develop into specific cell types needed for tissue regeneration.

Question 18

What determines tissue self-renewal and repair capability?

Answer 18

The ability of tissues to self-renew and repair depends on the presence of resident stem or progenitor cells. These cells are normally in a quiescent state until they receive molecular signals to enter the cell cycle and undergo division for tissue regeneration.

Question 19

What are intermediate differentiated progenitor cells?

Answer 19

Intermediate differentiated progenitor cells have undergone some differentiation but can further differentiate into specialised cell types. They are transitional between stem/progenitor cells and fully differentiated cells.

Question 20

What are the causes of cell injury?

Answer 20

Cell injury can occur due to various factors, including trauma, changes in osmotic pressure, thermal injury (extreme hot or cold), oxygen starvation (ischemia-reperfusion), infection (toxins), membrane failure, DNA damage (radiation, chemotherapy, free radicals), metabolic disruption, lack of growth factors, and exposure to drugs and poisons.

Question 21

How can trauma cause cell injury?

Answer 21

Trauma, such as physical injury or mechanical force, can directly damage cells, disrupt their structures, and lead to cellular dysfunction or death.

Question 22

What is the role of DNA damage in cell injury?

Answer 22

DNA damage caused by radiation, chemotherapy, or free radicals can impair the cell’s ability to function properly, affecting replication and transcription processes and potentially leading to cell death or genetic mutations.

Question 23

How can a lack of growth factors contribute to cell injury?

Answer 23

Growth factors promote cell survival, proliferation, and differentiation. A lack of these essential signals can deprive cells of necessary support, impairing cellular function or even causing cell death.

Question 24

What are some examples of metabolic disruptions causing cell injury?

Answer 24

Metabolic disruptions, such as electrolyte imbalances, nutrient deficiencies, or toxic metabolic byproducts, can disrupt cellular metabolism, impair energy production, and compromise cellular function.

Question 25

How do drugs and poisons cause cell injury?

Answer 25

Certain drugs and toxins can directly damage cells or interfere with cellular processes, leading to cell injury or death. Examples include overdose of medications, exposure to environmental toxins, or ingesting harmful substances.

Question 26

What are the fates of cell injury?

Answer 26

Cell injury can have different fates depending on the severity and nature of the injury. The possible outcomes include reversible cell injury, necrosis, and apoptosis.

Question 27

What is reversible cell injury?

Answer 27

Reversible cell injury occurs when cells can return to their normal state if the underlying cause of the injury is removed or resolved on time.

Question 28

How does reversible cell injury manifest in terms of morphology?

Answer 28

In reversible cell injury, cell morphology may show swelling due to the failure of cell membrane ion pumps, leading to the influx of water. The cytoplasm may contain lipid vacuoles, and increased eosinophil staining can be observed in histopathological examinations.

Question 29

What happens in irreversible cell injury?

Answer 29

Irreversible cell injury occurs when cellular damage reaches a point where the cells cannot recover and return to their normal state. This can lead to cell death, typically through necrosis.

Question 30

What are the characteristics of irreversible cell injury (necrosis)?

Answer 30

In irreversible cell injury leading to necrosis, the cell membrane develops, blebs and becomes distorted. The mitochondria may swell, and the nucleus becomes condensed.

Question 31

What factors can contribute to reversible or irreversible cell injury?

Answer 31

Reversible or irreversible cell injury can be influenced by various factors, including the duration and intensity of the injurious stimuli, the availability of oxygen and nutrients, the type of cells affected, and the overall health and resilience of the cells.

Question 32

What are some causes of reversible and irreversible cell injury?

Answer 32

Reversible cell injury can be caused by temporary ischemia (reduced blood flow), oxidative stress, mild infections or inflammation, and DNA damage that can be repaired. Irreversible cell injury can result from severe and prolonged ischemia, severe oxidative stress, extensive DNA damage, or overwhelming infections or inflammation.

Question 33

What is apoptosis?

Answer 33

Apoptosis is a programmed form of cell death orchestrated by specific signalling pathways. It is a normal physiological process that helps maintain tissue homeostasis, eliminate unwanted or damaged cells, and shape organ development.

Question 34

How is apoptosis different from necrosis?

Answer 34

Apoptosis is a controlled cell death process characterised by cellular shrinkage, nuclear fragmentation, and membrane-bound apoptotic bodies. In contrast, necrosis is an uncontrolled cell death involving cellular swelling, membrane rupture, and inflammation.

Question 35

What is apoptosis?

Answer 35

Apoptosis, also known as programmed cell death, is a tightly regulated process in which cells undergo controlled self-destruction. During development, it is a physiological process to remove excess cells and maintain tissue homeostasis.

Question 36

What happens to the cell membrane during apoptosis?

Answer 36

During apoptosis, the cell membrane remains intact and actively participates in the fragmentation of the cell body into smaller fragments known as apoptotic bodies.

Question 37

What happens to apoptotic bodies?

Answer 37

Apoptotic bodies, the fragmented remnants of apoptotic cells, are degraded and destroyed by phagocytes (cells specialised in engulfing and digesting cellular debris).

Question 38

How is apoptosis different from necrosis in terms of tissue response?

Answer 38

Apoptosis is a controlled process that does not involve the leakage of cellular components into the surrounding tissues. Therefore, it does not trigger an inflammatory response. In contrast, necrosis, an uncontrolled cell death, leads to cellular damage and inflammation.

Question 39

What are the mechanisms involved in apoptosis?

Answer 39

A family of proteins called caspases triggers apoptosis. Caspases cleave other proteins, leading to the execution of programmed cell death. There are two main pathways of apoptosis: the intrinsic pathway, which relies on mitochondrial involvement and the release of cytochrome c into the cytoplasm, and the extrinsic pathway, which depends on death receptors, including those belonging to the tumour necrosis factor receptor family.

Question 40

What is the role of the intrinsic pathway in apoptosis?

Answer 40

The intrinsic apoptosis pathway is responsible for most physiological or pathological apoptotic processes. It involves the mitochondria and the release of cytochrome c into the cytoplasm, which triggers a cascade of caspase activation and ultimately leads to cell death.

Question 41

How does the extrinsic pathway of apoptosis work?

Answer 41

The extrinsic apoptosis pathway relies on death receptors, many of which are part of the tumour necrosis factor receptor family. The binding of specific ligands to these receptors initiates a signalling cascade that activates caspases and promotes programmed cell death.

Question 42

Why is apoptosis tightly regulated?

Answer 42

Apoptosis is tightly regulated to ensure proper cell turnover, tissue homeostasis, and the removal of unwanted or damaged cells. Dysregulation of apoptosis can have detrimental effects and contribute to various diseases, including cancer and autoimmune disorders.

Question 43

What is apoptosis?

Answer 43

Apoptosis, also known as programmed cell death, is a tightly regulated process in which cells undergo controlled self-destruction. During development, it is a physiological process to remove excess cells and maintain tissue homeostasis.

Question 44

What happens to the cell membrane during apoptosis?

Answer 44

During apoptosis, the cell membrane remains intact and actively participates in the fragmentation of the cell body into smaller fragments called apoptotic bodies.

Question 45

What happens to apoptotic bodies?

Answer 45

Apoptotic bodies, the fragmented remnants of apoptotic cells, are degraded and destroyed by phagocytes, which engulf and remove them.

Question 46

How is apoptosis different from necrosis in terms of tissue response?

Answer 46

Apoptosis is a controlled process that does not involve the leakage of cellular components into the surrounding tissues. Therefore, it does not trigger an inflammatory response. In contrast, necrosis, an uncontrolled cell death, leads to cellular damage and inflammation.

Question 47

What are the mechanisms involved in apoptosis?

Answer 47

A family of proteins called caspases triggers apoptosis. Caspases cleave other proteins, leading to the execution of programmed cell death. There are two main pathways of apoptosis: the intrinsic pathway, which relies on mitochondrial involvement and the release of cytochrome c into the cytoplasm, and the extrinsic pathway, which depends on death receptors, including those belonging to the tumour necrosis factor receptor family.

Question 48

What is the role of the intrinsic pathway in apoptosis?

Answer 48

The intrinsic apoptosis pathway is responsible for most physiological or pathological apoptotic processes. It involves the mitochondria and the release of cytochrome c into the cytoplasm, which triggers a cascade of caspase activation and ultimately leads to cell death.

Question 49

How does the extrinsic pathway of apoptosis work?

Answer 49

The extrinsic apoptosis pathway relies on death receptors, many of which are part of the tumour necrosis factor receptor family. Binding specific ligands to these receptors initiates a signalling cascade that activates caspases and promotes programmed cell death.

Question 50

Can you provide examples of necrosis?

Answer 50

Examples of necrosis include: Coagulative necrosis: characterised by faint cell outlines, coagulated proteins, absence of nuclear stain, and a visible cytoplasm. It remains until phagocytosis takes place. Colliquative necrosis is seen in liquefying tissues, such as abscesses or brain infarcts. Caseous necrosis: observed in tuberculosis infections, forming a cheesy and granular appearance. Fat necrosis: occurs in the pancreas, leading to the formation of chalky white areas. Fibrinoid necrosis: caused by the deposition of antigens and antibodies at the vessel wall, appearing as a bright pink and amorphous structure in histopathology.

Question 51

What is autophagy?

Answer 51

Autophagy is a cellular process called "cellular self-eating." It responds to various conditions, including lack of nutrients, and involves degrading cellular components to provide nutrients for cell survival.

Question 52

How does autophagy occur?

Answer 52

Autophagosomes, which are double-membrane structures, are created from the membranes of the endoplasmic reticulum. They engulf portions of the cytoplasm and organelles. The autophagosome then fuses with a lysosome, forming an autophagic vacuole, where lysosomal enzymes degrade the contents.

Question 53

What is the purpose of autophagy?

Answer 53

The purpose of autophagy is to recycle cellular components and provide nutrients for cell survival during times of stress, such as nutrient deprivation or cellular damage.

Question 54

Can apoptosis follow autophagy?

Answer 54

Yes, autophagy can precede or be followed by apoptosis. Autophagy can serve as a protective mechanism to maintain cell survival. However, the cell may undergo apoptosis if the stress or damage is severe and cannot be resolved.

Question 55

When can autophagy occur?

Answer 55

Autophagy can occur in various circumstances, including during nutrient deprivation, when cells require internal nutrient sources for survival. It can also be triggered when restricted blood flow, such as in ischemic conditions, provides nutrients and promote cell survival.

Question 56

What are the main steps of autophagy?

Answer 56

The main steps of autophagy include autophagosome formation, autophagosome-lysosome fusion, and degradation of the autophagic vacuole contents. These steps collectively facilitate the recycling of cellular components and nutrient replenishment.

Question 57

How does autophagy contribute to cellular homeostasis?

Answer 57

Autophagy is crucial in maintaining cellular homeostasis by eliminating damaged or dysfunctional organelles and proteins, recycling cellular components, and providing energy and nutrients to support cell survival and function.

Question 58

What role does autophagy play in diseases?

Answer 58

Dysregulation of autophagy has been associated with various diseases, including neurodegenerative disorders, cancer, and metabolic conditions. Both excessive autophagy and impaired autophagy have been implicated in disease pathogenesis, highlighting the importance of maintaining proper autophagic balance.

Question 59

What is the characteristic of proliferative tissues?

Answer 59

Proliferative tissues are composed of cells that can divide and undergo cell proliferation. However, most cells in the human body are non-dividing, called G0, which can be reversible depending on the cell type and external stimuli.

Question 60

Which cells in the human body are terminally differentiated?

Answer 60

Neurons and muscle cells, such as myocytes and cardiomyocytes, are examples of terminally differentiated cells. They exist in a non-dividing state (G0) with their cell cycle mechanism turned off, meaning they do not actively divide or replicate.

Question 61

Can liver cells initiate the cell cycle after liver damage?

Answer 61

Most liver cells exist in a non-dividing state (G0). However, in response to liver damage, they can initiate the cell cycle and re-enter active division to regenerate and repair the damaged tissue.

Question 62

Which cell types periodically enter and exit the cell cycle in their lifetime?

Answer 62

Cell types such as fibroblasts (a type of connective tissue cell) and lymphocytes (a type of white blood cell) can periodically enter and exit the cell cycle throughout their lifetime, allowing them to undergo proliferation when necessary.

Question 63

Which tissues rely on regular self-renewal and contain reservoirs of stem/progenitor cells?

Answer 63

Tissues like epithelium (e.g., skin) and blood rely on regular self-renewal. They contain reservoirs of stem/progenitor cells that regularly undergo the cell cycle to replenish and regenerate the tissues.

Question 64

How do cells respond to stress?

Answer 64

Cells respond to stress through adaptation, which involves changes in the number, size, phenotype, metabolic activity, or function of cells.

Question 65

What are physiological adaptations?

Answer 65

Physiological adaptations occur in response to hormonal or signalling cues. Examples include uterus enlargement during pregnancy in response to hormonal changes or strengthening bones or muscles in response to mechanical pressure.

Question 66

What are pathologic adaptations?

Answer 66

Pathologic adaptations occur in response to stress or injury. Cells may modify their function to escape injury, but this often comes at the expense of normal function and can lead to abnormal tissue structure or function.

Question 67

What are the types of cell adaptation?

Answer 67

The types of cell adaptation include hypertrophy (increase in cell size), hyperplasia (increase in cell number), atrophy (decrease in cell size or number), and metaplasia (conversion of one cell type to another). These adaptations can occur in various tissues and organs responding to stimuli or conditions.

Question 68

What is physiologic hypertrophy?

Answer 68

Physiologic hypertrophy refers to the increased cell size as a normal response to specific stimuli or conditions. It is a regulated process and can occur in various tissues or organs.

Question 69

How does physiologic hypertrophy occur in pregnancy?

Answer 69

In pregnancy, the uterus undergoes physiologic hypertrophy. The smooth muscle cells of the uterus enlarge in size in response to hormonal stimulation, particularly estrogen. There is also hyperplasia, where smooth muscle cells proliferate, contributing to the overall growth of the uterus.

Question 70

How does physiologic hypertrophy occur in exercise?

Answer 70

In exercise, physiologic hypertrophy can occur specifically in skeletal muscle. Regular physical activity and exercise stimulate the enlargement of skeletal muscle fibres, increasing muscle mass and strength.

Question 71

What is pathologic hypertrophy?

Answer 71

Pathologic hypertrophy refers to the abnormal increase in cell size as a response to pathological conditions or stress. It is often associated with detrimental effects on tissue structure and function.

Question 72

How does pathologic hypertrophy occur in the heart?

Answer 72

In conditions of increased blood pressure, the heart muscle cells, known as cardiomyocytes, can undergo pathologic hypertrophy. The enlargement of cardiomyocytes leads to the enlargement of the heart itself, a condition known as cardiac hypertrophy.

Question 73

How does pathologic hypertrophy occur in reduced blood flow?

Answer 73

When there is reduced blood flow due to obstruction (ischemia), cardiomyocytes experience metabolic stress. Initially, this can cause reversible cell injury. However, if the ischemia persists or worsens, it can lead to cell death through a process known as coagulative necrosis.

Question 74

What are the consequences of pathologic hypertrophy in the heart?

Answer 74

Pathologic hypertrophy of the heart can lead to impaired cardiac function, including reduced pumping efficiency and an increased risk of heart failure. It can also be associated with other cardiac disorders, such as arrhythmias and ischemic heart disease.

Question 75

What is a reduction in cell size called?

Answer 75

A reduction in cell size is called atrophy. It refers to the decrease in the size of tissues or organs due to a decrease in the size of individual cells.

Question 76

What are some causes of atrophy?

Answer 76

Atrophy can be caused by reduced blood flow, loss of innervation (nerve supply), reduced workload or disuse, reduced nutrient supply, loss of endocrine stimulation, and ageing.

Question 77

What are the consequences of atrophy?

Answer 77

Although the cells in atrophied tissues or organs are still functional, their ability to function may be reduced. Atrophy can lead to a decrease in tissue or organ function and may result in impaired physiological processes.

Question 78

What are some examples of atrophy in the brain?

Answer 78

In the ageing brain, there is a reduction in the size of brain structures, such as the gyri (ridges), and widening of the sulci (grooves), resulting in a decrease in overall brain size. What are the mechanisms of atrophy?

Question 79

What are the mechanisms of atrophy?

Answer 79

Atrophy involves a reduction in protein synthesis, increased protein degradation, and activation of autophagy (the process of cellular self-eating), leading to the breakdown of cellular components.

Question 80

What is hyperplasia?

Answer 80

Hyperplasia is an increase in the number of cells in a tissue or organ. It involves the proliferation of differentiated or progenitor cells.

Question 81

What are the two types of hyperplasia?

Answer 81

Hyperplasia can be classified as either physiologic or pathologic. Physiologic hyperplasia occurs in response to hormonal stimuli or following the removal of part of a tissue or organ, such as the increased proliferation of liver cells after partial liver removal. Pathologic hyperplasia, on the other hand, is characterised by increased hormonal or growth factor stimulation.

Question 82

How is hyperplasia controlled?

Answer 82

Hyperplasia is tightly controlled through various regulatory mechanisms to maintain tissue homeostasis. However, a potential risk of malignancy (cancer) is associated with hyperplasia, especially if the regulatory mechanisms become dysregulated.

Question 83

Can you provide an example of pathologic hyperplasia?

Answer 83

Mammary gland hyperplasia is an example of pathologic hyperplasia. It involves the excessive growth and proliferation of cells in the mammary glands, which can lead to lumps or masses and may be associated with an increased risk of breast cancer.

Question 84

What is the process of replacing one adult cell type with another called?

Answer 84

The replacement of one adult cell type with another adult cell type is called metaplasia. It occurs as a response to cell stress or injury.

Question 85

How does metaplasia occur?

Answer 85

Metaplasia is believed to arise from reprogramming stem cell differentiation rather than a change in the phenotype of already differentiated cells. Under certain conditions, stem cells may differentiate into different cell types to adapt to the stress or environment.

Question 86

What is an example of metaplasia in the lungs of smokers?

Answer 86

In the lungs of smokers, the normal columnar epithelium changes into squamous epithelium. This transformation is believed to be a protective response to exposure to noxious smoke chemicals. However, the new squamous epithelium cannot secrete mucus or effectively clear small particles, increasing the risk of respiratory problems.

Question 87

What is an example of metaplasia in chronic acid reflux?

Answer 87

In cases of chronic acid reflux, the lower oesophagus can undergo metaplasia, where the normal squamous epithelium transforms into the gastric columnar epithelium. This change occurs due to exposure to acidic gastric contents, and it is thought to be a protective mechanism to withstand the acidic environment.

Question 88

Why does metaplasia occur in the cervix?

Answer 88

Metaplasia can occur in the cervix, where the normal columnar epithelium changes to squamous epithelium. This transformation is driven by the acidity in the vaginal environment, leading to a more suitable and protective epithelium for that particular area.

Question 89

Can you provide an example of pathologic metaplasia?

Answer 89

Pathologic metaplasia can occur in cases of abnormal tissue remodelling or injury. An example is the formation of bone tissue (ossification) in soft tissues, such as muscle, following significant injury or trauma. This is an abnormal metaplastic change that is not a normal occurrence in the affected tissues.