Apoptosis and Necrosis Overview

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Questions and Answers

What is apoptosis?

A mechanism to repair damaged cells.

A programmed form of cell death. (correct)

A form of cell death due to injury.

Cell division in response to stress.

Which example illustrates apoptosis?

Old skin cells being replaced by new ones. (correct)

Cancer cells proliferating uncontrollably.

Blood vessel blockage leading to tissue death.

Cells dying from bacterial infection.

What triggers the intrinsic pathway of apoptosis?

External immune response signals.

Cellular exposure to hypoxia or radiation. (correct)

Physical injury to the cell membrane.

Cytokine release from damaged cells.

What role do Bax and Bak proteins play in apoptosis?

They facilitate the leakage of mitochondrial proteins. Signup and view all the answers

What is the outcome of the caspase cascade during apoptosis?

Cleavage of structural proteins in the cell. Signup and view all the answers

What is a characteristic outcome of necrosis?

Tissue damage due to prolonged nutrient deprivation. Signup and view all the answers

What happens to the proteins during the apoptotic process?

They are cleaved to facilitate cell disassembly. Signup and view all the answers

How does cytochrome C contribute to apoptosis?

It binds with proteins to form the apoptosome. Signup and view all the answers

What characterizes caseous necrosis?

Presence of cottage cheese-like consistency Signup and view all the answers

Which type of necrosis is primarily associated with trauma to fatty organs?

Fat necrosis Signup and view all the answers

What is the primary cause of fibrinoid necrosis?

Hypertension and vasculitis Signup and view all the answers

Which statement about apoptosis is true?

It involves the cleaning of dead tissue by white blood cells. Signup and view all the answers

What type of necrosis is associated with hydrolytic enzymes?

Liquefactive necrosis Signup and view all the answers

Which of the following statements best describes necrosis?

Occurs due to external and internal injuries. Signup and view all the answers

What effect does lipase have during pancreatitis?

It breaks down fatty acids, leading to fat necrosis. Signup and view all the answers

Which type of necrosis can be confused with cancer due to its appearance?

Caseous necrosis Signup and view all the answers

What is a common result of fat necrosis?

Dystrophic calcifications in tissue Signup and view all the answers

Which statement differentiates necrosis from apoptosis?

Necrosis results from injury or disease. Signup and view all the answers

What happens to the cell membrane during apoptosis?

It develops blebs that can break off. Signup and view all the answers

What type of protein is released by macrophages to initiate apoptosis?

Tumor necrosis factor alpha (TNF-alpha) Signup and view all the answers

Which receptor is involved in the extrinsic pathway of apoptosis?

Fas receptor Signup and view all the answers

What is the primary mechanism by which necrosis occurs?

Cell membrane rupture and inflammation. Signup and view all the answers

What initiates the caspase cascade during apoptosis?

Formation of the death-inducing signaling complex (DISC). Signup and view all the answers

In which condition does coagulative necrosis most commonly occur?

Hypoxic tissue following ischemia. Signup and view all the answers

What characterizes liquefactive necrosis?

Formation of creamy pus from dead cells. Signup and view all the answers

What is the primary outcome of oncosis?

Cell swelling and bursting. Signup and view all the answers

In what scenario would red infarcts appear?

After a blocked blood vessel reopens. Signup and view all the answers

Which cell type is responsible for liquefactive necrosis in the brain?

Microglial cells Signup and view all the answers

What type of necrosis primarily affects the lower limbs and gastrointestinal tract?

Gangrenous necrosis Signup and view all the answers

What role do immune cells play in necrosis?

Release reactive oxygen species and proteases. Signup and view all the answers

Which of the following is NOT involved in the extrinsic pathway of apoptosis?

Mitochondrial involvement Signup and view all the answers

What happens to proteins during coagulative necrosis?

They retain some structure but lose function. Signup and view all the answers

Study Notes

Cell Death

Two major forms of cell death: apoptosis and necrosis.
Apoptosis is a programmed process, while necrosis is caused by injury or disease.
Apoptosis occurs more frequently than necrosis.

Apoptosis: Intrinsic Pathway (Mitochondrial Pathway)

Initiated by cellular stress, such as radiation, hypoxia, high calcium levels, and oxidative stress, and involves the mitochondria.
Stress triggers Bax and Bak proteins to move from the cytosol to the mitochondria, making the outer mitochondrial membrane permeable.
This releases SMACS and cytochrome C into the cytosol.
SMACS deactivates proteins that inhibit apoptosis, while cytochrome C forms a complex called an apoptosome with ATP and Apaf-1.
The apoptosome activates caspase-9, which in turn activates caspase-3 and other caspases.
The caspase cascade dismantles the cell's nucleus, organelles, and cytoskeleton.
This results in blebbing (bulges in the cell membrane), which attracts macrophages that clean up the cell fragments.

Apoptosis: Extrinsic Pathway (Death Receptor Pathway)

Initiated by external signals, such as recognition of an old, pathogenic, or completed-task cell by macrophages.
Macrophages release TNF-alpha, which binds to death receptors (e.g., tumor necrosis factor receptor 1) on the target cell.
This activates the death domain protein of the receptor, leading to binding with FADD and TRADD.
This forms the death-inducing signaling complex (DISC).
DISC triggers the activation of caspase-8, which activates caspase-3 and sets off the caspase cascade, ultimately resulting in apoptosis.
Similar process occurs when cytotoxic T cells detect foreign antigens and express Fas ligand that binds to the Fas receptor on the target cell.
This activates the death domain protein of the Fas receptor, leading to DISC formation and apoptosis.

Necrosis

Can be triggered by external factors (infection, extreme temperatures) and internal factors (tissue ischemia).
Two primary forms:
- Oncosis: Damage to mitochondria disrupts ATP synthesis, leading to ion imbalance, cell swelling, and ultimately bursting.
- Inflammatory process follows as immune cells release proteases and reactive oxygen species, potentially causing tissue damage and organ dysfunction.

Types of Necrosis

Coagulative Necrosis: Occurs when a tissue becomes hypoxic, caused by ischemia, resulting in protein denaturation and ineffective lysosomal enzyme activity.
- The tissue maintains some structure but becomes a gel-like substance.
- Red infarct: When blood re-enters the area of necrosed tissue, the tissue becomes dark red.
- Occurs in heart, kidney, and spleen tissues.
Liquefactive Necrosis: Complete digestion of dead cells by hydrolytic enzymes, leaving a creamy substance.
- Found in the brain due to microglial cell activity (microglia are brain-resident macrophages).
- Can also occur in pancreatic cells (due to enzyme activity) or within abscesses (due to neutrophil proteolytic enzymes).
Gangrenous Necrosis: Hypoxic condition that causes tissue drying (dry gangrene).
- Can progress to wet gangrene if infected, leading to liquefactive necrosis.
- Occurs in lower limbs and gastrointestinal tract.
Caseous Necrosis: A mix of coagulative and liquefactive necrosis, in which dead cells disintegrate but aren't fully digested, causing a cheesy texture.
- Commonly associated with fungal or mycobacterial (e.g., Mycobacterium tuberculosis) infections.
Fat Necrosis: Occurs in fatty organs like the pancreas or breasts due to trauma.
- Adipose cells rupture, releasing fatty acids into the extracellular space.
- Fatty acids bind with calcium, causing dystrophic calcification.
- Pancreatitis can also cause fat necrosis due to spillage of lipase.
Fibrinoid Necrosis: Occurs in malignant hypertension and vasculitis.
- High blood pressure damages blood vessel walls.
- Fibrin infiltrates the walls, leading to destruction.
- Vasculitis also involves an inflammatory response in blood vessel walls.

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Description

Explore the key differences between apoptosis and necrosis, alongside the intrinsic pathway of apoptosis. Learn how cellular stress activates specific proteins and cascades that lead to controlled cell death. This quiz delves into mechanisms and implications of these vital biological processes.