Cell Death : Necrosis & Apoptosis - Types, Morphology, Causes, Mechanism & Clinical Significance

Summary

This video delves into cell death mechanisms, comparing necrosis and apoptosis. Necrosis, often resulting from pathological conditions like ischemia or infection, involves disrupted cell membranes and an inflammatory response. The process is divided into different types like coagulative and liquefactive necrosis. On the other hand, apoptosis is a physiological, energy-dependent process where cells undergo programmed death, typically without inflammation. The video further explores the molecular pathways of both necrosis and apoptosis, including intrinsic and extrinsic signaling mechanisms involving various proteins like caspases, and highlights their significance in tissue repair and disease progression.

Takeaways

• 😀 Necrosis is a pathological process of cell death, occurring due to causes like ischemia, infections, and toxins.
• 😀 Apoptosis, or programmed cell death, is a physiological and controlled process that does not cause inflammation.
• 😀 Necrosis involves plasma membrane rupture, cellular content leakage, and inflammation, leading to tissue damage.
• 😀 In necrosis, cellular changes become visible between 1-6 hours after cell death, and diagnostic enzymes may appear in the blood shortly after.
• 😀 Coagulative necrosis is seen in solid organs like the heart and kidney and typically results from ischemia.
• 😀 Liquefactive necrosis occurs in tissues rich in lysosomal enzymes like the brain and pancreas, leading to tissue liquefaction.
• 😀 Caseous necrosis occurs in tuberculosis and some fungal infections, characterized by crumbling, cottage-cheese-like tissue.
• 😀 Fat necrosis results from trauma or pancreatic injury, causing triglyceride breakdown and calcium salt deposition.
• 😀 Apoptosis is initiated by either intrinsic (mitochondrial) or extrinsic (death receptor) pathways, both activating caspases.
• 😀 In apoptosis, the cell shrinks, chromatin condenses, and apoptotic bodies are formed, which are phagocytosed without inflammation.
• 😀 Gangrene is a severe form of tissue necrosis that can be wet (with infection) or dry (due to ischemia) and requires prompt intervention.

Q & A

What is the main difference between necrosis and apoptosis?

Necrosis is a pathological form of cell death that occurs due to injury or disease, leading to inflammation, while apoptosis is a programmed, physiological cell death mechanism that occurs without causing inflammation.

What causes necrosis to trigger an acute inflammatory response?

When a cell undergoes necrosis, its plasma membrane ruptures and cellular contents leak out. These substances are recognized as harmful by the body, prompting an acute inflammatory response.

Why does necrosis not show visible changes immediately after cell death?

It takes several hours for the cellular changes to become visible, typically 1-3 hours for electron microscopy and 4-6 hours for light microscopy, because it takes time for the cellular content to leak and trigger the inflammatory response.

What are the two main types of tissue necrosis?

The two main types of tissue necrosis are coagulative necrosis and liquefactive necrosis, which differ in how the tissue breaks down and is removed.

What is coagulative necrosis and where is it commonly seen?

Coagulative necrosis occurs when the tissue structure is preserved for several days despite cell death, commonly seen in solid organs like the heart, kidney, liver, and adrenal glands. It is often caused by hypoxia.

What is the role of autolysis and heterolysis in necrosis?

Autolysis is the self-digestion of necrotic cells by their own enzymes, while heterolysis involves digestion by enzymes from other cells, such as neutrophils or macrophages, typically seen in infection.

How does liquefactive necrosis differ from coagulative necrosis?

In liquefactive necrosis, the tissue is completely digested, forming a liquid material, while in coagulative necrosis, the tissue structure remains intact for some time. Liquefaction occurs in tissues like the brain and pancreas.

What is caseous necrosis and what causes it?

Caseous necrosis is a type of coagulative necrosis where the tissue becomes crumbled and yellowish, resembling cottage cheese. It is most commonly seen in infections like tuberculosis, where the body’s immune response damages the tissue.

What causes fat necrosis, and what are the two types?

Fat necrosis occurs when adipose tissue is damaged. There are two types: enzymatic fat necrosis, typically seen in acute pancreatitis, and traumatic fat necrosis, seen in physical injury to fat tissue.

What is the key difference between wet and dry gangrene?

Wet gangrene is caused by infection with anaerobic bacteria and leads to tissue liquefaction, oozing, and foul odor. Dry gangrene occurs due to ischemia, causing tissue desiccation, and does not involve infection.

How does the intrinsic pathway of apoptosis work?

The intrinsic pathway of apoptosis is triggered by mitochondrial dysfunction. It involves the release of cytochrome C from the mitochondria, which activates caspase-9, leading to the activation of executioner caspases and subsequent cell death.

What is the extrinsic pathway of apoptosis, and what initiates it?

The extrinsic pathway is activated by external signals, specifically the binding of Fas ligand to the Fas receptor on the cell membrane. This triggers the activation of caspase-10 and other caspases to initiate apoptosis.