Apoptosis and Necrosis Concepts

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following best describes the role of energy in apoptosis?

Energy is only required in the extrinsic pathway of apoptosis.

Apoptosis is an energy-dependent process. (correct)

Apoptosis is an energy-independent process.

Energy is only required in the mitochondrial pathway of apoptosis.

What is a key feature of DNA during apoptosis?

Mitochondrial DNA is primarily affected.

Random, haphazard fragmentation.

DNA remains intact until the cell membrane lyses.

Inter nucleosomal cleavage leading to DNA laddering. (correct)

How does the cytoplasm typically appear during apoptosis?

Swollen and ruptured.

Unchanged in size until cellular contents spill out.

Shrunk without membrane rupture. (correct)

Shriveled and condensed with membrane lysis.

What is the immediate fate of cellular content in apoptosis?

Packaged in membrane bound bodies. Signup and view all the answers

Which condition is generally a characteristic of necrosis, but not apoptosis?

Mitochondria swelling and rupture. Signup and view all the answers

Which term best describes the inflammatory response associated with necrosis?

General, due to cell content release. Signup and view all the answers

How does the nuclear membrane interact with chromatin during apoptosis?

Chromatin condenses and migrates towards the nuclear membrane. Signup and view all the answers

What are the key processes that differentiate apoptosis from necrosis?

Apoptosis features cell shrinkage while necrosis features cellular swelling. Signup and view all the answers

Which process triggers apoptosis?

Specific signals or lack of survival signals. Signup and view all the answers

Which of the following best describes the appearance of DNA during necrosis?

Random fragmentation. Signup and view all the answers

Which of the following is a key characteristic of reversible cell injury, as opposed to irreversible injury?

Formation of membrane blebs. Signup and view all the answers

What is the primary role of caspases in the context of apoptosis?

To execute the organized and controlled dismantling of cellular components. Signup and view all the answers

In a cell undergoing necrosis, which of the following cellular changes would you least likely expect to observe?

Active cell shrinkage. Signup and view all the answers

Which of the following best illustrates the morphological changes in a cell transitioning from healthy to necrotic, focusing on the mitochondria?

Mitochondria initially become puffy in early injury stages then swell and become very round in later necrosis. Signup and view all the answers

What role does the mitochondrial pathway play in apoptosis induction?

It uses mitochondrial membrane proteins to release factors that ultimately activate caspases inside the cell. Signup and view all the answers

Which of the following best describes a key morphological difference between cells undergoing necrosis and apoptosis when examined microscopically?

Necrotic cells demonstrate cell swelling and ruptured membranes, while apoptotic cells shrink in a regulated manner with blebbing. Signup and view all the answers

Which cellular process is most associated with free radical formation as a key mechanism of cell injury?

Mitochondrial damage leading to impaired electron transport. Signup and view all the answers

What is the most important distinction between reversible and irreversible cell injury based on cellular morphology?

The integrity of the cell membrane and internal structures. Signup and view all the answers

What is a hallmark process of apoptosis that distinguishes it from necrosis?

Energy-dependent process leading to cell shrinkage and DNA fragmentation. Signup and view all the answers

A cell undergoing hydropic change, where its internal environment changes due to disruptions to ion and water balance, would be classified as undergoing which process?

Reversible cell injury. Signup and view all the answers

Study Notes

Cell Injury and Cell Death

Cell injury occurs due to biochemical and morphologic changes
It is caused by exogenous factors (like trauma, heat, cold, radiation, chemicals, bacterial toxins and drugs) or endogenous factors (like inborn errors of metabolism, sickle cell disease, intestinal malabsorption, obesity and malnutrition)
Cell injury results in reversible damage or irreversible disruption of normal cell function
Hypoxia is a decrease in the supply of oxygen, caused by a complete block in the oxygen supply
Anoxia is a condition where there is a lower concentration of oxygen in the air; examples include high altitude or drowning and lung disease. Other examples of this are anemia, Ischemia, thrombosis, embolism, rupture of an aneurysm, and cyanide poisoning.

Learning Objectives

List causes of cell injury
Describe effects of cell injury
Define reversible and irreversible cell injury
Compare reversible and irreversible cell injury
Define necrosis and apoptosis and list main differences
List characteristic cellular changes observed in necrosis
List characteristic cellular changes observed in apoptosis
Compare/contrast healthy and necrotic cells based on morphology in H&E stained and electron micrograph images
Describe mechanisms of apoptosis and its regulation
Diagram intrinsic and extrinsic pathways of apoptosis induction, emphasizing proteins activating caspases
Differentiate between necrosis and apoptosis based on cellular morphology in microscopic images
Define anoikis and correlate it with tumor metastasis

Cell and Tissue Injury

Cell injury is a consequence of biochemical and morphologic changes
Causes include exogenous (e.g. trauma, heat/cold, radiation, chemicals) and endogenous factors (e.g., metabolic errors, nutritional deficiencies).
Reversible cell injury may involve swelling of endoplasmic reticulum and mitochondria, membrane blebs and myelin figures. Recovery is possible.
Irreversible injury results in necrosis or apoptosis

Exogenous Causes of Cell Injury

Physical injury: Trauma, heat or cold; ultraviolet light or ionizing radiation
Chemical injury: Alcohol or corrosive substances
Bacterial toxicity: Cholera toxin inducing watery diarrhea, mercury toxicity to the kidneys
Drug toxicity: Mercury toxicity to the kidneys

Endogenous Causes of Cell Injury

Genetic defects: Inborn errors of metabolism, sickle cell disease
Nutritional deficiency: Intestinal malabsorption resulting from celiac disease, obesity, malnutrition

What Happens to Injured Cells?

ATP depletion: Detachment of ribosomes; increased anaerobic glycolysis; lactic acid accumulation; decreased activity of enzymes; reduced activity of plasma membrane ATP-dependent sodium pumps; lysosomal membrane damage.
Mitochondrial damage: Swelling of the inner mitochondrial membrane; altered membrane permeability; affecting transmembrane potential and opening of pores
Calcium changes: Loss of calcium homeostasis; effects within the cell; activation of ATPases, proteases, phosphatases and endonucleases.
Free radical formation: Reactions with inorganic and organic material; production and removal rates of free radicals; lipid peroxidation leading to membrane damage; protein modifications leading to mis-folding; DNA damage leading to mutations

Types of Cell Injury

Two types: Reversible and irreversible
Reversible causes: Exposure to toxins in low concentration, brief hypoxia or anoxia
Irreversible causes: Heavy doses of toxins, anoxia, severe and prolonged hypoxia, or injury that is unable to recover from

Reversible Cell Injury

A form of cell injury in which the cell can recover to its original steady state
The changes produced are called reversible cell injury
If adverse environmental influences evoke a cellular response that remains within the range of homeostasis then responses remain within the range of homeostasis and cells return to original state after cessation of injury
Recognized by: Mild injury that happens in the body, short-lived, like a cold or virus, induced by low concentration of toxins, hypoxia, or brief period of anoxia during anaerobic respiration, disruption of Na+/K+ ATPase pump going back to normal
Leading to: Cell swelling, impaired cellular regulation; mitochondria and endoplasmic reticulum swelling with detachment of ribosomes; surface blebs due to increased calcium, leading to changes in the microfilaments of the cytoskeleton; loss of microvilli structure

Irreversible Cell Injury

Permanent damage; cannot come back to original function; may lead to cell death
Occurs when cells are exposed to causes of cell injury and cannot recover; this is a 'point of no return'
Cell death happens in two ways: necrosis and apoptosis
Depending on the cause of injury, either necrosis or apoptosis will be the outcome

Necrosis

The following nuclear changes occur:
Pyknosis: irreversible condensation of chromatin
Karyorrhexis: destructive fragment of the nucleus or nucleus burst
Karyolysis: complete dissolution of the chromatin by endonucleases; basophilia of the nucleus fades
The following cytoplasmic changes occur: swelling of the organelles (especially mitochondria) and rough ER; rupture of the plasma membrane leading to spillage of all cytoplasmic contents

Types of Necrosis

Coagulative necrosis: The most common; tissue remains firm; architecture is preserved; cell shape and organ structure are preserved for few days; caused by ischemia or infarction
Liquefactive necrosis: Tissue becomes liquefied through enzymatic action; maintains cheese-like appearance
Caseous necrosis: Dead tissue appears soft and white; frequently associated with TB
Gangrene: Dry gangrene is coagulative necrosis resembling mummified tissue; wet gangrene is superimposed infection and then liquefactive necrosis
Fat necrosis: Involves adipose tissue; restricted to smooth muscle wall of small arteries, arterioles, and renal glomeruli
Fibrinoid necrosis: Necrotic tissue and debris disappear by a combined process, or if not destroyed, they attract calcium salts and other minerals resulting in calcification

Apoptosis

A type of programmed cell death
Two types: Intrinsic (or Mitochondrial) pathway and Extrinsic (or Death Receptor) pathway
Intrinsic pathway: When mitochondria experience damage or an altered cell cycle, they secrete factors (e.g., cytochrome C) and activate procaspase 8
Extrinsic pathway: Cell surface death receptors (e.g., Fas receptor) are triggered.
When mitochondrial membranes become permeable, cytochrome C leaks to the cytoplasm; triggers procaspase 9 activation, leading to apoptotic death
AIF (Apoptosis-inducing factor): Moves to the nucleus, binds to DNA and leads to cell death without caspase participation
Granzyme B and Perforin: Cytotoxic T cells secrete granzyme B and perforin. Granzyme B enters the infected cell and perforin forms pores on the cell membrane.
Causes of apoptosis include growth factor withdrawal, DNA damage, and protein misfolding.

Anoikis

A special form of apoptotic process occurring in cells in response to loss of adhesion to the ECM
Critical for maintaining tissue homeostasis
Some cancer cells develop mechanisms to escape anoikis, which can lead to seeding in inappropriate sites

Other Forms of Programmed Cell Death

Autophagy, paraptosis, pyroptosis, mitotic catastrophe, and entosis are other types of programmed cell death, including the uncontrolled mechanism of necrosis.

Apoptosis vs Necrosis

Necrosis is a pathological response to cell injury and Apoptosis is a normal cell response for elimination, following specific signals.
Chromatin clumping and mitochondrial swelling/rupture are characteristics of necrosis. Cytoplasmic shrinkage is a feature of apoptosis.

Note: Please refer to the provided images for detailed illustrations of the cellular changes. This summary provides an overview and does not replace detailed study using the images.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your understanding of apoptosis and necrosis with this quiz. Explore key differences, features of cell death, and the role of energy in these processes. Perfect for students studying cell biology or related fields.