Path 1b: Cellular Responses pt 2

What is hypoxia?

oxygen deprivation

What is reduced during hypoxia?

aerobic oxidative respiration

What are possible causes of hypoxia?

- reduced blood flow (ischemia)

- inadequate oxygenation of the blood (cardiorespiratory failure)

- decreased oxygen-carrying capacity of blood

What are possible causes of decreased oxygen-carrying capacity of the blood?

anemia, CO poisoning, and severe blood loss

Depending on the severity, how may a cell respond to hypoxia?

may adapt, undergo injury, or die

What are possible physical agents that can lead to cell injury?

- Mechanical trauma

- Extremes in Temp

- Sudden changes in Atmospheric pressure

- Radiation

- Electric Shock

When might glucose or salt lead to cell injury?

when in hypertonic concentrations

When might oxygen lead to cell injury?

when in high concentrations

When might immunologic reactions lead to cellular injury?

Autoimmune - reactions to endogenous self-antigens. Can also occur in response to external agents such as microbes and environmental substances

Give an example of a subtle defect caused by genetic derangements

decreased life span of red blood cells due to single amino acid substitution inhemoglobin

sickle cell anemia

Give an example of a severe defect associated with genetic derangements

congenital malformations associated with down syndrome (due to trisomy 21, chromosomal anomaly)

What effect may variations in genetic makeup have on cells?

influence the susceptibility of cells by chemicals and other environmental insults

List nutritional imbalances that may cause cellular injury

- protein-calorie deficiencies

- vitamin deficiencies

- anorexia

- nutritional excess

What happens to cells immediately after the onset of injury?

Cells may become rapidly nonfunctional but are still viable, with potentially reversible damage.

What can a longer duration of injury lead to?

A longer duration of injury may eventually lead to irreversible injury and cell death.

What typically precedes ultrastructural, light microscopic, and grossly visible morphologic changes in cell injury?

Irreversible biochemical alterations typically precede these morphologic changes.

What are the generalized features of reversible cell injury?

- Generalized swelling of the cell and its organelles

- Blebbing of the plasma membrane

- Detachment of ribosomes from the ER

- Clumping of nuclear chromatin

What are the sequential morphologic alterations associated with reversible cell injury?

- Decreased generation of ATP

- Loss of cell membrane integrity

- Defects in protein synthesis

- Cytoskeletal damage

- DNA damage

What are the two characteristic features of reversible cell injury?

Cellular swelling and fatty change

What causes cellular swelling in reversible cell injury?

failure of energy-dependent ion pumps in the plasma membrane

What type of injury will cause fatty change?

hypoxic injury and many forms of toxic or metabolic injury

How will fatty change due to reversible injury be manifested?

by the appearance of lipid vacuoles in the cytoplasm

In what types of cells will fatty change be seen?

hepatocytes and myocardial cells

What three characteristics will be seen in regards to an organ undergoing cellular swelling?

pallor, turgor, and increase in weight of the organ

What will be seen on the microscopic level in cells undergoing cellular swelling?

- Small clear cytoplasmic vacuoles (distended and pinched-off ER)

- Hydropic change or vacuolar degeneration

- Cells may show increased eosinophilic staining

Be able to identify morphologic changes in reversible cell injury and necrosis histologically

A. Normal kidney tubules with viable epithelial cells.

B. Early (reversible) ischemic injury showing surface blebs, increased eosinophilia of cytoplasm, and swelling of occasional cells.

C. Necrosis (irreversible injury) of epithelial cells, with loss of nuclei, fragmentation of cells, and leakage of contents.

What plasma membrane alterations will be seen in a reversible injury?

blebbing, blunting, and loss of microvilli

What mitochondrial changes will be seen in reversible injury?

swelling and small amorphous densities

What changes will be seen in the ER in a reversible injury?

dilation of the ER, detachment of polysomes, and intracytoplasmic myelin figures

What nuclear alterations will be seen in a reversible injury?

disaggregation of granular and fibrillar elements

What will be the result of continuous damage to a cell?

cell injury will become irreversible, cell cannot recover and it dies

What are the two principle types of cell death?

necrosis and apoptosis

Understand the differences between necrosis and apoptosis

What is the key difference between apoptosis and necrosis?

apoptosis is regulated and non-inflammatory; necrosis causes inflammation (pathological)

What occurs to the cell during necrosis?

severe membrane damage, lysosomal enzymes enter the cytoplasm and digest the cell, cellular contents leak out

What causes the morphologic appearance of necrosis?

result of denaturation of intracellular proteins and enzymatic digestion of lethally injured cell, may take hours to develop

What happens to the surrounding tissue when necrosis occurs?

inflammation due to contents leaking from necrotic cell, cell cannot maintain membrane integrity

How will necrotic cells appear different in H&E and what causes this?

necrotic cells have loss of cytoplasmic RNA (binds to blue dye), and denatured cytoplasmic proteins (bind to red dye)

What causes the glassy homogeneous appearance of necrotic cells?

loss of glycogen particles

What are myelin figures, what type of cell are they seen in, and how are they disposed of?

whorled phospholipid masses seen in necrotic cells

Derived from damages cell membrane: phospholipid precipitates

Phagocytosed by other cells and further degraded into FA

What causes the moth-eaten appearance of necrotic cells?

digestion of cytoplasmic organelles leaving a vacuolated cytoplasm

What will replace cells that have died from necrosis?

large whorled phospholipid masses (myelin figures) derived from damaged cell membranes

What causes the nuclear changes seen in necrotic cells?

nonspecific breakdown of DNA

List nuclear changes of necrotic cells

karyolysis, pyknosis, and karyorrhexis

What is Karyolysis?

fading of the basophilia of the chromatin

change that reflects loss of DNA because of enzymatic degradation by endonucleases

What occurs during pyknosis?

nuclear shrinkage, increased basophilia

chromatin condenses into solid shrunken basophilic mass

What occurs in karyorrhexis?

pyknotic nucleus undergoes fragmentation

nucleus of the necrotic cell will totally disappear in 1-2 days

What is coagulative necrosis?

architecture of dead tissues that displays a firm texture

How long will coagulative necrosis persist and how is it removed?

persist for days or weeks, cellular debris removed by phagocytosis by infiltrating leukocytes

digestion of the dead cells by the action of lysosomal enzymes and leukocytes

Give an example of coagulative necrosis

ischemia caused by obstruction in a vessel may lead to coagulative necrosis of the supplied tissue

Infarct

What is an infarct, and what type of necrosis is associated?

necrosis of a localized area (caused by ischemia), can lead to coagulative necrosis

in this pick note the pink anucleate cells characteristic of coagulative necrosis

What is liquefactive necrosis?

transformation of tissue into a liquid viscous mass (characterized by digestion of the dead cells)

Where will liquefactive necrosis be seen?

focal bacterial infections and occasionally in fungal infections

What is the gross appearance of liquefactive necrosis?

creamy yellow due to dead leuocytes and purulent matter

What type of necrosis is hypoxic death of cells in the CNS?

liquefactive necrosis

What area of the body will gangrenous necrosis most likely be seen?

limb (usually lower limb)

What is the typical cause of gangrene?

loss of blood supply to the area leading to necrosis

What type of necrosis would be seen in a gangrenous situation in which there was not bacteria?

typically coagulative necrosis involving multiple tissue planes

think wet gangrene - liquafactive

Where is caseous necrosis most often encountered?

Tuberculous cavity (lungs) seen in tuberculosis infections

Describe the appearance of caseous necrosis

cheeselike, friable white appearance of the area of necrosis

Describe what will be seen upon microscopic examination of caseous necrosis

collection of fragmented or lysed cells, amorphous granular debris enclosed within distinctive inflammatory border (granuloma)

What will be seen upon examination of fat necrosis?

focal areas of fat destruction, release of activated pancreatic lipases into the substance of the pancreas and the peritoneal cavity

What will be seen upon microscopic examination of fat necrosis?

foci of shadowy outlines of necrotic fat cells, basophilic calcium deposits, and inflammatory reaction

What is fibrinoid necrosis?

special form of necrosis seen in immune reaction involving blood vessels

What is seen in arteries in fibrinoid necrosis?

complexes of antigens and antibodies deposited in the walls of arteries

What will be seen upon microscopic examination of fibrinoid necrosis?

deposits of immune complexes and fibrin, bright pink amorphous appearance ("fibrinoid")

What does cellular response to injurious stimuli depend upon?

- nature of the injury, it's duration and it's severity

- small doses of toxin or brief ischemia: may induce reversible injury

- large doses or prolonged ischemia: instantaneous death, slow irreversible injury leading to cell death

What is an example of the difference between skeletal and cardiac muscle in terms of cell injury

skeletal muscle deprived of it's blood supply can be placed at rest and preserved while cardiac muscle cannot

What mechanisms do cell injury result from?

different biochemical mechanisms

act on several essential cellular components such as mitochondria, cell membranes, and DNA in nuclei

What is the major and secondary pathway in which ATP will be made?

major: oxiadtive phosphorylation of adenosine diphosphate

secondary: glycolytic pathway, works in absence of oxygen and uses glucose

What results from oxidative phosphorylation and where does this occur?

reduction of oxygen through electron transfer system of mitochondria

How does the glycolytic pathway work?

generates ATP in the absence of oxygen, uses glucose derived from body fluids or hydrolysis of glycogen

What type of injury is ATP depletion associated with?

both hypoxic and chemical injury

What are the major causes of depletion of ATP?

reduced supply of oxygen and nutrients, mitochondrial damage, and actions of toxins (ex: cyanide)

Why is ATP depletion detrimental?

involved in virtually all synthetic and degradative processes within the cell

depletion of just 5-10% can have widespread effects

How will depletion of ATP affect the sodium potassium pump?

reduced activity of sodium potassium pump, sodium accumulates within the cell, water will enter leading to cell swelling and dilation of the ER

How does ischemia affect oxidative phosphorylation?

oxidative phosphorylation ceases without O2, decrease in cellular ATP, increase in adenosine monophosphate, and glycogen stores are rapidly depleted

How can ATP depletion affect the Ca2+ pump and how will this change with prolonged depletion?

influx of Ca2+ damages intracellular organelles

prolonged worsening depletion of ATP: detachment of ribosomes from the rough ER, reduced protein synthesis (dissociation of polysomes)

What may be the result of oxygen or glucose deprivation within a cell?

proteins may become misfolded which will trigger a cellular reaction leading to cell injury or death

How would a cell respond to irreversible damage to the mitochondrial and lysosomal membranes?

cell necrosis

How will ischemia affect the mitochondria and it's functions

Functional and morphologic consequences of decreased intracellular ATP during cell injury.

The morphologic changes shown here are indicative of reversible cell injury. Further depletion of ATP results in cell death, typically by necrosis. ER, endoplasmic reticulum.

List examples of things that can cause damage to mitochondria

increases of cytosolic Ca2+, reactive oxygen species, and oxygen deprivation

can also see mutations in mitochondrial genes cause of some inherited disease

How will formation of a high-conductance channel affect the mitochondria?

opening of the channel leads to a loss of mitochonrial membrane potential, results in failure of oxidative phosphorylation and depletion of ATP, will lead to necrosis of cell

How do mitochondria activate apoptotic pathways?

cytochrome c and caspases indirectly activate apoptosis-inducing enzymes

increased permeability of the outer mitochondrial membrane, leakage of proteins into the cytosol, death by apoptosis

Where is intracellular calcium sequestered?

in mitochondria and the ER

What affect would increased cytosolic Ca2+ levels have?

activates a number of enzymes, has deletrious cellular effects, and phospholipases (membrane damage)

What will be released when there are increased cytosolic Ca2+ levels?

proteases: break down both membrane and cytoskeletal proteins

endonucleases: responsible for DNA and chromatin fragmentation

ATPases: speed up ATP depletion

What will be the effect of increased intracellular Ca2+ levels?

induction of apoptosis: direct activation of caspases increasing mitochondrial permeability

What are free radicals?

chemical species that have a single unpaired electron in an outer orbit, energy is created by this unstable configuration

How is the energy in free radicals released? Provide an example

- Through reactions with adjacent molecules

- Ex: inorganic or organic chemicals/proteins, lipids, carbs, and nucleic acids q

Where are reactive oxygen species made within cells?

produced normally in cells during mitochondrial respiration and energy generation, also produced in large amounts by leukocytes (neutrophils and macrophages)

How are free radicals degraded?

Through enzymes, spontaneous decay, and antioxidants. (cellular defense systems)

In what ways can free radicals be made that are not normal to physologic processes?

UV light, xrays, and ionizing radiation (hydrolyzes water into OH and hydrogen free radicals), and enzymatic metabolism of exogenous chemicals or drugs

What type of reaction will lead to free radicals?

Reduction-oxidation reactions that occur normally in metabolic processes

When will rapid bursts of reactive oxygen species be seen?

during inflammation: made by activated leukocytes

What role do transition metals play in generation of free radicals?

iron and copper donate and accept free electrons during intracellular reactions

Ex: Fenton reaction (H2O2 + Fe2+ → Fe3+ + OH + OH

What is the function of nitric oxide?

important chemical mediator, acts as a free radical

Where is nitric oxide generated within the body?

endothelial cells, macrophages, neurons, and others

How are free radicals removed?

unstable and decay spontaneously

multiple nonenzymatic and enzymatic mechanisms in cells remove free radicals

iron and copper minimize levels by binding ions to storage and transport proteins (transferrin, ferritin, lactoferrin, and ceruloplasmin)

enzymes act as free radical-scavenging systems

How can free radicals affect membranes of cells?

leads lipid peroxidation within plasma and organellar membranes in presence of O2

leads to oxidative damage: double bonds of FA in membranes are attacked by O2 derived free radicals