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 cell injury..

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تاريخ التسجيل : 15/10/2007
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مُساهمةموضوع: cell injury..   الجمعة نوفمبر 16, 2007 1:23 pm

What are the two forms of calcification? Define each.



1- Dystrophic calcification, in which calcium deposition occurs in dead tissues,

It occurs albeit serum levels of calcium salts are normal.

- Seen in areas of necrosis or damage.

2- Metastasic calcification, in which calcium deposition occurs in living tissues,

- It almost results from hypercalcemia.





What are the effects caused by ATP depletion?



1- Cell swelling and ER dilation, caused by Na accumulation and K diffusion out of the cell, due to the reduced activity of energy-dependent Na pump.

2- Suppression of the oxidative phosphorylation pathway as the glycolytic pathway becomes brisk, causing accumulation of lactic acid and then lowering the intracellular pH, which results in decreased activity of some enzymes.

3- Ca influx, that causes increased activity of some enzymes such as ATPase, phospholipases, proteases, endonucleases, resulting in ATP depletion, Cellular membrane damage and DNA fragmentation respectively.

4- Detachment of ribosomes from the ER, and polyribosomes detach to form monosomes, resulting in reduction of protein synthesis.

5- Protein misfolding, which may cause cell injury then death.



How could a cell discard oxygen free radicals?



1- Particular enzymes: superoxide dismutases, catalase, glutathione peroxidase.

2- Antioxidants...e.g: vit A, vit E



Could oxygen free radicals be present normally within the cell? How?



Yes they could yet in small amounts that can be processed and removed by enzymes. They are produced during normal respiration.



What is an oxygen free radical?



Chemically it is an atom with a single electron in its outer orbit.



What marks can be implicated with irreversible injuries?



1- Extensive damage to the cellular membrane * Loss of function*

2- Mitochondrial swelling and vacuolization * Dysfunction and inability to reverse albeit removal of injury*

3- Lysosomal swelling

4- The appearance of large amorphous densities within a mitochondrion



In which of the pathological conditions does inflammation exist, necrosis or apoptosis? Explain



- Necrosis, since cellular contents are degraded by enzymes (either lysosomal enzymes of dead cells themselves, or lysosomal enzymes of immigrant leukocytes) then they are leaked out of the cell.

- As for apoptosis, no inflammation occurs since cellular contents are enveloped in apoptotic bodies which are rapidly phagocytosed by macrophages before leaking out * neither cells lysosomal enzymes nor leukocytes lysosomal enzymes are involved*



What is (Pyknosis)?



A characteristic of the nucleus in a necrotic cell,

It appears as nuclear shrinkage with increased basophilia due to chromatin condensation under the nuclear membrane.



How could a necrotic cell be characterized using an electric microscope?



- Disrupted cellular membrane.

- Swollen mitochondria with amorphous densities within.

- Myelin figures.

- Denatured proteins showing fluffy materials within the cytosol

- Amorphous debris.

- Pyknosis, karyorrhexis or karyolysis of the nucleus * Define each?*



Pyknosis: A nuclear change in a necrotic cell showing shrunk nucleus and a condensed basophilic mass of chromatin

Karyorrhexis: A nuclear change in a necrotic cell showing fragments of the nucleus.

Karyolysis: A nuclear change in a necrotic cell showing faded basophilia of the chromatin.



Does coagulative necrosis cause hypoxic death of all tissues?



No, since it does not cause hypoxic death of the brain as does the liquefactive necrosis.



What type of necrosis is seen in tuberculosis?



Caseous necrosis



What causes fat necrosis?



The release of pancreatic lipases into the pancreatic substance or the peritoneal cavity * occurs in acute pancreatitis*



How does fat necrosis appear microscopically?



Chalky white areas formed by the combination of the released fatty acids with Ca.



What is Apoptosis?



Programmed cell death, or cell suicide... it is usually caused physiologically yet could some pathological factors cause it.



Explain the cellular events implicated with apoptosis?



* The cell activates its own enzymes to break down its DNA, cytoplasmic and membranous proteins*

A- as for the size of the cell: it shrinks

B- as for the nucleus:

- The nucleus is fragmented into nucleusome-size fragments

- As the chromatin condenses peripherally under the nuclear membrane.

C- as for the cytoplasm: Blebs and apoptotic bodies are formed, containing cellular organelles with or without nuclear fragments.

D- as for the cellular contents: they are enveloped within the apoptotic bodies and are phagocytosed by macrophages; the rapid phagocytosis avoids leakage of these contents extracellularly, thus no inflammation exists.

E- as for the cellular membrane: is intact, with redistributed orientation of phospholipids to attract macrophages to the site of apoptosis.
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