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Archive for March, 2010

Pathology MCQs

Posted by Dr KAMAL DEEP on March 16, 2010

1. The following are example of apoptosis except-
a)Graft versus host disease(JIPMER 2002)
b)Menstrual cycle
c)Pathological atrophy following duct obstruction
d)Tumour necrosis

Type :- Controversial Question

Ans is None

Ref-Robbins

There are two principal patterns of cell death, necrosis and apoptosis.

 Necrosis or coagulation necrosis is the more common type of cell death after exogenous stimuli, occurring after such stresses as ischemia and chemical injury. It is manifested by severe cell swelling or cell rupture, denaturation and coagulation of cytoplasmic proteins, and breakdown of cell organelles.

 Apoptosis occurs when a cell dies through activation of an internally controlled suicide program. It is a subtly orchestrated disassembly of cellular components designed to eliminate unwanted cells during embryogenesis and in various physiologic processes. Doomed cells are removed with minimum disruption to the surrounding tissue. It also occurs, however, under pathologic conditions, in which it is sometimes accompanied by necrosis. Its chief morphologic features are chromatin condensation and fragmentation. Although the mechanisms of necrosis and apoptosis differ, as we shall see, there is
considerable overlap between these two processes. Recently, a new term has been introduced– oncosis–to define the prelethal changes preceding necrotic cell death. [2] These are characterized by cell swelling ( oncos, Greek for swelling) and can be distinguished from the prelethal changes in apoptosis, associated largely with cell shrinkage. Whether the term will achieve the status sought by its creators is still unclear.

Apoptosis was initially recognized in 1972 by its distinctive morphology and named after the Greek designation for "falling off." [33] [33A] It is a form of cell death designed to eliminate unwanted host cells through activation of a coordinated, internally programmed series of events effected by a dedicated set of gene products. It occurs in the following general settings: (1) during development; (2) as a homeostatic mechanism to maintain cell populations in tissues; (3) as a defense mechanism such as in immune reactions;  when cells are damaged by disease or noxious agents; and (5) in aging. [34] [35] It is responsible for numerous physiologic, adaptive, and pathologic events, including the following:

The programmed destruction of cells during embryogenesis, including implantation, organogenesis, developmental involution, and metamorphosis. Although apoptosis is a morphologic event, which may not always underlie the functionally defined "programmed cell death" of embryologists, the terms are currently used synonymously by most workers.

1.Cell deletion in proliferating cell populations, such as intestinal crypt epithelia.

2.Cell death in tumors, most frequently during regression but also in tumors with active cell growth.

3.Death of neutrophils during an acute inflammatory response.

4.Death of immune cells, both B and T lymphocytes after cytokine depletion, as well as deletion of autoreactive T cells in the developing thymus.

5.Cell death induced by cytotoxic T cells, such as in cellular immune rejection and graft-versus-host disease.

6.Pathologic atrophy in parenchymal organs after duct obstruction, such as occurs in the pancreas, parotid gland, and kidney.

7.Cell injury in certain viral diseases, as for example in viral hepatitis, in which apoptotic cells in the liver are known as Councilman bodies.

8.Cell death produced by a variety of injurious stimuli that are capable of producing necrosis, but when given in low doses. For example, heat, radiation, cytotoxic anticancer drugs, and hypoxia can induce apoptosis if the insult is mild, but large doses of the same stimuli result in necrotic cell death.

9. Hormone-dependent involution in the adult, such as endometrial cell breakdown during the menstrual cycle, ovarian follicular atresia in the menopause, the regression of the lactating breast after weaning, and prostatic atrophy after castration.

 

2. True about apoptosis-(PGI 03)
a)Migration of Leukocytes
b)End products are phagocytosed by macrophage
c)Intranuclear fragmentation of DNA
d)Activation of caspases
e)Annexin V is marker of apoptopic cell

Ans is B , C D and E

 

The following morphologic features, some best seen with the electron microscope, characterize cells undergoing apoptosis .

Cell shrinkage. The cell is smaller in size; the cytoplasm is dense; and the organelles, although relatively normal, are more tightly packed.

Chromatin condensation. This is the most characteristic feature of apoptosis. The chromatin aggregates peripherally, under the nuclear membrane, into well-delimited dense masses of various shapes and sizes (Fig. 1-17) . The nucleus itself may break up, producing two or more fragments.

Formation of cytoplasmic blebs and apoptotic bodies. The apoptotic cell first shows extensive surface blebbing, then undergoes fragmentation into a number of membrane-bound apoptotic bodies composed of cytoplasm and tightly packed organelles, with or without a nuclear fragment.

Phagocytosis of apoptotic cells or bodies by adjacent healthy cells, either parenchymal cells or macrophages. The apoptotic bodies are rapidly degraded within lysosomes, and the adjacent cells migrate or proliferate to replace the space occupied by the now deleted apoptotic cell.
Plasma membranes are thought to remain intact

Apoptosis is the endpoint of an energy-dependent cascade of molecular events, initiated by certain stimuli, and consisting of four separable but overlapping components

1.
Signaling pathways that initiate apoptosis (TNF,FAS,INJURY,WITHDRAWAL OF GROWTH FACTORS)

2.
Control and integration, in which intracellular positive and negative regulatory molecules inhibit, stimulate, or forestall apoptosis and thus determine the outcome (bcl PROTEINS ETC)

3.
A common-execution phase consisting of the actual death program and accomplished largely by the caspase family of proteases

4.
Removal of dead cells by phagocytosis

 

3. Morphological changes of apoptosis include –
a)Membrane blebs(PGI 02)
b)Inflammation
c)Nuclear fragmentation
d)Spindle formation
e)Cell swelling

Ans is A and C

 

4. Starting point of apoptosis for programme cell death is -(PGI 97)
a)Activation of endonuclease
b)Release of enzyme
c)Accumulation of calcium
d)Destruction by macrophages

Ans is A

 

5. One of the following is an apoptosis inhibitor gene

a) p53′      b) BcL-2          (SGPGI 04)
c) Rb        d) c-Myc

 

Ans is B

Control and Integration Stage of APOPTOSIS STAGE 2.
This is performed by specific proteins that connect death signals to the execution program. These proteins are important because their actions may result in either "commitment" (i.e., determination of the inevitability of cell death) or abortion of potentially lethal signals. The proteins involved in this regulation have clinical significance: by determining the life or death of cell communities involved in important biologic processes (such as the immune response or cancer), they can affect the outcomes of disease.
There are commonly two broad schemes for this stage, which are not mutually exclusive. One involves the direct transmission of signals by specific adapter proteins to the execution mechanism, as described for the Fas-Fas ligand model and target cell killing by cytotoxic T lymphocytes (see later). [46] [47] [48] The second involves members of the Bcl-2 family of proteins [49] which play major and ubiquitous roles in apoptotic regulation largely by regulating mitochondrial function. [50] As previously described (see Fig. 1-4 ), death agonists can generate signals that affect mitochondria in two ways (Fig. 1-21) :

Apoptotic signals result in mitochondrial permeability transitions. [50A] Formation of pores within the inner mitochondrial membrane results in reduction of membrane potential and mitochondrial swelling.

The signals also cause increased permeability of outer mitochondrial membranes, releasing an apoptotic trigger, cytochrome c, from mitochondria into the cytosol.  Cytochrome c is located between the inner and outer mitochondrial membranes and is an integral but soluble component of the respiratory pathway. Cytochrome c release precedes the morphologic changes of apoptosis, showing that it occurs early, consistent with a regulatory function

 

Several proteins regulate such mitochondrial permeability events, but the most important are members of the Bcl-2 family, detailed in Chapter 8 and involved in an important way in cancer formation. Bcl-2, the mammalian homolog of the anti-apoptotic ced-9 gene in C. elegans, is situated in the outer mitochondrial membrane, endoplasmic reticulum, and nuclear envelope. Its function is regulated by other family members. By selectively binding to Bcl-2, these related proteins can alter Bcl-2’s activities and either promote apoptosis (e.g., Bax, Bad) or inhibit the process (e.g., Bcl-XL). Bcl-2 suppresses apoptosis in two ways: by direct action on mitochondria to prevent increased permeability, and by effects mediated by interactions with other proteins. Indeed, it is thought that mitochondrial permeability is determined by the ratio of pro-apoptotic and anti-apoptotic members of the Bcl-2 family in the membrane. [49] [50]
In certain cells Bcl-2 can also suppress apoptosis by serving as a docking protein, binding proteins from the cytosol and sequestering them on the mitochondrial membrane (Fig. 1-21) . Protein binding may modulate the function of Bcl-2 itself or target the docked protein for interaction with other proteins. Notable among these Bcl-2-binding proteins is the pro-apoptotic protease activating factor (Apaf-1), the mammalian homolog of the nematode gene ced-4. [53] [54] This protein also associates with inactive zymogen forms of certain initiator caspases (e.g., caspase 9), so called to distinguish them from the execution caspases described later. It is speculated that when cytochrome c is released from mitochondria by death signals, it binds Apaf-1 and activates it, triggering an initiator caspase and setting in motion the proteolytic events that kill the cell (Fig. 1-21) . In this scenario, Bcl-2 binding protects because it sequesters Apaf-1 and inhibits its catalytic caspase-triggering function, even if cytochrome c has leaked out of mitochondria.

The two scenarios for the anti-apoptotic actions of Bcl-2, that is, to directly prevent cytochrome c release and to inhibit Apaf-1-induced caspase activation despite cytochrome c release, are not mutually exclusive. [52] Other important proteins are also involved in apoptotic regulation. These include the p53 protein and certain mammalian homolog of viral protease inhibitor proteins.

 

 

6.The process of programmed gene directed celldeath characterized by cell-shrinkage, nuclearcondensation and fragmentation is known as –

a) Necrosis b) Chromatolysis
c) Pyknosis d) Apoptosis

Ans is D

 

7. Internucleosomal Cleavage of DNA is characteristicof-(AIIMS NOV 05)
a)Reversible cell injury
b)Irreversible cell injury
c)Necrosis
d)Apoptosis

Ans is D

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