Cell Death Flashcards
A man has been diabetic with poorly controlled blood sugar for the past five years. Which of the following may be characteristic changes in his body organs as a result of the chronic illness?
A. Fatty liver
B. Atherosclerosis in blood vessels
C. Glycogen accumulation in hepatocytes
D. Carbon dust in the lungs
E. All of the above
A young lady walks into the clinic. She complains of black coloured urine. On examination, you notice black patches on her face. Which of the following may be implicated?
A. Melanin
B. Alkaptonuria/Homogentisic acid
C. Coal dust
D. Tatoo pigments in the urine
E. None of the above
48-year-old woman has a malignant lymphoma involving lymph nodes in the para-aortic region. She is treated with a chemotherapeutic agent which results in the loss of neoplastic cells through fragmentation of individual cell nuclei and cytoplasm.
Apoptosis
53-year-old man has had severe chest pain for the past 6 hours. Laboratory studies show a serum troponin I of 10 ng/mL. In this setting, an irreversible injury to myocardial fibers will have occurred when which of the following cellular changes occurs?
C Nuclei undergo karyorrhexis
A man is struck on the leg by a pallet rack.
Within 2 days there is a purple colour to the site of injury. Which of the following substances has 3/6 most likely accumulated at the site of injury to a yellow-brown colour within 16 days?
Hemosiderin
A 54-year-old man with a chronic cough has a lung squamous cell carcinoma. While performing a pneumonectomy, the hilar lymph nodes are small, and jet black in colour. Which of the following is the most likely cause for this appearance to the hilar nodes?
• A Anthracotic pigment
• B Lipochrome deposits
C Melanin accumulation
• D Hemosiderosis
• E Metastatic carcinoma
Anthracotic pigment
man with mild burning substernal pain following meals. Upper Gl endoscopy is performed and biopsies are taken of the lower oesophagus which show the presence of columnar epithelium with goblet cells
• A Dysplasia
• B Hyperplasia
• C Carcinoma
• D Ischemia
• E Metaplasia
Metaplasia
A woman suffers an acute myocardial infarction. tissue plasminogen activator (tPA) is administered to restore coronary blood flow. In spite of this therapy, the extent of myocardial fiber injury may increase because
• A Cytoskeletal intermediate filament loss
B Decreased intracellular pH from anaerobic glycolysis
C Increased free radical formation
• D Mitochondrial swelling
• E Nuclear chromatin clumping
• F Reduced protein synthesis
Increased free radical formation
Two broad types of cell death
Necrosis
Apoptosis (may be physiologic i.e. seen in non-diseased cells)
Necrosis results from 2 major things
DIP
EDC
denaturation of intracellular proteins
and enzymatic digestion of the irreversibly injured cell.
The enzymes are released from 2 places
from the lysosome of index cell
lysosomes of adjacent white blood cells (inflammatory infiltrate)
The dying cell loses its membrane integrity and cellular contents spill into surrounding tissues causing _____________
Inflammation
Necrotic changes may take hours to be morphologically visible, however, certain chemicals released from the injured cell may be detectable in body fluids e.g. _________ & _______
Myocardial infarction enzymes (Troponins, creatinine kinase)
cardiac specific enzymes
Morphological classification of necrosis
CLGCFF
- Coagulative necrosis
- Liquefactive necrosis e.g. C.N.S.
- Gangrenous necrosis e.g. Foot gangrene
- Caseous necrosis e.g. TB
- Fat necrosis e.g. pancreatitis, breast
- Fibrinoid necrosis e.g. blood vessels
Coagulation necrosis is the most _____ type of necrosis caused by?
• Commonly seen in these 3 organs
Common
focal injury to a tissue e.g. as a result of impaired blood flow (ischaemia).
heart, spleen, kidney.
Morphology of coagulative necrosis grossly and microscopically
- Gross (plain eyesight): pale, slightly swollen area called INFARCT
- Microscopically, the cells retain their outlines, however the cytoplasmic and
nuclear details are lost aka ‘Tombstone’/’Ghost’ appearance
The affected cells are swollen and more EOSINOPHILIC than usual.
In coagulative necrosis, cell liquefaction occurs, debris are cleared off by WBCs
T/F
False
Cell liquefaction FAILS to occur
Liquefaction necrosis can be caused by 3 things
Also caused by ischaemic injury
bacterial infection
fungal infections
•
The ____ _____ _____ play a dominant role in the digestion of the affected cells creating a _____ material.
cellular hydrolytic enzymes
semi-fluid
Examples of liquefaction necrosis are
brain infarcts (CVA/”stroke”) (cerebral vascular accident)
abscess cavities.
2 Characteristics of caseous necrosis
• Cheese-like
• Characteristically found in Tuberculous infections.
Morphology of caseous necrosis
Gross & microscopic
Grossly: soft, granular, yellowish.
Microscopically: characteristic granuloma (epithelioid cells, giant cells and
peripheral cuff of lymphocytes) with central area of necrosis
______ necrosis is not a distinctive pattern of cell death
Gangrenous
When bacteria infection is superimposed with gangrene the morphologic appearance changes to _____ necrosis because of the destructive contents of the bacteria and the attracted leukocytes resulting in so-called _______
Liquefaction
wet gangrene”
Apoptosis is?
Apoptosis is programmed cell death
5 Physiological examples of apoptosis is
• Embryogenesis
• Involution of hormone dependent tissues after hormone withdrawal e.g. shedding of endometrial lining, reduction in breast size at the end of breast feeding
• Involution of the thymus at an early age
• Elimination of self-reactive lymphocytes either before or after maturation to prevent damage to body tissues
• Death of cells which have served their function e.g. leukocytes after inflammation. The absence of necessary stimulatory signals induces apoptosis
4 Pathological conditions of necrosis
• DNA damage via radiation etc. Damaged DNA may lead to carcinogenesis
• Accumulation of misfolded proteins leads to ER stress which results in activation of apoptosis
• Certain viral infections e.g. Adenovirus, HIV. Cytotoxic T-lymphocytes which are specific for viral infected cells induce apoptosis in these cells. There may be significant resulting tissue damage.
• Obstruction of ducts in parenchymal organs e.g. salivary glands, pancreas.
Morphological changes in apoptosis
- Cell shrinkage
- Chromatin condensation under the nuclear membrane. The nucleus may be fragmented.
- Formation of cytoplasmic blebs and apoptotic bodies
- Phagocytosis of apoptotic bodies
There are 2 steps in apoptosis.
What happens in these phases
• Initiation phase: Caspases become active
• Execution phase: Caspases trigger the degradation of cellular components
There are 2 pathways in apoptosis
They are also known as ?
• Intrinsic (mitochondrial) pathway
• Extrinsic (death receptor-mediated) pathway
Mechanism of Apoptosis
Initiators of apoptosis
Intracellular (mitochondrial)
Extracellular (Fas/FasL)
¥ Activation of caspases Activation of death controlling genes (Bcl-2, p53) Activation of death receptors
¥ Membrane changes No inflammatory cells
Biochemical features of apoptosis
1. Activation of caspases: Caspases exist as____ _____.
Functionally divided into 2: initiator _____? and executioner ____?
inactive proenzymes
Caspases 8,9
Caspases 3,6
- DNA & protein breakdown – this involves the action of ___ & ____ endonucleases which _____ _____.
Endonuclease activity is the basis for detection of ____ _____by cytochemical techniqies
Ca & Mg
Cleave DNA
Cell death
- Membrane alteration and recognition by phagocytes – the plasma membrane phospholipid orientation changes how? so that it is easily recognised by phagocytes. These phospholipids are easily recognised by Annexin V staining (immunohistochemistry)
Phosphatidylserine located on the inner leaflet of the membrane flips to the outer leaflet where it is recognized by tissue macrophages
Anti- and Pro-apoptotic proteins
• These are proteins which promote or antagonise the process of apoptosis in the cell.
• The concentration of these proteins is tightly regulated by the cell.
• In a viable cell, growth factors lead to production of anti-apoptotic
proteins e.g. BCL2, BCL-XL, MCL1. Anti-apoptotic proteins maintain the integrity of the mitochondrial membrane thus preventing leakage of apoptosis inducing proteins e.g. cytochrome c.
• However when a cell is injured or deprived of survival signals,anti-apoptotic proteins are inhibited while pro-apoptotic proteins: ____& _____ activated.
Pro-apoptotic proteins create a channel in the outer mitochondrial membrane leading to leakage of ______ from the membranous space which activates the ______
BAX, BAK
cytochrome c
Caspases
Sensors: BH3-only proteins e.g. BAD, BID, BIM, Puma. They sense cellular stress levels and regulate anti-&prp-apoptotic proteins
Intrinsic and extrinsic pathways are part of the
_______ phase
Initiation
Intrinsic Pathway:
• Also known as the _______ pathway because of the key role of the mitochondria in the process.
• Cell injury results in permeability of the mitochondrial membrane release of pro-apoptotic proteins such as cytochrome c . This results in activation of caspase ___ leading to the onset of apoptosis.
Mitochondrial
Caspase 9
______________ is the major mechanism for apoptosis in all mammalian cells.
Mitochondrial/ intrinsic pathway
Extrinsic pathway aka
death receptor-mediated pathway
The death receptor-mediated pathway is activated following binding to the death receptors on the plasma membrane.
• These death receptors have a______ _____(death domain) which delivers apoptotic signals that activate _____
cytoplasmic domain
Caspase 8
This extrinsic mechanism is seen in ______ T-cell activity (kills virus infected and tumour cells) as well as on T-cells that ______ ______ _____ (eliminate self-reactive lymphocytes).
cytotoxic
recognize self-antigens
The death pathway can be inhibited by a protein called _____
produced by certain viruses e.g.?
FLIP
Herpes virus and normal cells)
• Both the intrinsic and extrinsic initiator pathways converge on the same _____
execution phase.
Activated caspase-8 (extrinsic pathway) and caspase 9 (intrinsic pathway) now activate caspases
3&6
What do activated caspases 3&6 do
Activate DNAase which cleaves DNA
Degrade structural components of the nuclear matrix leading to nuclear
fragmentation
5 examples of apoptosis
- Deprivation of growth factors: e.g. hormones, antigens (lymphocytes), nerve growth factor (nerves). Occurs via the intrinsic pathway
- DNA damage: this causes accumulation of p53 protein which in cases of excessive damage activates the intrinsic pathway of apoptosis. In the absence of p53 (Li Fraumeni syndrome), accumulation of damaged DNA may lead to cancer
- Protein misfolding: Seen in neuro degenerative diseases e.g. Alzheimer’s, cystic fibrosis, Alpha1 antitrypsin disease. Misfolded proteins accumulate in the cytosol and lead to apoptosis.
- Extrinsic pathway (Fas/FasL): FasL on T cells bind Fas on neighbouring lymphocytes leading to destruction of T lymphocytes that recognise self-antigen.
- Cytotoxic T-lymphocytes: recognise foreign Ag on the surface of infected cells. The T-cells secrete perforin which forms pores in the membrane of the infected cells. The T-cell now secretes granzymes through the pores into the affected cell. Granzymes activate caspases.
Dysregulated apoptosis
1.
Defective apoptosis and increased cell survival.
a. In cells with TP53 mutation, there is accumulation of damaged DNA which leads to cancer.
b. When self reactive lymphocytes are not eliminated, they may cause autoimmune disorders
- Increased apoptosis and excessive cell death
a. Neurodegenerative diseases e.g. Alzheimer’s, Parkinsons.
b. Death of virus infected cells
c. Ischaemic diseases (myocardial infarction)
Difference between necrosis and apoptosis according to
Cell size
Nucleus
Plasma membrane
- Cell size:
Necrosis: Enlarged (swelling)
Apoptosis: Reduced (shrinkage) - Nucleus
Necrosis: Pyknosis ➙ karyorrhexis ➙ karyolysis
Apoptosis: Fragmentation into nucleosome-size fragments - Plasma membrane
Necrosis: Disrupted
Apoptosis: Intact; altered structure, especially orientation of lipids
Differences based on
Cellular content
Inflammation
Physiologic or pathological?
- Cellular contents
Necrosis: Enzymatic digestion; may leak out of cell
Apoptosis: Intact; may be released in apoptotic bodies - Adjacent inflammation
Necrosis: frequent
Apoptosis: No - Physiologic or pathologic role
Necrosis: Invariably pathologic (culmination of irreversible cell injury)
Apoptosis: Often physiologic, means of eliminating unwanted cells; may be pathologic after some forms of cell injury, especially DNA damage
Morphological hall mark of cell death
Loss of nucleus
Loss of nucleus occurs via
Pyknosis
Karyorhexis
Karyolysis
Pyknosis: nucleus condensation/ Shrinkage
Karyorrhexis: Fragmentation
Karyolysis: Dissolution
Red infarction is ?
Occurs where
There is infarction but instead of tissue appearing pale, it’s red but there’s still deoxygenated blood coming to it
Testis
Lung
General morphology of necrosis
• Increased eosinophilia (the pink colour of the cytoplasm). This is due to loss of cytoplasmic RNA which binds hematoxylin.
• Increased glassy appearance due to the loss of glycogen particles.
• Vacuolated cytoplasm due to enzyme digested cytoplasmic
organelles.
• Myelin figures: from dead cell or organellar membranes. The myelin
figures may be phagocytosed by other cells or degraded into fatty acids. These fatty acids may become calcified leading to the calcification of dead cells.
In Gangrenous necrosis
Commonly used in clinical practice.
• Usually results from superimposed bacterial infection on a tissue
which has lost its blood supply (coagulative necrosis). The bacterial
infection leads to more liquefactive necrosis (Wet gangrene). Why?
• Examples: diabetic foot gangrene, frostbite gangrene
Fat necrosis
• Clinical term
• Refers to focal areas of fat destruction.
• Pancreatitis: release of lipases from pancreatic acinar cells liquefy the
membranes of adipocytes in the peritoneum. The released fatty acids can combine with calcium to form areas of saponification (chalk-white visible areas)
• Traumatic fat necrosis (breast): seen with loss of blood supply to breast adipose tissue resulting in the death of the adipocytes and their digestion by macrophages. May mimic a carcinoma
In fibrinoid necrosis
• Seen in immune reactions involving blood vessels.
• Deposition of Ab-Ag complexes on the blood vessel walls leading to
activation of immune reactions against the wall components. E.g. is
eosinophilic granulomatosis with polyangitis.
Biochemical features of apoptosis
- Activation of caspases: Caspases exist as inactive proenzymes. Functionally divided into 2: initiator (8 , 9) and executioner (3 , 6).
- DNA & protein breakdown – this involves the action of Ca and Mg endonucleases which cleave DNA. Endonuclease activity is the basis for detection of cell death by cytochemical techniqies
- Membrane alteration and recognition by phagocytes – the plasma membrane phospholipid orientation changes so that it is easily recognised by phagocytes. These phospholipids are easily recognised by Annexin V staining (immunohistochemistry).
Necroptosis
• Resembles both necrosis and apoptosis
• Sometimes called programmed necrosis
• Does NOT involve caspase activation
• Examples: Steatohepatitis, acute pancreatitis, back-up defense for
apoptosis evading microbes e.g. CMV (human cytomegalovirus )
Autophagy
Cell eats its own contents. Clinical correlation:
• Cancer
• Neurodegenerative diseases e.g. Alzheimers
• Infections e.g. Mycobacteria, HSV-1
• IBD
• Intermittent fasting
