Cell injury and apoptosis chapter 2

Question 1

what are the 7 causes of cell injury?

Answer 1

1- hypoxia and ischemia
2- physical agents
3- chemical agents and drugs
4- infectious agents
5- immunologic reactions
6- genetic abnormalities
7- nutritional abnormalities

Question 2

how does hypoxia and ischemia causes cell injury?

Answer 2

hypoxia is the decrease in O2 while ischemia is decrease in blood supply and ischemia can cause hypoxia so basically, a decrease in nutrients or O2 delivery will cause cell injury
as in blocking in arteries causing ischemia causing decrease in oxygenation or decrease in ability to arry O2 in the blood

Question 3

how does a genetic abnormalities cause cell injury

Answer 3

mutation in chromosome that can cause pathologic changes like down syndrome or single amino acid substitution making sickle cell anemia
mutations may cause a decrease or increase in function of enzymes or proteins or the accumulation of damadged DNA and misfolded proteins.

Question 4

what is reversible cell injury?

Answer 4

derangement of function and morphology that cells can recover from if the stimulus is removed

Question 5

charchateristics of Reversible cell injury

Answer 5

• Cellular swelling and there can be pallor due to compression of capillaries, increased turgor and increased organ weight; a clear vacule of cytoplasm in the ER ( Hydrobic change or vacuolar degenration)
• Fatty change is the appearance of lipid vacuoles in the cytoplasm and mostly encountered in organs involved in lipid metabolism like liver

Question 6

other intracellular changes assocaited with cell injury

Answer 6

1- plasma membrane alteration like blebbing, blunting or distortion of microvilli and loosening of intracellular attachments
2- mitochondrial changes like swelling and appearance of phosphholipid rich amorphous densities
3- dialation of ER with detacchment of ribosomes and dissociation of polysomes
4- nucleear alteration with clumping of chromatin ( mYelin fingers)

Question 7

charchtersitc of Point of no return and cell death

Answer 7

1- inability to make ATP and oxidative phophorylation
2- altered structure and loss of function of plasma membrane and intracellular membrane and loss of structural integrity of DNA and chromatin
3- injury to lysosomal membranes results in the enzymaticdigestion of injured cells

Question 8

what is necrosis

Answer 8

severe distrubances like loss of O2 and nutrient supply and action of toxins causing rapid and uncontrolled death ( accidental death)
resulted from ischemia, toxins,infections and trauma
charchterized
check Taple 1.1

Question 9

what is apoptosis

Answer 9

it is programmed cell death and when cell are eliminated without elicting a host reaction
it relies on defined genes and biochemical pathways which are heavly controlled ( regulated cell death)
happens when cell DNA or protien are damaged beyond repair or cell is deprived of necessary survival signals and only occurs in healty tissues
check taple 1.1

Question 10

characteristics of necrosis

Answer 10

denaturation of cellular proteins, leakage of cellular contents through damaged membranes, local inflammation and enzymatic digestion of lethally injured cells

Question 11

indication of necrosis for cardiac muscle, bile duct epithelium and hepatocytes

Answer 11

high serum level of:
1- Cardiac muscle: troponin
2- bile duct epithelium: alkaline phosphatase
3- hepatocytes: transmaminases

Question 12

Morphology of Necrosis

Answer 12

1: increased eosinophilia due to loss of cytoplasmic RNA and accumlation of denothered cytoplasmic proteins
2: glassy cell appearance due to loss of glycogen particles
3: vaculation (molth eaten)
4-myelin figured
5: nuclear changes

Question 13

Nuclear changes in necrosis

Answer 13

is one of 3 patterns and all of them due to breakdown of DNA
1. Karyolysis ( fading of basophilia of chromatin by endonucleases)
2: Pyknosis ( nuclear shrinkage and increased basophilia due to condensation of chromatin)
3: Karyorrhexis ( pyknotic nucleus undergo fragmentation)
the neucelus in necrotic cell disappears in 1 to 2 days

Question 14

indications of irreversible injury

Answer 14

1- inability to reverse mitochondrial dysfunction
2- profound disturbance in membrane functions

Question 15

Patterns of tissue necrosis

Answer 15

1- coaguative necrosis
2- liquefactive necrosis
3-gangernous necrosis
4- caseous necrosis
5- fat necrosis
6-fibrinoid necrosis

Question 16

what is coagulative necrosis?

Answer 16

1- due to ischemia by obstruction in a a vessel in all tissues except the brain
affected tissue is firm and the injury denatures structural protiens and enzymes blocking proteolysis of dead cells causing the cell to be eosinophilic and the nuceli to be red
the cell is broken down by leukocytes
2- include only one tissue

Question 17

what is liquefactive necrosis

Answer 17

due to bacterial or fungal infections
it is digestion of dead cells and transformint to them to viscous liquid and formation of pus at site of necrosis
ischemia in CNS causes it too

Question 18

what is gangernous necrosis

Answer 18

it is typically coagulative ecorsis and describing lower leg or extermities ( because it only have one major source of blood supply )
that has lost it blood supply.
when the bacterial infection is superimposed there is more liquefactive necrosis there and is called wet gangrene
involve all of the tissues

Question 19

What is caseous necrosis

Answer 19

most common in foci and TB infection and it is cheese like appearance at area of necrosis
it is a structural collection of fragmented cells and amorphous granular debris enclosed with inflammatory border, giving the name Granuloma

Question 20

What is fat necrosis?

Answer 20

due to release of pancreatic lipases in case of acute pancreatitis
the pancreatic enzyme leak from the acinar cells and liqufy the fat cells in peritoneum releasting triglycerides esters which are split by lipases and the fatty acids generated combine with Ca giving it the chalky white appearnce

Question 21

what is fibrinoid necrosis

Answer 21

special form of damade due to immune complexes depsoiting in wall of artieries and it gives it bright pink appearance and it is seen in immunologic meidated vasculitis syndromes

Question 22

why doesnt apoptotic cells cause inflammation

Answer 22

because apoptotic cells are killed by intrisic enzymes destroying the DNA and cellular components and making apoptotic body while the membrane is intact and during the process it releases eat me and find me signals for phagocytes to eat them before leakage of the bodies out

Question 23

apoptosis causes

Answer 23

1-physiologic
2-pathophysiologic

Question 24

physiologic importance of apoptosis

Answer 24

1- removal of supernumerary cells during developmen
2- involution of hormone dependent tissue like endometrial breakdown during menstrual cycle, ovaria follicular atresia during menopause and regression of lactating brests
3- cell turnover in proliferating cell population like immature lymphocytes in BM and thymus ( - selection)
4- Elimination of self reactive lymphocytes
5- Death of lymphocytes after immune response is done

Question 25

apoptosis due pathologic conditions

Answer 25

1- DNA damage due to radiation or cytotoxic cancer drugs where cells are beyond repair so they recieve proapoptotic signals or activatte intrinsic enzymes killing the cells to prevent malignant transformation of them 2-accimlation of missfolded protiens and endoplastic reticulum stress response 3- due to viral and bacterial infection by cytotoxic T cells which kill the resvoir of virus ( HIV and acute hepatitis) and cellular rejection in grat VS host reaction 4- apoptosis contribute to pathologic atrophiy in parenchymal organs after duct obstrucion like in pancreas,parotid gland and kidney

Question 26

apoptosis morphology

Answer 26

1- Cell shrinkage 2- Chromatin condensation ( most importnat) 3- Formation of cytoplasmic blebs and apoptotic bodies 4- phagocytosis of apoptocic cells or apopotic bodies by macrophages

Question 27

pathways of apoptosis and phases of apoptosis

Answer 27

1- mitochondrial ( intrinsic) 2- Death receptor ( extrinsic) 3- intiation phase when caspase become active ( indication of apoptosis) 4- excusion phase when cells are fragmented

Question 28

Explain the mitochondrial intrinsic pathway

Answer 28

mitochondrial apoptosis pathway is caused by leakage of cytochrome C from the mitochondria to the cytosol it is mediated by apoptotic protiens : BAX and BAK which upon activation make a dimer forming a channel allowing cytochrome C and other protiens to leak out activating Caspase 9 whihc also activate other caspases like Caspase 3 to inhibit this we have antiapoptoic protiens which are BCL2, BCL-XL and MCL1 which protect the mitochondrial membrane and prevent leakage we also have autoregulated Apoptosis inhibitor Which are BAD, BIM, BID, Puma and noxa ( BH3 only protiens) which are modulated by sensing cell stress and damage and when upregulated they initiate apoptosis

Question 29

Steps of intrinsic pathway

Answer 29

1- growth factor withdrawl, DNA damage or protien misfolding 2- BH3 only protiens are upregulated by post transitional modification and they activate BAX and BAK and at the same time BH3 only protiens block BCL2 and BCLXL 3- BAX and BAK make a channel and cytochome C leaks and activate Caspase Cascade 4-cytochrome C binds to APAF1 forming apoptosome which bind to caspase 9 and promote cleavage and activating of other caspases 5- DIBALO enter the cytoplasm and neutrlize cytopalsmic protiens (IAPs) blocking inappropriate activation of caspases

Question 30

how is extrinsic pathway of apoptosis is activated

Answer 30

Binding of Fas and TNF receptor to FasL

Question 31

Explain the extrinsic pathway

Answer 31

1- engament of TNF1 receptor and Fas (CD95) with death domain binding to FasL on activated T cells which recognize sAg and is found on CTL to kill virus infected cells and tumors 2- after binding of Fas and FasL 3 or more Fas molecules are brough and thier cytoplasmic domains for a binding side for FADD ( fas associated death domain) 4- FADD activates caspase 8 or 10 and caspase 8 do same shit as intrisinc pathway 5- it is inhibited by FLIP which bidns to pro capsase 8 blocking FADD binding but cannot acitvate caspase 8

Question 32

Excution phase of apoptosi s

Answer 32

1. the active form of caspases trigger activation of excutioner caspases like 3 or 6 2: the caspases cleave inhibitor of DNase making it active, causing DNA degradation, and caspase also proteolyze structural components of neuclear matrix, causating fragmentation of nuclei.

Question 33

Removal of dead cells ( Efferocytosis )

Answer 33

phosphotidyl serine which present on inner leaflet of plasma membraen flips to outer leaflet in apoptotic cells which act as a eat me signals for phagocytes nad macrophages apoptotic bodies can be coated by C1q which is reconized by phagocytes

Question 34

what are other type of cell death

Answer 34

1- necroptosis 2- pyroptosis 3-ferroptosis 4- autophagy

Question 35

Steps of necroptosis

Answer 35

Necroptosis is hybrid of apoptosis and necrosis also called programmed necrosis or caspase independent apoptosis 1- ligation of TNF1R which activates REceptor interacting protien kinase1 and 3 ( RIPK1 and RIPK3) 2- RIPK3 phophorylates MLKL which translocate from cytosole ot plasma membrane and cause plasma membrane disruption

Question 36

physiologic necroptosis and oathologic necroptosis

Answer 36

physiologic: during fomration of mammalian bone growth plate pathologic: atohepatitis, acute pancreatitis, ischemia-reperfusion injury and neurodegenrative diseases also for viruses that encode caspase inhibitors like CMV

Question 37

explain pyroptosis

Answer 37

1- induced by IL1 and inflammasome which acitvate caspase 1 ( IL1beta) 2- leuocyte recruitment and fever 3- induced by microbes that cause death of infected cell and at the same time inflammation

Question 38

explain Ferroptosis

Answer 38

1- indcued by high intracellular Fe or ROS overwhelm glutathione dependent antioxidant defenses to cause unchecked membrane peroxidation causing loss of plasma membrane permeability causing death resembling necrosis 2- stopped by decreasing Fe levels

Question 39

Features of ferroptosis

Answer 39

1- loss of mitochondrial cristae 2- ruptured outher mitochodnrial membrane 2- seen in cancer, neurodegenrative diseases and stroke

Question 40

steps of of autophagy

Answer 40

1- nucleation and formation of isolation membrane (phagophore) from ER 2- formation of autophagosome 3-autophasome bind with lysosome to make autophagolysosome

Question 41

activation of autophagy

Answer 41

1- deprivation of nutrients or GF activate intiation complex of four protiens Atgs( autophagy related genes) 2- elengation and closure of phagophore require 2 ubiquitin like conjugation resulting of covalent linkage of PE to microtubule associated protien light chain3 ( LC3) ( marker for autophagy) 3- autophagy is selective because LC3 is to target protien aggregates and organelles

Question 42

role of autophagy in human disease

Answer 42

1- cancer: autophagy promote and defend against cancer 2- neurodegenrative disorders ( alzhemier disease impaired autophagosome maturation) and huntingtin mutation impairs autophagy in huntington disease 3- infectious disease: shigella and HSV1 are degrated by autophagy deletion of atg5 increase Tb susceptibility 4- IBD and ulcerative colitis are llinked to single nuceltide polymorphism in autophagy related gene ATG16L1

Question 43

Mitochondrial damage consequences

Answer 43

it caused by increased Ca, ROS, oxygen deprivation and injurous stimuli and mutation in mitochondrial gene 1- ATP depletion 2- incomplete oxidative phosphorylating leading to ROS 3- leakage of mitochondirla protiens due to BAX and BAK

Question 44

what will ATP depeletion cause

Answer 44

1-ATP depletion by hypoxia or toxins which lead to formation of high conductance channel in mitochondria ( mitochondrial permeability transition pore) which cause failure of oxidative phosphrylation and ATP depletion causing necrosis ATP depletion will reduce activity of Na, K-ATPase causing accumlation of Na inside cells and K to decrease causing cell swelling and ER dilation ATP depletion will stimulate Phophorylase and phosphofructokinase leading to increased glycogenlysis adn glycolysis which cause glycogen to decrease causing accumlation of lactic acid and inorganic phophaes reducing intracellular pH decreasing acitvity of cytosoling enzymes ATP depletion will cause deatachment of ribosomes from rough ER and dissociation of polysome reducing protine synthesis

Question 45

consequence of membrane damage

Answer 45

it is a feature of all types of cell inury except apoptosis 1- ROS ainduce injury by lipid peroxidation 2- decreased phospholipid synthesis affecting all cellular membranes 3- increased phopholipid breakdown due to activation of Ca dependent phospholipase due to increased Ca in mitochondria causing accumlation of lipid breadown products like unsaturated FFA , acyl carnitine and lysophospholipids 4- cytoskeletal abnormalities to cytoskeletal filaments and proteases activated by cytosolic Ca may damage the tethers and it leads to deattchment of cell membrane causing it to rupture

Question 46

consequence of DNA damage

Answer 46

it activates p53 dependent pathways due to exposure to radiation, anticancer durgs and ROS or spontaneously due to deamination of cytosine to uracil 1- P53 triggers apoptosis by arresting cell to G1 phase of cell cycle and activate DNA repair mechansim and if it fails p53 triggers apoptosis

Question 47

Generation of free radicals mechansims

Answer 47

1- Redox reactions as a part of normal respiration by reducing O2 to H2O but sometimes it gives superoxide O2, hydrogen peroxide H2O2 and hydroxyl radicals OH- 2- absorption radiant energy by hydrloyzing wwater into OH- and H free radicals 3- rapid bursts of ROS by lymphocytes it is very controlled by NADPH oxidase 4- Enzymatic metabolism of exogenous chemicals or drugs can generate free radicals who are not ROS but have similar CCL4--> CCL3 5- TRansition metals like iron and copper 6-Nitric oxide by endothelial cells and macrophages and neurons act as free radicals and may be also converted to highly reactive peroxynitraet anion (ONOO-)

Question 48

Removal of free radicals mechanism

Answer 48

1- antioxidants block free radical formation or inactivate free radicals ( VitA, E, ascorbic acid and glutathione in the cytosole) 2- free iron and copper can catalyze formation ROS by binding to storage and transport protiens ( transferrin, ferritin, lactoferrin and creuloplasmin) 3- free radical scavenging enzymes

Question 49

what are the free radical scavenging enzymes

Answer 49

1- Catalase in perxisomes 2- supraoxide dismutase 3- glutahtione peroxidase

Question 50

Pathologic effects of free radicals

Answer 50

1- lipid peroxidation in membranes when double bonds in unsaturate fatty acids of lipids are attacked by Free radicals by OH yielidng peroxides 2- oxidative modification of amino acid side chains and formation of covalent protien-protien cross-links it may also disrupts active sides of enzymes and structural protiens and enhance proteosomal degradtion of protiens 3- lesions in DNA and forming adducts

Question 51

How does Ca cause Cell injur

Answer 51

Ca in cytosol in 0.1umol while in ECM is 1.3mmol ischemia and toxins will cause increase in cytosolic Ca due to release from intracellular stores and increased influx across the membrane 1- accumlation of Ca in mitochondria will icnrease mitochondrial permeability transition pore and failure ot ATP generation 2- Increaed cytosolic Ca activates phopholipase causing membrane damage, Protease breaking down membrane adn cytoskeletal protiens and endonuclease which is responsible for DNA and chromatin fragmentation and ATPase decreasing ATP

Question 52

Endoplasmic Reticulum stress

Answer 52

when the misfolded protiens are too much to handle by chaperons either by increased rate of misfolding or decreased rate of repair it activate caspases and induce apoptosis it may be increased by viral infection increased demand for secrator proiens in case of insulin resistnt states change in intracellular pH and redox state also Foldase require ATP to function and ischemia and hypoxia may increase burden of misfolded protiens

Question 53

diseases caused by misfolding protiens

Answer 53

1- Cystic fibrosis (loss of CTFR leading to defect chlorid etransport) 2- familia hypercholesterolemia ( Loss of LDL receptor) 3-Tay sachs disease (lack of lysosome enzymes leading to storage of GM2 gangliosides in neurons ) ( Hexosamindiase beta subunit affected) 4- alpha1 antitypsin deficncy ( storage of nonfucntional protien in hepatocytes causing apoptosis, absence of enzyme activity in lungs causing emphysema) 5- CJD ( abnormal folding of PrPsc causing neuronal cell death ) ( prions are affected) 6- Alzeheimer ( abnormal folding of Abeta peptides causing aggregation in neurons and apoptosis)

Question 54

Funcion of HIF-1 in ishcmeic cell injury

Answer 54

HIF1 is activated due to hypoxia and it promotes new blood vessel survival ( hypoxia inducble factor 1)

Question 55

Clincial ways to stop ischemic cell injury

Answer 55

transitent induction of hypothermia reducing metabolic demands and decreasing cell swelling and suppressing free radicals and inhibiting inflammation

Question 56

ischemia reprofusion injury mechansim

Answer 56

1- oxidative stress as a result of incomplete reduction of oxygen in leukoyte and damaged endothelial cells and parenchymal cells 2- intracellular calcium overload 3- infalmmation due to neutrophils influx 4- activaton of complement system by IgM which complement protiens bind to in reprefused tissues

Question 57

Types of Toxic injury

Answer 57

1- direct toxcity which affect cells directly like mercuric cholride poisoning which cause increased membrane permeability and inhibit ion transport by binding of mercury to sulfhydryl groups and cyanide posioning 2- indirect toxicity: conversion of untoxic substance to toxic by P450 cytochrome which can form free radicals and lipid peroxidation ( CCL4 is converted to CCL3 which causes lipid peroxidation) and acetaminophen is converted to toxic products

Question 58

Hypertrophy types

Answer 58

1- pathologic hypertrophy: due to increased work load like incase of hypertension there is hypertrophy and valvular disease in cardiac muscle but the overtime adaptaion fails risking heart disease 2- physilogic hypertrophy due to hromones enlargment like in case of uterine hypertrophy by estrogen and steroids

Question 59

Mechanism of hypertrophy

Answer 59

1- mechnical sensors detect increased workload 2- activation of PI3K/AKT pathway ( physiologic) and G protien coupled receptor intiaied pathway ( pathologic) 3- increase secretion of Growth factors ( TGF-beta, Insulin like growth factor 1 and fiborblast growth factor) and Vasoactive agents 4- activation of transcription factors like GATA4, NFAT and myocyte enhance factor 2

Question 60

Cardiac muscle hypertrophy mechanism

Answer 60

1- switch on gene encoding adult type contractile protiens ( alpha myosin heavy chain is replaced by Beta isoform) which is more economical 2- protiens are altered ( increased artrial natriuretic factor gene expresion whihc causes salt secretion from kidney decreased hemodynamic burden of cardiac muscle)

Question 61

hyperplasia mechanisms

Answer 61

physiologic : due to hormones and Growth factors to increase functional capacity of hormone or to compensation after damage or resection like in case of glandular apithelim in female breast at puberty and BM hyperplasia to defiency of mature blood cells 2- pathologic hyperplasia: due to excessive actions of hormones or grwoth factors like incase od fistrubted balance between estrogen and progestrol resulting increased amout of estrogen causing hyperplasia of endometrial glands and in case of bengin prostatic hyperplasia also can be caused by viruses like Papillomavirus which cause skin lesions of hyperplasic epithelim

Question 62

Atrophy causes

Answer 62

1- decreased workload 2- loss of innervation 3-deminished blood supply 4- inadequate nutrition 5- loss of endocrine stimulation 6- pressure