MoD Session 1: cell injury

Question 1

Causes of cell injury and death

Answer 1

Hypoxia
Toxins
Radiation
Microorganisms
Immune mechanisms (autoimmune, hypersensitivity)
Dietary deficiency or excess
Genetic abnormalities
Physical agents: trauma, extreme temperature, pressure, electric current

Question 2

What is the result of hypoxia and how does tolerance vary between cells?

Answer 2

Reduced aerobic respiration.

Fibroblasts can tolerate it for a few hours, neurones only a few minutes

Question 3

What are the causes of hypoxia?

Answer 3

1. Hypoxaemic hypoxia: at altitude or reduced oxygen absorption in lungs
2. Anaemic hypoxia: less ability of Hb to carry oxygen due to anaemia or carbon monoxide poisoning
3. Histiocytic anaemia: problem with oxidative phosphorylation enzymes e.g. cyanide poisoning
4. Ischaemic hypoxia: interruption to arterial blood supply or decreased venous drainage. Reduces oxygen and metabolic substances so injury more rapid and severe

Question 4

What toxins can cause cell injury?

Answer 4

Glucose and salt in hypertonic solutions
High oxygen
Insecticides, herbicides, pollutants etc
Asbestos
Narcotics, alcohol, medicines

Question 5

Hypersensitivity reactions?

Answer 5

Host tissue damaged after overly vigorous immune reaction, e.g. urticaria (hives)

Question 6

Autoimmune reactions?

Answer 6

Immune system fails to distinguish self from non-self, e.g. Grave’s disease

Question 7

What are the targets for cell damage?

Answer 7

Membranes
Nucleus
Proteins
Mitochondria

Question 8

Describe the events in reversible hypoxic injury

Answer 8

Decreased oxidative phos so decreased ATP
Loss of activity of Na+/K+ ATPase (as needs ATP)
[Na+]i increases, water enters, cell swells
Ca2+ enters, damages cell components
Anaerobic glycolysis produces lactate-affects enzymes as low pH
Ribosomes detach from ER causing disrupted protein synthesis

Question 9

Describe irreversible hypoxic injury

Answer 9

Not known exactly when injury becomes irreverible
Accumulation of Ca2+ causes activation of enzymes
Lysosomes are broken down and release more lytic enzymes
All cell membranes are damaged and start to show blebbing, and at some point die

Question 10

Which enzymes does Ca2+ activate in irreversible hypoxic injury?

Answer 10

ATPases (decreases ATP further)
Phospholipases (more membrane damage)
Proteases (break down membranes and cytoskeletal proteins)
Endonucleases (damage DNA)

Question 11

Ischaemia-reperfusion injury?

Answer 11

Blood flow returned to tissue that has had ischaemia but not yet necrotic, damage can be worse than if blood not restored
May be due to:
1. Increased production of free radicals with the reoxygenation
2. More neutrophils causing more inflammation and injury
3. Activation of the complement pathway

Question 12

What are free radicals and when are they produced?

Answer 12

Molecules with a singular unpaired electron (so unstable)
Produced in: chemical/radiation injury, cellular ageing, ischaemia reperfusion, high oxygen concentrations
OH radical (hydroxyl radical): most dangerous
O2- (superoxide)
H2O2 (hydrogen peroxide)
Produced in Fenton reaction: Fe2+ + H2O2 –> Fe3+ + OH- + hydroxyl radical
Also in Haber-Weiss reaction: O2 radical + H+ + H2O2 –> O2 + H2O + hydroxyl radical

Question 13

Effects of free radicals?

Answer 13

Chain reactions causing production of more free radicals
Lipid peroxidation of cell membranes
Damaged proteins, CHOs and nucleic acids
Kill bacteria
Used in cell signalling

Question 14

Antioxidant system

Answer 14

Superoxide dismutase: makes O2- into H2O2 so less damaging
Catalases and peroxidases: make H2O2 into O2 + H2O
Free radical scavengers: vitamins A,C,E and gluathione
Storage proteins

Question 15

Heat shock proteins

Answer 15

Unfoldases or chaperones
E.g. ubiquitin
Mend misfolded proteins and maintain cell viability
Triggered by any form of injury

Question 16

Dye exclusion technique

Answer 16

Morphological criteria for light microscopy to see if cell dead: put dye in cells medium and if cell takes it up cell is dead because membrane is permeable to something it wouldn’t normally be

Question 17

Cytoplasmic changes seen with cell swelling from oncosis light microscope

Answer 17

Decreased staining of cytoplasm due to H2O accumulation (reversible)
then
Increased staining due to loss of ribosomes from the ER (irreversible)
May also see abnormal intracellular accumulations

Question 18

Nuclear changes seen with cell swelling from oncosis light microscope

Answer 18

Chromatin subtly clumped (reversible)
then
Pyknosis (shrinkage), karryohexis (fragmentation), and karryolysis (dissolution) (irreversible)

Question 19

Reversible changes seen with electron microscope

Answer 19

Swelling
Cytoplasmic blebs
Clumped chromatin
Ribosome separation from ER

Question 20

Irreversible changes seen with electron microscope

Answer 20

Swelling
Nuclear changes: pyknosis, karryohexis, karryolysis
Membrane defects
Swelling and rupture of lysosomes
ER lysis
Amorphous densities in mitochondria

Question 21

Oncosis?

Answer 21

Cell death with swelling. Spectrum of changes prior to cell death. Morphologically most cells die by karyohexis or karyolysis

Question 22

Apoptosis?

Answer 22

Cell death with shrinkage induced by a regulated intracellular program. Membrane integrity preserved

Question 23

Physiological apoptosis?

Answer 23

Normal response to maintain steady state. Cytotoxic T cell killing.
Occurs in embryogenesis (limb sculpting) and insect metamorphis

Question 24

Process pathological apoptosis

Answer 24

Initiation: caspase activation
Execution: shrinkage, budding, chomatin condensation, see apoptotic bodies
Degradation: express molecules on surface that induce phagocytosis. No inflammation

Question 25

Important apoptotic molecules

Answer 25

p53: mediates apoptosis when DNA damaged cytochome C, APAF 1, caspase 9: apoptosome Bcl-2: prevents cytochrome C release from mitochondria so inhibits apoptosis TRAIL: death ligand TRAIL-R: death receptor caspases: effector molecules of apoptosis

Question 26

Necrosis?

Answer 26

Morphological changes that occur after a cell is dead for some time. An appearance not a process: due to progressive degradation by enzymes Main types coag and liq

Question 27

Coagulative necrosis?

Answer 27

Mainly denaturation of proteins. 'Ghost outline' of cells as slightly preserved. Proteins become less soluble Incites acute inflammation: neutrophils then phagocytes

Question 28

Liquefactive necrosis?

Answer 28

Mainly active enzyme degradation. Enzymatic digestion (liquefaction) of tissues. Seen in massive neutrophil infiltration (e.g. abscess) as neutrophils release proteases Seen in brain as fragile tissue without robust collagen network Tissue becomes a viscous mass so actue inflammation so pus

Question 29

Caseous necrosis?

Answer 29

'Cottage cheese' Amorphous debris Seen in infections especially TB

Question 30

Fat necrosis?

Answer 30

Destruction of adipose tissue Often in acute pancreatitis: release lipases from injured acinar cells Act on fat in abdominal cavity, release of free FAs, react with Ca2+ to form chalky deposits Seen on X-rays and with naked eye in surgery/autopsy Can occur after direct trauma to fatty tissue

Question 31

Gangrene?

Answer 31

Often seen in ischaemic limbs, tissue can't be saved | Not a type of necrosis but a clinical term to describe necrosis visible to the naked eye

Question 32

Dry gangrene?

Answer 32

Exposure to air causes drying of necrosis | E.g. dry crisp appearance of umbilical cord stump after birth, gangrenous toes, autumn leaves

Question 33

Wet gangrene?

Answer 33

Infection with a mixed bacterial culture, liquefactive necrosis, very serious as bacteria can cause septicaemia. Gas gangrene a form of this: tissue infected with anaerobic bacteria, produces visible and palpable gas bubbles. E.g. limb crushed in an accident, tissue loses blood supply becoming necrotic, anaerobic bacteria enter

Question 34

Infarction?

Answer 34

Ischaemia that causes necrosis. Causes: thrombosis, embolism, compression of a vessel or twisting of vessels Colour indicates how much haemorrhage in the infarct Consequences depend on alternative blood supply, ischaemia spread, hypoxia vulnerability and O2 of blood

Question 35

White infarct?

Answer 35

In 'solid' organs with good stromal support, after occlusion of an end artery Limited bleeding from capillaries due to solidity Tissue supplied by end artery dies and pale Mostly wedge-shaped with occluded artery at apex Usually coagulative In HEART, SPLEEN and KIDNEYS

Question 36

Red infarct?

Answer 36

Bleeding into dead tissue In organs with dual blood supply, main artery occuluded, second artery insufficient to rescue tissue but allows some blood to enter. E.g. LUNG Numerous anastomoses e.g. INTESTINES Loose tissues e.g. LUNG where poor stromal support for capillaries Where previous congestion occurred Raised venous pressure, transmitted to capillary bed, infarction then engorged with blood

Question 37

Molecules released by injured cells?

Answer 37

Potassium Enzymes Myoglobin

Question 38

Abnormal cellular accumulations

Answer 38

Carbohydrates Water and electrolytes Lipids: steatosis (fatty change due to more TAG, increase organ size) and cholesterol (skin and tendons in hyperlipidaemia, also in atheromas as taken up by foam cells) Proteins: Mallory's hyaline (abnormal keratin seen in alcoholic liver disease), alpha 1 antitrypsin deficiency (genetic, systemic deficiency so proteases act unchecked on lung breaking down tissue) Exogenous pigments: carbon/coal dust/soot/tattoos. Phagocytosed by aleveolar marophages but accumulate in lung tissue can cause fibrosis Endogenous pigmets: lipofuscin (brown, ageing, non injury), haemosiderin (yellow/brown, iron storage), bilirubin (breakdown of haem, toxic, jaundice)

Question 39

Pathological calcification?

Answer 39

Abnormal deposition of calcium salts in tissues 1. Dystrophic: common, local. Atherosclerotic plaques, damaged heart valves (not pulmonary valve), ageing, TB lymph nodes. No abnormality in Ca2+ metabolism. Nucleation of hydroxyapatite crystals, can cause organ dysfunction 2. Metastatic: body-wide. Hydroxyapatite crystals deposited in normal tissues when hypercalcaemia due to metabolism issues. Usually asymptomatic but can be lethal

Question 40

Replicative senescence?

Answer 40

Decrease in replication during cellular ageing. Each replication shortens telomeres, eventually too short to replicate. Germ and stem cells contain telomerase which maintains length

Question 41

Changes seen in chronic excessive alcohol intake in the liver

Answer 41

1. Fatty change: steatosis. Reversible and asymptomatic 2. Acute alcoholic hepatitis: direct toxicity of alcohol causes focal hepatocytic necrosis, formation of mallory bodies and neutrophil infiltrate. Fever, liver tenderness and jaundice. Usually reversible 3. Cirrhosis: hard, shrunken liver. Micronodule of regenerating hepatocytes surrounded by bands of collagen. Irreversible and sometimes fatal

Question 42

Enzymes raised in alcoholic liver disease

Answer 42

AST, ALT, albumin, bilirubin, GGT, ALP

Question 43

Enzymes raised in acute pancreatitis

Answer 43

Bilirubin, AST, ALT: indicate gallstones which are a common cause

Question 44

Enzymes raised in myocardial infarction

Answer 44

Cardiac troponins-T and I Creatine kinase-a few hours after Myoglobin levels after a couple of hours