Cell injury and death

Question 1

Know that the effects of cell injury causes pathogenesis from homeostasis > adaptation > reversible cell injury > cell death

The effects are:
1) at molecular/biochemical level then
2) at structural changes then
3) histochemical/ultrastructural changes occur mins to hrs after injury
4) changes observable by light microscope days later

Also know that: Principal biochemical mechanisms and sites of damage in cell injury:
Intracellular aerobic respiration, enzymatic & structural proteins, cell/nuclear membrane, genetic apparatus

Question:
Rank: CNS neurons, fibroblasts/epidermis/skeletal muscle, myocardium, hepatocytes, renal epithelium in how susceptible they are to damage by ischemia

Answer 1

Most susceptible: CNS neurons (3-5 mins)

Intermediate: myocardium, hepatocytes, renal epithelium (0.5-2 hours)

Lowest: Fibroblasts, epidermis, skeletal muscles: many hours

Question 1

List major causes of cell injury

Answer 1

1) Hypoxia - low oxygen supply
commonly caused by ischemia (inadequate and lowered blood supply) but also from lowered O2 carrying capacity of blood and poisoning of intracellular oxidative enzyme

2) Physical agents eg trauma/atmospheric pressure/ electricity/temperature/radiation

3) Chemical agents eg drugs/poisons/alcohol

4) biological agents eg bacti/fungus/virus/parasite

5) immunological reactions (hypersensitivity states/autoimmunity)

6) other factors - eg nutrition/genetics

Question 2

List 4 reversible cell injuries

1 form of sublethal cell injury

And the 2 forms of cell death

Answer 2

Fatty change

Intracellular edema

Hyaline degeneration

Intracellular accumulation

sublethal nuclear damage

Cell death:
apoptosis, necrosis

Question 3

Intracellular edema cause and morphology?

Answer 3

Morphology: cells become swollen with water and Na+ with or without vacuoles

Cause: Derangement of cell membrane, excessive influx of isotonic fluids

Question 4

Fatty change cause and morphology? Where can this occur?

Answer 4

Fats abnormally accumulate in non-adipocytes - morphology: fat vacuoles present in cells, nucleus may be displaced

Causes: Chemicals and toxins (esp ALCOHOL - alcoholic liver disease), hypoxia, starvation/wasting diseases, metabolic disorders eg diabetes mellitus

Occurs in: liver, heart muscle, renal tubule

Question 5

Hyaline degeneration morphology and examples

Answer 5

Glassy pink alterations (intra and extracellular)

Examples: Alcoholic liver disease, viral inclusion, arteriolosclerosis

Question 6

Intracellular accumulation of what pigments or possible?

Answer 6

lipofuscin (aging pigment)

haemosiderin

Lysosomal storage disease

Question 7

Some consequences of sublethal nuclear damage?

Sublethal nuclear damage method of action?

Answer 7

somatic cell neoplasia, heritable germ cell diseases

Causes altered gene transcription but no morphological changes

Question 8

Apoptosis and necrosis - how many cells die?

Answer 8

Apoptosis: programmed cell death of individual cells

Necrosis: entire sheets of cells die

Question 9

Know that for apoptosis:

1) tissue structure is preserved

2) no acute inflammation

Question: causes of apoptosis?

Answer 9

Pathological: UV/ionizing radiation, cytotoxic T cells, cell-mediated immunity, drugs, tumor cell death

Physiological: programmed cell destruction in embryonic development and normal cell turnover in adults

Question 10

Process of apoptosis? (this is just the basic concept - for the in depth details of death receptor and mitochondrial pathways check kihiro’s notes)

Answer 10

Process:
Triggered by the mitochondrial (intrinsic) or death receptor (extrinsic) pathway

DNA fragmentation,
chromatin and cytoplasm condensation,
formation of apoptotic bodies,
and being phagocytosed by adjacent cells

Question 11

Necrosis: Any tissue damage? Any inflammation?

The 2 forms of cell death in necrosis?

Can necrosis be caused physiologically?

Changes in nucleus for necrotic cells?

Answer 11

Tissue structure is disrupted, acute inflammation present, sometimes scarring present

autolysis and heterolysis -

autolysis: Structural disintegration due to digestion by lysosomal hydrolases

heterolysis: Digestion by immigrant leukocytes upon release of cytokines

NECROSIS IS ALWAYS PATHOLOGICAL

pyknosis (nuclear shrinkage), karyorrhexis (nuclear fragmentation), karyolysis (nuclear dissolution)

Question 12

Morphological types of necrosis?

Answer 12

Caseous necrosis

Coagulative necrosis

Liquefaction necrosis

Fat necrosis

Fibrinoid necrosis

Question 13

Caseous necrosis: most common locations and cause

morphology?

Answer 13

solid organs, commonly caused by infarctions

Tombstone appearance - acidophilic, opaque cells

Tissue architecture and outline preserved but loss of nucleus

Polymorphonuclear cells infiltrate to handle the infarcted area - blue rim in histological slides under H&E staining

Question 14

Liquefaction necrosis: causes?

Morphology?

Answer 14

Infarction, most commonly brain ischemia

tissue structure lost because of hydrolytic enzymes

cystic spaces left, cell debris cleared

Question 15

Caseous necrosis: causes and morphology?

Answer 15

Causes: mycobacterial infections eg TB

morphology: cream cheese appearance

Cell outline disappears, tissue changes into amorphous mass surrounded by granulomatous inflammation, with macrophage accumulation

Question 16

fat necrosis origins, causes and pathogenesis?

Answer 16

1) Enzymatic in origin, eg acute pancreatitis (necrosis of pancreatic cells)

Causes: bile stones, ALCOHOL

Enzymes released from the pancreatic cells would digest their neighbours. Pancreatic lipase hydrolyses TAG into glycerol and fatty acids, which complex with Ca2+ to form soap (deposited as chalky white patches)

2) traumatic in origin, eg in breast
Lipids released from fat cells provoke a chronic inflammatory and giant cell reaction.

A hard indurated mass is formed; patients may perceive it to be cancer

Question 17

Fibrinoid necrosis: Morphology and examples

Answer 17

Tissue death is accompanied by fibrin deposits

Examples:
Rheumatoid nodules, Arthus reaction, arteriolar lesions of malignant HTN

Question 18

Effects of necrosis?

Answer 18

1) loss of function

2) Release of cell contents

3) Acute inflammation

4) Acute inflammation

5) Effects of repair (scar formation) and regeneration

6) Dystrophic calcification

7) Infection

Question 19

Autophagy mechanism?

Functions of autophagy and consequences of dysregulation?

Answer 19

The cell components undergo lysosomal digestion; this is enhanced by nutrient deprivation.

Cellular organelles are sequestered into cytoplasmic autophagic vacuoles (autophagosomes), which fuse with lysosomes and digest the enclosed materials.

It plays a role in host defence against certain microbes.
It may be used as a renewable source of nutrients under stress.
Dysregulation occurs in diseases such as cancers, neurodegenerative disorders and inflammatory bowel disease.

Question 20

General tissue response to cell injury? In chronological order

Answer 20

1) acute inflammation
2) demolition of necrotic tissues and debris
3) Healing (stimulus removal, restoration of function)
4) resolution

Question 21

What does healing include

Answer 21

Repair and regeneration

repair: replacing lost tissue by granulation tissue (ingrowth of vascular tissue from surrounding connective tissue), granulation tissue matures to form scar (fibrous) tissue

regeneration: lost tissue replaced by similar type, driven by growth factors

Question 22

Granulation tissue components?

Answer 22

1)Fibroblasts,
2) myofibroblasts (to draw wound edges together and produce connective tissue stroma),
3) thin-walled capillaries,
4) inflammatory cells (macrophages)

Question 23

What do growth factors include

Answer 23

Vascular endothelial growth factors (VEGFs)
Fibroblast growth factors (FGFs) → collagen
Transforming growth factor-β (TGF-β) → connective tissue proteins
Mitogenesis: e.g. EGF

Question 24

3 types of cells based on their regenerative properties:

1) labile cells

2) stable cells

3) permanent cells

Question: describe their properties and give examples

Answer 24

1) Labile cells: constantly proliferating and lost, constant regeneration (as part of normal cell turnover - replaced by maturation of tissues and proliferation of cells)

Cells lining the surface epithelium, red blood cell lineage cells

2) Stable cells: usually quiescent (in G0 of cell cycle), minimal proliferation, can reenter cell cycle in response to injury

eg Solid organs (liver, kidney, pancreas), smooth muscle cells

3) permanent cells: CANNOT PROLIFERATE EVEN WHEN THERE IS LOSS (terminally proliferated)

eg most neurons, cardiac muscle cells

Question 25

Process of wound healing?

Answer 25

Mechanism:

1) Migration & regeneration of parenchymal cells

2) Migration & proliferation of connective tissue cells (repair); cell-cell and cell-matrix interaction causes cells to stop proliferating after defect healed

3) Synthesis of ECM proteins by fibroblasts (upon recruitment by macrophages): e.g. proteoglycans / type III collagen
o Remodelling of connective tissues & parenchyma
o Collagenization & acquisition of wound strength
¨ Type III collagen is eventually replaced by type I collagen to form a permanent scar.
¨ MMPs digest the ECM, and it is inhibited by TIMPs

Question 26

Process of healing for skin/epithelial ulceration?

Answer 26

1) stop bleeding (hemostasis)

2) form scab, acute inflammation

3) regenerate epithelial covering + granulation tissue formation

4) collagen deposition, resorption of capillaries

5) scar formed

Question 27

Compare healing by primary (abbreviated as 1 here) and secondary intention (abbreviated as 2) (in terms of wound type, tissue loss, amount of inflammatory and necrotic materials to remove, amount of granulation tissue, wound contraction, size of scar, healing speed, liability to infection)

Describe reasoning for incision during birth

Answer 27

Wound type:
1: clean incision
2: open wound

Tissue loss:
1: less
2: more

Amount of materials to remove:
1: less
2: more

Amount of granulation tissue:
1: less
2: more

Wound contraction:
1: No
2: yes

Scar size:
1: smaller
2: larger

healing speed:
1: faster
2: slower

Infection liability:
1: less liable
2: more liable

Reason for incision during birth:
gives a clean incision in vagina for fetus passage instead of irregularly shaped tear/wound

so doc can suture the wound for easier healing (primary intention) with less granulation tissue/scarring

Question 28

Bone fracture healing process?

Answer 28

1) Haematoma formation and inflammation

2) demolition of necrotic tissue by phagocytosis

3) Granulation tissue formed

4) Callus formation
- Osteoblasts are formed to deposit new bones.

• The provisional callus bridges the gap (first osteoid tissue, then
  woven bone).
• There is remodelling by resorption of healthy bones.
• As the callus forms and mineralizes to form a firm union, there is
  both osteoblastic and osteoclastic activity; remodelling proceeds.
• The trabeculae of the newly woven bone is rimmed by osteoblasts
  which produced it.

5) Lamellar bone formation to increase bone strength

6) remodelling and then final reconstruction

Question 29

Damage in cardiopulmonary system - 3 types, myocardial infarction, bronchopneumonia and inhalation of toxic fumes

Describe the pathogenesis of each form and what happens in subsequent healing

Answer 29

Bronchopneumonia: damage mainly in pneumocytes lining alveoli due to infection BUT alveolar wall connective tissue is minimally damaged - minimal granulation/scar tissue

so pneumocytes (they are labile cells and constantly regenerate) can regenerate to restore normal lung

Inhalation of toxic fumes: damage to BOTH pneumocytes and alveolar wall connective tissue - so alveolar wall has to undergo repairs and causes scarring (interstitial fibrosis)

Myocardial infarction (heart attack): Cardiac muscles die - they cannot regenerate anymore as they are permanent cells, replaced by granulation tissue that later forms scar tissue

Question 30

Damage to liver and kidneys: know the levels of damage

If hepatocytes/renal tubular cells die - CAN regenerate as they are stable cells

BUT if connective tissue stroma is broken what happens?

Answer 30

Formation of granulation tissues - SCARRING (eg liver cirrhosis)

Question 31

Regeneration capacity of muscles, cartilage and tendons?

Answer 31

Cartilage: very poor regeneration capacity

tendons: good regeneration capacity but very slow

Muscles:
cardiac cannot regenerate
skeletal muscles can regenerate by satellite cells
smooth muscles have highest regeneration abilities

Question 32

Damage to neurons: how does recovery occur

And pathogenesis of stroke?

Answer 32

Mature neurons are permanent cells, cannot regenerate (for CNS basically no chance of regeneration but possible for CNS)

1) wallerian degeneration at distal side of axon
2) If site of damage is not too close to cell body (soma) regeneration possible
3) Schwann cells proliferate and axons sprout (for 20mm/week)
4) apposition of nerve ends (reattachment) BUT if apposition is POOR can lead to traumatic neuroma (VERY PAINFUL) and severe muscle atrophy

Neuronal connection can only be re-established by re-growth and re-organisation of cell processes of surviving neurons

Stroke: Nerve cells in area of infarction destroyed, inflammation of surrounding brain, swelling and congestion occurs

inflammation subsides and affected area becomes smaller, so some function regained BUT NO REGENERATION where neurons are destroyed

Question 33

Know some factors affecting wound healing:

Local factors: e.g. type of wound, apposition of wound margins, blood supply, infection (delays healing), presence of foreign bodies (induce chronic inflammation), irradiation (prolong inflammatory response)

General factors (adverse effect): e.g. nutrition (protein / vitamin C deficiency), steroid administration (causes scar weakness),
systemic diseases (diabetes mellitus, renal failure, cancer cachexia)

General factors (enhancing effect): Exposure to UV light

Question 34

Name 3 possible complications of wound healing (more listed in the answer)

Answer 34

Infection

Wound dehiscence - breakdown of unhealthy sutured wound ends

Keloid formation - excessive scar tissue formation (with genetic predisposition)

Painful scars: caused by nerve damage, formation of traumatic neuromas by bundles of nerve endings (poor apposition of nerve endings)

Weak scars: caused by excessive motion/tension on wound

Pigmentation: Delayed healing / excessive bleeding → deposition of haemosiderin

Cicatrisation: Narrowing of lumen due to scarring

Question 35

Abdominal surgery and weak scars:

Know that patients become reluctant to cough to avoid aggravating the wound - more susceptible to chest infections, and should avoid lifting heavy objects

hernias: may cause bowel loop to protrude through abdominal wall and get strangled when abdominal muscles contract - may cause infarction and even death

Question 36

Stem cell key properties for wound healing?

Answer 36

asymmetric division, self renewal

Question 37

Stem cell sources?

Answer 37

In adults: bone marrow, blood, fat, muscle, skin, conjunctiva

Embryos: inner cell mass of blastocyst

Or by genetic engineering: program adult cells to assume stem cell-like state (induced pluripotent)

Question 38

How to extract embryonic stem cells

Answer 38

From inner cell mass of blastocyst at day 4 after fertilization from IVF embryos and then frozen

Question 39

Pros, cons and risks of embryonic stem cells?

Answer 39

Pros: versatile, can be cultured rapidly

Cons: BUT difficult to induce them into the desired tissues

Risks: immune rejection, tumor formation, infection transmission (they can grow on rat fibroblasts)

BUT HAVE NOT BEEN SUCCESSFULLY USED FOR TREATMENT

Question 40

Some advantages of adult stem cells?

Answer 40

Easier to coax them into the desired tissues (even though their lifespan is still finite)

Less risk of tumor growth and immune rejection

Versatility (less than embryonic but still there) -
eg bone marrow stem cells can develop into epithelial cells of: liver, lungs, GI tract, skin

human fat cells from liposuction can develop into fat cells/bone cells/cartilage cells/muscle cells