Topic 5.1 - injury and cell death

proteasome - role

tage and degrade cytosolic proteins

lysosome - role

contains enzymes that can degrade macromolecules

peroxisome - role

contains oxidative enzymes that can break down long-fatty acid chains

parenchyma - def and composition

functional tissues of organs

composed of unique parenchymal cells

parenchymal cell types (5)

• Heart -> cardiomyocytes

• Liver -> hepatocytes

• Lung -> pneumocytes

• Kidney -> podocytes

• Brain -> neurons

stroma - def and composition

support and give structure to an organ

composed of cells and extracellular matrix

stroma cell types (3)

epithelial cells → define boundary of organ

endothelial cells of blood vessels → supply oxygen and nutrients to the organ

mesenchymal cells → eg. fibroblasts that produce the ECM

stroma - components of ECM control (2)

Structure of organ by providing scaffolding and support + define boundaries of organ

Function of organ by storing growth factors and providing signalling receptors for cell growth and differentiation

features of stroma and ECM - list (6)

basement membrane

interstitial matrix

integrin

fibrous structural proteins

proteoglycans

fibroblasts

features of stroma and ECM - basement membrane (2)

highly organised type of ECM that forms around epithelium, endothelial cells and smooth muscle cells

composed of proteoglycans and collagen

features of stroma and ECM - interstitial matrix

amorphous gel that connects the components of the ECM

features of stroma and ECM - integrin (2)

connects elements of ECM together

initiate signalling cascades that effect locomotion, proliferation and differentiation

features of stroma and ECM - fibrous structural proteins

provide tensile strength and recoil

features of stroma and ECM - proteoglycans

form water-hydrated gels that give tissue compressive resistance and lubrication

features of stroma and ECM - fibrobalsts (2)

mesenchymal cells found in stroma

make components of extracellular matrix and contribute to repair of injury

factors determining cell proliferation - list (3)

growth factors

extracellular matrix

cell proliferation - growth factor roles (4)

promote cell cycle entry

relieves blocks in cell cycle arrest

prevent apoptosis

enhance biosynthesis

cell proliferation - ECM role

displays growth factors and signalling receptors

cell proliferation - cyclins role

regualte activity of cyclin dependent kinases and cyclin dependent inhibitors

how are tissues of the body divided into groups

based on intrinsic proliferative capacity and presence of tissue stem cells

tissues of the body - list (3)

1. labile

2. stable

3. permanent

tissues of the body - labile tissue (3)

composed of cells that are continuously lost and replaced by either proliferation of mature cells or stem cells

most hematopoietic and epithelial cells

eg. RBC, epithelial cells, lymphocytes

tissues of the body - stable tissue (3)

composed of quiescent cells → limited proliferative capacity but can enter cell cycle and proliferate in response to growth factors

parenchyma of most solid organs, endothelial cells, fibroblasts and smooth muscle cells

eg. hepatocytes, fibroblasts, endothelial cells

tissues of the body - permanent tissue (2)

composed of terminally differentiated cells that have left cell cycle and cannot re-enter + limited stem cell reserves

neurons, cardiac muscle cells, skeletal muscle cells

purpose of histological staining

most cells are transparent → staining procedures used to make cells more visible

haematocylin and eosin staining

haematoxylin = stain acidic or basophilic structures purple → eg. nucleic acids

eosin = acidic dye → stains basic or acdiphilic structures pink → eg. most proteins

aetiology - def

cause of disease

eg. toxins in cigarette smoke for lung cancer

pathogenesis - def

mechanism causing disease

eg. toxins introduce mutations into DNA

pathology - def

molecular and morphological changes to cells or tissues

eg. tumorigenesis

clinical manifestations - def

signs = observer can describe

symptoms = patient can describe

complications - def

secondary, systemic or remote consequences of disease

prognosis - def

anticipated course of disease

epidemiology - def

incidence, prevalence, distribution of disease

adaption - def

response to stress or increased demand that maintains the cell’s functions by a new stead state

reversible/ sublethal injury - def

response to stimuli that compromises cellular function

irreversible/ lethal injury - def

response to stimuli that compromises cellular function to point that cell cannot recover

how do cells respond to introduction of stress or increased demand

cells undergo adaption that involves change that enables cell or tissue to maintain a new steady state and perform its function

adaptions are reversible if stress or demand is removed → prolonged stress or demand can lead to failure to adapt and injury

classifications of adaptation (2)

physiological adaption = normal cellular response to normal stimulation

pathological adaptation = cellular response to stimulation secondary to underlying disease/ to avoid injury by changing structure and or function

types of adaptation - list (4)

hypertrophy

hyperplasia

atrophy

metaplasia

hypertrophy - features

increased workload due to physiological or pathological stimuli → increased amount of structural proteins and organelles → increased cell size → increased organ size

no new cells → just larger

typically associated with non-dividing cells

hypertrophy - physiological and pathological example

physiological body builder has increased workload → bigger muscles → ripped physique

• can be reversed by decreasing workload

hypertension → increased workload → enlarged heart → improved performance → degeneration if no modulation of stress

• can be reversed by hypertension management leading to improved heart function

hyperplasia - features (3)

increased cell number → increased organ size

only in cell populations capable of dividing

can be physiological or pathological response

hyperplasia - physiological and pathological examples (2)

physiological: compensatory growth of liver following partial resection

pathological: thickening of endometrium inr esponse to hormones produced secondary to an underlying disease

atrophy - feature

decreased protein synthesis or increased protein degradation → decreased amount of structural proteins and organelles → decreased cell size and or number → decreased organ size

atrophy - physiological and pathological example

physiological: embryonic structures removed in the growing foetus, shrinkage of uterus following pregnancy

pathological: atrophy of muscles due to decreased workload following paralysis

metaplasia - features

change in cell type → cells sensitive to stress replaced by a cell type better able to withstand stress

not replacement of one fully differentiated cell type with another fully differentiated cell type but process of stem cell reprogramming

types of injury inducing stimuli - list (7)

1. hypoxia

2. chemical agents

3. infectious agents

4. immunological reactions

5. genetic defects

6. nutritional imbalance

7. physical agents

factors influencing outcome of injury (2)

1. features of injury → severity of injury inducing stimuli and duration of exposure

2. factors intrinsic to cell or tissue → different in function and metabolic activity of different cell types

factors influencing outcome of injury - features intrinsic to cell or tissue (3)

cells ability to adapt to stress

genetics of individual

state of cell

first feature of most forms of cell injury under light mircoscoope (2)

cell swelling

fatty change → lipid vacuoles in cytoplasm

features of reversible injury (4)

cell swelling and fatty change

cell membrane blebbing → loss of structure of cell

endoplasmic reticulum and mitochondrial changes

nuclear alterations

types of irreversible cell death

differ in morphology, cause and roles in disease

necrosis and apoptosis

may have occured before morphological changes become apparent

features of irreversible injury (3)

disturbance of membrane function

inability to reverse mitochondrial dysfunction

nuclear changes

caspases - def

family of protease enzymes essential for apoptosis, pyroptosis and inflammation

principle targets of injurious stimuli and consequences

mitochondria, cell membranes, proteins and DNA

consequences of injury are distinct but overlapping

mechanisms of injury - generation of ROS

generated by inefficient aerobic respiration

ROS attacks macromolecules including proteins of cytoskeleton, DNA and lipid membranes

morphological features of reversible and irreversible injury - autolysis by ROS and lysosomal enzymes (4)

• Digestion of nucleic acid (karyolysis) -> decreased staining of nucleus with hematoxylin

• Denaturation of cytoplasmic proteins -> more staining with eosin

• Loss of RNA -> less hematoxylin staining giving cytoplasm bright pink appearance

• Loss of glycogen particles -> glassy appearance

mechanisms of injury - decreased ATP production

can occur in hypoxic environments → O2 not available for aerobic respiration or as consequence of mitochondrial damage

morphological features of reversible and irreversible injury - condensation or clumping of chromatin (3)

• Decreased aerobic respiration -> increased anaerobic respiration and lactic acid production

• Decreased pH of cell -> clumping of chromatin

• Observed as dense haematoxylin staining of nucleus

mechanism of injury - reduced macromolecule synthesis

Low ATP -> reduced synthesis of lipids and proteins needed to maintain structure of phospholipid membranes and cytoskeleton

mechanism of injury - failure of ATP dependent ion channels (2)

accumulation of intracellular sodium, efflux of potassium and net gain of water

ATP dependent ion channels also help keep cytoplasmic calcium levels low

morphological features of reversible and irreversible injury - cell swelling

failure of ATP dependent ion channels → isomotic gain of water and swelling cell and organelles

mechanisms of injury - endoplasmic reticulum stress

accumualtion of misfolded proteins in ER leading to ER sterss

mechanisms of injury - calcium dyschondrosteosis (2)

calcium levels tightly regulated and kept at low concentrations within cytoplasm and organelles in comparison to extracellular space

injury leading to increased cytoplasmic calcium concentrations -> activation of calcium dependent enzymes

mechanisms of injury - reduced synthesis of macromolecules and activation of calcium dependent enzymes (3)

Macromolecules being proteins and lipids

Calcium dependent enzymes being proteases and lipases

Damages cytoskeleton and membranes

morphological features of reversible and irreversible injury - cell membrane blebbing

loss of cytoskeletal proteins affects structure of cell → bulging of regions of cell membrane in response to swelling

mechanisms of injury - damaged organelle (2)

Intact mitochondrial membrane needed to maintain proton gradients used to synthesise ATP -> membrane damage or formation of channel in membrane can lead to reduced or less efficient ATP production and release of Ca2+

Damaged lysosomal membranes -> leakage of lysosomal enzymes into the cytoplasm

• Activated in acidic intracellular pH of injured cell

mechanisms of injury - damaged plasma membrane

leads to loss of osmotic balance and influx of fluids and ions

morphological features of reversible and irreversible injury - irreversible injury (3)

Integrity of plasma membrane is lost

Lysosomal membranes rupture and lysosomal enzymes digest contents of cell wall

Mitochondrial membranes are irreversibly damaged

steps of apoptosis caused by generation of ROS

1. generated ROS introduces mutations and breaks in DNA that can trigger apoptosis and denatures cytoplasmic proteins

2. decreased ATP production

3. reduced macromolecule synthesis

4. failure of ATP dependent ion channels

5. ER stress caused by accumulation of misfolded proteins and induction of unfolded protein response

6. calcium dyschomeostasis → activation of calcium dependent enzymes including caspases

7. DNA and protein damage

8. damaged organelle membranes

9. apoptotic bodies → caspases activate enzymes that degrade cell’s proteinsa nd nucleus

process of cell death leading to necrosis

disturbance of plasma membrane and organelle membranes to the point of irreversible mitochondrial dysfunction

morphological features of cell death in tissue (6)

• Increased eosinophilic staining -> denaturation of proteins and loss of RNA

• Vacuolation -> digested cytoplasmic organelles

• Swelling of ER and mitochondria

• Myelin figures -> whorls of phospholipid from damaged membranes due to charge of lipids

• Discontinuous plasma and organelle membranes

• Nuclear change due to breakdown of DNA and chromatin

types of nuclear change (3)

• Karyolysis -> decreased basophilia from DNA breakdown

• Pyknosis -> nuclear shrinkage and increased basophilia due to condensation of chromatin

• Karyorrhexia -> nuclear fragmentation

morphology of necrotic lesions - processes (2)

coagulative → denaturation of proteins

• Cells are dead but tissue architecture preserved

liquefactive → enzymatic digestion of macromolecules

• cells digested and no tissue structure

types of necrosis - list (6)

1. coagulative

2. liquefactive

3. caseous

4. fat

5. gangrenous

6. fibrinoid

types of necrosis - coagulative (5)

denaturation is greater than digestion

most common type

due to ischemia in solid organs except brain

nucleus is lost → can be observed by haemotoxulin staining

architecture of cells preserved

types of necrosis - liquefactive (4)

complete digestion of dead cells

associated with bacterial and fungal infections

inflammatory response contributes to digestion of tissue

ischemia in brain → necrotic area becomes fluid-filled cyst

types of necrosis - caseous (3)

fragmented lysed cells with amorphous granular appearance

tissue architecture obliterated

associated with infection with mycobacterium tuberculosis → large numbers of organisms and degenerating tissue

types of necrosis - fat (3)

refers to focal areas of fat destruction

enzymes liquefy membranes of fat cells → release fatty acids which combine with calcium to cause patchy white lesions (fat saponification)

most common in acute pancreatitis

types of necrosis - gangrenous (2)

usually describes coagulative necrosis that occurs in lower limb which has lost blood supply

if gangrene associated with liquefactive necrosis → may accompany a bacterial infection and is referred to as wet gangrene

types of necrosis - fibrinoid (2)

occurs in blood vessels in response to deposition of immune complexes → fibrin and inflammatory cells can leak into eextravascular space

observed by very pink eosinophilic staining which lacks nuclei → accumulation of just protein in tissue (fibrin) leaked out of damaged blood vessels

morphology of apoptosis (5)

cells shrink → intensely eosinophilic cytoplasm

nuclear chromatic condensation and fragmentation → no karyolysis

formation of apoptotic bodies and membrane bound vesicles of cytosol and organelles

quickly phagocytosed

no inflammatory response

two main pathways leading to apoptosis - list

intrinsic pathway

extrinsic pathway

both lead to activation of initiator caspases and then executioner caspases → caspases trigger packaing up of cellular contents into apoptotic bodies

two main pathways leading to apoptosis - intrinsic (5)

1. Injury intrinsic to cells

Eg. growth factor withdrawal, DNA and protein damage

1. Change in balance between pro-apoptotic and anti-apoptotic BCL2 proteins

2. Release of cytochrome C form mitochondria

3. Cytochrome C initiates cascade of events which lead o activation of initiator caspases ad then executioner caspases

4. Caspases lead to packaging up of cellular contents into apoptotic bodies

two main pathways leading to apoptosis - extrinsix (3)

1. Signal from outside the cell -> typically receptor ligand interaction

Eg. TNF receptor activation by FAS ligand

2. Downstream activation of initiator caspases and executioner caspases

3. Caspases lead to packaging up of cellular contents into apoptotic bodies

other forms of cell death (3)

Necroptosis -> programmed necrosis

Ferroptosis -> form of cell death associated with high levels of iron and excess ROS causing lipid peroxidation

Pyroptosis -> form of cell death associated with release of fever inducing IL-1

other form of cell survival (1)

Autophagy -> survival mechanism induced under stress conditions by recycling metabolites

tissue repair processes for successful elimination of cause and consequence of injury- list (2)

regeneration or repair by scar formation

both will restore function of damaged tissue

tissue repair processes for unsuccessful elimination of cause and consequence of injury- list

fibrosis

injury is not adequately resolved and function of damaged tissue is not resolved

steps of tissue repair by regeneration (4)

1. Tissue injury

2. Replacement of damaged components

3. Regeneration

4. Restoration of normal function of organ or tissue

steps of tissue repair by scar formation (5)

1. Tissue injury

2. Connective tissues replace damaged components

3. Repair by connective tissue

4. Scar formation

5. Restoration of normal function or fibrosis

factors influencing pathway of tissue repair (3)

1. Proliferative capacity of functional cells within a tissue -> parenchymal cells

2. Underlying structure of organ -> determined by extracellular matrix

3. Ability to effectively resolve the original injury

factors influencing pathway of tissue repair - regeneration

tissue composed of cells with proliferative capacity AND underlying structure of tissue not too severely damaged

factors influencing pathway of tissue repair - repair by scar formation

tissues composed of cells with limited or no proliferative capacity OR underlying structure of tissue is lost

pathway of tissue repair - ischemic stroke causing loss of neurons

scar

pathway of tissue repair - deep incision though skin penetrating into the underlying tissue

scar and regeneration

pathway of tissue repair - repair of liver following resection

regeneration

factors influencing healing - foreign bodies, nutrition, location and poor perfusion

Foreign bodies -> interfere with successful wound healing by prolonging inflammation and causing further injury

Nutrition -> good nutrition is essential for successful wound healing -> Vit C required for synthesis of collagen

Location -> can effect contraction of wound

Poor perfusion -> reduces supply of blood needed for successful wound healing by limiting inflammation

• Inhibits removal of cause and consequence of injury + prevent recruitment of cells required for healing process

factors influencing healing - diabetes, medication, mechanical factors, infection

Diabetes -> can delay wound healing

Medication -> some anti-inflammatory agents can inhibit chemical mediators (cytokines) that promote collagen deposition

Mechanical factors -> pressure caused by immobilisation or torsion caused by movement can cause wounds to tear apart

Infection -> prolongs inflammation and may increase local tissue injury