Introduction to pathology

• Pathology is the study (logos) of suffering (pathos)

• Pathology is devoted to the study of structuraland functional changes in cells, tissues and organsthat underlie diseases

Pathology

General pathologyBasic reactions of cells and tissues to abnormal

stimuli, i.e. common features of various

disease processes in various cells and tissues

Systematic pathology The descriptions of specific diseases as

they affect given organs or organ

systems

Pathology focuses on 5 aspects of disease

1) Occurrence in populations (epidemiology)2) Its cause (etiology)

environmental, genetic, multifactorial, etc.3) The mechanism of its development

(pathogenesis) 4) The structural alterations induced in organs,

tissues and cells: macroscopical andmicroscopical (patho)morphology

5) The functional consequences: clinicalsignificance

Pathology of cellular injury and deathCells react to adverse influences by

Reversible cell injury

Changes that can be reversed when the stimulus is removed

Pathology of cellular injury and deathCells react to adverse influences by

Reversible cell injury

Changes that can be reversed when the stimulus is removed

Irreversible cell injury

Changes that cause cell death

Pathology of cellular injury and deathCells react to adverse influences by

Cellular adaptation

Stimuli result in new but altered state that maintaines the viability of the cell

Reversible cell injury

Changesthat can be reversed when the stimulus is removed

Irreversible cell injury

Changes that cause cell death

Causes of cellular injury

Hypoxia• Ischemia (loss ofblood supply)

• Inadequateoxygenation(cardioresp. failure)

• Loss of oxygencarrying capacity ofthe blood (e.g., anemia, CO poisoning)

Causes of cellular injury

Hypoxia(⇓

of O2 )

• Ischemia (loss ofblood supply)

• Inadequateoxygenation(cardioresp. failure)

• Loss of oxygencarrying capacity ofthe blood (e.g., anemia, CO poisoning)

Physicalagents

• Trauma• Heat• Cold• Radiation• Electric shock

Infectiousagents

• Bacteria• Viruses• Fungi• Rickettsiae• Parazites

Causes of cellular injury

Hypoxia• Ischemia (loss ofblood supply)

• Inadequateoxygenation(cardioresp. failure)

• Loss of oxygencarrying capacity ofthe blood (e.g., anemia, CO poisoning)

Physicalagents

• Trauma• Heat• Cold• Radiation• Electric shock

Chemicalagents and

drugs

Infectiousagents

• Bacteria• Viruses• Fungi• Rickettsiae• Parazites

Others• Immunologic

reactions• Genetic

derangements• Nutritional

imbalances

Intracellular mechanisms vulnerable tocellular injury

• Maintenance of membrane integrityCritical for cell and organellar ionic and osmotic homeostasis

• Aerobic respiration, involving mitochondrialoxidative phosphorilation and ATP production

• Synthesis of enzymes and structural proteins

• Preservation of the integrity of the geneticapparatus

Features of

Hypoxic injury

Injury induced by

free radicals

Chemical injury

Hypoxic injuryMain biochemical events

• ATP depletion

• Influx of intracellular Ca ++ ions and loss of Ca++

homeostasisCa ++ ions activates

phospholipases ⇒ degradation of membranephospholipids

proteases ⇒ membrane and cytoskeletal protein degradation

ATPases ⇒ enhance ATP depletionendonucleases ⇒ chromatin fragmentation

Reversible hypoxic injury

• Hypoxia prevents oxidative phosphorilation, thusreducing the capacity to generate ATP

• ATP provides fuel for the Na+/K+ ATPase, which actsas a pump, keeping the high concentration of sodiumin the intercellular fluid and the high concentration ofpotassium inside the cell

Reversible hypoxic injury

• ATP provides fuel for the Na+/K+ ATPase, which actsas a pump, keeping the high concentration of sodiumin the intercellular fluid and the high concentration ofpotassium inside the cell

• Hypoxia prevents oxidative phosphorilation ⇒ ATP ⇓

• Hypoxia ⇒ malfunction of Na+/K+ ATPase ⇒ influxof sodium and water from the extracellular space ⇒cellular swelling: hydropic change

Reversible hypoxic injury

• ATP provides fuel for the Na+/K+ ATPase, which actsas a pump, keeping the high concentration of sodiumin the intercellular fluid and the high concentration ofpotassium inside the cell

• Hypoxia prevents oxidative phosphorilation ⇒ ATP ⇓

• Hypoxia ⇒ malfunction of Na+/K+ ATPase ⇒ influxof sodium and water from the extracellular space ⇒cellular swelling: hydropic change

• Anaerobic glycolysis starts ⇒ depletion of cytoplas-mic glycogen ⇒ ⇑ of lactic acid in the cytoplasm ⇒⇓

of the intracellular pH, ⇓action of enzymes

Hydropic change in the proximal tubule: water ⇑

in the cytoplasm, in the invaginations of the surface plasma

membrane (hydropic vacuoles), in the cisterns of the RER, and in the mitochondria. Loss of microvilli.

Hydropic change in the proximal tubule: water ⇑

in the cytoplasm, in the invaginations of the surface plasma

membrane (hydropic vacuoles), in the cisterns of the RER, and in the mitochondria. Loss of microvilli.

The changes are rever-sible if oxygena- tion is restored

Irreversible hypoxic injury

• The transition from reversible to irreversible state is gradual and occurs when adaptive mechanisms havebeen exhausted

• Signs of irreversible injury- Amorphous densities in swollen mitochondria- Formation of myelin figures from whorls ofmitochondrial membranes

-

Irreversible hypoxic injury

• The transition from reversible to irreversible state is gradual and occurs when adaptive mechanisms havebeen exhausted

• Signs of irreversible injury- Amorphous densities in swollen mitochondria- Formation of myelin figures from whorls ofmitochondrial membranes

- Surface membrane blebs- Rupture of cell and plasma membranes- Leakage of lysosomal enzymes ⇒ digestion of celland nuclear components

The mitochondria are swollen, their membranes are ruptured, and amorphous densities are in their matrix

Lethal hypoxic injury: rupture of cell membranes

and lysis of chromatinSublethal hypoxic injury

LM features of lethal hypoxic injury: loss of nuclear staining, the cytoplasm is eosinophilic (pink)

Dead cells show typical nuclear changes

• Pyknosis (pyknos, dense) - condensation of chromatin• Karyorrhexis - (rhexis, tearing apart) - fragmentationof nuclear material

• Karyolysis - lysis of chromatin due to the action ofendonucleases (loss of nuclear staining)

Laboratory markers of irreversible cell injury

• Cytoplasmic enzymes are released through damagedcell membranes into the blood

• Creatine kinase (CK) - cardiac or skeletal muscleinjury

• Aspartate aminotransferase (AST) and alanineaminotransferase (ALT) - liver cell injury

• Lactate dehydrogenase (LDH) is released fromruptured RBCs and many other cells

Can hypoxic cell injury be reversed or repaired by providing the cells with adequate

oxygen?

• Irreversibly damaged cells cannot be revived by O2

• The function of reversibly damaged cells can be improved by O2

Can hypoxic cell injury be reversed or repaired by providing the cells with adequate

oxygen? • Irreversibly damaged cells cannot be revived by O2• The function of reversibly damaged cells can be improved by O2

• Reestablished blood flow to a myocardium madehypoxic to coronary obstruction may causereperfusion injury of still living myocardial cells at

the marginal zone of a myocardial infarction

Can hypoxic cell injury be reversed or repaired by providing the cells with adequate

oxygen?

• Irreversibly damaged cells cannot be revived by O2• The function of reversibly damaged cells can be improved by O2

• Reestablished blood flow to a myocardium madehypoxic to coronary obstruction may causereperfusion injury of still living myocardial cells at

the marginal zone of a myocardial infarction• Reperfusion injury is caused by oxygen-derived freeradicals that may form under such conditions, and is an irreversible damage to cells injured previously byhypoxia

Oxygen free radicals

• Superoxide anion radical (O2 .-), hydrogen peroxide(H2 O2 ), hydroxyl radical (OH.) and nitric oxide (NO.)

• Free radicalscause lipid peroxidation ⇒ membrane damagecross-link proteins ⇒ inactivation of enzymescause DNA breaks ⇒ blockade of DNA transcription

Chemical injury

• Two mechanisms• Direct damage, by binding to some critical molecular

component of cell membrane proteins, causing⇑

permeability

• Indirect damage, by conversion to reactive toxicmetabolites, which cause cell injury by- direct binding to membrane proteins and lipids- formation of free radicals

Necrosis(morphology of irreversible injury)

• Necrosis (necros, dead) is death of cells, tissues, ororgans in a living organism

• Histological signs: same as those of irreversiblehypoxic injury: cell membrane rupture, nuclearchanges: pyknosis, karyorrhexis or karyolysis

Main types of necrosis

• Coagulative necrosis• Liquefactive necrosis• Caseation• Fat necrosis• Gangrene• Fibrinoid necrosis

Main types of necrosis

• Coagulative necrosis• Liquefactive necrosis• Caseation• Fat necrosis• Gangrene• Fibrinoid necrosis

Grosslyvisible

Coagulative necrosis

• Most common form of necrosis, predominatedby protein denaturation with preservation of thecell and tissue framework

• This pattern is characteristic of hypoxic death inall tissues except the brain

Coagulative necrosis

Anaemic infarct• Cause: occlusion of an

end artery• In the heart, spleen, kidney• Gross: pale tissue, with

well-defined boundaries; later it becomes yellowishbecause the lysosomalenzymes of the necrotizedcells autodigest theinfarcted area

• Healing: by connectivetissue replacement (fibrosis)

Haemorrhagic infarct

Coagulative necrosis

Anaemic infarct• In the heart, spleen, kidney• Cause: occlusion of an

endartery• Gross: pale, firm tissue,

with well-defined bounda-ries; later yellowishbecause the lysosomalenzymes of the necrotizedcells autodigest theinfarcted area

• Healing: by connectivetissue replacement (fibrosis)

Haemorrhagic infarct• In the lungs• Cause: occlusion of a

segm. pulmonary artery• The necrotized area

undergoes secondaryhaemorrhage viabronchial arteries

• Firm, wedge-shaped, pleural-based, haemorr-hagic, airless focus

• Healing: by fibrosis

Anaemic infarction of the myocardium, the margins are hyperaemic

The infarcted myocardial fibers are eosinophilic, there is no nuclear staining; neutrophilic granulocytes accumulated at

the margins of infarction (vital sign)

Liquefactive necrosis: softening of the necrotic tissue due to action of hydrolytic enzymes released

from

• Dead cells, as in brain infarct• Healing: with glial scar

Liquefactive necrosis: softening of the necrotic tissue due to action of hydrolytic enzymes released

from

• Dead cells, asin brain

infarct•Healing: withglial scar

• Neutr. granulocytes invadingthe tissue, as in an abscess

• Healing: with fibrosis

Caseous necrosis• Distinctive form of coag. necrosis in foci of

tuberculous infection• Gross: caseous necrosis is white and cheesy

The necrotic area is eosinophilic, amorphous, and is surrounded by epitheloid cells and Langhans’ giant cells.

Healing: by fibrosis + calcification

Fat necrosis

• Refers to necrosis in adipose tissue, induced bythe action of lipases derived from injured

pancreatic cells or macrophages

• Lipases catalyse decomposition of triglycerides tofatty acids, which complex with calciumto create calcium soaps

Fat necrosis

• Refers to necrosis in adipose tissue, induced bythe action of lipases derived from injured

pancreatic cells or macrophages

• Lipases catalyse decomposition of triglycerides tofatty acids, which complex with calciumto create calcium soaps

• Observed in the course of pancreatitis, or intraumatic injury of subcutis or breast

• Healing: by fibrosis

Yellowish foci of enzymatic fat necrosis in acutepancreatitis

Gangraene

• Gangraene results when putrefactive bacteriainvade necrotic tissue

• Three types (detailed later)

• Dry gangraene: in the leg of patients sufferingfrom atherosclerosis-related occlusion of thetibial arteries

Gangraene

• Gangraene results when putrefactive bacteriainvade necrotic tissue

• Three types (detailed later)

• Dry gangraene: in the leg of patients sufferingfrom atherosclerosis-related occlusion of thetibial arteries

• The affected tissues appear black because of thedeposition of iron sulphide from degradedhaemoglobin

Gangraene of the great toe

Fibrinoid necrosis

• Limited to medium-sized and small arteries

• The wall of these vessels undergo necrosis and is impregnated with fibrinogen and other plasmaproteins

• It can be recognized only in histologic slides

• Observed in malignant hypertension, arteritis, rejection

Fibrinoid necrosis of small arteries, the necrotized SMCs are eosinophilic

Apoptosis: programmed cell death

• A form of energy-dependent process fordeletion of unwanted individual cells

• Cell death occurs by activation of the internalsuicide program

Apoptosis: programmed cell death

• A form of energy-dependent process fordeletion of unwanted individual cells

• Cell death occurs by activation of the internalsuicide program

• Prevented or induced by a variety of stimuli

• ⇓

Apo contributes to cell accumulation, e.g. neoplasia

• ⇑

Apo results in extensive loss, e.g. atrophy

Inhibitors

• Growth factors• Sexual steroids (e.g., testosteron)

Inducers

• Growth factor withdrawal• Glucocorticoids• Injuries:

- Viruses (hepatitis virus, HIV) - Free radicals- Ionising radiation- DNA damage

Intrinsic (mitochondrial) pathway of apoptosis

Mitochondrion

Bcl-2 inhibitsBax activates

Executioncaspases

When cells are deprived of survival signals or subjected tostress, anti-apoptotic Bcl-2 protein is lost from themitochondrial membrane, and is replaced by pro-apoptoticBax protein

Extrinsic (death receptor) pathway of apoptosis

Mitochondrion

Bcl-2 , Bax

Executioncaspases

Death receptors CytotoxicT-cells

If death receptors on the cell surface (TNF-R, FAS-R) cross-link with the ligand, activation of execution

caspases occurs. Cytotoxic molecules derived fromCD8+ T-cells directly activate these caspases

Execution pathway of apoptosis

Bax Execution caspases:cascade of proteolytic

enzymes

• Breakdown of cytoskeleton• Cell shrinkage• Chromatin condensationand fragmentation

• Formation of apoptoticbodies

Death receptors(TNF, FAS)

CytotoxicT-cells

Apoptosis: cell shrinkage, and condensation of nucleusinduced by cytotoxic T- lymphocytes

Adaptations

Changes that occur in cells and tissues in response to prolonged stimulation or chronic injury• Atrophy• Hypertrophy• Hyperplasia• Metaplasia• Dysplasia (to be lectured later)• Intracellular accumulation of various

substances

Atrophy

• Decreased cell mass: reduction in size of cells(nucleus and cytoplasm), tissue, or organs.

• Atrophied organs are smaller than normal.• Normal weight (g) of parenchymal organs:

- spleen 150- kidneys 150-150 - heart 300 to 350 - lungs 400-400 - brain 1300- liver 1500

Physiologic atrophy

- Involution of the thymus in adolescence- Senile atrophy in aging- Atrophy of female genitalia in menopause

Pathologic atrophy

• Disuse. Muscles atrophy in people who donot use them (prolonged bed rest, immobilization of an extremity for healingof fracture)

• Loss of innervation of skeletal muscle• Lack of trophic hormones in pituitary

disease•

Pathologic atrophy

• Disuse. Muscles atrophy in people who donot use them (prolonged bed rest, immobilization of an extremity for healingof fracture)

• Loss of innervation of skeletal muscle• Lack of trophic hormones in pituitary disease• Ischaemia. Reduced blood supply leads torenal atrophy or atrophy of the brain

• Malnutrition. Protein-energy deficiency cause atrophy of skeletal muscles, parenchymal organs, and general wasting

(marasmus)• Increased pressure, e.g., hydrocephalus orhydronephrosis

Obstruction of the CSF flow leads to pressure atrophy of the brain, with the enlargement of

ventricles: hydrocephalus

Hydronephrosis: obstruction of the ureter leads to sac-like dilation of renal pelvis and calyces,

and pressure atrophy of parenchyma

Hydronephrosis: dilated calices, atrophiedpapillae, thinned parenchyma

Hypertrophy• An increased cell mass leading to an increased

size of organs

• Physiologic: hypertrophy of uterus in pregnancy, compensatory hypertrophy of the remnant kidneyafter unilateral nephrectomy

(in both conditions, cell division is also present)

Hypertrophy• An increased cell mass leading to an increased

size of organs

• Physiologic: hypertrophy of uterus in pregnancy, compensatory hypertrophy of the remnant kidneyafter unilateral nephrectomy(in both conditions, cell division is also present)

• Pathologic: occurs e.g. in the muscles

• Muscles are not able to divide, therefore anincreased demand for action can be met only byenlarging the size of cells

Increased exerciseleads tohypertrophyof muscles

Hypertrophy of heart, triggered by action of mechanical stimuli (⇑ workload) and vasoactive substances (e.g., angiotensin II). Free wall

thickness: above 15 mm

Hypertrophy of the muscles of urinary bladder due to urethra obstruction

Hyperplasia• An increase in the size of a tissue or organ due toan increased number of constituent cells. The cellsmay have an increased volume.

• Physiologic: hormonal hyperplasia: - proliferation of the glandular epithelium of the breastduring lactation;

- compensatory hyperplasia of liver after partialhepatectomy

Hyperplasia• An increase in the size of a tissue or organ due toan increased number of constituent cells. The cellsmay have an increased volume.

• Physiologic: hormonal hyperplasia: - proliferation of the glandular epithelium of the breastduring lactation;

- compensatory hyperplasia of liver after partialhepatectomy

• Pathologic: due to hormonal stimulation- endometrial hyperplasia, induced by oestrogens- adrenal cortex hyperplasia, induced by ACTH- hyperplasia of prostate, induced by dihydrotestosterone, oestrogens and peptide growth factors

- hyperplasia of thyroid, induced by anti-TSH antibodies

Metaplasia• Replacement of one mature cell type by anothertype.

• E.g.: - Squamous metaplasia of the bronchus: chronicirritation-induced replacement of bronchialstratified columnar epithelium by squamousepithelium in smokers

Metaplasia• Replacement of one adult cell type by anotheradult cell type; reversible.

• E.g., - Squamous metaplasia of the bronchus: chronicirritation-induced replacement of bronchialstratified columnar epithelium by squamousepithelium in smokers

- Gastric metaplasia of the oesophagus: chronicirritation induced by gastric juices in gastrooeso-phageal reflux leads to the replacement ofsquamous epithelium by gastric epithelium

• If the adverse circumstances persist, metaplasiamay progress to dysplasia

Squamous metaplasia of the bronchus

Intracellular accumulations

• Lipids - triglycerides, cholesterol• Proteins• Pigments

Accumulation of triglycerides

• Most common in the liver, but also occurs in theheart; reversible

• Fatty change/steatosis of liver: due to- alcohol abuse- morbid obesity- diabetes- protein-energy malnutrition- hypoxia- hepatotoxins

• Biochemical pathways of uptake and metabolismof fatty acids by the liver, formation of triglyce-rides, and secretions of lipoproteins: not detailed here

Steatosis: the liver is enlarged, yellow and greasy, resembles to goose liver

The lipid molecules accumulate in large vacuoles

Frozen section, Oil Red O

Accumulation of cholesterols and cholesterol esters

• In the intima of aorta and large arteries inatherosclerosis.

• In macrophages- in hyperlipidaemia: collections of foamy

macrophage produce yellowish nodules in thepalpebra (xanthomas)

-

Accumulation of cholesterols and cholesterol esters

• In the intima of aorta and large arteries inatherosclerosis.

• In macrophages- in hyperlipidaemia: collections of foamy

macrophage produce yellowish nodules in thepalpebra (xanthomas)

- in cholesterolosis: foamy macrophagesaccumulate in the lamina propria of gallbladder

-

Accumulation of cholesterols and cholesterol esters

• In the intima of aorta and large arteries inatherosclerosis.

• In macrophages- in hyperlipidaemia: collections of foamy

macrophage produce yellowish nodules in thepalpebra (xanthomas)

- in cholesterolosis: foamy macrophagesaccumulate in the lamina propria of gallbladder

- in cerebral infarction: macrophages phagocytosemembrane lipids derived from dead oligodendrocytes

Atheromatous plaque: the lipids are dissolved during normal histologic processing

The dissolved cholesterol crystals appear as cleftlike cavities

Foamy macrophages scavenge necrotic debris rich in lipids

Accumulation of proteins

• Hyaline change: any alteration within cells thatimparts a homogeneous, glassy pink appearance inH&E-stained histologic sections

•

Accumulation of proteins

• Hyaline change: any alteration within cells thatimparts a homogeneous, glassy pink appearance inH&E-stained histologic sections

• Intracellular: - Hyaline droplets in proximal tubular cells in

heavy proteinuria- Mallory-hyaline in hepatocytes in alcoholic

liver injury

Hyaline droplets in proximal tubular epithelial cells

Mallory-hyaline in chronic alcohol abuse

Accumulation of pigments• Exogeneous

- Inhaled coal dust (black) - leading to anthracosis of lungs; stored in pulmonary macrophages

- Pigments of tattooing, taken up by macrophages

Accumulation of pigments• Exogeneous

- Inhaled coal dust (black) - leading to anthracosis of lungs; stored in pulmonary macrophages

- Pigments of tattooing, taken up by macrophages• Endogeneous

- Lipofuscin (brown), associated with tissue atrophy, in the myocardium of elderly people

Accumulation of pigments• Exogeneous

- Inhaled coal dust (black) - leading to anthracosis

of lungs; stored in pulmonary macrophages- Pigments of tattooing, taken up by macrophages

• Endogeneous- Lipofuscin (brown), associated with tissue atrophy,

in the myocardium of elderly people- Haemosiderin (brown), haemoglobin-derivedintracellular pigment composed of aggregated ferritin, indicates previous haemorrhage. Systemic accumulation: termed haemosiderosis

- Melanin (brown): product of naevus cells- Jaundice (icterus): systemic bilirubin retention; yellowskin and sclera discoloration

Pathologic calcificationAbnormal deposition of Ca-salts in soft tissues

DystrophicIn nonviable or dying tissues; the serum Ca++ level is normal.

•Arteries in atherosclerosis•Damaged heart valves•Areas of various necrosis

Precipitation of a crystallineCa-phosphate starts withnucleation (initiation) on membrane fragments, followed by propagation of crystal formation

Pathologic calcificationAbnormal deposition of Ca- salts in soft tissues

DystrophicIn nonviable or dying tissues; the serum Ca++ level is normal.

•Arteries in atherosclerosis•Damaged heart valves•Areas of various necrosis

Precipitation of a crystallineCa-phosphate starts withnucleation on membrane fragments, followed by propagation of crystal formation

MetastaticResults from hypercalcaemia:• ⇑

secretion of parathormone

in hyperparathyroidism• Destruction of bones by

myeloma, metastases, acce-lerated bone turnover, orimmobilization [space travel]

• Vitamin D-intoxication• Systemic sarcoidosis• In chronic renal failure ⇒sec. hyperparathyroidism dueto phosphate retention

Deposits in the arteries, kidneys, lungs, and stomach

Dystrophic calcification: calcifying aortic stenosis

Metastatic calcification of arteries in ESRD

Radial art.

Ulnar art.

Bereczki Csaba, SZTE Pediatrics

Metastatic calcific deposits of the lung

The calcific deposits fill the alveolar spaces