What is disease?

• A condition in which the presence of an abnormality causes a loss of normal health

• Manifests in signs and symptoms subjective: e.g., pain objective: confirmed by diagnostic tests

• Duration of disease: short lasting - acute long lasting - chronic

• Outcome: varies; can be lethal What is pathology?

• The study (logos) of suffering (pathos)

• Devoted to the study of - the cause of the disease (etiology) - the mechanism(s) of disease development (pathogenesis) - the structural alterations induced in cells and tissues by the disease (morphologic change) - the functional consequences of the morphologic changes (clinical significance)

• The morphologic change can be focal (localized abnormality) or diffuse Teaching program of pathology for medical students

General pathology • Basic 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

The descriptions and terms used are the basis of medical language

Students are expected to attend the lectures, the autopsy and histopathology practicals, and the organ demonstrations.

Attendance at the practicals the attendence is always verified. There is no possibility for missed practicals to be repeated later.

Students who are absent from more than 25% of the practicals, automatically fail the semester.

The grade achieved in the fall-semester examinations will be calculated from the sum of the following: - the first mid-term assessment (maximum 5 points) - the second mid-term assessment (max. 5 points) - the histology examination (max. 5 points) - the autopsy examination (max. 5 points) - the final test (max. 80 points).

The final grades: from 0 to 50 points: failed (grade 1), from 51 to 59 points: passed (grade 2); from 60 to 69 points: accepted (grade 3); from 70 to 79 points: good (grade 4); from 80 to 100 points: very good (grade 5).

Pathology of cellular injury and death

Cells react to adverse influences by

1) Reversible cell injury Changes that can be reversed when the stimulus is removed

2) Irreversible cell injury Changes that cause cell death

3) Cellular adaptation Stimuli result in new but altered state that maintains the viability of the cell

Intracellular mechanisms particularly vulnerable to cellular injury

• Maintenance of membrane integrity - critical for ionic and osmotic homeostasis of the cell

• Aerobic respiration - oxidative phosphorilation and ATP production in mitochondria

• Synthesis of enzymes and structural proteins

Common cellular injuries

• Hypoxic/ischemic injury

• O2-derived free radicals

• Others: chemical injury (acid and alkali solutions), burns, frostbite, trauma, electric shock, etc.

Hypoxia

Reduction in available oxygen

Common causes 1. Upper airway obstruction (eg., sudden swelling of laryngeal mucosa, foreign body aspiration)

2. Inadequate oxygenation of blood in lung diseases

3. Inadequate O2 transport in blood because of decreased number of RBCs (anemia)

4. Inadequate perfusion of blood in the tissues in heart failure Aspiration of gastric content caused obstruction of airways and led to death in the patient with deep coma • Inadequate blood supply to an organ or part of it due to impeded arterial flow or reduced venous drainage

Reversible ischemic injury • Leads to hydropic change of cells • Commonly observed in kidney biopsies

Pathomechanism • A decrease of blood pressure for hours • Hypoxia of tubular epithelial cells  ATP depletion  malfunction of Na+/K+ ATPase  influx of sodium and water into tubular cells

Morphologic features • Light microscopy (LM).... • Electron microscopy (EM)....

LM: the tubular epithelial cells are vacuolated, and the brush border of proximal tubules is lost. Hydropic change on EM: accumulation of 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 of proximal tubules Clinical consequence • Acute renal failure: decreased urinary output; hemodialysis is necessary • If systemic hypotension can be corrected, the renal function normalizes within days

Irreversible ischemic injury and cell death • The transition from reversible to irreversible state is gradual and occurs when adaptive mechanisms have been exhausted • Depletion of ATP, influx of Ca 2+, activation of multiple cellular enzymes, such as

phospholipases  degradation of membrane phospholipids proteases  degradation of membrane and cytoskeletal protein ATPases  enhance ATP depletion endonucleases  chromatin fragmentation EM features indicative of death of ischemic cells

• Within 2 to 3 hours after the death of cells

• Ruptured cell and plasma membranes

• Lysis of cell and nuclear components (leakage of lysosomal enzymes result in digestion of organelles and other cytosolic components) Irreversible hypoxic injury: rupture of cell Reversible hypoxic injury membranes and lysis of chromatin LM features indicative of death of ischemic cells

• Evident approximately 24 hours after the death of ischemic cells

• Loss of nuclear staining

• Eosinophilia of the cytoplasm Important • The cellular function is lost before cell death occurs, and the morphologic features of cell death lag far behind loss of function

Injury induced by O2-derived free radicals

Inflammation, radiation, chemicals, reperfusion lead to the formation of - • superoxide anion radical (O2. ) • hydrogen peroxide (H2O2) • hydroxyl radical (OH.) • nitric oxide (NO.)

These molecules cause oxidative stress of cells: • lipid peroxidation  membrane damage • cross-linkage of proteins  inactivation of enzymes • DNA breaks  blockade of DNA transcription Note Insidiously ongoing oxidative stress of cells plays a role in the process of aging Laboratory markers of irreversible cell injury

Cytoplasmic enzymes released through damaged cell membranes into the blood

• Creatine kinase (CK) - cardiac or skeletal muscle injury

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

• Lactate dehydrogenase (LDH) – from ruptured RBCs Necrosis - morphology of irreversible injury

• Necrosis (necros, dead): death of cells in a living organism characterized by loss of membrane integrity and enzymatic digestion of cells

• Histological sign: loss of nuclear staining

• Healing: substances released from dead cells induce a local inflammatory reaction, which serves to eliminate the debris and initiates the repair process Types of necrosis

1. Coagulative necrosis 2. Liquefactive necrosis Grossly 3. Caseation visible 4. Fat necrosis 5.

1. Fibrinoid necrosis Coagulative necrosis

Most common form of necrosis, predominated by protein denaturation with preservation of the cell and tissue framework

Arterial occlusion  distally: hypoxic (anoxic) death in tissues

Types: Anemic infarct

Cause: occlusion of an end artery

In the heart, spleen, kidney

Gross: circumscribed yellowish lesion, the margins are hyperemic

Circumscribed yellowish lesion, the margins are hyperemic Anemic infarct

Cause: occlusion of an end artery

In the heart, spleen, kidney

Gross: yellowish lesion, the margins are hyperemic

LM: dead cells become eosinophilic with loss of nuclear staining, the border of necrotic tissue is hyperemic and infiltrated by neutrophils

LM of myocardial : eosinophilia of necrotic fibers, disappearance of nuclear staining. Neutrophils in the interstitium Hemorrhagic infarct

In the lungs, due to occlusion of a segmental pulmonary artery; sec. hemorrhage via bronchial arteries

Hemorrhagic infarct of lung: wedge shaped, raised, dark-red area Hemorrhagic infarct

In the small bowels, due to occlusion of the mesenteric superior artery; sec. hemorrhage via anastomosing arcades Hemorrhagic infarct of small bowels

36 Liquefactive necrosis

The necrotic tissue undergoes softening due to action of hydrolytic enzymes

Examples 1. Brain infarct 2. Abscess

1. Brain infarct Occlusion of cerebral artery leads to anemic infarct; then enzymes released from dead cells liquefy the necrotized area

Brain infarct: the necrotic area is softened and pale

Infarcted area

Caudate nucleus

Internal capsule Brain infarct. Macrophages scavenge necrotic, lipid-rich debris. Liquefactive necrosis

2. Abscess - localized purulent inflammation.

Hydrolytic enzymes derived from neutrophil granulocytes induce necrosis of infected area Liquefactive necrosis: abscess Caseous necrosis • Distinctive form of coag. necrosis in foci of tuberculous infection of the lung • Grossly, caseous necrosis is white and cheesy LM features: the necrotic area is eosinophilic, amorphous, surrounded by activated macrophages (epitheloid cells) which mediate the tissue necrosis and kill the bacteria Enzymatic fat necrosis

• Occurs in pancreatitis, induced by the action of lipases derived from injured pancreatic cells

• Lipases catalyse decomposition of triglycerides to fatty acids, which complex with calcium to create calcium soaps

The swollen pancreas displays several yellowish foci of necrosis Gangrene

• This (mostly) clinical term refers to the severemost forms of necrosis

• Total destruction of all tissue components; often putrefactive bacteria invade the necrotic tissue

• Three types (detailed in Inflammation chapter)

One subtype: dry gangrene

• In the leg of patients suffering from atherosclerosis-related occlusion of the tibial arteries

• The affected tissues appear black because of the deposition of iron sulphide from degraded hemoglobin Dry gangrene of the great toe Fibrinoid necrosis

• Occurs in arteries, arterioles, and capillaries; seen in autoimmune disoders (SLE, arteritis) for example

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

Fibrinoid necrosis of small arteries. The necrotized smooth muscle cells are eosinophilic. Inflammatory cells have infiltrated the periarterial space Apoptosis: programmed cell death

• A form of energy-dependent process for selective deletion of unwanted individual cells

• An internal suicide program becomes activated

• The dead cell’s membrane remain intact

• The dead cell is rapidly cleared by phagocytosis before its content have leaked out; therefore, apoptosis does not induce an inflammatory reaction

Remember! Features of necrosis: loss of membrane integrity, enzymatic digestion of cells, and an inflammatory reaction

Apoptosis

• Prevented or induced by a variety of stimuli

•  Apo contributes to cell accumulation, e.g. neoplasia

•  Apo results in extensive loss, e.g. atrophy Intrinsic (mitochondrial) pathway of apoptosis

Mitochondrion

Bcl-2 inhibits Execution Bax activates caspases

When cells are deprived of survival signals or subjected to stress, anti-apoptotic Bcl-2 protein is replaced by pro-apoptotic Bax protein in the mitochondrial membrane and in turn, the execution caspases become activated Extrinsic (death receptor) pathway of apoptosis

Mitochondrion Execution caspases Bcl-2 , Bax

Death receptors Cytotoxic T-cells If death receptors on the cell surface (TNF-R, FAS-R) cross-link with the ligand, activation of execution caspases occurs. Execution pathway of apoptosis

Bax Execution caspases: cascade of proteolytic enzymes

Death receptors Cytotoxic (TNF, FAS) T-cells • Breakdown of cytoskeleton • Cell shrinkage • Chromatin condensation and fragmentation • Formation of apoptotic bodies Apoptosis of tubular epithelial cells (cell shrinkage, and condensation of nucleus) induced by cytotoxic T- lymphocytes in acute T-cell-mediated rejection of transplanted kidney 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 1. In skeletal muscles due to - disuse as in prolonged bed rest or immobilization of limb for healing of bone fracture - loss of innervation 2. Loss of endocrine stimulation - lack of trophic hormones in pituitary disease 3. Diminished blood supply. Slow but progressive reduction of blood supply leads to renal atrophy or atrophy of the brain 4. Malnutrition. Atrophy of parenchymal organs, skeletal muscles, and general wasting (marasmus) 5. Increased pressure, e.g., hydrocephalus or hydronephrosis Obstruction of the CSF flow leads to pressure atrophy of the brain, with the enlargement of ventricles: hydrocephalus Hydronephrosis: obstruction of the ureter (arrow) leads to sac-like dilation of renal pelvis and calyces, and pressure atrophy of parenchyma Hypertrophy

• An increased cell mass leading to an increased size of organs

• Physiologic: - hypertrophy of uterus in pregnancy, - compensatory hypertrophy of the remnant kidney after unilateral nephrectomy, - exercise

Increased exercise leads to hypertrophy of muscles Hypertrophy

• An increased cell mass leading to an increased size of organs

• Physiologic: ...

• Pathologic: in the muscles

• Muscles are not able to divide, therefore an increased demand for action can be met only by enlarging the size of cells

• Examples: hypertrophy of the myocardium, hypertrophy of the detrusor muscles of urinary bladder 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 urethral obstruction Hyperplasia

• Hormonal stimulation results in an increase in the size of a tissue or organ due to an increased number of constituent cells. The cells may have an increased volume.

• Physiologic: - proliferation of the glandular epithelium of the breast during lactation

Pathologic hyperplasias

- Endometrial hyperplasia, induced by estrogens; clinical feature: bleeding from the uterus between menstrual periods (metrorrhagia)

- Hyperplasia of prostate, induced by dihydrotestosterone, estrogens and peptide growth factors; clinical consequence: urinary tract obstruction

- Bilateral adrenal cortex hyperplasia, induced by increased ACTH secretion; clinical consequence: increased production of corticosteroids leading to the Cushing’s sy

Metaplasia

• Replacement of one adult cell type by another adult cell type; reversible.

• Squamous metaplasia of the bronchus: chronic irritation-induced replacement of bronchial stratified columnar epithelium by squamous epithelium in smokers • Gastric metaplasia of the oesophagus: chronic irritation induced by gastric juices in gastrooeso- phageal reflux leads to the replacement of squamous epithelium by gastric epithelium

• If the adverse circumstances persist, metaplasia may progress to dysplasia (precancerous)

Bronchus: squamous metaplasia (right) Intracellular accumulations

• Lipids - triglycerides, cholesterol • Proteins • Pigments Accumulation of triglycerides

• Most common in the liver, but also occurs in the heart; reversible • Fatty change/steatosis of liver: due to - alcohol abuse - morbid obesity - diabetes - protein-energy malnutrition - hypoxia - hepatotoxins • Biochemical pathways of uptake and metabolism of fatty acids by the liver, formation of triglycerides, and secretions of lipoproteins: not detailed here Steatosis: the liver is enlarged, yellow and greasy, resembles to goose liver

Courtesy of E. Kemény, SZTE Pathology The hepatocytes are vacuolated; representing accumulations of neutral lipids that have been removed by lipid solvents during tissue processing

Frozen section, Oil Red O • In atherosclerosis, cholesterols and cholesterol esters accumulate extra- and intracellularly in the intima of aorta and large arteries and form atheromatous plaques.

Atheromatous plaque: the lipids are dissolved during normal histologic processing The dissolved cholesterol crystals appear as cleftlike cavities Accumulation of lipids in macrophages

In , macrophages phagocytose membrane lipids derived from dead oligodendrocytes and transform into foamy macrophages Accumulation of proteins

Hyaline change: any alteration within cells that imparts a homogeneous, glassy pink appearance in H&E-stained histologic sections

- 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-hyalin 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 • Jaundice (icterus): systemic bilirubin retention; yellow skin and sclera discoloration

• Hemosiderin (brown), hemoglobin-derived intracellular pigment composed of aggregated ferritin, indicates previous hemorrhage. Systemic accumulation: termed hemosiderosis

• Melanin (brown): product of nevus cells Jaundice: yellowish discoloration of skin Pathologic calcification

Abnormal deposition of Ca-salts in soft tissues

Dystrophic • In nonviable or dying tissues; the serum Ca++ level is normal. • Precipitation of a crystalline Ca-phosphate starts with nucleation (initiation) on membrane fragments, followed by propagation of crystal formation. • Very common, with serious clinical consequences

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

Dystrophic calcification of aortic valves (calcifying aortic stenosis) Metastatic calcification

Results from hypercalcemia

• Destruction of bones by myeloma, metastases, • Increased secretion of parathormone in hyperparathyroidism • Etc.

Deposits in the arteries, and at sites of acidification: kidneys, lungs, and stomach Metastatic calcification of arteries in end-stage renal disease

Radial art.

Ulnar art.

Bereczki Csaba, SZTE Pediatrics