Reaction to Injury:Cell Injury,

Renewal & Repair

Rob Edwards, M.D., Ph.D.Department of Pathology and Laboratory Medicine

August 15, 2011

Outline

• The facts behind Pathology rocking…..

• Cellular responses to stress and injury

• Key vocabulary in cell injury

• Morphology of Cell injury and necrosis

• Reading:

Ground Rules for Lecture:

• 1. It’s in the (e-)book. Robbin’s 8th.http://store.vitalsource.com/show/978-1-4160-3121-5

• 2. If we’re not making sense, STOP us!

• 3. If you have a question, see #2

• 4. Come to lab! -Reinforces lecture (game situations)

Why Pathology is the finest of clinical specialties:

• Endlessly challenging (The ABMS 24)• You know every cool case in the hospital• The doctor’s doctor (Read: Pathology is a

consult service)– The 70/70 rule– People skills/communication is key– We tell surgeons what to do all day long…..

• Civilized day-to-day environment• Relatively hard to outsource

Pathology- Subdivisions

• Anatomic (Surgical) Pathology– Biopsies & Cytology (little bits of patient)– Surgicals (larger bits of patient)– Autopsies (the entire patient)– Frozen sections (intraoperative consultation)

• Clinical Pathology– Clinical Chemistry– Blood Bank/Transfusion Medicine– Microbiology/Molecular Diagnostics– Hematology/Flow Cytometry

Principle:

• Injuries occur at the molecular, cellular, tissue, organ, and organismal level

• Integration of responses to injury occur at the cellular level

• SO- We focus on cellular responses

• *Every organ system has a limited repertoire of responses:– Adaptive (maintain homeostasis)– Reversible Injury– Death

Adaptation vs. Reversible vs. Irreversible Injury:

Cellular adaptation to stress

• Hyperplasia– Increased cell number in response to ↑ demand– Reversible if stimulus is removed– Physiologic hyperplasia

• Hormonal (lactational change of the breast)• Compensatory (liver regeneration, wound repair)

– Pathologic Hyperplasia• Excessive hormone/growth factor stimulation (endometrial

hyperplasia – menorrhagia)• BPH – chronic androgenic stimulation• ‘Fertile soil’ for subsequent neoplastic transformation

Cellular adaptations to stress• Hypertrophy:

– Increased cell (& organ) size

– Physiologic:• EXAMPLE: • Skeletal muscle

of Our Governator

• Post-mitotic, respond by hypertrophy

• Each sarcomere can do more work, avoids cellular injury

Physiologic Hypertrophy

1100g; 70 g

Limits of Physiologic Hypertrophy

• Hypertrophy compensates for increased workload up to a point

• Decompensation = Cardiac failure• In cardiac failure:

– Degenerative myocyte changes/fibrosis/cell death

– Mechanism? • Insufficient vascular supply (Ischemia)• Structural alterations of sarcomeres?

Atrophy

• DEF: Shrinkage of cells due to loss of substance, after full development

• Physiologic– Post-partum uterus

• Pathologic– Decreased workload (disuse)– Loss of innervation (skeletal muscle)– Decreased blood supply– Malnutrition/aging/extrinsic compression

Disuse Atrophy:Pathologist Brain Surgeon Brain

Atrophy, Hypoplasia, Aplasia

• Atrophy: Decrease in size after full development

• Hypoplasia: Failure to develop fully

• Aplasia: Failure of primordium to develop

Metaplasia• DEF: Reversible, adaptive change in cell

type in response to stress

• Example:– Squamous metaplasia in smokers’ respiratory

tract 2o to chronic noxious stimuli– Tougher cells, but mucociliary clearance is lost

Barrett’s Metaplasia → Esophageal Cancer:

Ischemic Injury & Hypoxia

• Hypoxia = Reduced O2 availability• Switch to Glycolysis

• Ischemia = Reduced/Inadequate blood flow– Obstruction (atherosclerosis, embolus)– Hypotension

• Blood loss• Sepsis• Blocks nutrient delivery, no ox phos OR glycolysis

Question

– Which condition damages tissue faster, ischemia or hypoxia?

– Why?

Cell Death: Final Common Pathways

• Two main types:– Necrosis :

• Follows from irreversible injury• Always pathologic

– Apoptosis• Pre-programmed cell death• Normal part of development• Removing ‘bad’ cells (immunity, cancer)

Morphology of Necrosis

• Results from denaturation of cell proteins• Eosinophilia due to loss of chromatin, RNA

– (-) charged PO4’s bind hematoxylin

– Acidosis neutralizes these, so loss of blue staining…

• Nuclear changes:• Karyolysis- loss of chromatin’s basophilia• Pyknosis – shrunken, raisin-like nuclei• Karyorrhexis – nuclear fragmentation

Necrosis- Subtypes• Coagulative necrosis

– Preservation of the outline of cells, (everything denatured, including all the “-ases”)

– Loss of basophilia– Characteristic of hypoxic death (except brain)

Necrosis- Subtypes• Liquefactive Necrosis:

– Complete digestion of dead cells into a gelatinous mass

– Seen in bacterial/fungal infections

– If associated with an acute inflammatory response: pus

Necrosis- Subtypes

• Gangrenous necrosis– Not technically a subtype of necrosis– Used in the context of extremities sans blood

supply– Subdivided into dry and wet gangrene

• Dry: coagulative necrosis• Wet: = Dry + bacterial infection; coag+ liquefactive

Necrosis- Subtypes• Caseous Necrosis

– Typically found in the context of TB, fungal infections

– ‘Caseous’ refers to cheesy gross appearance

– Distinct foci compsed of necrotic core surrounded by granulomatous inflammation (Sept. 16, 1-2PM)

Necrosis- Subtypes• Fat necrosis

– Again, not technically a subtype of necrosis

– Localized fat destruction due to acute pancreatitis:

• Activated enzymes autodigest membranes; fatty acids + Ca2+ = chalky deposits

• Also seen in traumatic injury to breast tissue

Apoptosis• DEF: Intentional,

programmed cell death– Tightly regulated– Cell dies from within,

fragments, membrane stays intact

– No cell guts leak out, no inflammatory response

• Eliminates unwanted/potentially harmful, or irreversibly damaged cells

MS1- Physiology PTSD:

• Baldwin- Circulatory Blood Flow

• Longhurst – Heart Failure, AMI

• Longmuir- Hypoxemias

• Vickery- Clotting Cascade

• Refresher: Robbins 111-129 (Shock to be covered specifically in CF2)

Normal Homeostasis vs. Edema

• Changes in any of these can alter homeostasis:– Vessel wall integrity/endothelial function– Intravascular pressure– Intravascular osmolarity– Balance of pro- and anti- clotting mechanisms

DEF of Edema: Excessive water in the interstitial space– Synonyms: hydrothorax, hydroperitoneum (AKA

ascites), anasarca

Categories of Edema:Inflammatory vs. Non-inflammatory

(Exudative vs Transudative)

Inflammatory: increases vascular permeability (More on that on Wednesday…) -Leads to protein rich fluid; = EXUDATE (specific gravity >1.012)

Non inflammatory: due to imbalances in hydrostatic and oncotic pressures-Leads to watery fluid; = TRANSUDATE (specific gravity < 1.012)( edema [protein]/plasma [protein] <0.5 )( Protein conc <2g/100 cc)

Things that lead to non-inflammatory edema:

• Increased hydrostatic pressure (CHF/DVT)

• Decreased plasma oncotic pressure (nephrotic syndrome, cirrhosis)

• Lymphatic obstruction (s/p mastectomy)• Sodium retention (renal insufficiency)

Figure 4.1

Morphology of Edema

Congestion/Hyperemia

Definition: Overfilling of Small Vascular Spaces in a particular tissue

• Hyperemia- Active process due to arterial dilation, increased inflow– Tissue is ‘red’ (arterial)

• Congestion: Passive: impaired venous outflow– Can be systemic (as in CHF),

or local (venous obstruction)– Tissue is ‘blue’ (venous)

Chronic Passive Congestion in CHF

-In CPG, stasis of deoxygenated blood (congestion) lead to hypoxia and cell death.

-OUTCOME: centrilobular coagulative liver necrosis.

-CLINICOPATHOLOGICAL CORRELATE: The ‘nutmeg’ liver

Hemorrhage• Definition: Extravasation of Blood due to

Rupture of Blood Vessels

• Bleeding within a tissue: Hematoma. Range from bruises to fatal)

• Little ‘uns: Petechiae (1-2 mm) – 2o to low platelet counts or function

• Bigger ‘uns: Purpura (3-10 mm) – 2o to trauma, vasculitis

• Big ‘uns: Ecchymoses (>1-2 cm) – 2o to trauma

– Color changes over time, Hb breakdown: Red- Blue- Green-Brown-Yellow

• In body cavities (hemoperitoneum, hemopericardium, hemothorax, hemarthrosis, etc.)

Consequences of Hemorrhage

• Tissue destruction• Jaundice (2° to hemoglobin breakdown)• Anemia• Shock• Death

Hemostasis & Thrombosis• Normal Hemostasis: Gotta keep your blood liquid and clot-free,

UNTIL you need a rapid hemostatic clot at the site of injury!

Thrombosis- Endothelial Cell Injury

• DEF: Inappropriate, pathologic clotting of blood. Risk factors include:

– Endothelial injury (most important)- converts endothelium to prothrombotic state

– Stasis (or turbulent) blood – Anything that alters hemodynamics stresses can affect endothelial cell function.

– Hypercoagulability - Can still have thrombosis w/o endothelial disruption, ‘injury’ can lead to imbalances in coagulation states

Thrombosis-Altered Blood Flow

• Turbulent (non-laminar) blood flow OR Stasis- injures/activates endothelium

• RESULT:– 1) Allows platelet access to vessel wall

– 2) Prevents dilution of activated clotting factors

– 3) Blocks influx of clotting inhibitors

Turbulent flow contributes to thrombosis in coronary arteries, aneurysms, post AMI endocardium, valve disease

Stasis arises in hyperviscosity syndromes, SS anemia.

Thrombosis- Hypercoagulable States

• Less common but still important!• DEF: Any alteration of the coagulation

pathways that predispose to thrombosis• Primary (Genetic)

– Factor V Leiden Q506R (2-10% Caucasians, but carrier freq = 60% in pts with DVT)

• Resistant to Protein C, leads to unchecked coagulation

– Prothrombin G20210A (1-2%) – 3x risk of DVT– Hyperhomocysteinemia – thrombosis AND

atherosclerosis

Thrombosis- Hypercoagulable States

• Acquired Hypercoagulable states:– Prolonged bedrest

– AMI

– Atrial fibrillation

– Tissue damage (surgery, fracture)

– Cancer

– Heparin-Induced Thrombocytopenia- pts develop Ab’s that activate platelets, thrombosis. Rx: Lovenox

-Antiphospholipid syndrome (1o vs. 2o): Anti-cardiolipin Ab’s cause multiple thrombi, miscarriages, valve vegetations

But wait, there’s more!

• Current approach to workup of the patient with established venous thrombosis:

• http://www.uptodate.com/contents/evaluation-of-the-patient-with-established-venous-thrombosis?source=related_link

Arterial Thrombosis

• Caused by thrombogenic atherosclerotic plaques (coronaries, aorta, etc)– These can also embolize to any organ

• Also occur in akinetic segments of heart post-MI– (mural thrombi)

Venous ThrombosisVast majority occur in superficial (saphenous)/deep veins of

leg• Superficial: Congestion, pain, tenderness, rarely

embolize– Predispose to cellulitis, varicose ulcers

• Deep (femoral/popliteal/iliac) At least half are Asymptomatic– RISK OF EMBOLIZATION!

Fates of Thrombi

• Propagation, with vessel obstruction

• Embolization (dislodge and migrate)

• Dissolution (only for young thrombi)

• Organization/Recanalization

Embolism• DEF: Intravascular solid/liquid/gas that is

carried a distance from its origin. • Most are thromboemboli• Other types:

– Fat or bone marrow (trauma)– Air (diving accidents)– Tumor fragments– Amniotic fluid (s/p 1:50K deliveries – 20-40% mortality)

Targets & Sequelae of Embolization

• Lungs (Pulmonary Embolism)

-60-80% are clinically silent

-200,000 deaths per year in the US

-95% from DVT above the knee

-Often multiple/serial

-Where it embolizes depends on size

-Saddle embolus: acute Right heart failure,

(cor pulmonale), circ collapse)

-If ASD/VSD, ‘paradoxical emboli’

Infarction: The wedge on the edge!

DEF: Area of ischemic necrosis 2° to (mostly arterial) vascular occlusion

• 99% of infarcts are secondary to arterial thrombosis or embolization– Rare causes – vasospasm, extrinsic

compression by tumor, edema, torsion,

• Red (hemorrhagic) infarcts arise where:– Venous occlusion – Loose tissue with space for hemorrhage– Dual blood supplies (lung)

• White (anemic) infarcts:– Solid end-organs

Factors Influencing Infarct Severity• Nature of the blood supply

– Liver and lung = dual blood supply, fewer infarcts

– Kidney and spleen: Notsomuch…..

• Rate of vascular occlusion:– Fast = infarct- no time to

compensate/develop collaterals

• Tissue vulnerability to hypoxia (neurons>myocytes >fibroblasts

• Patient’s O2 saturation

Onward to Lab #1……