Chapter 11 Pathophysiology Textbook
Normal Cellular Environment and Homeostasis
Pathophysiology integrates knowledge of major human body systems and their cellular environments to understand disease processes.
Homeostasis: the body's ability to maintain a stable internal environment (temperature, pH, fluid/electrolyte balance).
Key homeostatic mechanisms strive to maintain optimal fluid and electrolyte balance; include hormonal regulatory systems (e.g., RAAS, ADH, aldosterone) and natriuretic peptides.
Cellular environment characteristics underpinning homeostasis include stable pH, electrolyte concentrations, nutrient supply, waste removal, and intact cell membranes.
Fluid Compartments and Total Body Water (TBW)
TBW is the total amount of water in the body; it varies with age, sex, and hydration status: approximately .
Major fluid compartments:
Intracellular fluid (ICF): inside cells; about two-thirds of TBW; roughly in typical adults.
Extracellular fluid (ECF): outside cells; about one-third of TBW; roughly in typical adults.
Within ECF, two major subcompartments:
Plasma (intravascular) fluid: about of body weight.
Interstitial fluid (IF): about of body weight.
In older adults, TBW decreases (risk of dehydration/electrolyte abnormalities rises with illness or injury).
TBW distribution (conceptual): Plasma + Interstitial Fluid = Extracellular Fluid; Intracellular Fluid separate.
Water movement between compartments is dynamic; turnover is balanced under normal conditions but shifts occur with illness, injury, or fluid losses.
Osmosis, Diffusion, and Mediated Transport
Osmosis: net movement of water through a semipermeable membrane from region of lower solute concentration to higher solute concentration; primary mechanism for water movement across cell membranes.
Osmotic pressure: pressure required to prevent water movement across a semipermeable membrane; depends on particle number/size and membrane permeability.
Semipermeable membranes regulate passage of fluids/solutes; channels may be open or gated; regulation maintains cellular homeostasis.
Diffusion: passive movement of solutes down their concentration gradient (high to low) across membranes.
Mediated transport mechanisms use carrier molecules to move large or charged molecules across membranes; includes:
Carrier-mediated transport: binds solute on one side, changes shape, and releases on the other side.
Facilitated diffusion: passive, down a concentration gradient; faster than simple diffusion but requires no energy.
Active transport: moves substances against a concentration gradient; requires energy.
Important nuance: osmosis involves the solvent (water); diffusion involves solutes; diffusion across membranes is rate-limited by membrane permeability and gradient.
Capillary Exchange and the Starling Forces
Capillary network exchanges fluids/solutes between blood and tissues; nutrition and waste exchange occur at capillary level.
Starling hypothesis defines net filtration across capillaries as: More explicitly, at the capillary wall: where:
$P_{cap}$ = capillary hydrostatic pressure (tends to push fluid out of capillary).
$P_{IF}$ = interstitial hydrostatic pressure.
$\pi_{cap}$ = plasma oncotic (colloid osmotic) pressure (protein-driven pulling fluid into capillary).
$\pi_{IF}$ = interstitial oncotic pressure.
Net movement of fluid at arteriole end favors filtration (fluid leaves capillary); at venous end, reabsorption dominates (fluid returns to capillary).
Capillary permeability affects protein leakage; increased permeability raises interstitial oncotic pressure, promoting edema.
Lymphatic clearance removes excess interstitial fluid; obstruction leads to edema.
Edema: Causes, Mechanisms, and Clinical Manifestations
Edema: accumulation of fluid in interstitial spaces; may be localized or generalized.
Major mechanisms/etiologies based on Starling forces include:
1) Increased capillary hydrostatic pressure (e.g., venous obstruction, fluid overload from heart/renal failure).
2) Decreased plasma oncotic pressure (e.g., hypoalbuminemia from liver disease or malnutrition).
3) Increased capillary permeability (inflammation, burns, trauma).
4) Lymphatic obstruction (surgery, infection, malignancy).Clinical phenomena:
Edema can be pitting (Box 11-2 scales +1 to +4).
Edema can be localized (injury site) or generalized (dependent edema).
Ascites = edema/fluid accumulation in peritoneal cavity.
Volume balance and edema are tied to plasma volume, interstitial fluid, and lymphatic drainage; dehydration/overhydration interplay with edema risk.
Volume-regulatory systems balancing water and sodium include:
Antidiuretic hormone (ADH, vasopressin): promotes water reabsorption in kidneys; triggered by increased plasma osmolality and decreased circulating volume; thirst mechanism also driven by osmolality.
Renin–angiotensin–aldosterone system (RAAS): renin is released with reduced volume/sodium; angiotensin II → aldosterone release → sodium and water reabsorption; increases blood pressure.
Atrial natriuretic peptide (ANP/ANH): promotes sodium and water excretion; counterregulatory to RAAS/ADH to reduce plasma volume.
ADH is regulated by volume and osmoreceptors; volume-sensitive receptors in atria and thoracic vessels influence ADH release; baroreceptors respond to blood pressure changes.
Acid–Base Balance: Buffers, Lungs, Kidneys
pH definition: the negative logarithm of hydrogen ion concentration:
Normal blood pH: approximately (slightly basic).
Acids vs bases:
Acids release hydrogen ions; bases accept hydrogen ions.
Buffer systems maintain pH through reversible reactions; key buffers include:
Bicarbonate buffering:
Carbonic acid (H2CO3) to bicarbonate (HCO3−) ratio is normally about ; at physiologic pH ~7.4, the ratio is maintained.
Protein buffering, particularly intracellular proteins and hemoglobin.
Renal buffering: kidneys reabsorb bicarbonate and excrete hydrogen ions; slower but important for long-term pH control.
Respiratory vs metabolic components:
Respiratory system regulates CO2 (carbonic acid) via ventilation; rapid response.
Renal system regulates bicarbonate (base) and excretion of acids; slower response but essential for chronic balance.
Normal carbonic acid/bicarbonate balance at pH 7.4: ratio ~ 1:20 (H2CO3:HCO3−).
Acid–base disturbances (overview):
Acidosis: pH < 7.35; increased hydrogen ions; can be respiratory (CO2 retention) or metabolic (excess acid or bicarbonate loss).
Alkalosis: pH > 7.45; decreased hydrogen ions; can be respiratory (excess ventilation) or metabolic (base gain or acid loss).
Acute vs compensatory responses:
Respiratory acidosis: primary problem is CO2 retention; kidneys compensate by increasing HCO3− reabsorption and H+ excretion (slower).
Respiratory alkalosis: primary problem is CO2 loss; kidneys compensate by excreting bicarbonate and retaining H+ (slower).
Metabolic acidosis: accumulation of acid or loss of base; compensation via increased ventilation (to exhale CO2). Common causes: lactic acidosis, diabetic ketoacidosis, renal failure, toxins, diarrheal dehydration; treatment targets underlying cause and perfusion.
Metabolic alkalosis: loss of hydrogen ions or excess base; compensation via hypoventilation; volume depletion addressed with isotonic fluids; consider potassium status.
Mixed acid–base disturbances can occur in shock and other complex states; recognition guides management (Box 11-4; Table 11-3).
Blood gas analysis and monitoring:
Blood gas measurements often include arterial blood gas (ABG) for pH and PCO2; end-tidal CO2 (EtCO2) provides indirect CO2 levels and ventilation status; prehospital pH via ABG is not typically performed by paramedics.
Cellular Adaptation, Injury, Aging, and Death
Cells adapt to environment via five major adaptive changes:
Atrophy: decrease in cell size; reversible in some cases. Examples: disuse atrophy (casted limb).
Hypertrophy: increase in cell size (not number); organ enlarges due to increased work demand; can be physiologic (e.g., muscle) or pathologic (e.g., cardiac hypertrophy).
Hyperplasia: increase in cell number; may be normal adaptive mechanism or pathologic (e.g., endometrial hyperplasia).
Metaplasia: change from one differentiated cell type to another better able to withstand adverse conditions (e.g., smoking-induced bronchial metaplasia from ciliated columnar to squamous epithelium).
Dysplasia: abnormal changes in mature cells; often precancerous; not true adaptive change but a hyperplastic/atypical process.
Cellular injury concepts:
Hypoxic injury is most common; due to ischemia, hypoxemia, or toxins (e.g., CO poisoning); prolonged ischemia → infarction.
Free radical injury: reactive oxygen species damage membranes and organelles; aging-related changes linked to free radicals.
Chemical injury: toxins directly or via metabolites; membrane damage; mitochondria disruption.
Infectious injury: pathogens invade and damage cells; host response includes inflammation.
Immunologic injury: excessive or misdirected immune responses cause tissue injury (e.g., hypersensitivity, autoimmunity).
Genetic factors: congenital or acquired genetic defects causing cellular injury or altered metabolism.
Nutritional imbalances: deficits or excesses in essential nutrients leading to cellular injury.
Physical agents: temperature extremes, radiation, mechanical injury, etc.
Cellular injury pathways:
Early injury leads to ATP depletion; failure of Na+/K+ pump, cellular swelling, and acidosis.
Inflammatory response is activated; macrophages phagocytose debris; necrosis may result if injury is not reversible.
Necrosis vs apoptosis: necrosis is uncontrolled cell death due to injury; apoptosis is programmed cell death.
Aging and organ system changes: aging affects immunity, metabolism, and organ function; increased susceptibility to disease with age.
Inflammation and the Immune Response
Inflammation is a protective, local tissue response to injury or infection; aims to remove injurious agents and start tissue repair.
Stages of inflammation can be viewed as three fronts:
1) Cellular response to injury: energy depletion, membrane damage, and release of lysosomal enzymes; cells swell, die if injury persists.
2) Vascular response: vasodilation, increased permeability, exudation, and leukocyte trafficking.
3) Phagocytosis: leukocytes (neutrophils, monocytes/macrophages) ingest pathogens and debris; formation of pus (exudate).Mast cells: release histamine and chemotactic factors upon degranulation, amplifying the inflammatory response.
Inflammation signs: heat, redness, tenderness, swelling, pain; exudates can be serous, fibrinous, purulent, or hemorrhagic depending on fluid type.
Systemic inflammatory response syndrome (SIRS) criteria (for sepsis risk assessment in EMS/ED): two or more of the following:
Temperature >38°C or <36°C
Heart rate >90 bpm
Respiratory rate >20 breaths/min or PaCO2 <32 mm Hg
WBC abnormalities (leukocytosis, leukopenia, or bands)
Hypersensitivity and Immunity
Hypersensitivity reactions classified into four types: I (IgE-mediated), II (tissue-specific), III (immune complex–mediated), IV (cell-mediated).
Immunoglobulin classes:
IgG: predominant in secondary responses; crosses placenta; long-term immunity.
IgM: first antibody produced in response; strong complement activation.
IgA: found in secretions; protects mucosal surfaces.
IgE: mediates immediate hypersensitivity (allergies, anaphylaxis).
IgD: function less well understood.
Blood group antigens (ABO) and Rh factor explain transfusion compatibility; Rh positivity is common (roughly 85% of Americans).
Tissues can mount immune responses (cell-mediated immunity) and humoral immunity (antibodies).
Immune deficiencies can be primary (genetic) or secondary (acquired); infections and aging can suppress immune function.
Vaccination and toxoids: immune protection via immunogens/toxoids; vaccines can prime immune responses to pathogens.
Stress, Neuroendocrine Regulation, and Disease
Stress activates the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, shifting metabolism and immune function.
Catecholamines (epinephrine, norepinephrine) and cortisol regulate many organ systems:
Cardio: increased heart rate and contractility; vasoconstriction in many beds; maintained perfusion of vital organs.
Metabolic: increased glucose production; altered lipid metabolism; immune modulation.
Immune: cortisol generally immunosuppressive; reduced leukocyte migration and dampened inflammatory response in some contexts.
Psychoneuroimmunology studies the interaction among emotional state, CNS, and immune response; stress can influence susceptibility to disease.
Endocrine mediators:
Cortisol (glucocorticoid): broad metabolic effects; anti-inflammatory actions; immunosuppressive effects in chronic stress.
Adrenal medullary hormones: epinephrine/norepinephrine influence cardiovascular and metabolic responses.
Genetics and environment interact in disease risk:
Heredity sets baseline risk; environment (lifestyle, exposures) modifies expression.
Epigenetics: environment can alter gene expression without changing DNA sequence.
Life-course determinants of health (Social Determinants of Health): genes/biology, health behaviors, social environment, physical environment, access to health care.
Aging, gender, and disease prevalence: age-related changes in immunity, metabolism, and organ systems influence disease risk and presentation.
Fluid Balance, Electrolytes, and Their Disorders
Sodium and water balance are tightly linked; water follows osmotic gradients set by sodium changes.
Sodium balance is regulated by aldosterone and the RAAS; aldosterone increases distal tubule reabsorption of Na+ and excretion of K+.
Renin is secreted when blood volume is reduced or sodium balance disrupted; renin converts angiotensinogen to angiotensin I, subsequently converted to angiotensin II by ACE; angiotensin II constricts vessels and stimulates aldosterone release, increasing Na+ and water reabsorption and raising blood pressure.
Atrial natriuretic peptide (ANP) promotes renal Na+ excretion and reduces extracellular volume.
Antidiuretic hormone (ADH) promotes water reabsorption in renal collecting ducts; ADH release is triggered by increased plasma osmolality or decreased circulating volume.
Water balance disorders:
Isotonic dehydration: loss of water and sodium in equal amounts; treatment with isotonic saline or LR.
Hypernatremic dehydration: loss of water exceeds Na+; treatment begins with isotonic fluids; rehydration is often slower to prevent cerebral edema.
Hyponatremic dehydration: loss of Na+ exceeds water; treatment with IV fluids (NS or LR) and careful correction to avoid osmotic demyelination.
Overhydration: water excess leading to dilutional hyponatremia; management depends on cause (diuretics, fluid restriction, sodium management).
Electrolyte imbalances discussed include potassium, calcium, magnesium, phosphate, and their fluid/electrolyte dynamics.
Potassium: major intracellular cation; tight regulation is essential for neuromuscular function and cardiac conduction.
Hypokalemia: often due to diuretics; signs include malaise, weakness, arrhythmias; treatment involves potassium replacement; caution with digoxin use.
Hyperkalemia: can cause dangerous ECG changes and arrhythmias; treatment includes shift K+ into cells (glucose + insulin, nebulized albuterol, bicarbonate) and calcium to stabilize myocardium; definitive management may require dialysis.
Calcium: essential for neuromuscular function and cardiac conduction; hypocalcemia presents with paresthesias, tetany, seizures; hypercalcemia may cause weakness, arrhythmias, renal stones; treatment targets underlying cause and hydration; calcium and vitamin D management may be used.
Magnesium: important cofactor; hypomagnesemia causes neuromuscular hyperreactivity; severe cases treated with IV magnesium; hypermagnesemia treated with dialysis.
Acid–base disturbances can coexist with electrolyte disorders and shocks; management includes addressing underlying causes, ventilation, and perfusion status.
Hypoperfusion, Shock, and MODS
Hypoperfusion: decreased circulation leading to insufficient tissue oxygen delivery; may progress to shock and MODS if prolonged.
Shock types (brief classifications):
Hypovolemic shock: from hemorrhage or dehydration; reduced circulating volume.
Cardiogenic shock: heart cannot pump effectively despite adequate blood volume.
Neurogenic shock: loss of sympathetic vascular tone due to spinal injury.
Obstructive shock: obstruction to blood flow into or out of the heart (e.g., tamponade, tension pneumothorax).
Distributive shock: systemic vasodilation (e.g., septic or anaphylactic shock).
MODS (multiple organ dysfunction syndrome): progressive failure of two or more organ systems after severe illness/injury; severe septic shock is a common cause.
Compensatory mechanisms to maintain perfusion in shock include baroreceptor and chemoreceptor reflexes, CNS ischemic response, hormonal responses (RAAS, vasopressin/ADH), tissue fluid reabsorption, and splenic blood release.
Baroreceptors regulate blood pressure via autonomic reflexes; they adapt to chronic changes over days and are not long-term regulators of blood pressure.
Quick SOFA (qSOFA) and SOFA scores are used to assess organ dysfunction/sepsis risk in clinical settings; qSOFA uses three criteria (low BP, high RR, altered mental status) and has limitations in sensitivity in prehospital care.
Endpoints for prehospital assessment include end-tidal CO2 (EtCO2) as a surrogate for perfusion and ventilation status.
Immunology, Inflammation, and Immunodeficiencies
The immune system comprises innate (nonspecific) and adaptive (specific) components. Inflammation is the immediate, nonspecific response; the immune system provides targeted, specific responses.
Immune responses can be protective but may become dysregulated (hypersensitivity, autoimmunity, isoimmunity).
Acquired immune deficiencies (secondary) can arise from nutrition, infection (e.g., HIV/AIDS), stress, medical treatments, or other illness; primary immune deficiencies are genetic.
Immunoglobulin classes and roles (Box 11-10):
IgG: most abundant; crosses placenta; secondary response.
IgM: first produced; strong complement activation.
IgA: mucosal defense; found in secretions.
IgE: mediates immediate hypersensitivity and anaphylaxis.
IgD: function less defined.
Blood groups and transfusion compatibility: ABO system and Rh factor; Type O negative often called universal donor (recipient compatibility caveats apply); low-titer group O whole blood use in trauma/transfusion protocols.
Hypersensitivity and antigens:
An antigen is any substance capable of triggering an immune response; an immunogen is an antigen that can provoke antibody formation.
Antigen exposure leads to lymphocyte activation and formation of plasma cells (antibodies) and sensitized T cells.
Vaccination and immune memory: active immunization trains immune system to respond to future exposures.
Inflammation and immune responses can be triggered by stress and may interact with endocrine responses (e.g., cortisol modulates immune activity).
Delayed-type hypersensitivity (cell-mediated): takes hours to days; example: graft rejection, poison ivy contact.
Infectious Agents: Viruses, Bacteria, and Toxins
Bacteria and viruses employ diverse strategies to cause disease; toxins (exotoxins and endotoxins) contribute to pathophysiology.
Exotoxins: secreted toxins (e.g., diphtheria, botulinum, cholera); often protein-based and highly toxic.
Endotoxins: part of gram-negative bacterial cell walls; released upon lysis; potent inflammatory triggers; vaccines typically target exotoxins rather than endotoxins.
The complement system is part of the innate immune response that coats bacteria, enhances phagocytosis, and modulates inflammation.
Leukocytes (neutrophils, macrophages) and the reticuloendothelial system clear debris and dead cells; pus formation is a consequence of these processes.
Fever is mediated by endogenous pyrogens released by macrophages and other immune cells during infection/inflammation.
RNA and DNA viruses rely on host cells for replication; viruses can cause both lytic and non-lytic infections; the immune response to viruses is predominantly cell-mediated.
Coronaviruses and other emerging pathogens highlight the role of vaccines and public health measures in infection control (COVID-19 context noted).
Aging and Genetic Factors in Disease
Genetics and environment interplay shapes disease risk; heritable predispositions interact with lifestyle, environment, and socioeconomic factors.
Epigenetics describes how environmental factors can change gene expression without altering DNA sequence.
Common familial diseases (e.g., CAD, hypertension, cancer) often have polygenic influences and interacting risk factors.
Social determinants of health (SDOH) influence disease burden and access to care; examples include biology/age, health behaviors, social environment, physical environment, and health care access.
Aging is associated with decreased immunity, altered metabolism, and greater susceptibility to infection and chronic disease; age/gender influence disease risk and presentation.
Practical Clinical Pearls and Key Terms (Selected)
Box 11-1 Fluid Replacement Therapy: IV therapy options include hypotonic, isotonic, and hypertonic solutions; examples: 0.9% NaCl (NS), Lactated Ringer's (LR), 5% dextrose in water (D5W acts as hypotonic), 3% NaCl, D50, D10; caution with hypertonic saline in trauma.
Box 11-2 Pitting Edema Scale: +1 to +4 gradations describing pit depth and return time.
Box 11-3 pH Values (illustrative): a table showing pH scale from highly acidic to highly basic.
Box 11-4 Acid–Base Determination: blood gas analysis basics; ABG interpretation involves pH and PCO2; ABG is typically arterial; respirator status influences PCO2; ABG supplements (ETCO2) used for noninvasive monitoring.
Box 11-7 Baroreceptor Responses: reflex pathways that regulate blood pressure via parasympathetic and sympathetic outputs; adaptation over time.
Box 11-8 Common Etiologic Classifications of Shock: hypovolemic, cardiogenic, obstructive, distributive, including anaphylactic and septic shock; MODS can follow prolonged shock.
Box 11-10 Immunoglobulins: IgG, IgM, IgA, IgE, IgD with primary roles described.
Box 11-11 Replacement Therapies for Immune Deficiencies: IVIG, transplantation, blood products, biologic therapy.
Box 11-12 Acquired Immune Deficiency Disorders: lists conditions that contribute to immune compromise.
Box 11-13 Environmental Influence in Genetic Selection: sickle cell trait example and malaria resistance illustrating gene–environment interaction.
Box 11-21 Blood group ABO visualization: A, B, AB, O with receptor/antibody interactions.
Box 11-22 SIRS and Sepsis references: Sepsis definitions and scoring context in clinical practice.
// Equations used in the notes (LaTeX):
pH definition:
Carbonic acid–bicarbonate buffering (simplified):
Bicarbonate ratio at normal pH (approximately):
Net filtration pressure (Starling):
General form for net filtration (textual):
"Note: The notes above summarize and organize the content provided in the transcript into a structured, study-ready format with key definitions, mechanisms, and illustrative formulas. Where specific page references or BOX/FIGURE labels appeared in the transcript, they are paraphrased here to preserve essential concepts for exam preparation."