Pathophysiology of common diseases

In short

Pathophysiology is the study of the functional changes - cellular, tissue and organ-level - that produce the signs, symptoms and laboratory abnormalities of disease. For a Pharm.D graduate it is the bridge between a diagnosis and a drug: you cannot justify an ACE inhibitor in heart failure, an inhaled corticosteroid in asthma or a PPI in reflux unless you know which mechanism the drug interrupts. It is examined in PCI-regulated Pharm.D courses under Pathophysiology (second year) and reappears in Pharmacotherapeutics, Clinical Pharmacy and the project/internship viva. In jobs, it is tested in clinical-pharmacist interviews at Apollo, Fortis, Manipal, AIIMS and CMC Vellore, in medical-affairs and pharmacovigilance roles (Cipla, Sun, IQVIA, Novartis, Parexel) and in GPAT/NIPER-style entrance questions.

Explained

Core concepts: cell injury, inflammation and healing

• Etiology = cause; pathogenesis = the sequence of events from cause to disease; clinical manifestation = the resulting signs, symptoms and lab changes; morphology = structural change.
• Reversible cell injury: ATP depletion → failure of Na⁺/K⁺-ATPase → cellular swelling, ribosome detachment, fatty change. Irreversible: mitochondrial permeability, massive Ca²⁺ influx, membrane and lysosomal rupture.
• Mechanisms of injury: hypoxia/ischaemia, free radicals (reactive oxygen species), chemicals and drugs, infection, immune reactions, genetic and nutritional defects.
• Necrosis (coagulative - MI; caseous - tuberculosis; liquefactive - brain abscess; fat necrosis - pancreatitis) is pathological and inflammatory; apoptosis is programmed, energy-dependent, caspase-mediated and non-inflammatory.
• Acute inflammation: vasodilation → increased permeability → stasis → neutrophil margination, adhesion (selectins, integrins), transmigration, chemotaxis, phagocytosis. Cardinal signs: redness, heat, swelling, pain, loss of function.
• Mediators: histamine and serotonin (immediate permeability), bradykinin and prostaglandins (pain, vasodilation), leukotrienes (bronchoconstriction, chemotaxis), TNF-α, IL-1, IL-6 (fever, acute-phase response), complement C3a/C5a, nitric oxide, platelet-activating factor. Most anti-inflammatory drug targets sit in this list.
• Chronic inflammation: macrophages, lymphocytes, plasma cells; granuloma = epithelioid macrophages + Langhans giant cells, typical of TB, leprosy and sarcoidosis.
• Healing: regeneration (labile tissues) versus repair by fibrosis; granulation tissue → collagen → scar. Delayed by infection, ischaemia, diabetes, corticosteroids, protein and vitamin C deficiency.
• Oedema follows Starling's forces: raised capillary hydrostatic pressure (heart failure), fallen plasma oncotic pressure (nephrotic syndrome, liver disease, kwashiorkor), lymphatic blockage (filariasis - still endemic in parts of India), increased permeability (inflammation).

Cardiovascular disorders

• Hypertension: chronically raised arterial pressure. BP = cardiac output × peripheral resistance; essential (primary) hypertension, about 90-95% of cases, involves overactive sympathetic drive, an overactive renin-angiotensin-aldosterone system (RAAS), sodium and volume retention, endothelial dysfunction with reduced nitric oxide and vascular remodelling. Secondary causes: renal parenchymal and renal artery disease, primary aldosteronism, phaeochromocytoma, thyroid disease, oral contraceptives, NSAIDs, steroids.
• RAAS cascade: low renal perfusion/low Na⁺/β1 stimulation → renin → angiotensinogen to angiotensin I → ACE converts to angiotensin II → vasoconstriction (AT1), aldosterone (Na⁺/water retention), ADH, thirst, cardiac and vascular hypertrophy. Target-organ damage: left ventricular hypertrophy, retinopathy, nephrosclerosis, stroke.
• Atherosclerosis: endothelial injury → LDL entry and oxidation → monocyte recruitment → foam cells → fatty streak → smooth-muscle migration and fibrous cap → atheromatous plaque. Plaque rupture exposes collagen and tissue factor → platelet adhesion/activation → thrombus. Risk factors: LDL, smoking, diabetes, hypertension, obesity, family history; Indians show premature CAD at lower BMI with high triglycerides and low HDL ("Asian Indian phenotype").
• Ischaemic heart disease: stable angina = fixed stenosis, demand-supply mismatch on exertion, relieved by rest. Acute coronary syndromes = plaque rupture with thrombus: unstable angina and NSTEMI (partial occlusion, no ST elevation; troponin raised in NSTEMI), STEMI (complete occlusion, ST elevation, transmural coagulative necrosis). Troponin I/T rises in 3-4 h, peaks about 24 h, stays raised 7-10 days; CK-MB normalises in 2-3 days and is better for re-infarction.
• Heart failure: the heart cannot deliver output adequate to tissue demand at normal filling pressures. Systolic (reduced ejection fraction) - impaired contractility after MI, dilated cardiomyopathy; diastolic (preserved EF) - stiff ventricle, hypertension, LVH. Compensation by Frank-Starling dilation, sympathetic activation, RAAS and remodelling becomes maladaptive: afterload and preload rise, oxygen demand rises, apoptosis and fibrosis progress. Left failure → pulmonary congestion, dyspnoea, orthopnoea, paroxysmal nocturnal dyspnoea; right failure → raised JVP, hepatomegaly, ascites, pedal oedema. BNP/NT-proBNP rises with wall stress.
• Arrhythmias: abnormal impulse generation (enhanced automaticity, ectopic focus) or conduction (re-entry circuit, block). Atrial fibrillation causes stasis in the left atrium and embolic stroke.

Endocrine and metabolic disorders

• Type 1 diabetes: autoimmune T-cell destruction of pancreatic β cells (anti-GAD, IA-2 antibodies) → absolute insulin deficiency → hyperglycaemia, lipolysis, ketogenesis → diabetic ketoacidosis (hyperglycaemia, high anion-gap metabolic acidosis, ketonuria, Kussmaul breathing, dehydration).
• Type 2 diabetes: insulin resistance in muscle, liver and adipose tissue (post-receptor defect in GLUT4 translocation, free fatty acids, adipokines, inflammation) plus progressive β-cell failure; hepatic gluconeogenesis is unrestrained. Chronic complications: microvascular - retinopathy, nephropathy (microalbuminuria → proteinuria → falling GFR), neuropathy, driven by polyol/sorbitol pathway, advanced glycation end-products, protein kinase C and oxidative stress; macrovascular - MI, stroke, peripheral arterial disease; diabetic foot from neuropathy plus ischaemia plus infection. India's burden is very large and rising (ICMR-INDIAB estimated roughly 10 crore adults with diabetes and a larger prediabetic pool - figures are periodically revised).
• Hyperosmolar hyperglycaemic state: very high glucose, profound dehydration, minimal ketosis - typical of elderly type 2 patients.
• Thyroid: hypothyroidism (Hashimoto's autoimmune thyroiditis, iodine deficiency, post-ablation) → low T3/T4, high TSH → fatigue, weight gain, cold intolerance, bradycardia, constipation, dyslipidaemia, myxoedema. Hyperthyroidism (Graves' disease - TSH-receptor stimulating antibodies; toxic nodule) → high T3/T4, suppressed TSH → weight loss, tremor, tachycardia, heat intolerance, exophthalmos in Graves'. Universal salt iodisation under the food safety regulations has cut endemic goitre, but pockets of deficiency remain.
• Metabolic syndrome: central obesity plus two of - raised triglycerides, low HDL, raised BP, raised fasting glucose. Indian cut-offs are lower (waist about ≥90 cm men, ≥80 cm women).
• Thyroid and adrenal extremes: Cushing's syndrome (cortisol excess - truncal obesity, striae, hyperglycaemia, osteoporosis); Addison's disease (cortisol and aldosterone deficiency - hypotension, hyperkalaemia, hyponatraemia, pigmentation).

Respiratory disorders

• Asthma: chronic airway inflammation with reversible obstruction and bronchial hyper-responsiveness. Allergen → IgE on mast cells → early phase (histamine, leukotrienes, prostaglandins) → bronchospasm; late phase (4-8 h) → eosinophils, Th2 cytokines IL-4/IL-5/IL-13 → mucosal oedema, mucus plugging, and over years airway remodelling (basement membrane thickening, smooth-muscle hypertrophy). Triggers: dust mite, pollen, cold air, exercise, NSAIDs/aspirin, beta-blockers, infection, pollution.
• COPD: largely irreversible obstruction from chronic bronchitis (mucus gland hyperplasia, goblet-cell metaplasia, productive cough) and emphysema (alveolar wall destruction, loss of elastic recoil, air trapping, reduced surface area). Neutrophil/macrophage protease-antiprotease imbalance; α1-antitrypsin deficiency in the rare inherited form. In India smoking plus biomass-fuel smoke exposure matters greatly, and COPD affects many non-smoking women.
• Spirometry: FEV1/FVC below 0.70 after bronchodilator defines obstruction; reversibility (FEV1 improvement ≥12% and ≥200 mL) favours asthma.
• Pneumonia: alveolar consolidation with exudate (S. pneumoniae commonest), impairing gas exchange → hypoxaemia. Tuberculosis: inhaled M. tuberculosis → alveolar macrophage infection → cell-mediated (Th1/IFN-γ) response → caseating granuloma; latent infection reactivates with HIV, diabetes, steroids, malnutrition. India runs the National TB Elimination Programme with free drugs, notification being mandatory.

Gastrointestinal, hepatic and renal disorders

• Peptic ulcer: imbalance between aggressive factors (acid, pepsin, H. pylori urease and cytotoxins, NSAIDs blocking protective COX-1 prostaglandins, smoking, stress) and defence (mucus-bicarbonate layer, prostaglandins, mucosal blood flow, epithelial renewal). Duodenal ulcer - high acid, pain relieved by food; gastric ulcer - normal/low acid, pain worsened by food. Complications: bleeding, perforation, outlet obstruction.
• GERD: incompetent lower oesophageal sphincter and delayed clearance → acid reflux → heartburn, oesophagitis, Barrett's metaplasia.
• Cirrhosis: chronic injury (alcohol, hepatitis B/C, non-alcoholic fatty liver) → hepatocyte necrosis → stellate cell activation → fibrosis and regenerative nodules → portal hypertension (varices, splenomegaly, ascites, caput medusae) plus hepatocellular failure (jaundice, hypoalbuminaemia, coagulopathy, hyperammonaemia → hepatic encephalopathy). Reduced first-pass metabolism and low albumin change drug dosing.
• Chronic kidney disease: sustained loss of GFR with nephron loss; hyperfiltration of surviving nephrons → glomerulosclerosis → progression. Diabetes and hypertension are the leading causes in India. Consequences: fluid overload, hyperkalaemia, metabolic acidosis, hyperphosphataemia with low calcitriol → secondary hyperparathyroidism and renal osteodystrophy, erythropoietin deficiency anaemia, uraemia. Staged G1-G5 by eGFR with albuminuria categories.
• Acute kidney injury: prerenal (hypovolaemia, NSAIDs, ACE inhibitors in renal artery stenosis), intrinsic (acute tubular necrosis from ischaemia, aminoglycosides, contrast), postrenal (stones, prostate).

Neurological, haematological, musculoskeletal and infectious

• Stroke: ischaemic (about 80%; thrombosis, embolism from AF, small-vessel disease) with an infarct core and salvageable penumbra - the basis of the thrombolysis window; haemorrhagic (hypertensive bleed, aneurysm rupture) raises intracranial pressure.
• Epilepsy: excessive synchronous neuronal discharge from imbalance of glutamate excitation and GABA inhibition, with ion-channel dysfunction; focal or generalised.
• Parkinson's disease: degeneration of dopaminergic neurons in the substantia nigra pars compacta (Lewy bodies) → striatal dopamine loss → rigidity, bradykinesia, resting tremor, postural instability. Alzheimer's disease: amyloid-β plaques, hyperphosphorylated tau tangles, cholinergic neuron loss.
• Anaemias: iron deficiency (microcytic hypochromic, low ferritin - the commonest in India, especially in women and children), megaloblastic (B12/folate - macrocytic), haemolytic (sickle cell, thalassaemia, G6PD deficiency - all significant in Indian populations), anaemia of CKD (erythropoietin lack).
• Rheumatoid arthritis: autoimmune synovitis - citrullinated antigens, anti-CCP and rheumatoid factor, TNF-α and IL-6 driven pannus → cartilage and bone erosion; symmetrical small-joint involvement with morning stiffness. Osteoarthritis: mechanical cartilage degeneration, osteophytes, no systemic inflammation. Gout: hyperuricaemia → monosodium urate crystals → NLRP3 inflammasome → acute monoarthritis.
• Shock: inadequate tissue perfusion - hypovolaemic (blood/fluid loss), cardiogenic (pump failure), distributive (sepsis, anaphylaxis - vasodilation and leak), obstructive (tamponade, pulmonary embolism); leads to anaerobic metabolism, lactic acidosis, multi-organ failure.
• Sepsis: dysregulated host response to infection with organ dysfunction; cytokine storm, capillary leak, disseminated intravascular coagulation.
• HIV: CD4 T-cell depletion → opportunistic infections (TB, candidiasis, PCP) when CD4 falls, typically below 200 cells/µL.
• Pharm.D relevance of law and practice: Pharm.D is regulated by the Pharmacy Council of India under the Pharmacy Act, 1948 (Pharm.D Regulations, 2008 as amended); medicines are controlled by the Drugs and Cosmetics Act, 1940 with its Rules, 1945 (Schedule H, H1, X); adverse-event reporting goes to the Pharmacovigilance Programme of India (IPC, Ghaziabad); clinical trials follow the New Drugs and Clinical Trials Rules, 2019.

Key points

• Pathogenesis - the ordered sequence from cause to clinical disease; drugs act at one identified step in it.
• Apoptosis vs necrosis - programmed, ATP-requiring, non-inflammatory vs accidental, membrane-rupturing, inflammatory.
• Inflammatory mediators - histamine, bradykinin, prostaglandins, leukotrienes, TNF-α, IL-1/IL-6, complement; they explain NSAID, antihistamine and biologic targets.
• BP equation - BP = CO × PVR; every antihypertensive class lowers one of the two terms.
• RAAS - renin → angiotensin II → vasoconstriction + aldosterone; blocked by ACE inhibitors, ARBs, aldosterone antagonists, renin inhibitors.
• Atherosclerosis - endothelial injury, oxidised LDL, foam cells, fibrous plaque; rupture causes acute coronary syndrome.
• STEMI vs NSTEMI - total vs partial occlusion; troponin confirms necrosis in both NSTEMI and STEMI.
• Heart failure compensation - Starling, sympathetic and RAAS activation initially helps, then worsens remodelling.
• Type 1 vs type 2 diabetes - absolute autoimmune insulin deficiency vs insulin resistance with progressive β-cell failure.
• Diabetic complication pathways - polyol, AGE, PKC and oxidative stress explain retinopathy, nephropathy and neuropathy.
• Asthma vs COPD - eosinophilic, reversible, variable vs neutrophilic, largely irreversible, progressive.
• Peptic ulcer - aggression (acid, H. pylori, NSAIDs) exceeding mucosal defence.
• Portal hypertension - fibrosis raises portal resistance → varices, ascites, splenomegaly, encephalopathy.
• CKD consequences - anaemia, acidosis, hyperkalaemia, bone disease; eGFR drives renal dose adjustment.
• Stroke penumbra - hypoperfused but viable tissue; the reason early reperfusion saves function.
• Shock types - hypovolaemic, cardiogenic, distributive, obstructive; all end in tissue hypoxia and lactic acidosis.
• Autoimmunity markers - anti-CCP/RF in RA, anti-GAD in type 1 diabetes, TSH-receptor antibodies in Graves'.
• Indian epidemiology - premature CAD, high diabetes prevalence, iron-deficiency anaemia, TB and biomass-related COPD dominate practice.

Formulas and examples

Example 1 - MAP and antihypertensive need. A 58-year-old man in a Chennai OPD records 166/96 mmHg.

• Pulse pressure = 166 − 96 = 70 mmHg (wide - stiff large arteries).
• MAP = 96 + (70/3) = 96 + 23.3 = 119.3 mmHg, far above the 70-100 range.
• Interpretation: stage 2 hypertension; raised PVR from vascular remodelling and RAAS activity is the dominant term in BP = CO × PVR, so a RAAS blocker or calcium channel blocker addresses the mechanism.

Example 2 - Cardiac output and ejection fraction in heart failure. Echo shows end-diastolic volume 180 mL, end-systolic volume 117 mL, heart rate 92/min.

• Stroke volume = 180 − 117 = 63 mL.
• EF = 63/180 × 100 = 35% → heart failure with reduced ejection fraction.
• CO = 92 × 63 = 5,796 mL/min = 5.80 L/min (near-normal at rest because tachycardia compensates for the low stroke volume - the Frank-Starling/sympathetic compensation that later becomes harmful).

Example 3 - Diabetic ketoacidosis workup. Na⁺ 131 mEq/L, Cl⁻ 95 mEq/L, HCO₃⁻ 8 mEq/L, glucose 540 mg/dL, BUN 28 mg/dL.

• Anion gap = 131 − (95 + 8) = 131 − 103 = 28 mEq/L → high anion-gap metabolic acidosis from ketoacids.
• Serum osmolality = 2(131) + 540/18 + 28/2.8 = 262 + 30 + 10 = 302 mOsm/kg (raised; osmotic diuresis dehydration).
• Pathophysiology chain: insulin deficiency + glucagon excess → lipolysis → hepatic ketogenesis → acidosis; glycosuria → osmotic diuresis → volume and K⁺ depletion.

Example 4 - Renal function and dose adjustment. Female, 68 years, 52 kg, serum creatinine 2.0 mg/dL.

• CrCl = [(140 − 68) × 52 × 0.85] / (72 × 2.0) = (72 × 52 × 0.85)/144 = 3,182.4/144 = 22.1 mL/min.
• Interpretation: severe reduction (CKD stage G4 range) - renally cleared drugs need dose reduction, and metformin and NSAIDs are inappropriate. Note eGFR equations are estimates; creatinine is lower in low-muscle-mass Indian elderly, so CrCl can be overestimated.

Example 5 - Lipid profile in the Asian Indian phenotype. Total cholesterol 232 mg/dL, HDL-C 32 mg/dL, triglycerides 330 mg/dL.

• LDL-C = 232 − 32 − (330/5) = 232 − 32 − 66 = 134 mg/dL.
• Non-HDL-C = 232 − 32 = 200 mg/dL - a better risk marker here because high TG and low HDL make LDL look falsely reassuring.

Where it is used

• Hospital clinical pharmacy: ward rounds, medication review, renal and hepatic dose adjustment, ADR assessment and discharge counselling at Apollo, Fortis, Manipal, CMC Vellore, AIIMS and PGIMER.
• Medical affairs and medical science liaison roles in Sun Pharma, Cipla, Dr Reddy's, Lupin, Novartis and Abbott - explaining disease mechanism and drug positioning to clinicians.
• Pharmacovigilance and drug safety (IQVIA, Accenture, Parexel, Syneos, Cognizant): causality assessment needs disease-versus-drug differentials, and reports flow to the Pharmacovigilance Programme of India.
• Clinical research and CRO work: writing protocols, inclusion/exclusion criteria and endpoints (HbA1c, FEV1, eGFR, EF) that are chosen from pathophysiology.
• Community pharmacy and chronic-disease counselling: inhaler technique in asthma/COPD, foot care in diabetic neuropathy, salt restriction in hypertension and heart failure.
• Public health programmes: National Programme for Prevention and Control of NCDs, National TB Elimination Programme, Anaemia Mukt Bharat and insulin/antihypertensive supply under Ayushman Bharat health and wellness centres.

Interview questions

• Q: Differentiate necrosis from apoptosis. A: Necrosis is uncontrolled death after severe injury with membrane rupture, cell swelling and inflammation; apoptosis is programmed, caspase-mediated, ATP-dependent single-cell death with cell shrinkage and no inflammation.
• Q: Explain the RAAS and where drugs block it. A: Renin converts angiotensinogen to angiotensin I, ACE converts it to angiotensin II which vasoconstricts and releases aldosterone; aliskiren blocks renin, ACE inhibitors block the converting enzyme, ARBs block the AT1 receptor and spironolactone blocks aldosterone.
• Q: Why does left ventricular failure cause breathlessness on lying flat? A: Recumbency redistributes blood from the legs to the thorax, raising pulmonary capillary pressure in a ventricle that cannot clear the load, so transudation into alveoli worsens - orthopnoea and paroxysmal nocturnal dyspnoea.
• Q: How does plaque rupture lead to myocardial infarction? A: A thin-cap plaque tears, exposing collagen and tissue factor; platelets adhere and a thrombus forms, occluding the artery and causing ischaemic coagulative necrosis of the downstream myocardium.
• Q: What is insulin resistance? A: Normal or raised insulin fails to produce its usual effect - reduced GLUT4-mediated glucose uptake in muscle and fat and unsuppressed hepatic gluconeogenesis - driven by free fatty acids, adipokines and low-grade inflammation of visceral obesity.
• Q: Why do NSAIDs cause peptic ulcers and also precipitate acute kidney injury? A: They inhibit COX-1 prostaglandins that maintain gastric mucus, bicarbonate and mucosal blood flow, and the same prostaglandins maintain renal afferent arteriolar vasodilation, so renal perfusion falls in hypovolaemic or CKD patients.
• Q: Which biomarkers confirm myocardial infarction and in what time course? A: Cardiac troponin I or T rises within 3-4 hours, peaks around 24 hours and remains raised 7-10 days; CK-MB returns to normal in 2-3 days, making it useful to detect re-infarction.
• Q: Distinguish asthma from COPD pathologically. A: Asthma is eosinophilic, IgE-driven, largely reversible airway inflammation with hyper-responsiveness; COPD is neutrophil and macrophage driven with mucus gland hyperplasia and alveolar destruction, giving persistent poorly reversible obstruction.
• Q: Why is anaemia common in chronic kidney disease? A: Damaged peritubular interstitial cells produce less erythropoietin, and uraemia, iron deficiency, inflammation and shortened red-cell survival add to it.
• Q: What is the ischaemic penumbra and why does it matter clinically? A: It is the hypoperfused but still viable brain tissue surrounding the infarct core; it can be salvaged if blood flow is restored early, which is the rationale for thrombolysis and thrombectomy time windows.
• Q: How does cirrhosis alter drug handling? A: Reduced hepatic enzyme mass and blood flow cut first-pass metabolism and clearance, portosystemic shunting raises bioavailability, and low albumin raises the free fraction of highly bound drugs - so doses of hepatically cleared and sedating drugs must be cut.
• Q: A patient has pedal oedema. How do you reason through the mechanism? A: Use Starling's forces - raised hydrostatic pressure suggests heart failure or venous obstruction, low oncotic pressure suggests nephrotic syndrome or liver disease or malnutrition, lymphatic block suggests filariasis or node disease, and increased permeability suggests inflammation or sepsis.

Common mistakes

• Describing symptoms instead of mechanism - exams ask for the pathogenesis sequence, not a clinical picture.
• Treating compensatory responses in heart failure as beneficial throughout, and so missing why beta-blockers and RAAS blockers improve survival.
• Calling type 2 diabetes simply "less insulin" - it is resistance plus progressive β-cell failure, with hyperinsulinaemia early on.
• Confusing DKA with hyperosmolar hyperglycaemic state, or forgetting that total-body potassium is depleted in DKA even when serum K⁺ reads normal or high.
• Mixing up ESR/CRP (non-specific inflammation) with specific markers such as anti-CCP, troponin or BNP.
• Arithmetic and unit slips - using mmol/L in the Friedewald equation written for mg/dL, or omitting the 0.85 female factor in Cockcroft-Gault.
• Assuming eGFR equations are exact; they are estimates and misread renal function in the elderly, the very obese and those with low muscle mass.

Related topics

Pharmacodynamics: how drugs act · Cardiovascular drugs · Drugs for diabetes and thyroid disorders · Antimicrobial drugs · Clinical pharmacokinetics and dose adjustment · Pharmacotherapeutics and clinical laboratory interpretation