Untitled
Summary: Immune system disorders arise from three main mechanisms: excessive response (hypersensitivity), misdirected attack on self-tissue (autoimmunity), or insufficient response (immunodeficiency). Additionally, the immune system can react to genetically different antigens from other individuals (isoimmunity). Understanding these mechanisms is crucial for diagnosing and treating a wide range of conditions.
Immune System Disorders
Immune system disorders manifest in three primary ways:
1. Excessive Response: Produces hypersensitivity reactions.
2. Misdirected Response: Causes the immune system to attack the body's own tissues, leading to autoimmune diseases.
3. Insufficient Response: Leaves the patient vulnerable to infection, resulting in immunodeficiency.
Hypersensitivity (Excessive Response)
Hypersensitivity is an excessive immune response to a relatively harmless antigen, causing inflammation and tissue damage instead of protection.
Mechanism of Hypersensitivity
• Initial Exposure: Patient exposed to an antigen; the immune system becomes sensitized.
• Later Exposure: Re-exposure triggers a damaging immune response.
Classification
Hypersensitivity reactions are classified by:
• Speed of development.
• Causative mechanism (e.g., antibodies or T cells).
Immediate Hypersensitivity
• Mediators: Caused by antibodies (specifically IgE).
• Mechanism:
• Allergy: Excessive immune response to a normally harmless environmental antigen (allergen), e.g., pollen, dust mites, certain foods.
• First Exposure (Sensitization):
1. Allergen enters the body.
2. B cells activate, differentiate into plasma cells.
3. Plasma cells produce allergen-specific IgE antibodies.
4. IgE antibodies attach to receptors on mast cells (and circulating basophils).
5. Mast cells become sensitized and store inflammatory mediators (like histamine) in granules, preparing for re-exposure.
• Later Exposure (Re-exposure & Reaction):
1. Same allergen re-enters the body.
2. Allergen binds to IgE antibodies already attached to mast cells.
3. This triggers mast cell degranulation, rapidly releasing histamine and other inflammatory mediators.
• Effects of Histamine:
• Vasodilation: Widens blood vessels.
• Increased Capillary Permeability: Makes vessels leaky, leading to swelling (edema).
• Increased Mucus Production:
• Bronchoconstriction: Contraction of smooth muscles around bronchioles, narrowing airways (can contribute to allergic asthma).
• Symptoms: Running nose, swelling, itching, watery eyes, congestion, redness.
• Treatment: Antihistamines block histamine effects, reducing symptoms.
• Types of Reactions:
• Local Reactions: Limited to one area (e.g., skin rash, allergic rhinitis, asthma, food allergy gastrointestinal symptoms).
• Systemic Reactions: Affect multiple organs throughout the body; can develop into anaphylaxis.
• Anaphylaxis: Rapid, severe, systemic allergic reaction (e.g., insect stings, food, medications, latex).
• Widespread mast cell degranulation releases large amounts of mediators.
• Respiratory: Bronchoconstriction, increased mucus, upper airway swelling (difficulty breathing).
• Cardiovascular: Widespread vasodilation, increased capillary permeability leads to fluid leaving bloodstream, decreased circulating blood volume, falling blood pressure.
• Can cause anaphylactic shock (circulatory failure).
• Treatment: Epinephrine (given intramuscularly, e.g., EpiPen). It constricts blood vessels, raises blood pressure, relaxes bronchial smooth muscles, and reduces airway swelling. Anaphylaxis is a medical emergency requiring emergency assistance after epinephrine.
Delayed Hypersensitivity
• Mediators: Caused by T cells (cell-mediated immunity), not antibodies.
• Mechanism:
• First Exposure: Antigen sensitizes specific T cells.
• Later Exposure: Memory T cells recognize the antigen and release inflammatory signals (cytokines).
• Cytokines recruit and activate other immune cells (e.g., macrophages and other antigen-presenting cells), leading to inflammation and tissue injury. Some reactions involve cytotoxic T cells directly destroying cells.
• Timeline: Symptoms appear 24 to 72 hours after re-exposure because cell recruitment takes time.
• Examples:
• Allergic Contact Dermatitis: Skin inflammation from contact allergens (e.g., poison ivy chemical urushiol, nickel, certain chemicals). Haptens bind to skin proteins, forming new antigens recognized by T cells.
• Tuberculosis (TB) Skin Test: Small amount of TB agent injected. If previously exposed, memory T cells cause local swelling/induration within 48-72 hours.
Autoimmunity (Misdirected Response)
Autoimmunity occurs when the immune system loses self-tolerance and mistakenly recognizes the body's own molecules (self-antigens) as foreign, leading to an attack on healthy tissues.
Mechanism
• Molecular Mimicry: Sometimes, a microbial antigen resembles a molecule in the body's own tissues. The immune response against the microorganism can then cross-react with self-tissue.
• Tissue Damage: Caused by autoantibodies (bind to self-antigens) or auto-reactive T cells (directly damage cells or promote inflammation).
• Distinction from Allergy: Allergy targets harmless external antigens; autoimmunity targets the body's own self-antigens.
Examples of Autoimmune Diseases
1. Rheumatoid Arthritis:
• Target: Primarily synovial lining of joints.
• Mechanism: Persistent inflammation damages cartilage and bone.
• Symptoms: Painful, swollen, stiff joints (often symmetrical, affecting both sides of the body), reduced movement, prolonged morning stiffness, deformity (e.g., ulnar deviation of fingers).
2. Myasthenia Gravis:
• Target: Neuromuscular junction (impairs nerve-muscle connection).
• Mechanism: Autoantibodies block or destroy acetylcholine receptors on muscle cells, weakening the signal from nerve to muscle.
• Symptoms: Muscle weakness that worsens with activity and improves with rest (fatiguable muscle weakness); drooping eyelids (ptosis), double vision, difficulty speaking, chewing, or swallowing. Respiratory muscle weakness can lead to myasthenic crisis (medical emergency).
3. Multiple Sclerosis (MS):
• Target: Myelin in the central nervous system (brain, spinal cord, optic nerves).
• Mechanism: Immune cells attack myelin, causing demyelination and scar tissue formation (sclerosis). This slows or interrupts nerve impulse conduction.
• Symptoms: Vision problems, numbness, weakness, poor balance, difficulty walking, muscle stiffness.
4. Graves' Disease:
• Target: Thyroid gland.
• Mechanism: Autoantibodies bind to TSH (Thyroid Stimulating Hormone) receptors on thyroid cells, continuously stimulating the thyroid to produce excessive thyroid hormones (hyperthyroidism).
• Symptoms: Increased metabolic activity, weight loss (despite increased appetite), heat intolerance, sweating, tremors, anxiety, rapid heart rate, goiter (enlarged thyroid), exophthalmos (bulging eyes due to inflammation/tissue expansion behind eyes).
5. Type 1 Diabetes Mellitus:
• Target: Pancreatic beta cells (insulin-producing cells).
• Mechanism: Immune system destroys beta cells.
6. Systemic Lupus Erythematosus (SLE):
• Target: Multiple organs and tissues (systemic).
• Mechanism: Immune system produces autoantibodies against components of the body's own cells (e.g., nuclear material). These combine with antigens to form immune complexes that deposit in tissues, causing inflammation.
• Symptoms: Highly variable; characteristic malar rash (butterfly-shaped rash across cheeks and nose), photosensitivity (rashes triggered by sunlight), affects joints, kidneys (glomerulonephritis), heart, lungs, and nervous system.
7. Glomerulonephritis (some forms):
• Target: Kidney glomeruli (filtering structures).
• Mechanism: Immune-mediated damage (antibodies or immune complexes) to glomeruli, leading to blood and protein leaking into urine.
Treatment of Autoimmune Diseases
Aims to reduce the immune attack while preserving normal immune protection.
• Immunosuppression:
• Anti-inflammatory drugs (e.g., corticosteroids) reduce inflammation and symptoms.
• Targeted Therapies:
• Blocking co-stimulatory molecules: Reduces T cell activation (e.g., abatacept for rheumatoid arthritis).
• Activating regulatory T cells: Suppress inappropriate immune responses.
• Directing antibodies against reactive immune cells: e.g., rituximab targets B cells in some autoimmune conditions.
• Treatment choice depends on the specific disease, organs involved, and disease severity.
Isoimmunity (Alloimmunity)
Isoimmunity (or alloimmunity) occurs when the immune system reacts to genetically different antigens from another person of the same species. It is a normal immune response correctly recognizing foreign antigens, but the reaction is generally harmful.
Examples
1. RhD Incompatibility (during pregnancy):
• Rh-negative mother carries an Rh-positive fetus.
• During pregnancy or delivery, maternal exposure to fetal Rh antigens sensitizes the mother, producing anti-RhD IgG antibodies.
• In subsequent Rh-positive pregnancies, maternal IgG antibodies can cross the placenta and destroy fetal red blood cells, causing hemolytic disease of the fetus and newborn.
2. Transplant Rejection:
• Allograft: Organ or tissue transplant from one person to another (same species).
• Recipient's immune system recognizes donor's HLA (Human Leukocyte Antigen) markers (also called MHC - Major Histocompatibility Complex) and other antigens as foreign.
• To Reduce Rejection Risk:
• ABO blood group compatibility matching.
• Matching HLA markers as closely as possible (these act as identification markers on cell surfaces).
• Immunosuppressive therapy: Patients require long-term immunosuppression post-surgery to prevent rejection, even with a close match. This increases the patient's susceptibility to infection.
Immunodeficiency (Insufficient Response)
Immunodeficiency occurs when the immune response is too weak, leaving the patient vulnerable to infection.
• Types:
• Congenital: Resulting from genetic abnormalities present at birth (e.g., Severe Combined Immunodeficiency - SCID).
• Acquired: Developed later in life (e.g., AIDS).
Cardiovascular System Disorders & Diagnostics
This document provides comprehensive notes on various cardiovascular disorders, including vessel, myocardial, inflammatory, and congenital defects, alongside diagnostic tests and treatments. Key takeaways cover the mechanisms of common conditions like varicose veins, heart attack (myocardial infarction), heart failure, and shock, emphasizing the structural and functional issues in the heart and blood vessels. Diagnostic tools range from imaging (echocardiogram, CT scan) to electrical activity monitoring (ECG) and stress tests, while treatments like angioplasty address blockages.
I. Cardiovascular Vessel Disorders
Varicose Veins
Definition: Veins in which walls preventing backflow of blood are not working properly.
Mechanism: Blood flows backward due to improper valve closure, pooling at the site, increasing venous blood pressure, causing veins to dilate and enlarge.
Cause: Incompetent venous valves, often influenced by gravity (blood traveling against gravity from legs to heart).
Appearance: Twisted, bulging veins, especially in lower extremities.
Distinction from Thrombophlebitis: Varicose veins are a wall malfunction; no blood clot is present.
Thrombophlebitis
Definition: Inflammation of a vein caused by a thrombosis (blood clot).
II. Myocardial Disorders
Myocardial Infarction (MI) - Heart Attack
Definition: Death of myocardial (heart muscle) tissue due to interrupted blood supply.
Terminology:
Myo: muscles
Cardial: heart
Infarction: death of tissue due to interrupted blood supply.
Mechanism:
Affected artery (e.g., coronary artery) has a block, not flowing blood normally.
Heart receives insufficient blood, oxygen (hypoxia), nutrients, and metabolites.
Lack of blood flow is ischemia.
If ischemia is severe or prolonged, myocardial cells begin to die.
Cause: Often due to a significantly blocked coronary artery (e.g., atherosclerotic plaque disrupted, blood clot forms).
Angina Pectoris
Definition: Chest discomfort (pressure, squeezing, heaviness, or pain) caused by temporary or reversible myocardial ischemia.
Key Words: Temporary and reversible.
Mechanism:
Coronary artery narrowed by atherosclerosis.
At rest, blood supply may be adequate.
During exercise (increased heart workload, increased heart rate, increased oxygen demand), narrowed artery cannot supply enough oxygen.
Myocardial cells become hypoxic, relying on anaerobic metabolism, leading to accumulation of lactate and hydrogen ions, which stimulate pain.
Distinction from MI:
Angina: Ischemia is temporary and reversible; myocardial cells are stressed but not irreversibly damaged. Pain resolves with rest.
MI: Ischemia is severe or prolonged, leading to myocardial cell death.
Congestive Heart Failure (CHF)
Definition: Heart is unable to pump enough blood to meet the body's metabolic needs; one ventricle is not as efficient as the other.
Mechanism:
Inefficient forward pumping by a ventricle causes blood to back up behind it.
Pressure increases in vessels behind the failing ventricle.
Increased pressure pushes fluid out of blood vessels into surrounding tissues, causing edema (fluid accumulation).
Types of CHF:
Left-Side Heart Failure
Cause: Defect in the left ventricle (receives blood from lungs, pumps to body).
Result: Blood backs up into the lungs.
Edema Type: Pulmonary edema (fluid in pulmonary tissue/alveolar spaces).
Symptoms: Difficulty breathing (dyspnea), shortness of breath.
Right-Side Heart Failure
Cause: Defect in the right ventricle (receives blood from body, pumps to lungs).
Result: Blood backs up in the systemic venous circulation.
Edema Type: Systemic edema (fluid in body tissues).
Symptoms: Swelling of feet, ankles, and legs.
III. Shock
Definition: Life-threatening condition where the body's tissues are not receiving enough blood flow to meet their metabolic needs, leading to cell hypoxia and organ malfunction.
Affected Organs: Brain, kidneys, heart.
Categories of Shock:
Cardiogenic Shock: Heart (the pump) fails to pump enough blood.
Hypovolemic Shock: Insufficient circulating blood volume (e.g., severe bleeding, major fluid loss).
Septic Shock: Severe infection causes major circulatory abnormalities, including widespread vasodilation.
Neurogenic Shock: Loss of sympathetic vascular tone causes widespread vasodilation, leading to falling vascular resistance and blood pressure.
IV. Inflammatory Cardiac Disorders
Suffix "-itis" denotes inflammation.
Endocarditis: Inflammation of the endocardium (inner lining of the heart, including valve surfaces).
Myocarditis: Inflammation of the myocardium (heart muscle layer responsible for contraction).
Effect: Weakens contraction, disturbs heart's electrical activity.
Pericarditis: Inflammation of the pericardium (sac surrounding the heart).
Symptoms: Sharp chest pain (worsens with deep breathing/lying flat, improves by sitting up/leaning forward).
Complication: Pericardial effusion (fluid accumulation in pericardial space) can lead to cardiac tamponade.
V. Congenital Heart Defects
Definition: Structural defects present at birth due to malformation during gestation.
Fetal vs. Adult Circulation:
Fetal lungs are non-functional for gas exchange.
Blood bypasses lungs via special pathways, notably the ductus arteriosus, connecting the pulmonary artery to the aorta.
After birth, the ductus arteriosus normally closes.
Specific Defects:
Patent Ductus Arteriosus (PDA): Ductus arteriosus remains open after birth (incomplete closure).
Atrial Septal Defect (ASD): A hole in the septum dividing the right and left atria.
Ventricular Septal Defect (VSD): A hole in the septum dividing the right and left ventricles (often superior part of interventricular septum fails to form). Blood typically shunts from the stronger left ventricle to the right. Occurs in about 1 in 500 births.
Coarctation of the Aorta: Narrowing of a portion of the aorta, increasing workload for the left ventricle due to increased resistance to blood flow. Occurs in about 1 in 1500 births.
Tetralogy of Fallot (TOF): A combination of four defects:
Pulmonary valve stenosis: Narrowing of the pulmonary outflow tract.
Right ventricular hypertrophy: Thickening of the right ventricle muscle due to increased workload from stenosis.
Ventricular Septal Defect (VSD): Opening between the right and left ventricles.
Overriding aorta: Aorta positioned to receive blood from both ventricles (displaced over the VSD).
Clinical Impact: Results in less oxygenated blood to tissues, potentially causing cyanosis (bluish discoloration). Occurs in about 1 in 2000 births.
Congenital Valve Disorders:
Stenosis: Narrowed valves.
Atresia: Valve lacks a hole for blood flow.
Regurgitation: Valve does not close tightly, allowing backflow.
VI. Additional Cardiovascular Disorders
Cardiac Tamponade
Definition: Buildup of excessive fluid within the pericardium (sac surrounding the heart).
Mechanism: Pericardium has limited expansion ability; accumulating fluid compresses the heart, impairing its ability to fill properly during diastole.
Consequences: Decreased ventricular filling, stroke volume, and cardiac output.
Rheumatic Heart Disease
Cause: Complication of rheumatic fever, typically following a bacterial infection (e.g., Streptococcus pyogenes or "strep throat").
Mechanism: Body's immune response to infection causes reactive inflammation of heart tissues (carditis).
Consequences: Repeated or severe inflammation leads to scarring and permanent damage to heart valves (most commonly the mitral valve), resulting in valve stenosis (doesn't open properly) or insufficiency (doesn't close tightly).
VII. Diagnostic Tests for Heart & Vessel Disorders
These tests assess heart physiology, structure, electrical activity, and blood flow.
Echocardiography (Echo)
Method: Uses sound waves to create a picture of the heart.
Information: Visualizes heart movement, chambers, walls, and valve function; assesses cardiac function.
Electrocardiography (ECG/EKG)
Method: Records the heart's electrical activity.
Information: Detects abnormal heart rates/rhythms and heart damage.
Heart CT Scan (Computed Tomography)
Method: Uses X-rays and computer processing to create detailed cross-sectional (3D) images.
Information: Provides detailed anatomy of the heart and blood vessels, including coronary arteries (calcification, atheroma).
Nuclear Heart Scan
Method: Administers a small amount of radioactive tracer; a special camera detects its travel.
Information: Shows blood flow to the heart muscle.
VIII. Diagnostic Tests for Intermittent/Stress-Induced Problems
Holter Monitor
Method: Wearable device with electrodes that continuously monitors heart rhythm during everyday activity for an extended period (e.g., 24-48 hours).
Information: Detects intermittent arrhythmias or symptoms not caught by a standard ECG.
Stress Test
Method: Monitors heart's electrical activity (ECG), blood pressure, and heart rate while the patient exercises (treadmill or stationary bicycle).
Information: Assesses heart function under increased workload, revealing myocardial ischemia that might not be apparent at rest (e.g., in narrowed coronary arteries).
IX. Normal & Abnormal ECG Tracing
Normal ECG Waves:
P wave: Atrial depolarization (electrical activation and contraction of atria, initiated by SA node).
QRS complex: Ventricular depolarization (electrical activation and contraction of ventricles; atrial repolarization is hidden within this complex).
T wave: Ventricular repolarization (electrical recovery of ventricles before the next beat).
Abnormal ECG Tracings:
Junctional Rhythm: SA node is non-functional; P wave is absent. AV node takes over as pacemaker (rate of 40-60 beats per minute).
Second-Degree Heart Block: Some P waves are not conducted through the AV node, resulting in more P waves than QRS complexes (e.g., 2:1 ratio).
Ventricular Fibrillation (V-fib): Grossly irregular ECG deflections; chaotic, disorganized electrical activity in the ventricles. No identifiable P waves, QRS complexes, or T waves. Prevents effective ventricular contraction, often seen in acute heart attack or electrical shock.
X. Diagnostic Tests for Blood Vessels
Cardiac Catheterization
Method: A catheter is threaded into a vessel (e.g., in the leg) to the heart. Contrast dye is injected, and its movement through heart chambers and coronary arteries is monitored by X-ray.
Information: Visualizes vessel blockages (e.g., 95% stenosis in the Left Anterior Descending (LAD) artery).
CT Angiography: Non-invasive coronary angiography using CT.
Ultrasound: Imaging technique using sound waves to visualize internal structures.
Venography: Contrast dye injected into a vein; X-ray monitors dye movement.
XI. Treatments for Blocked Coronary Arteries
Angioplasty
Method: A thin catheter with a small balloon is guided to the blocked coronary artery. The balloon is inflated to expand the narrow area, compressing plaque against the vessel wall to widen the lumen.
Goal: Restore adequate blood flow to the heart.
Stent Placement
Method: A small, expandable mesh-like tube (scaffold) is deployed after angioplasty to keep the vessel open and prevent re-narrowing.
XII. Degenerative Changes in the Cardiovascular System
Atherosclerosis: Often begins in adulthood, leading to blockages in critical arteries.
Prevention/Delay: Lifestyle factors significantly impact progression:
Regular exercise (thickens myocardium, increases blood vessel supply).
Healthy diet.
No smoking.