The cardiovascular system centers on the heart and blood vessels. Arteries carry oxygenated blood away from the heart (except the pulmonary arteries) under high pressure and have thick muscular walls, while veins return deoxygenated blood to the heart under lower pressure with valves that prevent backflow. Coronary artery disease (CAD), caused by atherosclerotic plaque narrowing the coronary arteries, can lead to angina, heart attacks, or heart failure. A heart attack (myocardial infarction) occurs when a clot blocks a coronary artery, causing heart tissue to die; symptoms include chest pain or pressure, shortness of breath, nausea, and pain radiating to the arm or jaw. Cardiac arrest, by contrast, is an electrical problem in which the heart suddenly stops beating and requires immediate CPR and defibrillation. Heart failure is a chronic condition where the heart cannot pump adequately to meet body needs, producing shortness of breath, fatigue, and swelling.
Common cardiovascular conditions include atrial fibrillation (an irregular, often rapid atrial rhythm that increases stroke risk and is treated with anticoagulants), arrhythmias (abnormal rhythms diagnosed by ECG/EKG), cardiomyopathy (diseases of the heart muscle), endocarditis (infection of the heart's inner lining), and valve disorders such as aortic stenosis, mitral regurgitation, and mitral valve prolapse. Hypertension (blood pressure consistently above 130/80 mmHg) is called the "silent killer" because it usually has no symptoms but increases the risk of heart attack, stroke, and kidney disease. Hypertensive crisis (above 180/120 mmHg) with organ damage is a medical emergency. Treatment of cardiovascular disease relies on several drug classes: ACE inhibitors and ARBs block the renin-angiotensin-aldosterone system, beta-blockers slow the heart rate and reduce blood pressure, statins lower LDL cholesterol, anticoagulants prevent clotting, and diuretics reduce fluid volume. Procedures such as angioplasty with stenting, coronary artery bypass grafting (CABG), pacemaker and ICD implantation, and cardiac catheterization restore or support cardiovascular function.
The respiratory system exchanges gases and is vulnerable to chronic and acute diseases. Chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis (exflammation with excess mucus) and emphysema (destruction of alveoli), is primarily caused by smoking. Asthma is a chronic inflammatory condition with reversible airway narrowing, causing wheezing and shortness of breath, treated with bronchodilators and inhaled corticosteroids. Other respiratory conditions include pneumonia, tuberculosis (caused by Mycobacterium tuberculosis), pulmonary embolism (a clot blocking a pulmonary artery), pulmonary fibrosis, pleural effusion, pneumothorax (collapsed lung), sleep apnea, and acute respiratory distress syndrome (ARDS). Diagnostic tools include spirometry (which measures FEV1 and FVC to distinguish obstructive from restrictive patterns), pulse oximetry (SpO2 normally 95–100%), chest X-ray, CT pulmonary angiography (the gold standard for pulmonary embolism diagnosis), and arterial blood gas analysis. Lung cancer, the leading cause of cancer death, has two main types: non-small cell (NSCLC, more common) and small cell (SCLC, more aggressive), with smoking as the predominant risk factor.