Cardiovascular system Study Guide

📖 Core Concepts Circulatory system – closed network of heart, blood vessels (arteries, veins, capillaries) and blood that continuously loops. Pulmonary vs. systemic circulation – pulmonary moves de‑oxy blood to lungs → oxy blood back; systemic delivers oxy blood to tissues → returns de‑oxy blood to heart. Blood composition – plasma (soluble proteins, minerals, hormones, gases) + cellular elements (RBCs ≈ 45 % volume, WBCs, platelets). Heart chambers & valves – 4 chambers (RA, RV, LA, LV); AV valves (tricuspid, mitral) prevent back‑flow into atria; semilunar valves (pulmonary, aortic) prevent back‑flow from arteries. Vessel hierarchy – elastic arteries (aorta) → muscular arterioles → capillaries (exchange) → venules → veins (valves). Specialized circuits – coronary (heart), cerebral (brain, circle of Willis), renal (≈20 % CO), hepatic portal (GI → liver). 📌 Must Remember Closed system: blood never leaves vascular network (except lymphatic return). O₂ transport: 98.5 % bound to hemoglobin, 1.5 % dissolved in plasma. Pulmonary circuit: RA → RV → pulmonary artery → lungs → pulmonary veins → LA. Systemic circuit: LV → aorta → (arteries → arterioles → capillaries) → veins → RA. Portal vein exception: hepatic portal carries nutrient‑rich blood to a second capillary bed (liver). Fetal shunts: ductus arteriosus & foramen ovale close at birth → separate pulmonary & systemic circuits. Atherosclerosis → plaque → rupture → thrombosis → MI or stroke. Deep vein thrombosis – common in immobile legs; risk of pulmonary embolism. 🔄 Key Processes Blood flow through heart (one cardiac cycle) Venous return → RA → tricuspid → RV → pulmonary semilunar → pulmonary artery → lungs → pulmonary veins → LA → mitral → LV → aortic semilunar → aorta → body. Capillary exchange (Fick principle) Diffusion of O₂, CO₂, nutrients, waste across thin walls driven by concentration gradients. Coronary perfusion Aortic root → right & left coronary arteries → myocardium → coronary veins → coronary sinus → RA. Hepatic portal flow GI capillaries → hepatic portal vein → liver sinusoids → hepatic veins → IVC. Fetal to neonatal transition Birth → increased lung ventilation → ↓ pulmonary resistance → ↑ left‑heart preload → foramen ovale & ductus arteriosus close. 🔍 Key Comparisons Arteries vs. Veins Arteries: thick elastic/muscular walls, high pressure, no valves (except semilunar). Veins: thin walls, low pressure, contain valves, larger lumen. Pulmonary vs. Systemic circulation Pulmonary: low pressure, short circuit, gas exchange. Systemic: high pressure, long circuit, nutrient/waste transport. Portal vs. Systemic veins Portal: deliver blood to a second capillary bed before returning to heart. Systemic: return blood directly to heart. Atherosclerosis vs. Aneurysm Atherosclerosis: plaque buildup → lumen narrowing/rupture. Aneurysm: wall weakening → focal dilation, often secondary to atherosclerosis. ⚠️ Common Misunderstandings “Blood leaves the body” – only lymphatic vessels are open; the blood circulatory system is closed. “All arteries carry oxygenated blood” – pulmonary arteries carry de‑oxygenated blood; pulmonary veins carry oxygenated blood. “Venous valves prevent all backflow” – they prevent large‑scale reflux; low‑pressure gradients can still cause venous pooling. “Platelets are a type of blood cell” – they are cell fragments, not true nucleated cells. 🧠 Mental Models / Intuition “Pump → Highway → Destination” – Heart = pump, arteries = high‑speed highway (elastic recoil), arterioles = speed‑limit signs, capillaries = local streets (exchange), veins = return lanes with turn‑around signs (valves). “Two‑circuit subway” – Pulmonary line (short, low‑pressure) loops to the “lung station”; Systemic line (long, high‑pressure) loops around the city. “Filter‑and‑re‑filter” – Hepatic portal acts like a checkpoint where nutrients are screened before entering the general circulation. 🚩 Exceptions & Edge Cases Hepatic portal system – a venous system that feeds a second capillary network. Cerebral circulation – dual supply (anterior via internal carotids, posterior via vertebrals) merging at the circle of Willis; important for collateral flow. Fetal shunts – ductus arteriosus (connects pulmonary artery → aorta) and foramen ovale (RA ↔ LA) bypass lungs. 📍 When to Use Which Identify vessel type: look at wall thickness & presence of valves → artery vs. vein. Determine circulation involved: if question mentions lungs or gas exchange → pulmonary; if mentions systemic organs, blood pressure, or aortic branches → systemic. Assess pathology: plaque‑related narrowing → atherosclerosis; wall dilation → aneurysm; clot formation in low‑flow veins → deep‑vein thrombosis. Choose diagnostic tool: Rapid bedside assessment of heart rhythm → ECG. Visualize arterial lumen & stenosis → angiography or CT angiography. Evaluate venous thrombosis → vascular ultrasonography (Doppler). 👀 Patterns to Recognize “De‑oxy → lungs → oxy” pattern in any pathway description → pulmonary circuit. “Large elastic → small muscular → compliant” progression in arterial trees. “Valves present in veins of extremities” → indicates potential for venous pooling if valves fail. “Plaque → rupture → thrombosis” sequence → classic cause of acute myocardial infarction or stroke. 🗂️ Exam Traps Distractor: “Pulmonary veins carry de‑oxygenated blood.” – Wrong: they carry oxygenated blood from lungs to LA. Distractor: “Aorta is a vein.” – Wrong: aorta is the largest elastic artery. Distractor: “All capillaries are permeable to proteins.” – Wrong: most systemic capillaries are continuous and restrict large proteins; fenestrated capillaries (e.g., renal glomeruli) are the exception. Distractor: “Aneurysm results from plaque blockage alone.” – Wrong: aneurysms are due to wall weakening; plaque can predispose but is not the direct cause. Distractor: “Deep‑vein thrombosis is common in the arms.” – Wrong: DVT most often occurs in the legs after prolonged immobility.