Cardiovascular System Vocabulary

Overview and Terminology of the Cardiovascular System

  • Definition & Fundamental Purpose: The cardiovascular system consists of the heart, blood vessels (the vascular network), and blood. It functions as an integrated body-wide system for transportation and communication, delivering essential oxygen (O2O_2), nutrients, and hormones to peripheral tissues while simultaneously collecting carbon dioxide (CO2CO_2) and metabolic waste products for excretion. Through these mechanisms, it maintains internal balance (homeostasis) and preserves the body's internal environment (internal milieu).

  • Key Cardiovascular Terminology:

    • Afterload: The degree of peripheral vascular resistance that the ventricles must overcome to contract and eject blood into the aorta and pulmonary artery.

    • Aorta: The largest systemic artery in the body, originating from the left ventricle to deliver oxygenated blood to systemic circulation.

    • Aortic Valve: The semilunar valve located between the left ventricle and the aorta.

    • Apex: The inferior, pointed tip of the heart, directed toward the left hip.

    • Atria (Atrium): The two superior receiving chambers of the heart (right atrium and left atrium).

    • Baroreceptor: Specialized sensory nerve endings located in blood vessels that monitor stretch and blood pressure changes.

    • Bicuspid Valve (Mitral Valve): The dual-flap atrioventricular valve situated between the left atrium and left ventricle.

    • Collateral Circulation: An alternative circulatory path formed by interconnected blood vessels (anastomoses) that enlarge to provide blood flow around an obstructed vessel to nourish endangered tissue.

    • Coronary Sinus: A large venous structure on the posterior heart surface that collects venous blood from cardiac veins and drains directly into the right atrium.

    • Diastole: The phase of the cardiac cycle when heart muscle relaxes and chambers fill with blood.

    • Electrocardiogram (ECG / EKG): A graphic recording of the electrical currents generated by the heart during depolarization and repolarization.

    • Endocardium: The smooth, innermost endothelial lining of the heart walls, heart chambers, and valves.

    • Epicardium: The outermost structural layer of the heart wall, which also forms the visceral layer of the serous pericardium.

    • Ischemia: A reversible state of cellular tissue injury resulting from inadequate blood and oxygen supply.

    • Mediastinum: The central thoracic cavity space located between the lungs, housing the heart, esophagus, and thoracic trachea.

    • Microcirculation: Blood circulation through the smallest vessels (arterioles, capillaries, and venules).

    • Mitral Valve: Another term for the bicuspid valve located between the left atrium and left ventricle.

    • Myocardium: The middle, muscular tissue layer of the heart wall responsible for pumping action.

    • Perfusion: The passage of fluid or blood through the circulatory system or lymphatic system to an organ or tissue.

    • Pericardial Fluid: Serous fluid contained within the pericardial cavity that reduces friction between pericardial membranes during cardiac contraction.

    • Pericardium: The double-walled sac that surrounds and protects the heart.

    • Preload: The end-diastolic volume and stretch of cardiac muscle fibers immediately before ventricular contraction.

    • Pulmonic Valve: The semilunar valve situated between the right ventricle and the pulmonary artery.

    • Pulse: The rhythmic expansion and elastic recoil of arterial walls caused by ventricular ejection of blood.

    • Pulse Pressure: The numerical difference between systolic blood pressure (sBPsBP) and diastolic blood pressure (dBPdBP).

    • Semilunar Valve: A crescent-shaped valve (aortic or pulmonic) that prevents backflow from major arteries into the ventricles.

    • Septum: A muscular wall partitioning the heart into left and right sides (e.g., interatrial and interventricular septa).

    • Systole: The contraction phase of the cardiac cycle during which blood is pumped out of heart chambers.

    • Tricuspid Valve: The three-flap atrioventricular valve located between the right atrium and right ventricle.

    • Ventricle: The two inferior pumping chambers of the heart (right ventricle and left ventricle).

  • Standard Medical Acronyms:

    • AV: Atrioventricular

    • BP: Blood Pressure

    • CO: Cardiac Output

    • CO2: Carbon Dioxide

    • dBP: Diastolic Blood Pressure

    • ECG / EKG: Electrocardiogram

    • HR: Heart Rate

    • IVC: Inferior Vena Cava

    • LAD: Left Anterior Descending (Artery)

    • LCA: Left Coronary Artery

    • LCX: Left Circumflex (Artery)

    • LMCA: Left Main Coronary Artery

    • MI: Myocardial Infarction

    • O2: Oxygen

    • PDA: Posterior Descending Artery

    • RCA: Right Coronary Artery

    • S1: First Heart Sound ("lub")

    • S2: Second Heart Sound ("dub" or "dup")

    • SA Node: Sinoatrial Node

    • sBP: Systolic Blood Pressure

    • SV: Stroke Volume

    • SVC: Superior Vena Cava

    • SVR: Systemic Vascular Resistance

Cardiac Anatomy and Structure of Heart Walls

  • Anatomic Location: The heart resides within the thoracic cavity inside the central space known as the mediastinum. It is oriented obliquely, with its base situated superiorly and its apex pointing inferiorly toward the left side of the body.

Interior Anatomy of the Heart

  • Layers of the Heart Wall:

    • Endocardium: The innermost layer composed of smooth endothelial tissue lining the interior of all four cardiac chambers, covering the cardiac valves, and continuing into the inner lining of major blood vessels. Inflammation of this layer is termed endocarditis.

    • Myocardium: The thick middle layer composed of specialized cardiac muscle fibers responsible for mechanical pumping. The thickness of the myocardium varies according to chamber workload; the left ventricle contains the thickest myocardial muscle layer to generate sufficient pressure to supply the entire systemic circulation. Inflammation of this layer is termed myocarditis.

    • Epicardium: The thin outer protective layer forming the external surface of the heart wall. It doubles as the visceral layer of the serous pericardium. Inflammation of this layer is termed epicarditis.

  • The Pericardial Sac (Pericardium):

    • Structure: A double-walled fibroserous protective enclosure wrapping around the heart.

    • Fibrous Pericardium: The tough, non-distensible outermost layer of connective tissue that anchors the heart within the mediastinum and prevents acute acute heart overdistension.

    • Parietal Layer: The smooth inner lining of the fibrous pericardium.

    • Visceral Layer (Epicardium): The innermost serous membrane directly adherent to the outer myocardium.

    • Pericardial Cavity (Space): The potential space located between the visceral and parietal layers of the serous pericardium.

    • Pericardial Fluid: Contains a normal physiological volume of 15-30\n\text{mL} of serous fluid that lubricates membrane surfaces to eliminate friction during cardiac cycles.

    • Pericarditis & Cardiac Tamponade: Inflammation of the pericardium (pericarditis) can cause fluid accumulation within the pericardial cavity (pericardial effusion). Rapid or excessive fluid build-up causes cardiac tamponade, a life-threatening medical emergency where high pressure compresses the heart chambers, severely impeding diastolic filling, decreasing stroke volume (SVSV) and cardiac output (COCO).

Layers of the Pericardium and Heart Wall

Heart Chambers, Valves, and Internal Dynamics

  • Cardiac Chambers:

    • Right Atrium: Superior receiving chamber for deoxygenated systemic venous blood returning via the superior vena cava, inferior vena cava, and coronary sinus.

    • Left Atrium: Superior receiving chamber for oxygenated blood returning from the lungs via four pulmonary veins.

    • Right Ventricle: Inferior muscular pumping chamber that receives deoxygenated blood from the right atrium and propels it under low pressure into the pulmonary trunk and arteries toward the lungs.

    • Left Ventricle: Inferior, thick-walled muscular pumping chamber that receives oxygenated blood from the left atrium and propels it under high pressure into the aorta for systemic distribution.

  • Heart Valves:

    • Atrioventricular (AV) Valves: Prevent blood from flowing backward into the atria during ventricular contraction (systole).

      • Tricuspid Valve: Located between the right atrium and right ventricle, featuring three distinct tissue cusps.

      • Mitral (Bicuspid) Valve: Located between the left atrium and left ventricle, featuring two distinct tissue cusps.

    • Semilunar Valves (Overflow Valves): Prevent blood from flowing backward from major outgoing arteries into the ventricles during relaxation (diastole).

      • Pulmonic Valve: Located at the exit of the right ventricle into the pulmonary trunk.

      • Aortic Valve: Located at the exit of the left ventricle into the ascending aorta.

  • Subvalvular Apparatus (Chordae Tendineae and Papillary Muscles):

    • Chordae Tendineae: Tendon-like fibrous strands attached directly to the free margins of the AV valve cusps.

    • Papillary Muscles: Muscular projections extending from the ventricular walls.

    • Mechanism: As the ventricles contract during systole, papillary muscles contract simultaneously, pulling the chordae tendineae taut. This prevents the AV valve cusps from turning inside out (everting) into the atria under high pressure.

    • Valvular Dysfunction & Regurgitation: Damage to the AV valve cusps, chordae tendineae, or papillary muscles (e.g., due to ischemia or rupture) prevents complete closure, leading to blood regurgitation back into the atria during ventricular contraction.

Pathways of Blood Flow and Circulation

  • Step-by-Step Pathway of Blood Flow:

    1. Deoxygenated venous blood from the body enters the Right Atrium through the Superior Vena Cava (SVC), Inferior Vena Cava (IVC), and Coronary Sinus.

    2. Blood flows through the Tricuspid Valve into the Right Ventricle.

    3. During ventricular contraction, blood is pumped through the Pulmonic Valve into the Pulmonary Trunk and Pulmonary Arteries.

    4. Blood travels through the pulmonary microcirculation of the lungs, releasing carbon dioxide (CO2CO_2) and picking up oxygen (O2O_2).

    5. Oxygenated blood returns to the heart via four Pulmonary Veins into the Left Atrium.

    6. Blood flows through the Mitral (Bicuspid) Valve into the Left Ventricle.

    7. During ventricular contraction, oxygenated blood is forcefully pumped through the Aortic Valve into the Aorta for distribution to systemic tissue capillary beds throughout the body.

  • Functional Circulatory Pathways:

    • Pulmonary Circulation: The low-pressure loop carrying deoxygenated blood from the right heart to the lungs for gas exchange and returning oxygenated blood to the left heart.

    • Systemic Circulation: The high-pressure loop delivering oxygenated blood from the left heart to body tissues and returning deoxygenated blood to the right heart.

    • Oxygenation Rule Exception: Pulmonary arteries are the only arteries in the human body that carry deoxygenated blood; pulmonary veins are the only veins in the human body that carry oxygenated blood.

Vascular System Anatomy and Histology

  • Classification of Systemic Blood Vessels:

    • Arteries: Vascular channels that transport blood away from the heart. The aorta is the largest systemic artery, branching sequentially into the ascending aorta, aortic arch, thoracic aorta, and abdominal aorta.

    • Arterioles: The smallest arterial branches that act as primary resistance vessels regulate blood flow into capillary networks.

    • Capillaries: Microscopic, single-celled thin-walled vessels connecting arterioles to venules. They constitute the largest combined length of the body's vascular network and serve as the sole functional site for exchange of gas, nutrients, and cellular waste between blood and surrounding tissues.

    • Venules: Small venous vessels that collect blood from capillary networks and merge into larger veins.

    • Veins: Capacitance vessels that return blood toward the heart. The superior vena cava (SVC) and inferior vena cava (IVC) are the largest veins in the body.

Comparison of Artery, Vein, and Capillary Structure

  • Histological Layers of Blood Vessels (Tunicae):

    • Tunica Adventitia (Externa): The outermost layer composed primarily of collagenous and elastic connective tissue fibers that support