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# Cardiovascular System ## Blood Vessels ### Arteries * Carry blood away from the heart. * Walls have three layers: * **Tunica intima:** Inner layer; endothelium. * **Tunica media:** Middle layer; smooth muscle (vasoconstriction/ vasodilation). * **Tunica externa:** Outer l...

# Cardiovascular System ## Blood Vessels ### Arteries * Carry blood away from the heart. * Walls have three layers: * **Tunica intima:** Inner layer; endothelium. * **Tunica media:** Middle layer; smooth muscle (vasoconstriction/ vasodilation). * **Tunica externa:** Outer layer; connective tissue. * Types of Arteries: * **Elastic arteries:** Largest arteries; closest to the heart; lots of elastin; pressure reservoirs. * **Muscular arteries:** Thick tunica media; more smooth muscle; distribute blood to specific areas/organs. * **Arterioles:** Smallest arteries; feed into capillaries; control blood flow into capillary beds (vasoconstriction/ vasodilation). ### Capillaries * Smallest blood vessels. * Walls are only one cell layer thick (endothelium) for exchange of gases, nutrients, & wastes. * **Capillary beds:** network of capillaries; fed by arterioles; drained by venules. * **Precapillary sphincters:** control blood flow into capillary beds. ### Veins * Carry blood back to the heart. * Walls have three layers (same as arteries, but thinner). * **Venules:** Smallest veins; receive blood from capillaries. * **Veins:** thinner walls, larger lumens, lower blood pressure than arteries; have valves to prevent backflow of blood. * **Venous sinuses:** specialized, flattened veins with very thin walls (e.g., coronary sinus). ## Circulatory Pathways ### Pulmonary Circulation * Right ventricle $\rightarrow$ pulmonary trunk $\rightarrow$ pulmonary arteries $\rightarrow$ lungs $\rightarrow$ pulmonary veins $\rightarrow$ left atrium. ### Systemic Circulation * Left ventricle $\rightarrow$ aorta $\rightarrow$ systemic arteries $\rightarrow$ systemic capillaries $\rightarrow$ systemic veins $\rightarrow$ superior & inferior $\rightarrow$ venae cavae $\rightarrow$ right atrium. ## Heart Anatomy ### Coverings of the Heart * **Pericardium:** Double-layered sac that encloses the heart. * **Fibrous pericardium:** Outer layer; dense connective tissue. * **Serous pericardium:** Inner layer; thin, slippery. * **Parietal layer:** lines the fibrous pericardium. * **Visceral layer (epicardium):** covers the heart; part of the heart wall. * **Pericardial cavity:** between parietal & visceral layers; contains serous fluid (reduces friction). ### Heart Wall * **Epicardium:** Visceral layer of serous pericardium. * **Myocardium:** Cardiac muscle; contracts. * **Endocardium:** Inner lining of the heart; endothelium. ### Heart Chambers * **Atria (Right & Left):** Receiving chambers. * **Auricles:** "flaps" on the atria. * **Ventricles (Right & Left):** Pumping chambers. ### Heart Valves * Ensure one-way blood flow through the heart. * **Atrioventricular (AV) valves:** Between atria & ventricles. * **Right AV valve (tricuspid valve):** 3 cusps. * **Left AV valve (bicuspid/mitral valve):** 2 cusps. * **Chordae tendineae:** "heart strings"; anchor cusps to papillary muscles. * **Papillary muscles:** project from ventricular walls; prevent valve eversion. * **Semilunar (SL) valves:** Between ventricles & great vessels. * **Pulmonary SL valve:** Between right ventricle & pulmonary trunk. * **Aortic SL valve:** Between left ventricle & aorta. ### Heart Vessels * **Superior & Inferior venae cavae:** Bring deoxygenated blood to right atrium. * **Pulmonary trunk:** Splits into pulmonary arteries; carries deoxygenated blood to lungs. * **Pulmonary veins:** Carry oxygenated blood from lungs to left atrium. * **Aorta:** Carries oxygenated blood from left ventricle to the body. * **Coronary arteries:** Branch from aorta; supply oxygenated blood to the heart. * **Cardiac veins:** Drain deoxygenated blood from the heart muscle; empty into coronary sinus. * **Coronary sinus:** Empties into right atrium. ### Internal Heart Anatomy * **Interatrial septum:** Separates atria. * **Fossa ovalis:** Remnant of foramen ovale (fetal heart). * **Interventricular septum:** Separates ventricles. * **Pectinate muscles:** ridges on anterior atrial walls. * **Trabeculae carneae:** irregular ridges of muscle on ventricular walls. ## Physiology ### Heart Sounds * **Lubb:** closing of AV valves (ventricular systole). * **Dubb:** closing of SL valves (ventricular diastole). ### Intrinsic Conduction System * **Sinoatrial (SA) node (pacemaker):** Generates impulses; sets the heart rate. * **Atrioventricular (AV) node:** Delays the impulse from SA node. * **Atrioventricular (AV) bundle (bundle of His):** Conducts the impulse to the bundle branches. * **Bundle branches:** Carry the impulse down the interventricular septum. * **Purkinje fibers:** Spread the impulse throughout the ventricular myocardium. ### Electrocardiography * **Electrocardiogram (ECG or EKG):** recording of the electrical activity of the heart. * **P wave:** Atrial depolarization. * **QRS complex:** Ventricular depolarization (atrial repolarization is hidden). * **T wave:** Ventricular repolarization.