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The Cardiovascular System Ch. 18,19 Introduction • Cardiovascular system – Heart – Blood vessels • Arteries • Capillaries • Veins Heart anatomy Structure of the heart • Description-hollow, cone-shaped, muscular pump • 12 cm by 9 cm • Located behind sternum, within mediastinum (space) Coverings of the heart • Pericardium – encloses heart – tough connective tissue. • Fibrous pericardium surrounds visceral serous pericardium. – Visceral pericardium- surrounds heart – Parietal pericardium-lines the cavity • Paricardial cavity- space containing serous fluid between parietal and visceral pericardium – contains serous fluid Wall of the heart • 3 layers – Epicardiumoutermost layer • Connective tissue and epithelium – contains blood vessels and lymph vessels – Myocardium – cardiac muscle, middle layer – Endocardium – innermost layer, contains nervous tissue for control of the heart. Skeleton of the heart • Rings of dense connective tissue • Surround pulmonary trunk and aorta Heart chambers and valves • Chambers – Atria – Ventricles • Septum • Atrioventricular (AV) valve – Tricuspid – Bicuspid or mitral • Cordae tendinae • Pulmonary valves • Aortic valve Path of blood through heart • Inferior or superior vena cava • Right atrium • Right AV valve • Right ventricle • Pulmonary artery • Pulmonary valve • Lungs • • • • • • • Pulmonary vein Left atrium Left AV valve Left ventricle Aorta Aortic valve Body Blood supply to the heart • Branches of aorta, carry oxygenated blood – right and left coronary arteries – feed heart • Branches from coronary arteries feed capillaries of myocardium • Smaller branches of arteries – anastomoses – alternate pathways for blood – Blocked artery – angina pectoris – myocardial infarction – heart attack • Cardiac veins- drain blood from heart Heart beating Heart actions • Cardiac cycle – pressure in chambers rises/falls with contraction/relaxation of atria and ventricles • Atria fill, open av valves • Ventricles fill • Valves close • Ventricles contract, blood goes through pulmonary artery and aorta • Ventricles relax, valves close in vessels Heart sounds • Heart sounds caused by valve closure – First sound (lubb) – ventricles contract and AV valves close – Second sound (dupp) ventricles relax and aortic and pulmonary valves close. Cardiac conduction system • Functional synctium – atrial and ventricular – mass of fibers that works as a unit • Cardiac tissue conducts impulses through myocardium – cardiac conduction system. • Sinoatrial node in right atrium – pacemaker – self exciting • Impulses spread through atrial synctium then ventricular synctium. • Purkinje fibers contract tiny muscles attached to chordae tendinae Electrocardiogram • ECG – electrical recording of changes that occur in cardiac cycle • P wave – depolarization of atria • QRS complex – depolarization of ventricles • T wave – ventricular repolarization Regulation of the cardiac cycle • Amount of blood pumped must adjust according to body needs • SA node innervated by sympathetic and parasympathetic nervous system divisions so CNS controls heart rate. • Cardiac control center in medulla oblongata – adjusts heart rate based on blood pressure measurements from baro receptors. • Cerebrum/hypothalamus influence heart rate as well Blood vessels • Blood vessels – include:Arteries , arterioles, capillaries, venules, veins • Create closed system – carries blood away from heart to cells in body then back to the heart. Arteries and veins • Arteries –strong, elastic • Divide into arterioles • Wall of artery - smooth muscles and connective tissue • Capable of vasoconstriction/vasodilation – increases/decreases blood flow/pressure • Clogged vessels – artherosclerosis – diets high in fat – Diets high in fruits/vegetables=add phyto sterols to blood – scour out plaque deposits capillaries • Smallest vessels – layer of endothelium – Allows substances to be exchanged with cells – More permeability in capillaries of liver, intestines, glands – More metabolic activity – higher number of capillaries – Precapillary sphincters – regulate amount of blood entering capillary bed – Capillary beds can close down if more is needed elsewhere. Exchanges in the capillaries • Blood in capillaries – high oxygen/nutrients • Diffuse through wall to tissue • Plasma proteins stay in capillary • Hydrostatic pressure – drives passage of fluids/small molecules. • Osmosis causes tissue fluid to return to blood • Lymphatic vessels collect extra fluid and return it to circulation Venules and veins • Venules – lead from capillaries – merge to form veins – veins return blood to heart. • 3 layers with valves to prevent backflow • Thinner, less muscular than arteries • No high pressure blood • Function as blood reservoirs Blood circulation Paths of circulation • Two divisions – Pulmonary circuit – right ventricle through pulmonary artery to lungs, then pulmonary veins to left atrium. – Systemic circuit – carries blood from left ventricle through aorta to body cells and back through veins into the left atrium Arterial system Venous system Blood pressure • Factors that affect blood pressure – – – – Heart action Blood volume Peripheral resistance Blood viscosity Control of blood pressure • adjusting Cardiac output and Peripheral resistance • If blood pressure increases, heart rate slows and blood vessels dilate • If BP drops, heart rate increases and blood vessels constrict. • Vasomotor center of medulla oblongata controls Fetal circulation • Two umbilical arteries – carry blood to placenta • Placenta – structure attached to uterine wall – substances exchanged between blood of mother and baby • Umbilical vein – returns blood from placenta to baby. • Ductus venosus – returns blood from placenta to inferior vena cava, bypassing liver • Foramen ovale – opening in septum between right and left atria that allows most of blood to bypass fetal lungs • Ductus arteriosus-small vessel connecting pulmonary artery with descending aorta, allows more blood to bypass fetal lungs • After birth: Ovale closes, Ductus arteriosus contracts Changes after birth