Cardiovascular System Chapter 13

Heart Anatomy Approximately the size of your fist Location: – Superior surface of the diaphragm – Left of the midline – Anterior to the vertebral column, posterior to the sternum

Coverings of the Heart: Anatomy Pericardium – a double-walled sac around the heart composed of: – Superficial fibrous pericardium – Deep two-layer serous pericardium Parietal layer lines the internal surface of the fibrous pericardium Visceral layer or epicardium lines the surface of the heart They are separated by the fluid-filled pericardial cavity

Coverings of the Heart: Physiology The pericardium: – Protects & anchors the heart – Prevents overfilling of the heart with blood – Allows for the heart to work in a relatively friction- free environment

Heart Wall Epicardium – visceral layer of the serous pericardium Myocardium – cardiac muscle layer forming the bulk of the heart Endocardium – endothelial layer of the inner myocardial surface

External Heart: Major Vessels of the Heart Vessels returning blood to the heart: – Superior & inferior venae cavae – Right & left pulmonary veins Vessels conveying blood away from the heart: – Pulmonary trunk, splits into right & left pulmonary arteries – Ascending aorta (three branches) – brachiocephalic, left common carotid, & subclavian arteries

External Heart: Vessels that Supply/Drain the Heart Arteries: – Right & left coronary (in the atrioventricular groove), marginal, circumflex, and anterior interventricular Veins: – Small cardiac, anterior cardiac, and great cardiac

Atria of the Heart Atria are the receiving chambers of the heart Each atrium has a protruding auricle Pectinate muscles mark atrial walls Blood enters right atrium from superior and inferior venae cavae and coronary sinus Blood enters left atrium from pulmonary veins

Ventricles of the Heart Ventricles are the discharging chambers of the heart Papillary muscles and trabeculae carneae muscles mark ventricular walls Right ventricle pumps blood into the pulmonary trunk Left ventricle pumps blood into the aorta

Pathway of Blood Through the Heart & Lungs Right atrium  tricuspid valve  right ventricle Right ventricle  pulmonary semilunar valve  pulmonary arteries  lungs Lungs  pulmonary veins  left atrium Left atrium  bicuspid valve  left ventricle Left ventricle  aortic semilunar valve  aorta Aorta  systemic circulation

Coronary Circulation Coronary circulation is the functional blood supply to the heart muscle itself Collateral routes ensure blood delivery to heart even if major vessels are occluded

Heart Valves Heart valves ensure unidirectional blood flow through the heart Atrioventricular (AV) valves lie between the atria and the ventricles AV valves prevent backflow into the atria when ventricles contract Chordae tendineae anchor AV valves to papillary muscles Right side  tricuspid Left side  bicuspid

Heart Valves Aortic semilunar valve lies between the left ventricle and the aorta Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk Semilunar valves prevent backflow of blood into the ventricles

Microscopic Anatomy of Heart Muscle Cardiac muscle is striated, short, fat, branched, and interconnected Intercalated discs anchor cardiac cells together & allow free passage of ions – Sends impulses from cells Heart muscle behaves as a functional syncytium – All muscle cells are connected & act as 1 unit

Blood Vessels Blood is carried in a closed system of vessels that begins and ends at the heart Three major types of vessels: – Arteries – carry blood away from the heart – Veins – carry blood toward the heart – Capillaries – contact tissue cells & directly serve cellular needs

Generalized Structure of Blood Vessels Arteries and veins are composed of three tunics – tunica interna, tunica media, tunica externa Lumen – central blood-containing space surrounded by tunics Capillaries are composed of endothelium w/ sparse basal lamina *arteries have more pressure flowing through them

Elastic Arteries Thick-walled arteries near the heart; the aorta & its major branches – Allow low-resistance conduction of blood – Withstand & smooth out large blood pressure fluctuations – Serve as pressure reservoirs – Help pump blood by stretching & constricting, moves the blood

Muscular Arteries & Arterioles Muscular arteries – distal to elastic arteries; deliver blood to body organs – Have thick tunica media w/ more smooth muscle – Active in vasoconstriction Arterioles – smallest arteries; lead to capillary beds – Control flow into capillary beds via vasodilation and constriction

Capillaries Capillaries are the smallest blood vessels – Walls consisting of a thin tunica interna, one cell thick – Allow only a single RBC to pass at a time – Pericytes on the outer surface stabilize their walls There are three structural types of capillaries: – Continuous – Fenestrated – Sinusoids

Continuous Capillaries Abundant in the skin, muscles, & brain – Endothelial cells provide an uninterrupted lining  because of tight junctions between cells Continuous capillaries of the brain: – Have tight junctions completely around the endothelium – Constitute the blood-brain barrier

Fenestrated Capillaries Found wherever active capillary absorption or filtrate formation occurs (e.g., small intestines, endocrine glands, kidneys) Characterized by: – An endothelium riddled with pores (fenestrations) – Greater permeability than other capillaries

Sinusoids Highly modified, leaky, fenestrated capillaries w/ large lumens Found in the liver, bone marrow, lymphoid tissue, & in some endocrine organs Allow large molecules (proteins & blood cells) to pass between the blood and surrounding tissues Blood flows sluggishly, allowing for modification in various ways

Capillary Beds A microcirculation of interwoven networks of capillaries, consisting of: – Vascular shunts – metarteriole-thoroughfare channel connecting an arteriole directly with a postcapillary venule Closes blood flow if the tissues don’t need the blood & helps blood keep its oxygen – True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed – Metarteriole – passageway between terminal arteriole & the postcapillary venuole

Capillary Beds

Venous System: Venules Venules are formed when capillary beds unite – Allow fluids and WBCs to pass from the bloodstream to tissues Postcapillary venules – smallest venules, composed of endothelium and a few pericytes Large venules have one or two layers of smooth muscle (tunica media)

Venous System: Veins Veins are: – Formed when venules converge – Composed of three tunics: Thin tunica media Thick tunica externa  consists of collagen fibers and elastic networks – Capacitance vessels (blood reservoirs) that contain 65% of the blood supply

Venous System: Veins Veins have much lower blood pressure & thinner walls than arteries To return blood to the heart, veins have special adaptations – Large-diameter lumens – offer little resistance to flow – Valves (resembling semilunar heart valves), which prevent backflow of blood Venous sinuses – specialized, flattened veins w/ extremely thin walls

Blood Pressure (BP) Force per unit area exerted on the wall of a blood vessel by its contained blood The differences in BP within the vascular system provide the driving force that keeps blood moving from high to low pressure areas