Cardiovascular System: The Heart PDF

Cardiovascular System The Heart Ch 21 Intro Continuous exchange between the interstitial fluid (IF) and blood stabilizes the levels of gases, nutrients, and waste. The constant blood supply is essential for homeostasis This continuous supply of blood is the responsibility of the cardiovascular syste...

Cardiovascular System The Heart Ch 21 Intro Continuous exchange between the interstitial fluid (IF) and blood stabilizes the levels of gases, nutrients, and waste. The constant blood supply is essential for homeostasis This continuous supply of blood is the responsibility of the cardiovascular system Relies on the heart IF is monitored by the ANS which adjusts heart rate Heart pumps between 5-30 liters of blood per minute. Overview The heart is a small organ, roughly the size of your fist. Consists of 4 chambers (2 Atria & 2 Ventricles) Pumps blood through a network of blood vessels The network of blood vessels is divided into 2 circuits: 1. The pulmonary Circuit Carries blood to the lungs for oxygenation 2. The systemic Circuit Carries oxygen rich blood to the Each circuit begins and ends at the The 2 circuits are completed in sequence Pericardium The pericardium surrounds the heart and is composed of two parts: 1. An outer fibrous pericardium Composed of dense network of collagen fibers that stabilize the position of the heart 2. An inner serous pericardium Composed of an outer parietal layer and inner visceral layer (epicardium) Parietal cavity lies between these layers Contains parietal fluid that cushions the heart The Heart Wall A section through the heart wall reveals 3 distinct layers: 1. The Visceral Layer or epicardium Covers the outer surface of the heart 1. The Myocardium Cardiac muscle tissue that forms the atria and ventricles 2. The endocardium Covers the inner surface of the heart including the valves Cardiac Muscle Compared to skeletal muscle: Cardiac muscle is: Smaller and uninucliate But still contain organized myofibrils-appear striated Almost totally dependent on aerobic respiration Have a large number of blood vessels Contract without nervous stimulation Interconnected by special cell junctions: Intercalated discs Intercalated Discs Specialized junctions, Intercalated Discs, connect adjacent heart muscle cells. Features include: Plasma membrane of 2 adjacent cells are bound together by desmosomes Possess a specialized junction, the fascia adherens Location of attachment of actin filaments Allow two muscles cell to pull together with maximum efficiency Cardiac muscle cells also connected by gap junctions Allow passage of ions and small molecules Because cardiac muscles are mechanically, chemically, and electrically connected to each other, cardiac muscle tissue functions as one giant muscle cell. Cardiac Skeleton Each cardiac muscle is wrapped in an elastic sheath of fibers. These connective tissue layers (Cardiac Skeleton) are continuous with bands of dense connective tissue that: Encircle the base of the pulmonary trunk and the valves of the heart Connect the tissues that surround the valves and separate the atria and ventricles Functions to: Stabilize position of heart Distribute the force of contraction Reinforce valves and provide elasticity to heart Physically isolate atrial and ventricular muscle cells Orientation & Superficial Anatomy Positionally the heart lies: Slightly to the left of the midline At an angle to the longitudinal axis of the body Rotated slightly to the left The base of the heart is its superior portion Attaches the major arteries and veins of the systemic and pulmonary circuits Lies posterior to the sternum The apex of the heart is the inferior pointed end Formed mainly by the left ventricle External groves, sulci , show the approximate borders of the 4 internal chambers. A shallow interatrial grove separates the L/R Atria The deeper coronary sulcus separates the atria from the ventricles On the anterior side, the anterior interventricular sulcus separates the L/R ventricles On the posterior side, the posterior interventricular sulcus separates the L/R ventricles Internal Anatomy & Organization Blood flows from each atria to the ventricle on the same side of the heart The interatrial septum separates the atria The interventricular septum separates the ventricles The valves are folds of endocardium that extend into the openings between the atria and ventricles The functional demands placed on the R/L atria are similar and they look almost identical The functional demands placed on the R/L ventricals are very different & there are significant differences between these two chambers Atria, Ventricles and Cardiac Circulation The Rt Atrium receives deoxygenated blood from the body Return via the Superior/Inferior Vena Cava Blood passes from the Rt atrium into the Rt Ventricle Three flaps, cusps, make up the Rt Atrioventricular valve (tricuspid valve) Cusps attach to cardiac skeleton through chordae tendineae These attach to the papillary muscles within the ventricle The superior end of the Rt Ventricle tapers to the conus arteriosus Ends at the Pulmonary Valve ( semilunar valve) Blood leaves via the pulmonary trunk then to the L/R pulmonary arteries. Oxygen enters the blood via the pulmonary capillaries Oxygenated blood returns to the heart via the L/R pulmonary veins Blood from the pulmonary veins enters the Lt Atrium As blood passes from the Lt Atrium to Lt Ventricle is passes through the Lt Atrioventricular valve ( mitral valve) The wall of the Lt Ventricle is 3x’s thicker than that of the right There are only 2 papillary muscles as well As a result, the mitral valve has only 2 cusps and is also called the bicuspid valve Blood leaving the ventricle passes through the aortic (semilunar) valve From here it passes through the ascending aorta to the aortic arch and descending aorta The Cardiac Cycle The heart functions is a cycle of contraction (systole) and relaxation (diastolic) Proper functions of the heart relies on coordinated contraction between the atria and ventricles The heart beats under myostatic , autorhythmic, control The heart contains specialized 2 types of conducting cells 1. Nodal Cells establish the rate of contraction Plasma membranes possess unique qualities that allow them the depolarize spontaneously When depolarization occurs an action potential is generated The action potential starts the cardiac cycle 2. conducting Cells distribute the contractile stimulus to the myocardium Not all nodal cells depolarize at the same rate The normal rate of contraction is determined by which cell reach threshold These rapidly depolarizing cells are the pacemaker cells Found in the sinoatrial Node Found in the posterior wall of the Rt Atrium The cells of the SA Node are electrically connected to those of the larger atrioventricular node The sympathetic and parasympathetic divisions of the ANS innervate the heart via the cardiac plexus Cardiac centers of the medulla activate the cardioacceleratory (sympathetic) and cardioinhibitory (parasympathetic) neurons