2 Coronary CirculationBlood in the heart chambers does not nourish the myocardiumThe heart has its own nourishing circulatory systemCoronary ArteriesBranch from the base of the aorta and encircle the heart in the atrioventricular grooveCardiac VeinsBlood empties into the right atrium via the Coronary Sinus
5 Heart Attacks Angina Pectoris – Crushing chest pain The result of a situation in which the myocardium is deprived of oxygenThis pain is a warning that should never be ignored, because if angina is prolonged, the ischemic heart cells may die.
6 Heart AttacksMyocardial Infarction – “Heart attack”; Heart cells die because of a lack of oxygen
7 Amount of Work Done by the Heart The amount of work the heart does is incredible!In one day it pushes the body’s supply of ~6 quarts of blood through the blood vessels over 1000 times.It actually pumps about 6000 quarts of blood in a single day!
8 The Heart: Conduction System Two types of controlling systems act to regulate heart activity:Autonomic Nervous SystemAct like “brakes” and “accelerators” to decrease or increase the heart rate depending on which division is activatedIntrinsic Conduction System (Nodal System)Built into the heart tissueHeart muscle cells contract (without nerve impulses) in a regular, continuous, coordinated wayCauses heart muscle depolarization in only one direction – from the atria to the ventricles.
9 The Heart: Conduction System Special tissue sets the pace:Sinoatrial Node (SA Node) – PacemakerTiny cell mass located in the right atriumIt starts each heartbeat and sets the pace for the whole heartAtrioventricular Node (AV Node)Located at the junction of the atria and ventriclesFrom the SA node, the impulse spreads through the atria to the AV node, and then the atria contractAt the AV node, the impulse is delayed briefly to give the atria time to finish contracting
11 The Heart: Conduction System After the impulse travels through the AV node, it then passes rapidly through the:Atrioventricular Bundle (AV bundle)Also called bundle of HisBundle BranchesRight and left branchesLocated in the interventricular septumPurkinje FibersSpreads within the muscles of the ventricle
13 The Heart: Conduction System First the impulse travels from the SA Node → AV NodeCauses the atria to contractThen the impulse travels from the AV Node → AV Bundle → Bundle Branches → Purkinje FibersResults in the “wringing” contraction of the ventricles that begins at the heart apex and moves toward the atria.
15 Some Heart Problems Damage to the SA node Can install artificial pace-makersIschemia - Lack of blood flow to the heart muscleMay lead to fibrillationFibrillation - A rapid uncoordinated shuddering of the heart muscleIt looks like a bag of wormsMakes the heart totally useless as a pump and is a major cause of death from heart attacks
16 The Heart: Cardiac Cycle Atria contract simultaneouslyAtria relax, then ventricles contractSystole = Contraction of the ventriclesDiastole = Relaxation of the ventricles
17 The Heart: Cardiac Cycle Cardiac Cycle – Events of one complete heart beatAverage heart beats ~75 times per minuteThe length of the cardiac cycle is normally about 0.8 seconds
18 Heart SoundsYou can hear two distinct sounds during each cardiac cycle: “lub-dup”The first heart sound (“lub”) is caused by the closing of the AV valvesSound is longer and louder than the second soundThe second heart sound (“dup”) is caused by the closing of the semilunar valvesSound tends to be short and sharp
19 Heart SoundsBlood flows silently as long as the flow is smooth and uninterrupted.If it strikes obstructions, its flow becomes turbulent and generates sounds, which can be heard with a stethoscope.Unusual heart sounds, or murmurs, usually indicate valve problems.
20 The Heart: Cardiac Output Cardiac Output (CO) - Amount of blood pumped by each side of the heart in one minuteCO = (heart rate [HR]) x (stroke volume [SV])Stroke Volume - Volume of blood pumped by each ventricle in one contraction
21 Regulation of Stroke Volume The more the cardiac muscle cells are stretched, the stronger the contraction will be.The important factor stretching the heart muscle is venous return, the amount of blood entering the heart and distending its ventricles.Exercise speeds venous return because it results in increased heart rate and force.Blood loss decreases venous return.
23 Regulation of Heart Rate Stroke volume tends to be relatively constant.However, when blood volume drops suddenly or when the heart has been seriously weakened, SV declines, and CO is maintained by a faster heartbeat.Regulation of Heart RateAlthough heart rate does not depend on the nervous system, its rate can be changed temporarily by the autonomic nervous system.Also modified by various chemicals, hormones, and ions.
24 Congestive Heart Failure Congestive Heart Failure – Occurs when the pumping efficiency of the heart is depressed so that circulation is inadequate to meet tissue needs.Usually a progressive condition that reflects weakening of the heart by coronary atherosclerosis (clogging of the coronary vessels), persistent high blood pressure, or multiple myocardial infarcts.
25 Congestive Heart Failure Each side can fail independently of the other.Failure of one side puts a greater strain on the opposite side, and eventually the whole heart fails.Pulmonary Congestion – Failure of the left heartLeft side is unable to eject the returning bloodBlood vessels within the lungs become swollen and fluid leaks into the lung tissue causing pulmonary edema. If untreated, the person suffocates.Peripheral Congestion – Failure of the right heartBlood backs up in the systemic circulationEdema is noticeable in the distal parts of the body (feet, fingers)