Copyright 2010, John Wiley & Sons, Inc. Chapter 15 The Cardiovascular System: The Heart

Amazing heart facts The heart in numbers: - the heart beats about 100,000 times a day - does 35 million beats a year - it pumps 30-times of its own weight each minute - it pumps about 5 liters of blood every minute - it pumps about 10 million liters (2.6 million gal) of blood every year! - the heart has (if well maintained) an average life span of about years! It’s hard to find a pump as good as this at your hardware store! Copyright 2010, John Wiley & Sons, Inc.

Many humans show “no heart” for their own heart According to WHO, cardiovascular diseases are the leading cause of death especially in developed nations; in 2005, about 17.5 million people died from cardio- vascular disease which is 30% of the global mortality. About 5 million people in the U.S. have heart failure, a condition in which the heart cannot pump enough blood; - each year in the U.S. alone about 4 million people are hospitalized in connection with heart failure In U.S., each year about 80,000 seemingly healthy people under the age of 55 have a stroke for no apparent reason, but most likely due to undiagnosed cardiac defects; Copyright 2010, John Wiley & Sons, Inc.

Location of the Heart Thoracic cavity between two lungs  ~2/3 to left of midline surrounded by pericardium: Fibrous pericardium -  Inelastic and anchors heart in place Inside is serous pericardium - double layer around heart  Parietal layer fused to fibrous pericardium  Inner visceral layer adheres tightly to heart  Filled with pericardial fluid - reduces friction during beat.

Copyright 2010, John Wiley & Sons, Inc. Position of the Heart

Copyright 2010, John Wiley & Sons, Inc. Position of the Heart

Copyright 2010, John Wiley & Sons, Inc. Heart Wall Epicardium - outer layer Myocardium - cardiac muscle  Two separate networks via gap junctions in intercalated discs - atrial & ventricular  Networks- contract as a unit Endocardium - Squamous epithelium  lines inside of myocardium

Copyright 2010, John Wiley & Sons, Inc. Pericardium

Copyright 2010, John Wiley & Sons, Inc. Cardiac Muscle Fibers

Copyright 2010, John Wiley & Sons, Inc. Cardiac Muscle Tissue

Copyright 2010, John Wiley & Sons, Inc. Chambers of the Heart 4 chambers 2 upper chambers = Atria  Between is interatrial septum  Contains fossa ovalis - remnant of foramen ovalis 2 lower chambers = ventricles  Between is interventricular septum Wall thickness depends on work load  Atria thinnest  Right ventricle pumps to lungs & thinner than left

Copyright 2010, John Wiley & Sons, Inc. Structure of the Heart

Copyright 2010, John Wiley & Sons, Inc. Structure of the Heart

Copyright 2010, John Wiley & Sons, Inc. Structure of the Heart

Copyright 2010, John Wiley & Sons, Inc. Great Vessels Of Heart-Right Superior & inferior Vena Cavae  Delivers deoxygenated blood to R. atrium from body  Coronary sinus drains heart muscle veins R. Atrium  R. Ventricle pumps through Pulmonary Trunk  R & L pulmonary arteries  lungs

Copyright 2010, John Wiley & Sons, Inc. Great Vessels Of Heart-Left Pulmonary Veins from lungs  oxygenated blood  L. atrium  Left ventricle  ascending aorta  body Between pulmonary trunk & aortic arch is ligamentum arteriosum fetal ductus arteriosum remnant

Copyright 2010, John Wiley & Sons, Inc. Posterior View of Heart

Copyright 2010, John Wiley & Sons, Inc. Anterior View of Frontal Section

Copyright 2010, John Wiley & Sons, Inc. Valves Designed to prevent back flow in response to pressure changes Atrioventricular (AV) valves  Between atria and ventricles Right = tricuspid valve (3 cusps) Left = bicuspid or mitral valve Semilunar valves near origin of aorta & pulmonary trunk Aortic & pulmonary valves respectively

Copyright 2010, John Wiley & Sons, Inc. Atrioventricular Valves: Bicuspid Valves

Copyright 2010, John Wiley & Sons, Inc. Atrioventricular Valves: Superior View

Copyright 2010, John Wiley & Sons, Inc. Blood Flow Through Heart

Copyright 2010, John Wiley & Sons, Inc. Blood Flow

Copyright 2010, John Wiley & Sons, Inc. Blood Supply Of Heart Blood flow through vessels in myocardium = coronary circulation Left & right coronary arteries  branch from aorta  branch to carry blood throughout muscle Deoxygenated blood collected by coronary sinus (posterior) Empties into right atrium

Copyright 2010, John Wiley & Sons, Inc. Conduction System 1% of cardiac muscle generate action potentials= Pacemaker & Conduction system Normally begins at sinoatrial (SA) node  Atria & atria contract  AV node - slows  AV bundle (Bundle of His)  bundle branches  Purkinje fibers  apex and up- then ventricles contract

Copyright 2010, John Wiley & Sons, Inc. Pacemaker Depolarize spontaneously sinoatrial node ~100times /min also AV node ~40-60 times/min in ventricle ~20-35 /min Fastest one run runs the heart = pacemaker Normally the sinoatrial node

Copyright 2010, John Wiley & Sons, Inc. Frontal plane Right atrium Right ventricle Left atrium Left ventricle Anterior view of frontal section Frontal plane Left atrium Left ventricle Anterior view of frontal section SINOATRIAL (SA) NODE 1 Right atrium Right ventricle Frontal plane Left atrium Left ventricle Anterior view of frontal section SINOATRIAL (SA) NODE ATRIOVENTRICULAR (AV) NODE 1 2 Right atrium Right ventricle Frontal plane Left atrium Left ventricle Anterior view of frontal section SINOATRIAL (SA) NODE ATRIOVENTRICULAR (AV) NODE ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) Right atrium Right ventricle Frontal plane Left atrium Left ventricle Anterior view of frontal section SINOATRIAL (SA) NODE ATRIOVENTRICULAR (AV) NODE ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) RIGHT AND LEFT BUNDLE BRANCHES Right atrium Right ventricle Frontal plane SINOATRIAL (SA) NODE ATRIOVENTRICULAR (AV) NODE Left atrium Left ventricle Anterior view of frontal section ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) RIGHT AND LEFT BUNDLE BRANCHES PURKINJE FIBERS Right atrium Right ventricle

Copyright 2010, John Wiley & Sons, Inc. Electrocardiogram Recording of currents from cardiac conduction on skin = electrocardiogram (EKG or ECG) P wave = atrial depolarization  Contraction begins right after peak  Repolarization is masked in QRS QRS complex = Ventricular depolarization  Contraction of ventricle T-wave = ventricular repolarization  Just after ventricles relax

Copyright 2010, John Wiley & Sons, Inc. ECG

Copyright 2010, John Wiley & Sons, Inc. Cardiac Cycle after T-wave  ventricular diastole  Ventricular pressure drops below atrial & AV valves open  ventricular filling occurs After P-wave  atrial systole  Finishes filling ventricle (`25%) After QRS  ventricular systole  Pressure pushes AV valves closed  Pushes semilunar valves open and ejection occurs  Ejection until ventricle relaxes enough for arterial pressure to close semilunar valves

Copyright 2010, John Wiley & Sons, Inc. Action Potential Review muscle Heart has addition of External Ca 2+ Creates a plateau Prolonged depolarized period Can not go into tetanus

Copyright 2010, John Wiley & Sons, Inc. Cardiac Cycle

Copyright 2010, John Wiley & Sons, Inc. Flow Terms Cardiac Output (CO) = liters/min pumped Heart Rate (HR) = beats/minute (bpm) Stroke volume (SV) = volume/beat CO = HR x SV

Copyright 2010, John Wiley & Sons, Inc. Controls - Stroke Volume (S.V.) Degree of stretch = Frank-Starling law  Increase diastolic Volume increases strength of contraction  increased S.V.  Increased venous return  increased S.V. increased sympathetic activity High back pressure in artery  decreased S.V.  Slows semilunar valve opening

Copyright 2010, John Wiley & Sons, Inc. Controls- Heart Rate Pacemaker adjusted by nerves  Cardiovascular center in Medulla parasympathetic- ACh slows  Via vagus nerve Sympathetic - norepinephrine speeds Sensory input for control:  baroreceptors (aortic arch & carotid sinus)- B.P.  Chemoreceptors- O 2, CO 2, pH

Copyright 2010, John Wiley & Sons, Inc. Other Controls Hormones:  Epinephrine & norepinephrine increase H.R.  Thyroid hormones stimulate H.R.  Called tachycardia Ions  Increased Na + or K + decrease H.R. & contraction force  Increased Ca 2+ increases H.R. & contraction force

Copyright 2010, John Wiley & Sons, Inc. Autonomic Nervous System Regulation of Heart Rate

Copyright 2010, John Wiley & Sons, Inc. Exercise and the Heart Aerobic exercise (longer than 20 min) strengthens cardiovascular system Well trained athlete  doubles maximum C.O. Resting C.O. about the same but resting H.R. decreased

Copyright 2010, John Wiley & Sons, Inc. Heart & Blood pressure Result of contraction force of left heart ventricle and the elasticity and diameter of the arteries in the peripheral circulatory system Due to the pulsating heart contractions, blood pressure is highest after chamber contraction = systolic blood pressure Pressure observed after relaxation of the ventricle is called the diastolic blood pressure Typical resting blood pressure of a human individual is: 120 mm Hg in systole and 80 mm Hg in diastole usually termed short: 120 over 80 Blood pressure is routinely measured with a sphygmomanometer or a "blood pressure cuff“ Permanently increased blood pressure in a person is considered to be one of the major risk factors for heart dys-function and stroke

Copyright 2010, John Wiley & Sons, Inc. Causes of high blood pressure High blood pressure can be due or caused by several factors 1. Hereditary reasons - predisposition due to genetic defects & hyperthyroidism 2. Life style habits - e.g. lack of exercise and sessile life style - e.g. smoking - nicotine is potent vasoconstrictor and smoke contains a lot of chemically reactive "free radicals", which can lead to a lowering of the levels of the cell's and body's protective antioxidants, most prominently vitamin C, vitamin E, cysteine and glutathione - e.g. stress & increased norepinephrine - e.g. “bad” nutritional habits - high consumption of caffeine-containing beverages, e.g. coffee, tea, Coke, Red Bull, etc. - high salt intake 3. Temperature - sauna visit, extreme sun bathing or desert hiking