Heart

 Hold up your clenched fist  Your heart is about the size of your fist ◦ Varies by gender, and age of the owner  Age changes are due to increases in the size of cells, not number of cells  Average mass of a heart  grams (0.5 – 0.8 pounds)

 Location and Coverings of the Heart ◦ Heart located between two lungs in thoracic cavity ◦ 2/3 of mass is left of body’s midline ◦ Apex  pointed end formed at tip of left ventricle ◦ Base  formed by atria, mostly left atrium  Major blood vessels enter and exit at the base

 Pericardium: membrane that surrounds and protects the heart and holds it in place  Two parts of pericardium: (1) Fibrous pericardium (2) Serous pericardium

 Pericarditis  build up of pericardial fluid; compresses the heart = cardiac tamponade

 Heart Wall ◦ Three layers: ◦ EXTERNAL (1) epicardium or visceral layer of serous pericardium  Thin, transparent outer layer of the wall  Composed of mesothelium and connective tissue

 MIDDLE (2) myocardium  Bulk of heart wall  Consists of cardiac muscle  Responsible for pumping action of heart

 Cardiac muscle  two separate networks connected by intercalated discs ◦ Atrial ◦ Ventrical  Gap junctions in the discs allow action potential conduction from one muscle fiber to the next

 INTERNAL (3) endocardium  Thin layer of squamous epithelium lining inside of myocardium  Covers valves of heart and tendons attached to the valves  Continuous with epithelial lining of large blood vessels

 Chambers of the Heart ◦ Four chambers:  Two upper are the atria  Right atrium  Left atrium

 Two lower are the ventricles  Right ventricle  Left ventricle

 Great Vessels of the Heart ◦ Right atrium receives deoxygenated blood through three veins…  Superior vena cava  Inferior vena cava  Coronary sinus

◦ Right ventricle pumps blood into the pulmonary trunk  Right pulmonary artery goes to right lung  Left pulmonary artery goes to left lung  Blood becomes oxygenated

 Valves of the Heart (4) ◦ Prevent blood from flowing backward ◦ Composition: dense connective tissue covered by endothelium ◦ TWO Atrioventricular (AV) valves lie between the atria and ventricles  Between the right atrium and right ventricle is the AV called the (1) tricuspid valve, which has the three cusps

 Chordae tendineae ◦ tendon-like chords that connect the pointed ends of the cusps to cardiac muscle projections on inner surface of the ventricles ◦ prevent the cusps from pushing up into the atria when the ventricles contract

◦ AV between the left atrium and left ventricle is called the (2) bicuspid (mitral) valve  It has two cusps

◦ TWO Semilunar valves are located near origin of pulmonary trunk and aorta  Prevent blood from flowing back into the heart  Pulmonary valve  Aortic valve Both consists of three semi-lunar cusps attached to the artery wall

 Blood Flow Through the Heart ◦ Flow follows pressure  high to low

 Blood Supply of the Heart

 Natural ‘pacemaker’ of the heart

 Recordings of the electrical changes that accompany the heartbeat are called electrocardiograms or EKG or ECG

 Heart Sounds ◦ Come mainly from turbulence created by blood flow when valves close  First sound  lubb  Loud booming sound from AV valves closing after ventricular systole begins  Second sound  dubb  Short, sharp sound from SL valves closing at end of ventricular systole  Next a pause…so lubb, dubb, pause, lubb, dubb, pause

 Cardiac output  volume of blood ejected per minute from left ventricle into aorta ◦ Determined by stoke volume (SV) and heart rate (HR)  Stroke volume  amount of blood ejected by left ventricle during each beat  Heart rate  number of heart beats per minute Sample calculation of cardiac output: Average resting adult male stroke volume = 70 mL Average heart rate = 75 beats per minute SO…average cardiac output SV X HR 70 mL/beat X 75 beats/min 5250 mL/ min or 5.25 L / min

 Regulation of Stroke Volume  Three factors: ◦ The degree of stretch in the heart before it contracts  More stretch means more forceful contraction ◦ The forcefulness of contraction of individual ventricular muscle fibers ◦ The pressure required to eject blood from the ventricle

 Autonomic Regulation of Heart Rate ◦ Originates in cardiovascular center (CV) in medulla oblongata ◦ Input comes in from a variety of sensory receptors (barorecptors and chemoreceptors) from higher brain centers ◦ Then output is directed through increasing or decreasing frequency of nerve impulses sent to sympathetic and parasympathetic branches  Sympathetic neurons reach heart through cardiac accelerator nerves that innervate conduction system, atria, and ventricles releasing norepinephrine to increase heart rate  Parasympathetic neurons reach heart through vagus (X) nerves that extend conduction system and atria releasing acetylcholine (ACh) to decrease heart rate

 Chemical Regulation of Heart Rate ◦ Hormones  Epinedrine  Norepindrine  Increase heart pumping effectiveness by increasing heart rate and contraction force ◦ Ions  K + and Na +  Decrease heart rate and contraction force  Ca +  Increase heart rate and contraction force

 Other Factors in Heart Rate Regulation ◦ Age ◦ Gender ◦ Physical fitness ◦ Body temperature