Heart

Location Within the thorax Pointed APEX extends to left Rests on diaphragm at the 5 th intercostal space Broad BASE, lies under the 2 nd rib

Pericardium A double membrane sac encloses heart thin visceral pericardium = epicardium hugs the surface of the heart loose outer layer = parietal pericardium

Pericardial Fluid Slippery lubricating fluid produced by the membrane between the pericardial layers. It allows the heart to beat in a frictionless environment

Myocardium Heart walls are thick cardiac muscle

Chambers 4 hollow chambers Lined with thin lining called endocardium

Atria 2 superior RECEIVING chambers Thin walled Blood flows into and fills the atria under low pressure

Ventricles 2 inferior DISCHARGING (pumping) chambers Thick walled Forces blood out of the heart into large arteries

A Septum divides the heart longitudinally Interatrial Septum Interventricular Septum

Double Pump Pulmonary circulation to lungs and back Systemic circulation to body tissue and back

Pulmonary Circulation Right side of the heart  lungs  left side of the heart

Systemic Circulation Left side of the heart  Body Tissue  Right side of the heart

Valves 4 valves allow blood to flow in only one direction Prevent backwash 2 AV valves = atrioventricular valves 2 Semilunar valves

AV valves Between atria and ventricle Prevent backwash into atria Left AV = bicuspid or mitral (2 flaps) Right AV = tricuspid (3 flaps)

The AV valves are anchored to the wall of the ventricles by the Chordae Tendineae Valves are open when ventricle is relaxed closed when ventricle is contracted

Semilunar valves Guard the base of the large arteries leaving the ventricles Each valve has 3 cusps (flaps) When ventricles contract, they open, when relaxed they close to prevent backwash

Pulmonary semilunar- from the right ventricle to the pulmonary trunk (Artery) Aortic semilunar- from the left ventricle to the aortic artery

Each set of valves open at different times: AV opens when ventricle relaxes Semilunar opens when ventricles contract

Oxygen Poor Blood From the veins of the body tissue  Superior and Inferior Vena Cava  Right atria  tricuspid valve  Right ventricle  pulmonary semilunar valve  Pulmonary Trunk  Pulmonary arteries  (branch right and left)  lungs  picks up oxygen and dumps off carbon dioxide

Oxygen Rich Blood Drained from the lungs  4 Pulmonary Veins  Left atria  bicuspid valve  Left ventricle  aortic semilunar valve  Aorta  body tissues  dumps off oxygen and picks up carbon dioxide

Cardiac Circulation Although the heart chambers are filled with blood almost continuously, that blood does NOT nourish the myocardium

The right and left coronary arteries branch from the base of the aorta and encircle the heart in a groove at the junction of the atria and ventricles

Those arteries are compressed when the ventricles contract and are only able to supply blood to heart muscle between beats

Rapid heart rate may cause inadequate blood supply The lower your resting heart rate, the better nourished your heart muscle is

The myocardium is drained by the coronary veins  coronary sinus  the right atrium

Cardiac Cycle The time and events occurring from one heartbeat to the next

Systole = contraction Diastole = relaxation

Lub – Dup - Pause “lub” – closing of the AV valves- longer and louder – ventricles contracting “dup” – closing of semilunar valves – shorter and sharper- ventricles relaxing “pause” is the heart in complete relaxation Murmurs are usually problems with the valves leaking

Atria contract simultaneously As they begin to relax  the ventricles contract (ventricular systole)  ventricles relax (ventricular diastole)

Conduction System Cardiac muscle cells can contract spontaneously and independently 2 types of control systems: -Intrinsic -Extrinsic

Intrinsic -Purkinje or Nodal system -A cross between nerve and muscle tissue -Auto-rythmic cells -Can initiate action potentials or trigger contractions

SA Node SA = sinoatrial On the right atrial wall PACEMAKER – starts each beat

AV Node Atrioventricular On interatrial septum Bundle of His  Bundle branches  Purkinje fibers  Ventricles contract

Extrinsic System Heart contractions can be changed by autonomic nerves, chemicals, hormones, and ions (Na+, potassium, Calcium) Stress (sympathetic influence) affects SA node which increases heart rate