Cardiac Physiology The heart chambers the valves Cardiac

Cardiac Physiology • The heart: chambers, the valves • Cardiac muscle cells – Some cardiac muscle cells are autorhythmic – Arrangement of cardiac muscle cells – Excitation-contraction coupling

Atrioventricular (AV) Valves • guard the passageway between the atria and the ventricles – Tricuspid valve between right atrium and right ventricle – Bicuspid (mitral) valve between left atrium and left ventricle

Semilunar valves • Between ventricles and arteries – Pulmonary valve between right ventricle and pulmonary artery – Aortic valve between left ventricle and aorta

All myocardial cells • Gap junctions at intercalated discs, waves of depolarization spread from one cell to another

Autorhythmic myocardial cells • (pacemakers) are small myocardial cells with few contractile fibers • Spontaneously generate action potentials • Enables the heart to contract without any outside signal • The heart is myogenic: signal for contraction originates from heart muscle itself

Most myocardial cells • • Remaining myocardial cells are striated Have sarcomeres Much smaller than skeletal muscle fibers Connected by gap junctions at intercalated discs • Lots of mitochondria • Lots of blood flow to myocardial cells

More facts about myocardial cells • Large branching t-tubules • Sparse sarcoplasmic reticulum • Source of Ca++ is largely extracellular

Excitation-contraction coupling • Depolarization cell membrane voltage gated Ca++ channels open • Ca++ enters cell • calcium-induced calcium release: Ca++ released from SR • Ca++ binds to troponin contraction

Myocardial cell relaxation • Ca++ dissociates from troponin • Ca++ returns to SR by Ca++ ATPase • Ca++ also transported from cell by Na+Ca++ indirect active transport protein: Ca++ is exchanged for Na+, which moves in along its electrochemical gradient Na+ removed by active transport