Cardiac Cycle NOTES

The Cardiac Cycle The primary function of the heart is to circulate oxygenated and deoxygenated blood throughout the body. The RIGHT chambers of the heart carry deoxygenated blood to travel to the lungs, where it RELEASES CO2 and RECEIVES O2 The LEFT chambers pump oxygenated blood back to the body’s organs and muscles

REVIEW: PATHWAY OF BLOOD THROUGH THE HEART Blood low in oxygen from the body returns to the right atrium of the heart via the inferior and superior vena cava The right atrium contracts, forcing blood through the tricuspid valve into the right ventricle. The right ventricle contracts, closing the tricuspid valve, and forcing blood through the pulmonary valve into the pulmonary arteries The pulmonary arteries carry deoxygenated blood to the lungs to release excess carbon dioxide (CO2) while red blood cells pick up a new supply of oxygen (O2) Freshly oxygenated blood returns to the left atrium of the heart via the pulmonary veins. The left atrium contracts, forcing blood through the bicuspid/mitral valve into the left ventricle. The left ventricle contracts, closing the bicuspid valve and forcing open the aortic valve . Blood enters the aorta to provide oxygenated blood to the entire body after a journey through the blood vessels!

Cardiac Muscle Contraction Cardiac muscle contraction occurs in specific steps to ensure that blood is routed to the proper location. Contraction is caused by action potentials depolarizing the cardiac muscle cells leading to sarcomere shortening

Remember… Molecules do NOT like being crowded and will move to the LESS crowded side Depolarization: Sodium (Na+) IN Repolarization: Potassium (K+) OUT

Cardiac Muscle: Calcium (Ca+) goes into cardiac cells, prolonging depolarization, increasing force of contraction, and increasing amount of calcium available to initiate sarcomere shortening (SFT)

Cardiac Muscle Anatomy Gap junctions @ intercalated discs allow for rapid movement of molecules (sodium, potassium, calcium) in and out of cell, and thus, quick action potentials and muscle contractions

Cardiac Muscle Contraction Contraction starts at the Sinoatrial (SA) Node which contains specialized pacemaker cells. These cells can generate spontaneous action potentials without input from the nervous system.

Pacemaker Potential Slow influx of Na+ into cardiac cells between action potentials Increases membrane potential positively toward threshold potential, allowing for autorhythmicity of cardiac cells at the SA node (all-or-none response).

Sinoatrial (SA) node (Pacemaker) Atrioventricular (AV)node Bundle of His Left & Right Bundle branches Purkinje Fibers

Electrical Conduction System of the Heart SA NODE  AV NODE  BUNDLE OF HIS  LEFT & RIGHT BUNDLE BRANCHES  PURKINJE FIBERS SA node: 50 msec. The pacemaker. AV node: 100 msec: Atrial contraction occurs. AV delay: Action potential travels more slowly This delay ensures the ventricles relax and receive blood from atrial contraction BEFORE the ventricles get the signal to contract and pump blood out. 25 msec – Bundle of His: signal travels down septum Right and left bundle branches: depolarization splits signal between the right and left ventricles

Electrical Conduction System of the Heart 4. Purkinje fibers: 50 msec Widespread fibers conduct action potentials throughout left and right ventricles. Ventricular contraction begins.

Impulse Conduction through the Heart

Video Clip http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter22/animation__conducting_system_of_the_heart.html