The Heart & Cardiac Cycle Flashcards (Chapter 48)

Learning Objectives

• Structure of the Vertebrate Heart:

  • Understand the anatomical layout of a vertebrate heart, including the separation into chambers and circuits.

• Trace Blood Flow:

  • Be able to trace a drop of blood through both pulmonary (to/from lungs) and systemic (to/from the body) circuits.

• Sequence of the Cardiac Cycle:

  • Learn the events that occur during the cardiac cycle including contraction and relaxation phases.

• Systole vs Diastole:

  • Define and differentiate between systole (contraction) and diastole (relaxation) phases of the heart.

• Action Potential of Cardiac Muscle:

  • Outline how action potentials are generated in cardiac muscle and their significance in heart function.

• Electrocardiogram (ECG) Connection:

  • Relate cardiac cycle events to the ECG readout; recognize how electrical activity correlates with mechanical events of the heart.

Structure of Vertebrate Hearts

• Double Circulation System:

  • Composed of 2 atria and 2 ventricles; enables efficient blood circulation.

• Separation of Sides:

  • Two sides of the heart are separated by the septum (a wall).

The Mammalian Cardiac Cycle

• Heart Rate:

  • Average heart contractions occur around 70 times per minute.

• Phases of the Cycle:

  • Contraction: Pumps blood.

  • Relaxation: Chambers fill with blood.

  • Cardiac cycle: Complete sequence of pumping and filling.

• Blood Flow:

  • Right atrium receives deoxygenated blood from:

    • Superior vena cava

    • Inferior vena cava

    • Coronary sinus

  • Blood moves from the left atrium to the left ventricle through the bicuspid AV valve.

• Valves of the Heart:

  • AV Valves:

    • Control blood movement between atria and ventricles (Tricuspid = right, Bicuspid = left).

  • Semilunar Valves:

    • Located between ventricles and arteries (Pulmonary = right ventricle to pulmonary artery; Aortic = left ventricle to aorta).

• Heart Sounds:

  • “Lub” sound: Closure of tricuspid AV valve.

  • “Dub” sound: Closure of pulmonary semilunar valve.

Systole vs Diastole

• Cardiac Cycle Phases:

  • Systole: Contraction phase where blood is pushed from the heart.

  • Diastole: Relaxation phase where chambers fill with blood.

• Pressure Gradients:

  • Blood flows from higher to lower pressure areas, influencing the opening and closing of valves.

Electrical Activity and Cardiac Contraction

• Myogenic Heart:

  • Vertebrates have myogenic hearts, capable of generating action potentials independently.

• Sinoatrial (SA) Node:

  • Acts as pacemaker, setting heart rate and timing for contractions.

  • Produces electrical impulses that initiate heartbeats.

• Cardiac Muscle Structure:

  • Interconnected myocytes form networks through intercalated discs with gap junctions for electrical coupling.

Cardiac Contraction Phases

• Ion Concentrations:

  • Sodium (Na+), Calcium (Ca2+) higher outside; Potassium (K+) higher inside.

• Phases of Action Potential:

  • Phase 0: Depolarization begins; rapid influx of Na+.

  • Phase 1: Na+ channels close.

  • Phase 2: Plateau phase; K+ exits, Ca2+ enters slowly.

  • Phase 3: Rapid repolarization; K+ continues to exit.

  • Phase 4: Resting potential restored.

  • Absolute Refractory Period: Phases 0-3, ensuring coordinated contractions.

Maintaining a Rhythmic Heartbeat

• Conduction Pathway:

  • Impulse travels from the SA node to the AV node, then to ventricles through the AV bundle and its branches.

• Ventricular Contraction:

  • Both ventricles contract simultaneously, forcing blood through semilunar valves into the systemic or pulmonary arteries.

Electrocardiogram (ECG)

• ECG Functionality:

  • Monitors electrical events during the cardiac cycle.

  • Electrode placement on skin tracks electrical activity produced by the heart.

• ECG Wave Components:

  • P wave: Atrial depolarization.

  • QRS complex: Ventricular depolarization and contraction.

  • T wave: Ventricular repolarization during diastole.

  • Understand the correlation between ECG waves and cardiac cycle events.