Heart and Circulation

The Cardiovascular System: The Heart

Introduction

• The heart is a double pump responsible for:
  • Pulmonary circulation: Delivers blood to the lungs.
  • Systemic circulation: Delivers blood to the body.

Location and General Features of the Heart

• Location:

  • Lies in the chest wall, slightly left and posterior to the sternum.
  • Base: Superior end where major blood vessels are attached.
  • Apex: Inferior end resting in the pericardial cavity.

• General Features:

  • Four chambers:
    • Atria (Left and Right): Thin muscular walls.
    • Ventricles (Left and Right): Thicker muscular walls, especially the left ventricle.
  • Arteries: Carry blood away from the heart.
  • Veins: Carry blood into the heart.

Blood Flow Through the Heart

Right Side of the Heart

• Superior Vena Cava: Receives blood from the head and upper body.
• Inferior Vena Cava: Receives blood from the trunk and lower limbs.
• Right Atrium: Receives blood from systemic circulation.
• Tricuspid Valve (AV Valve): Prevents backflow into the atrium.
• Right Ventricle: Receives blood from the right atrium; pumps blood to the lungs; thin wall.
• Pulmonary Artery: Receives blood from the right ventricle.
  • Left pulmonary artery.
  • Right pulmonary artery.
• Pulmonary Valve: Prevents backflow into the ventricle.

Left Side of the Heart

• Pulmonary Veins:
  • Left pulmonary vein.
  • Right pulmonary vein.
• Left Atrium: Receives blood from pulmonary circulation.
• Bicuspid Valve (AV Valve): Prevents backflow into the atrium.
• Left Ventricle: Receives blood from the left atrium; pumps blood to systemic circulation; thick wall.
• Aorta: Receives blood from the left ventricle; beginning of systemic circulation.
• Aortic Valve: Prevents backflow into the ventricle.

Valves of the Heart During Ventricular Relaxation (Diastole) and Contraction (Systole)

Relaxed Ventricle (Diastole)

• Mitral Valve: Open.
• Aortic Valve: Closed.
• Chordae Tendineae: Loose.
• Papillary Muscle: Relaxed.

Contracting Ventricle (Systole)

• Mitral Valve: Closed.
• Aortic Valve: Open.
• Chordae Tendineae: Tight.
• Papillary Muscle: Contracted.

Conducting System of the Heart

• Nodal Cells: Autorhythmic.
• Sinoatrial (SA) Node:
  • Lies in the right atrial wall.
  • Pacemaker cells with a fast rate of spontaneous activity.
• Atrioventricular (AV) Node:
  • Located at the junction between the atria and ventricles.
  • Slow rate of spontaneous activity.

Impulse Conduction Through the Heart

• The conducting system facilitates the coordinated contraction of the heart chambers.

Electrocardiogram (ECG)

• Detects electrical events via electrodes on the body surface.
• Specific nodal, conducting, and contractile components of the heart produce recognizable deflections.
  • P Wave: Atrial contraction (atrial systole).
  • QRS Complex: Atrial relaxation (atrial diastole), ventricular contraction (ventricular systole).
  • T Wave: Ventricular relaxation (ventricular diastole).

The Cardiac Cycle

• Alternating contraction (systole) and relaxation (diastole) of the atria and ventricles.

Systole

• Chambers contract, moving blood to the next chamber or blood vessel.
• Atrial Systole
• Ventricular Systole

Diastole

• Chambers relax and fill with blood.
• Atrial Diastole
• Ventricular Diastole

Phases of the Cardiac Cycle

1. Ventricular Filling (Ventricular Diastole - Late): 800 msec
2. Atrial Contraction (Atrial Systole Begins): 100 msec
3. Isovolumetric Contraction (Ventricular Systole - First Phase)
4. Ventricular Ejection (Ventricular Systole - Second Phase)
5. Isovolumetric Relaxation (Ventricular Diastole - Early)

Pressure and Volume Changes During the Cardiac Cycle

• Atrial Systole: Atria eject blood into ventricles.
• Ventricular Systole:
  • Isovolumetric ventricular contraction.
  • Ventricular ejection occurs.
• Ventricular Diastole:
  • Semilunar valves close.
  • Isovolumetric relaxation occurs.
  • AV valves open; passive ventricular filling occurs.

Heart Sounds

• **First Heart Sound (