Blood Circulation in the Heart

• Oxygenated Blood Flow

  • Blood from the lungs enters the left atrium through pulmonary veins.
  • The bicuspid valve (Mitral valve) opens, allowing blood to flow into the left ventricle.
  • At this point, papillary muscles are relaxed, and chordae tendineae are slack.
  • The semilunar valve between the left ventricle and the aorta is closed.

• Blood Ejection

  • As papillary muscles contract, they pull on the chordae tendineae, closing the mitral valve and opening the semilunar valve.
  • This allows the left ventricle to contract vigorously, pushing blood into the aorta and subsequently into systemic circulation.

Cardiac Skeleton

• The cardiac skeleton or fibrous skeleton is a plate of connective tissue providing support to the heart's valves, including atria and ventricles.
• Function:
  • Defines the shape of heart valves, ensuring structural integrity.
  • Provides electrical insulation, preventing unwanted electrical conductivity between atria and ventricles.

Heart Valves

• Four Main Heart Valves:
  • Atrioventricular Valves:
    • Tricuspid valve: Between right atrium and right ventricle.
    • Bicuspid (Mitral) valve: Between left atrium and left ventricle.
  • Semilunar Valves:
    • Pulmonary semilunar valve: Between right ventricle and pulmonary trunk.
    • Aortic semilunar valve: Between left ventricle and aorta.

Blood Flow Pathway

• Deoxygenated Blood:
  • Enters through superior/inferior vena cava into right atrium.
  • Flows through tricuspid valve into right ventricle.
  • Moves through pulmonary semilunar valve to the pulmonary trunk, which divides into pulmonary arteries heading towards the lungs for gas exchange.
• Oxygenated Blood:
  • After gas exchange, oxygen-rich blood returns to the heart via the pulmonary veins into the left atrium.
  • Flows into the left ventricle through the bicuspid valve, then to the aorta through the aortic semilunar valve, distributing oxygen throughout the body.

Coronary Circulation

• Coronary Arteries:
  • Supply blood to the heart muscle itself; originate from the base of the aorta.
  • Left Coronary Artery: Supplies blood to the anterior heart wall.
  • Right Coronary Artery: Supplies blood to the right ventricle.
• Cardiac Veins:
  • Drain deoxygenated blood from the heart muscle into the coronary sinus, which empties into the right atrium.

Cardiac Muscle Characteristics

• Layers of Heart Wall:
  • Epicardium: Outer layer.
  • Myocardium: Middle layer composed of cardiac muscle.
  • Endocardium: Smooth inner surface.
• Cardiac Muscle Cells:
  • Feature centrally located nucleus, branching cells, high mitochondrial content, and intercalated discs for contraction coordination.

Cardiac Conduction System

• Initiates and coordinates heartbeats:
  • Sinoatrial Node (SA Node): Main pacemaker located in the right atrium.
  • Atrioventricular Node (AV Node): Located in the right atrium; receives signals from SA node before sending them to ventricles.
  • Conduction Pathway:
    • SA Node ➔ AV Node ➔ AV Bundle ➔ Right and Left Bundle Branches ➔ Purkinje Fibers.
  • This system allows the atria to contract before the ventricles, optimizing blood flow.

Electrocardiogram (ECG or EKG)

• Records the electrical activity and rhythm of the heart:
  • Components:
    • P wave: Atrial depolarization.
    • QRS complex: Ventricular depolarization.
    • T wave: Ventricular repolarization.

Cardiac Cycle

• Represents all events during a single heartbeat:
  • Atrial Systole: Contraction of atria.
  • Ventricular Systole: Contraction of ventricles.
  • Diastole: Relaxation phase (atria and ventricles)

Heart Sounds

• First Sound (Lubb): Closure of atrioventricular valves.
• Second Sound (Dupp): Closure of semilunar valves.
• Utilized by healthcare professionals via stethoscope to assess cardiac function.

Regulation of Heart Function

• Cardiac Output: Volume of blood pumped per minute; calculated using:
  • Stroke Volume (ml/beat) × Heart Rate (beats/min) = Cardiac Output (liters/min).
  • Typical Values: ~70 ml/beat × 72 beats/min = 5 liters/min.
• Intrinsic Regulation: Mechanisms within the heart itself (e.g., preload and stroke volume related by Starling's law).
• Extrinsic Regulation: Influences from external factors (e.g., nervous or hormonal control).
  • Sympathetic (increases heart rate) vs. Parasympathetic control (decreases heart rate).