Detailed Anatomy and Physiology of the Heart

Pericardium

• 3-layered sac surrounding the heart

  • Fibrous pericardium (tough outer layer):

  • Protective outer layer

  • Attached to the great vessels (aorta, pulmonary artery & veins)

  • Anchors heart to diaphragm

  • Serous pericardium:

  • Two layers: Parietal (outer lining) and Visceral (inner lining directly covering heart; also called epicardium)

Function of the Pericardium:

• Fixes heart in mediastinum (central chest cavity), limits motion

• Protects against infections from nearby organs (e.g., lungs)

• Prevents excessive dilation (stretching) in acute volume overload situations

• Provides lubrication

Heart Wall Layers

• Epicardium: Visceral layer of serous pericardium

• Myocardium:

  • Composed of cardiac muscle fibers

  • Responsible for contraction and pumping

• Endocardium:

  • Thin inner lining; continuous with vascular endothelium (lining of blood vessels)

Blood Flow through the Heart
Flow Pathway (trace one drop of blood):

1. Deoxygenated blood returns from body via:

   • SVC (from upper body)

   • IVC (from lower body)

   • Coronary sinus (from heart muscle)

2. → Right atrium → through tricuspid valve

3. → Right ventricle → through pulmonary semilunar valve

4. → Pulmonary trunk → to lungs (for oxygenation)

5. → Left atrium (receives oxygenated blood via 4 pulmonary veins) → through mitral valve

6. → Left ventricle → through aortic semilunar valve

7. → Aorta → out to body

External and Internal Landmarks

• Coronary groove (also called atrioventricular sulcus): groove separating atria and ventricles

• Anterior interventricular sulcus: Front groove between ventricles

• Posterior interventricular sulcus: Back groove between ventricles

Chambers of the Heart

• Right Atrium: Contains SVC, IVC, and right auricle (small ear-like pouch)

• Left Atrium: Receives 4 pulmonary veins + left auricle

• Right Ventricle: Forms most of front of heart; pumps blood to pulmonary trunk

• Left Ventricle: Forms apex and 2/3 of back; pumps to systemic circulation (whole body)

Coronary Arteries and Blood Supply

• Right Coronary Artery (RCA): Supplies right heart

• Left Coronary Artery (LCA):

  • Left Main Stem splits into:

  • LAD (Left Anterior Descending): supplies front/inferior walls

  • Circumflex artery: follows groove between left atrium/ventricle

Cardiac Veins:

• Collect waste → drain into coronary sinus → empties into right atrium

Functional Anatomy of Heart Valves

• Atrioventricular (A-V) Valves:

  • Tricuspid (right side) & Mitral/Bicuspid (left side)

  • Open in diastole (when heart is relaxed)

  • Close during systole (when ventricles contract) to prevent backflow

• Semilunar Valves (pulmonary & aortic):

  • Open in systole, close in diastole

  • Prevent backflow from arteries into ventricles

Heart's Conducting System

• Cardiac muscle fibers are connected by gap junctions (allow electrical signals to spread)

• Atrial and ventricular conduction systems are separated by fibrous skeleton (non-conductive tissue)

Key parts:

• SA Node (pacemaker): initiates heartbeat

• AV Node: delays signal → sends to Bundle of His

• Bundle branches → down septum → to Purkinje fibers (trigger contraction from apex upwards)

Innervation of the Heart

• Cardiac Plexus: contains nerve fibers from both:

  • Sympathetic (↑ heart rate/force via cardioacceleratory center)

  • Parasympathetic (↓ heart rate via vagus nerve and cardioinhibitory center)

Cardiac Pain:

• Caused by ischemia (lack of blood flow)

• Pain is referred (felt elsewhere, e.g., arm or jaw) due