Heart Anatomy & Physiology Lab Review

Heart Location

• Sits inside the pericardial cavity, which itself is located in the mediastinum (the central compartment of the thoracic cavity)
  • Posterior to the sternum, slightly left of the midsagittal (midline) plane
  • Flanked by the right and left lungs, resting on the superior surface of the diaphragm
• Surrounded by a double-layered pericardial membrane (see Pericardium section)
• Clinical significance
  • Leftward orientation explains why left-sided chest pain is an important diagnostic clue
  • Mediastinal position allows for compression‐only CPR to be effective when applied to the lower half of the sternum

Heart Chambers, Valves, and Great Vessels

• Chambers (superior to inferior / right to left)
  • Right atrium (RA)
  • Left atrium (LA)
  • Right ventricle (RV)
  • Left ventricle (LV)
• Valves
  • Atrioventricular (AV)
  • Tricuspid valve (RA ➜ RV)
  • Bicuspid / Mitral valve (LA ➜ LV)
  • Semilunar (SL)
  • Pulmonary valve (RV ➜ Pulmonary trunk)
  • Aortic valve (LV ➜ Aorta)
• Great vessels (blood entrance & exit routes)
  • Pulmonary trunk ➜ right & left pulmonary arteries ➜ lungs
  • Aorta (ascending, arch, descending) ➜ systemic circulation
  • Venae cavae
  • Superior vena cava (SVC) – drains head, neck, upper limbs
  • Inferior vena cava (IVC) – drains trunk, abdomen, lower limbs
• Functional highlights
  • AV valves are anchored by chordae tendineae & papillary muscles, preventing prolapse during ventricular systole
  • SL valves rely on cup-shaped cusps; no chordae tendineae required

Internal Features of the Heart

• Right Atrium
  • Fossa ovalis – embryologic remnant of the foramen ovale; thin, oval depression on interatrial septum
  • Openings: coronary sinus (posterior RA wall), SVC, IVC
• Right Ventricle
  • Trabeculae carneae – irregular muscular ridges lining ventricular wall (increase turbulence, reduce suction)
  • Papillary muscles (anterior, posterior, septal) anchor chordae tendineae to tricuspid cusps
• Left Atrium
  • Receives four pulmonary veins (2R + 2L) visible on posterior view
• Left Ventricle
  • Thickest myocardium (systemic pressure)
  • Two large papillary muscles anchor mitral valve
  • Aortic vestibule leads to ascending aorta

Septal Structures

• Interatrial septum – separates RA & LA; contains fossa ovalis
• Interventricular septum – muscular (inferior) & membranous (superior) parts divide RV & LV
• Atrioventricular septum – area between atria and ventricles that carries the fibrous skeleton & AV node
• Clinical tie-in: Ventricular septal defects (VSDs) are most common congenital cardiac anomalies

Pericardium and Wall Layers

• Pericardium (from superficial to deep)
  • Fibrous pericardium – dense irregular CT, anchors heart to diaphragm & great vessels; limits over-distention
  • Serous pericardium (double-layered)
  • Parietal layer – lines inner fibrous sac
  • Visceral layer (epicardium) – outer surface of heart wall
  • Pericardial cavity – potential space w/ serous fluid (⟶ frictionless beating)
• Heart wall layers
  • Epicardium – visceral serous layer; areolar + adipose CT, vasculature & nerves
  • Myocardium – cardiac muscle (thicker in LV); responsible for pumping action
  • Endocardium – simple squamous endothelium + areolar CT; continuous with vascular endothelium

Histology of Cardiac Muscle

• Cells: short, branched cardiomyocytes with single centrally located nucleus
• Intercalated discs
  • Desmosomes – mechanical linkage
  • Gap junctions – electrical coupling ➜ functional syncytium
• Striated appearance due to organized sarcomeres; more mitochondria than skeletal muscle (high oxidative demand)
• In lab microscopy, identify: nucleus (central), intercalated discs (dark transverse lines), striations (lighter, parallel lines)

External (Surface) Anatomy – Key Landmarks

• Anterior (sternocostal) view
  • Coronary (atrioventricular) sulcus – houses right & left coronary arteries
  • Anterior interventricular sulcus – contains LAD (left anterior descending) artery & great cardiac vein
  • Right/Left auricles – ear-like appendages of atria
  • Apex – inferior LV tip, typically left 5th intercostal space, mid-clavicular line
• Posterior (base/diaphragmatic) view
  • Coronary sinus – major venous collection emptying into RA
  • Posterior interventricular sulcus – contains posterior interventricular artery & middle cardiac vein
  • Multiple pulmonary veins (2 per lung) entering LA

Coronary Circulation

• Coronary Arteries (originate from ascending aorta immediately distal to aortic valve)
  • Right Coronary Artery (RCA)
  • SA nodal branch ➜ sinoatrial node (60% of hearts)
  • Right marginal artery – along inferior RA/RV border
  • Posterior interventricular artery (PDA) – supplies posterior 1/3 of IV septum & both ventricles (in right-dominant hearts)
  • Left Coronary Artery (LCA)
  • Left anterior descending (LAD) / Anterior interventricular artery – anterior 2/3 IV septum, anterior LV & RV
  • Circumflex artery – courses in coronary sulcus to posterior LV; gives left marginal branches
• Coronary dominance determined by origin of PDA (≈70% right-dominant)
• Coronary Veins
  • Great cardiac vein – parallels LAD; empties into coronary sinus
  • Middle cardiac vein – parallels PDA
  • Small cardiac vein – parallels right marginal artery
  • Oblique, posterior LV veins ➜ all drain into coronary sinus ➜ RA
• Applied physiology
  • Coronary blood flow occurs mainly during ventricular diastole when myocardium is relaxed and aortic valve cusps no longer block coronary ostia
  • Myocardial ischemia ➜ angina pectoris; prolonged obstruction ➜ myocardial infarction (MI)

Cardiac Conduction System

• Specialized nodal & conducting fibers generate and propagate action potentials
  1. Sinoatrial (SA) node – pacemaker (≈ 60–100 bpm intrinsic rate)
  2. Internodal pathways / Bachmann’s bundle (to LA) ➜ atrial depolarization
  3. Atrioventricular (AV) node – conduction delay (~0.1 s) allows ventricular filling
  4. AV bundle (Bundle of His) ➜ right & left bundle branches (in IV septum)
  5. Purkinje fibers ➜ ventricular myocardium (including papillary muscles)
• Electrical activity produces surface voltage changes measured by ECG

Electrocardiogram (ECG) Waves, Segments & Intervals

• P wave – atrial depolarization (contraction follows)
• QRS complex – ventricular depolarization; atrial repolarization hidden
• T wave – ventricular repolarization
• P–Q (or P–R) segment – AV nodal delay (atria in diastole, ventricles filling)
• S–T segment – early ventricular repolarization; should be isoelectric (deviation ⟶ ischemia)
• P–R interval – onset of P to onset of QRS; normal 0.12–0.20 s
• Q–T interval – onset of QRS to end of T; reflects total time of ventricular depolarization + repolarization
• Rate calculation example: HR = \frac{60}{RR\, interval\,(s)}

Cardiac Cycle Terminology

• Depolarization – electrical excitation; triggers contraction
• Repolarization – electrical reset; triggers relaxation
• Systole – mechanical contraction phase (atrial systole or ventricular systole)
• Diastole – mechanical relaxation phase (filling)

Rhythm Disorders (Seen on ECG)

• Bradycardia – resting HR < 60 bpm (e.g., athlete’s heart, SA node dysfunction)
• Tachycardia – resting HR > 100 bpm (stress, fever, hyperthyroidism)
• Fibrillation
  • Atrial fibrillation – chaotic atrial activity, absent P waves, irregularly irregular ventricular rhythm
  • Ventricular fibrillation – rapid, disorganized ventricular activity; no cardiac output, requires defibrillation

Laboratory Activities & Practical Notes

• ECG Activity
  • Vernier EKG Sensor setup: RED (positive), BLACK (negative), REF (ground/neutral)
  • Lead II configuration typically used (RA ➜ RL ground ➜ LL positive)
  • Students expected to label waves, segments, and calculate intervals
• Gross-anatomy identification practice (models & cadaveric):
  • Label chambers, valves, vessels, coronary arteries/veins, septa
  • Recognize histology slide of cardiac muscle vs. skeletal/smooth muscle
• Ethical / clinical connections
  • Understanding coronary anatomy critical for angioplasty, bypass graft planning
  • Knowledge of conduction system vital for pacemaker lead placement
  • ECG interpretation forms basis for diagnosing MI, arrhythmias, electrolyte disturbances