BS

Heart and Circulation – Comprehensive Lab Notes

Lab Context & Integration

  • Summer‐semester "wrap-up" lab focused on Heart Anatomy & Circulation.
    • Complements previous blood-focused lab and lecture material; heavy content overlap → studying one reinforces the other.
    • Core deliverables for practical:
    • Identify chambers, valves, and all labeled internal structures.
    • Trace blood flow through the heart (physiology meets anatomy).
    • Recognize and name major systemic vessels that enter/exit the heart.
    • Locate and name coronary arteries & veins.
    • Relate vessel color schemes (red/blue) to oxygenation state rather than artery/vein status.
    • Additional—but lecture-only—topics briefly referenced: cardiac conduction system, tissue layers (endocardium, myocardium, epicardium).

Heart Position, Orientation & Pericardium

  • Sits in the mediastinum; rests on diaphragm.
  • Rotation concept
    • Right side swings anteriorly (like turning right shoulder toward viewer).
    • Posterior view exposes more of left side.
    • Explains why “midline” grooves & vessels appear off-center.
  • Pericardium = double-walled sac ↓ friction during beats.
    • Visceral pericardium (epicardium): adheres to heart surface.
    • Parietal pericardium: outer fibrous layer.
    • Pericardial cavity contains lubricating fluid.

Chambers Overview

  • Total: 4 chambers.
    • Atria (Right & Left)
    • Thin-walled “catcher’s mitts” that receive blood.
    • Very little muscle ≈ pastel pink/white in diagrams.
    • Ventricles (Right & Left)
    • Muscular pumping chambers (especially left ventricle).
    • Left ventricle must generate systemic pressure; right only needs pulmonary pressure.
  • Apex = pointed inferior tip (actually not the top; think mountain peak).
  • Interventricular septum
    • Muscular wall separating ventricles; houses major conduction pathways (lecture topic).

Heart Valves & Support Structures

  • Total valves 4 = 2+2 ( 2 atrioventricular + 2 semilunar ).
    • Atrioventricular (AV) valves
    • Right = Tricuspid (3 cusps).
    • Left = Bicuspid / Mitral (2 cusps).
    • Held by chordae tendineae (tendinous cords) → anchored to papillary muscles projecting from ventricular walls.
    • Semilunar valves
    • Pulmonary semilunar: between right ventricle & pulmonary trunk.
    • Aortic semilunar: between left ventricle & ascending aorta.
  • Fibrous skeleton of dense collagen stabilizes valve rings & limits overstretching.

Vessel Categories & Color Logic

  • Arteries: carry blood away from heart.
  • Veins: carry blood to heart.
  • Color code in diagrams
    • Red = oxygenated (usually arteries, but pulmonary veins are red).
    • Blue = deoxygenated (usually veins, but pulmonary arteries are blue).

Major Systemic Vessels at the Heart

  • Entering Right Atrium
    • Superior vena cava (SVC) → drains body above heart.
    • Inferior vena cava (IVC) → drains body below heart.
    • Coronary sinus (heart’s own venous return; see coronary section).
  • Exiting Right Ventricle
    • Pulmonary trunk → splits into Right & Left pulmonary arteries.
  • Entering Left Atrium
    • Right & Left pulmonary veins (oxygenated).
  • Exiting Left Ventricle
    • Ascending aorta → Aortic arch → Descending aorta.

Branches of the Aortic Arch

  1. Brachiocephalic trunk (a.k.a. brachiocephalic artery)
    • Bifurcates into:
      • Right subclavian artery (right upper limb).
      • Right common carotid artery (right side of head/brain).
  2. Left common carotid artery (left side of head/brain).
  3. Left subclavian artery (left upper limb).
  • Variants: some individuals show 4 separate branches or shorter combined trunks.

Coronary Circulation (Heart’s Own Blood Supply)

Arteries (originate just above aortic semilunar valve)

  • Left coronary artery (LCA)
    • Anterior interventricular artery (a.k.a. LAD): runs in anterior interventricular sulcus; supplies septum & anterior walls.
    • Circumflex branch → gives off Left marginal artery along left margin.
  • Right coronary artery (RCA)
    • Right marginal artery: along right margin.
    • Continues posteriorly → Posterior interventricular artery (posterior interventricular sulcus).
    • RCA therefore supplies right side & posterior aspect.

Veins (drain into coronary sinus → right atrium)

  • Great cardiac vein: parallels anterior interventricular artery; wraps to left side.
  • Left marginal vein: accompanies left marginal artery.
  • Middle cardiac vein: runs with posterior interventricular artery.
  • All three converge into the coronary sinus, a dilated venous pouch on posterior atrioventricular groove, which empties directly into right atrium (guarded by small valve).

Interior Surface Landmarks

  • Trabeculae carneae: muscular ridges in ventricular walls.
  • Pectinate muscles: ridges in atrial walls (mentioned visually, not emphasized in lab questions).
  • Endocardium / Myocardium / Epicardium
    • Inner endothelial lining, muscular middle layer, and outer visceral pericardium respectively (lecture detail).

Step-by-Step Blood Flow Through the Heart

  1. Systemic veins → SVC / IVC / Coronary sinus → Right Atrium.
  2. Through Tricuspid (Right AV) valve → Right Ventricle.
  3. Via Pulmonary semilunar valve → Pulmonary trunk → Right & Left pulmonary arteries.
  4. Gas exchange in lungs (pulmonary capillaries).
  5. Oxygenated blood returns via Right & Left pulmonary veins → Left Atrium.
  6. Through Bicuspid (Left AV/Mitral) valve → Left Ventricle.
  7. Via Aortic semilunar valve → Ascending aorta → Aortic arch → Descending aorta.
  8. Systemic arteries distribute to body; systemic veins return to step 1.
  • Sample practical question logic:
    • “Blood returning from the lungs encounters which heart valve next?” → Left AV (Mitral).

Anterior vs Posterior Perspectives (Visual Cues)

  • Anterior view: pulmonary trunk obscures aortic valve; right ventricle dominates visual field; anterior interventricular artery & great cardiac vein visible.
  • Posterior view: left atrium & left ventricle better seen; posterior interventricular artery & middle cardiac vein identifiable; coronary sinus obvious.

Heart Sounds & Valve Function (preview)

  • Systole (ventricular contraction): AV valves snap shut ("lub"); chordae & papillary muscles prevent inversion.
  • Diastole (ventricular relaxation): semilunar valves close ("dup") preventing arterial backflow.
  • Detailed auscultation points & timing discussed elsewhere; reminder only for lab.

Practical Study Tips & Connections

  • Rehearse the flow pathway verbally until automatic.
  • Use vessel color as oxygenation indicator, not artery/vein label.
  • Pair coronary arteries with companion veins (location & naming parallels help memory).
  • Recognize the three aortic-arch branches in situ (learn orientation relative to SVC).
  • Remember: left coronary = front + left; right coronary = right + back.
  • Lab models will likely have removable pulmonary trunk to expose hidden aortic valve & coronary outlets—practice both assembled & disassembled views.