Exercise 30: The Heart – Structure and Conduction System

Heart Anatomy

The heart is a muscular organ responsible for pumping blood throughout the body. Understanding its external and internal structures is essential for identifying its function and clinical relevance.

• Base: The broad, superior aspect of the heart where major vessels attach.

• Apex: The pointed, inferior tip of the heart, directed toward the left hip.

• Atrium (Right & Left): Upper chambers that receive blood returning to the heart.

• Ventricle (Right & Left): Lower chambers that pump blood out of the heart.

• Auricles: Ear-like extensions of the atria that increase atrial volume.

• Coronary Arteries: Supply blood to the heart muscle itself.

  • Left Coronary Artery: Branches into the anterior interventricular branch and circumflex branch.

  • Right Coronary Artery: Branches into the posterior interventricular branch and marginal branch.

• Coronary Sinus: Collects deoxygenated blood from the myocardium and returns it to the right atrium.

• Aortic Arch & Descending Aorta: Major arteries carrying oxygenated blood from the left ventricle to the body.

• Pulmonary Trunk: Carries deoxygenated blood from the right ventricle to the lungs.

• Superior & Inferior Vena Cava: Return deoxygenated blood from the body to the right atrium.

• Ligamentum Arteriosum: Remnant of the fetal ductus arteriosus, connecting the pulmonary trunk to the aorta.

• Interatrial Septum: Wall separating the right and left atria.

• Fossa Ovalis: Depression in the interatrial septum, remnant of the fetal foramen ovale.

• Valves:

  • Tricuspid Valve: Between right atrium and right ventricle.

  • Bicuspid (Mitral) Valve: Between left atrium and left ventricle.

  • Pulmonary Valve: Between right ventricle and pulmonary trunk.

  • Aortic Valve: Between left ventricle and aorta.

• Chordae Tendineae: Tendinous cords connecting AV valves to papillary muscles.

• Papillary Muscles: Muscles in ventricles anchoring the chordae tendineae.

• Trabeculae Carneae: Irregular muscular columns on the inner surface of ventricles.

• Interventricular Septum: Wall separating the right and left ventricles.

Example: On a sheep heart, the apex is easily identified as the pointed end, while the base is broader and where the major vessels enter and exit.

Conduction System of the Heart

The heart's conduction system ensures coordinated contraction for effective pumping.

• Sinoatrial (SA) Node: Located in the right atrium; initiates the heartbeat (pacemaker).

• Atrioventricular (AV) Node: Located at the junction of atria and ventricles; delays impulse to allow atrial contraction.

• AV Bundle (Bundle of His): Conducts impulses from AV node to ventricles.

• Right and Left Bundle Branches: Carry impulses through the interventricular septum.

• Purkinje Fibers: Distribute impulse throughout ventricular myocardium, causing contraction.

Function: This system allows the atria to contract before the ventricles, ensuring efficient blood flow.

Exercise 31: Electrocardiogram (ECG) and Cardiac Cycle

ECG Components

An ECG records the electrical activity of the heart and is used to assess cardiac function.

• P wave: Atrial depolarization (contraction).

• QRS complex: Ventricular depolarization (contraction); atrial repolarization occurs here but is masked.

• T wave: Ventricular repolarization (relaxation).

• P-Q interval: Time from atrial to ventricular depolarization.

• Q-T interval: Time from ventricular depolarization to repolarization.

• S-T segment: Period when ventricles are depolarized.

Heart Rate Calculation

• Heart rate can be calculated from the ECG by measuring the interval between R waves (R-R interval).

Formula:

Cardiac Cycle Timing

• Systole: Period of ventricular contraction.

• Diastole: Period of ventricular relaxation.

• Cardiac cycle duration = time between two consecutive R waves.

Example: If the R-R interval is 0.8 seconds, heart rate is bpm.

Arrhythmias

• Tachycardia: Heart rate > 100 bpm.

• Bradycardia: Heart rate < 60 bpm.

• Identified by measuring R-R intervals on ECG.

Exercise 32: Major Arteries and Veins

Major Arteries

Arteries carry oxygenated blood away from the heart (except pulmonary arteries).

• Aorta: Main artery; includes ascending aorta, aortic arch, descending (thoracic and abdominal) aorta.

• Branches of Aortic Arch: Brachiocephalic trunk, left common carotid, left subclavian.

• Other Major Arteries: Coronary arteries, celiac trunk, superior mesenteric, renal, gonadal, common iliac, femoral, axillary, radial, ulnar, etc.

Major Veins

Veins return deoxygenated blood to the heart (except pulmonary veins).

• Superior and Inferior Vena Cava: Main veins returning blood to the right atrium.

• Brachiocephalic, Jugular, Subclavian, Axillary, Brachial, Cephalic, Basilic, Radial, Ulnar, Renal, Gonadal, Iliac, Femoral, Popliteal, Great Saphenous Veins: Major veins draining various regions.

Exercise 33: Blood Vessels, Heart Sounds, and Blood Pressure

Blood Vessel Structure

Blood vessels have three layers (tunics):

• Tunica intima: Inner endothelial layer.

• Tunica media: Middle smooth muscle layer.

• Tunica externa (adventitia): Outer connective tissue layer.

Arteries have thicker tunica media than veins; veins have larger lumens and valves.

Heart Sounds and Auscultation

• Stethoscope: Device for listening to heart sounds.

• Auscultation: Process of listening to heart sounds.

• Four Auscultation Areas:

  1. Aortic area (right 2nd intercostal space)

  2. Pulmonic area (left 2nd intercostal space)

  3. Tricuspid area (left 4th/5th intercostal space)

  4. Mitral area (left 5th intercostal space, midclavicular line)

• Heart Sounds: "Lub" (S1, AV valves close), "Dub" (S2, semilunar valves close).

• Heart Murmur: Abnormal sound due to turbulent blood flow, often from valve issues.

Pulse and Blood Pressure

• Pulse: Palpable rhythmic expansion of an artery due to heartbeat; common sites include radial, carotid, femoral arteries.

• Sphygmomanometer: Instrument to measure blood pressure.

• Systolic Pressure: Pressure during ventricular contraction.

• Diastolic Pressure: Pressure during ventricular relaxation.

• Normal Range: ~120/80 mmHg (systolic/diastolic).

Blood Pressure Calculation:

• Pulse Pressure: Difference between systolic and diastolic pressures.

• Mean Arterial Pressure (MAP): Average pressure in arteries during one cardiac cycle.

Exercise 35: The Lymphatic System

Lymphatic Vessels and Organs

The lymphatic system returns interstitial fluid to the bloodstream and participates in immune defense.

• Lymphatic Vessel: Contains valves to prevent backflow; lined by endothelium.

• Right Lymphatic Duct: Drains lymph from right upper body into right subclavian vein.

• Thoracic Duct: Drains lymph from rest of body into left subclavian vein.

• Cisterna Chyli: Enlarged sac at the lower end of the thoracic duct.

• Spleen: Filters blood, recycles old red blood cells, and stores white blood cells.

Lymph Node Structure

• Capsule: Outer connective tissue covering.

• Trabeculae: Extensions of capsule into the node.

• Cortex: Outer region with lymphatic nodules (follicles).

• Medulla: Inner region with medullary cords and sinuses.

• Lymphatic Nodules: Densely packed lymphocytes in cortex.

Spleen Structure

• Capsule: Outer covering.

• Trabeculae: Internal extensions.

• Red Pulp: Contains blood-filled sinuses; filters blood.

• White Pulp: Contains lymphocytes; immune function.

Summary Table: Key Cardiovascular and Lymphatic Structures

Additional info: Academic context and definitions have been added for clarity and completeness.