Cardiac Muscle Structure

Key Features of Cardiac Muscle

Cardiac muscle is specialized for continuous rhythmic contraction and is found only in the heart. Its unique structure supports its function in pumping blood throughout the body.

• Intercalated Discs: Specialized connections between cardiac muscle cells that facilitate synchronized contraction by allowing rapid transmission of electrical impulses.

• Nucleation: Cardiac muscle cells are typically uninucleate but may occasionally be binucleate.

• Striations: Cardiac muscle fibers display striations due to the organized arrangement of actin and myosin filaments, similar to skeletal muscle.

Coronary Circulation

Coronary Arteries and Veins

The heart receives its blood supply from the coronary arteries and returns deoxygenated blood via the coronary veins. This circulation is essential for delivering oxygen and nutrients to cardiac tissue.

• Coronary Arteries:

  • Left Coronary Artery: Branches into the Anterior Interventricular Artery (also known as the Left Anterior Descending Artery) and the Circumflex Artery.

  • Right Coronary Artery: Supplies the right side of the heart.

• Coronary Veins:

  • Great Cardiac Vein: Drains blood from the anterior surface of the heart.

  • Coronary Sinus: Collects blood from the cardiac veins and empties into the right atrium.

Cardiac Conduction System

Electrical Pathways of the Heart

The cardiac conduction system coordinates the heartbeat through a series of specialized structures that generate and transmit electrical impulses.

• Sinoatrial (SA) Node: The primary pacemaker of the heart, located in the right atrium; initiates each heartbeat.

• Atrioventricular (AV) Node: Receives impulses from the SA node and delays them before passing to the ventricles.

• Atrioventricular (AV) Bundle (Bundle of His): Conducts impulses from the AV node to the bundle branches.

• Right and Left Bundle Branches: Carry impulses down the interventricular septum toward the apex.

• Apex: The pointed end of the heart where the bundle branches converge.

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

ECG (Electrocardiogram): A diagnostic tool that records the electrical activity of the heart. Key components include:

• P wave: Represents atrial depolarization.

• QRS complex: Represents ventricular depolarization.

• T wave: Represents ventricular repolarization.

Heart Sounds

Valvular Closure and Auscultation

Heart sounds are produced by the closing of heart valves and can be heard using a stethoscope. They provide important information about cardiac function.

• Lub (S1): First heart sound, caused by closure of the atrioventricular (mitral and tricuspid) valves.

• Dub (S2): Second heart sound, caused by closure of the semilunar (aortic and pulmonary) valves.

• Auscultation: The process of listening to heart sounds at specific anatomical locations to assess valve function.

Heart Defects and Arrhythmias

Common Cardiac Disorders

Heart defects and arrhythmias can disrupt normal cardiac function and may require medical intervention.

• Bradycardia: Abnormally slow heart rate.

• Tachycardia: Abnormally fast heart rate.

• Pacemakers: Devices implanted to regulate abnormal heart rhythms.

• Fibrillation: Rapid, irregular contractions of the heart muscle, which can be life-threatening.

Major Arteries of the Body

Systemic and Pulmonary Arteries

Arteries carry oxygenated blood away from the heart (except pulmonary arteries, which carry deoxygenated blood to the lungs). The following list includes major arteries and their branches.

• Aortic Arch: Gives rise to major arteries supplying the head, neck, and upper limbs.

• Descending Aorta: Continues as the thoracic and abdominal aorta.

• Pulmonary Trunk: Splits into pulmonary arteries leading to the lungs.

• Brachiocephalic Artery: Supplies the right arm and head.

• Common Carotid Artery: Divides into internal and external carotid arteries.

• Subclavian, Axillary, Brachial, Radial, Ulnar: Major arteries of the upper limb.

• Renal, Celiac Trunk, Superior/Inferior Mesenteric: Supply abdominal organs.

• Iliac, Femoral, Popliteal, Tibial: Major arteries of the lower limb.

• Circle of Willis: An arterial circle at the base of the brain providing collateral blood flow.

Major Veins of the Body

Systemic and Pulmonary Veins

Veins return deoxygenated blood to the heart (except pulmonary veins, which carry oxygenated blood from the lungs to the heart). The following list includes major veins and their branches.

• Vena Cava: Superior and inferior vena cava return blood from the body to the right atrium.

• Brachiocephalic, Jugular, Subclavian, Axillary, Cephalic, Basilic, Median Cubital: Major veins of the head, neck, and upper limb.

• Renal, Hepatic, Portal, Testicular, Ovarian: Major veins of the abdomen.

• Iliac, Femoral, Popliteal, Tibial, Great Saphenous: Major veins of the lower limb.

• Ductus Venosus: Fetal vein that shunts blood from the umbilical vein to the inferior vena cava.

Arterial and Venous Pathways Table

Comparison of Major Arteries and Veins

The following table summarizes the main arteries and veins, their locations, and the regions they supply or drain.

Additional info:

• Some anatomical terms and vessel names were inferred based on standard cardiovascular anatomy.

• Details about the ECG and heart sounds were expanded for academic completeness.

• Table entries were logically grouped and completed for clarity.