Anatomy of the Heart

Anatomical Location of the Heart

• The heart is roughly the size of a closed fist, measuring 12cm long, 9 cm wide, and 6 cm thick.
• The heart weighs approximately 250g.
• Situated in the mediastinum, between the sternum, vertebral column, first rib, and between the lungs.
• Two-thirds of the heart's mass lies to the left of the midline.

Heart Surface Anatomical Markings

• Anterior (Sternocostal) Surface: Right atrium and right ventricle.
• Inferior (Diaphragmatic) Surface: Right and left ventricles.
• Posterior Surface: Predominantly the left atrium.

Borders and Apex

• The heart has three borders, forming a pyramidal shape:
  • Inferior Border: Right ventricle.
  • Left Border: Left ventricle and a portion of the left atrium.
  • Right Border: Right atrium.
• The apex, the tip of the left ventricle, rests on the diaphragm.
• The base is formed by the atria.

Pericardium

• The pericardium is the membranous sac surrounding the heart.
• It anchors the heart within the mediastinum while allowing for vigorous contractions.
• Consists of two parts:
  • Fibrous Part: Tough, inelastic connective tissue that connects to the heart and blood vessels. It prevents overstretching.
  • Serous Part: Thinner layer, comprising a double layer. The outer parietal layer is attached to the fibrous part, while the inner visceral layer forms the epicardium.

Pericardial Fluid

• Between the two layers of the serous pericardium, a lubricating fluid (about 30 ml) reduces friction during heart movement.

Pericarditis

• Inflammation of the pericardium.
• Can be caused by various factors, including viral, bacterial infections, and radiation.
• Characterized by chest pain radiating to the left shoulder and arm.
• Often mistaken for a heart attack.
• ST elevation across all leads is observed.
• Pericardial friction rub: A creaking sound heard with a stethoscope in about 40% of patients.

Muscular Structures of the Heart

• The heart wall is composed of three layers:
  • Epicardium: The visceral layer of the serous pericardium, containing adipose tissue and blood vessels supplying the myocardium.
  • Myocardium: Cardiac striated muscle tissue responsible for heart contraction.
  • Endocardium: Smooth inner lining on connective tissue, lining the chambers and valves.

Chambers of the Heart

• The heart has four chambers:
  • Atria (superior): Increase the heart's capacity.
  • Ventricles (inferior): Responsible for pumping blood.
• Sulci: Grooves on the heart's surface:
  • Coronary Sulcus: Divides the atria from the ventricles.
  • Anterior and posterior Interventricular Sulci: Divide the two ventricles.

Right Atrium

• Receives blood from the:
  • Inferior vena cava
  • Superior vena cava
  • Coronary sinus
• Pectinate muscles: Rough muscular ridges on the anterior wall.
• Interatrial septum: A thin wall separating the right and left atrium.
• Blood from the right atrium enters the ventricle through the tricuspid valve (3 cusps).

Right Ventricle

• Trabeculae carneae: Raised bundles of cardiac muscle fibers.
• Chordae tendineae: Tendons connecting to the leaflets of the tricuspid valve.
• Papillary muscles: Muscles attached to chordae tendineae.
• Interventricular septum: Divides the two ventricles.
• Blood exits the heart through the pulmonary valve, entering the pulmonary trunk.

Left Atrium

• Receives blood from the four pulmonary veins.
• Blood passes from the atrium to the ventricle through the bicuspid (mitral) valve (2 cusps).

Left Vetricle

• Similar to the right ventricle, it contains trabeculae carneae, chordae tendinae that anchor the mitral valve cusps to papillary muscles.
• Blood exits the ventricle via the aortic valve, entering the ascending aorta.
• Coronary arteries and descending aorta originate from the ascending aorta.

Myocardial Thickness

• The thickness of the myocardium varies based on the chamber's function:
  • Atria: 2-3 mm thick, as they only need to deliver blood to the ventricles.
  • Ventricles: Thicker due to their need to pump blood further with higher pressure.
    • Right ventricle: 4-5 mm thick.
    • Left ventricle: 10-15 mm thick, due to its responsibility for pumping blood throughout the body.

Fibrous Skeleton

• A dense connective tissue that provides structural support for the heart.
• It serves as an insertion point for muscle bundles and acts as an electrical insulator between the atria and ventricles.

Valves of the Heart

• Atrioventricular Valves (Tricuspid and Mitral):

  • Open during atrial contraction (high pressure): The cusps project into the ventricle.
  • Close during ventricular contraction (high pressure): The cusps are pulled upwards and closed.
  • Papillary muscles: Contract to prevent cusps from opening into the atrium.

• Semilunar Valves (Aortic and Pulmonary):

  • Open during ventricular contraction (high pressure): Blood flows into the arteries, and cusps project into the lumen.
  • Close during ventricular relaxation (low pressure): Blood flows back, filling the cusps and promoting closure, preventing backflow.

Main Great Vessels

• Five great vessels enter and exit the heart:
  • Superior vena cava & Inferior vena cava: Carry deoxygenated blood from the body to the right atrium.
  • Pulmonary artery: Carries deoxygenated blood from the right ventricle to the lungs (oxygenation).
  • Pulmonary veins: Carry oxygenated blood from the lungs to the left atrium.
  • Aorta: Carries oxygenated blood from the left ventricle into general circulation.