Lecture Notes: Anatomical Position and Structure of the Heart

Anatomical Position of the Heart

• Located in the mediastinum (space between pleural cavities of lungs).
• Superior to the diaphragm.
• Two-thirds of the heart lies left of the midline, known as the mid-sternal line.
• Anteriorly protected by the sternum and posteriorly by the vertebral column.

Point of Maximal Intensity (PMI)

• Key location on the chest where heartbeats are best heard/felt.
• Important for diagnosing heart murmurs and potential disorders.

Major Anatomical Regions of the Heart

Base

• Attached to major blood vessels: aorta, superior vena cava, pulmonary arteries.

Apex

• Narrow end projecting into the left lung.

Heart Wall Layers (Interior to Exterior)

1. Endocardium: Innermost layer, lined with endothelium and loose areolar tissue.
2. Myocardium: Muscular layer with cardiac muscle cells.
3. Epicardium (Visceral Pericardium): Directly covers heart surface.
4. Pericardial Cavity: Contains lubricating fluid.
5. Parietal Pericardium: Lines heart cavity wall.
6. Fibrous Pericardium: Outermost layer, prevents heart enlargement.

Heart Chambers

• 4 chambers: 2 atria (receiving chambers) and 2 ventricles (discharging chambers).
• Right Atrium (RA): Receives systemic blood.
• Left Atrium (LA): Receives pulmonary blood.
• Right Ventricle (RV): Pumps blood to lungs.
• Left Ventricle (LV): Pumps blood to body.
• Interatrial and Interventricular Septa: Walls separating chambers.

Valves

Atrioventricular Valves

• Tricuspid Valve (TV): Between RA and RV.
• Mitral Valve (MV)/Bicuspid Valve: Between LA and LV.

Semilunar Valves

• Pulmonary Semilunar Valve (PSV): Between RV and pulmonary arteries.
• Aortic Semilunar Valve (ASV): Between LV and aorta.

Blood Flow Pathway

• Right Side: Deoxygenated blood flows from SVC/IVC -> RA -> TV -> RV -> PSV -> lungs.
• Left Side: Oxygenated blood flows from pulmonary veins -> LA -> MV -> LV -> ASV -> aorta -> body.

Principles of Blood Vessels

• Veins: Carry deoxygenated blood towards the heart (except pulmonary veins).
• Arteries: Carry oxygenated blood away from the heart (except pulmonary arteries).

Coronary Circulation

• Coronary Arteries: Deliver oxygenated blood to heart muscle.
• Coronary Veins: Carry deoxygenated blood from heart muscle.

Key Muscles

• Pectinate Muscles: Found in atria, increase contraction force without increasing heart mass.
• Trabeculae Carneae & Papillary Muscles: Found in ventricles, prevent blood regurgitation.

Chordae Tendineae

• Tendinous cords preventing valve backflow.
• Work with papillary muscles and trabeculae carneae to seal atrioventricular valves during contraction.