Anatomy and Physiology of the Heart

The Systemic Circuit (Oxygenated Blood)

Once oxygenated, blood returns to the heart via the right pulmonary veins and left pulmonary veins into the left atrium. It then moves through the mitral (bicuspid) valve into the left ventricle. Finally, the left ventricle—the strongest chamber—ejects blood through the aortic semilunar valve into the aorta for systemic distribution throughout the entire body.

Internal Structures and Valve Mechanics

The heart contains specialized structures to ensure that blood flows in only one direction and that the chambers maintain their structural integrity.

• Valves: The atrioventricular valves (tricuspid and mitral) prevent backflow into the atria, while the semilunar valves (pulmonary and aortic) prevent backflow from the great vessels into the ventricles.
• Chordae Tendineae and Papillary Muscles: These structures work in tandem to anchor the atrioventricular valves. The papillary muscles contract to pull on the chordae tendineae (often called "heart strings"), which prevents the valves from prolapsing into the atria during the high-pressure ventricular contraction.
• Trabeculae Carneae: These are irregular muscular ridges located within the ventricles that help prevent suction and assist in contraction.
• Fossa Ovalis: This is a shallow indentation located in the interatrial septum, representing the remnant of the fetal foramen ovale.

Protective Layers and Myocardium

The heart is not an isolated organ; it is encased in protective layers and possesses its own dedicated blood supply. The muscular tissue that makes up the bulk of the heart wall is known as the myocardium. The heart is further protected by the visceral pericardium.

Coronary Circulation: The Heart's Own Supply

Because the myocardium is so thick, it cannot rely on the blood passing through its chambers to nourish its own cells. Instead, it receives oxygenated blood directly through the coronary arteries. Key components of this system include:

1. Left main coronary artery
2. Left anterior descending coronary artery
3. Circumflex coronary artery
4. Right coronary artery

Failure of these vessels to provide adequate blood flow can lead to significant cardiac issues, as the myocardium requires constant oxygenation to maintain its rhythmic pumping action.

img-2.jpeg External anatomy showing the relationship between the aorta and coronary arteries.