Understanding the Human Heart
The Heart
The heart, a muscular organ roughly the size of a fist, pumps blood throughout the body via blood vessels. It’s located in the center of the chest, between the lungs.
Heart Walls and Chambers
The heart walls consist of myocardial muscle, responsible for involuntary contractions. The heart’s interior is divided into right and left halves, separated by a wall to prevent mixing. Each half contains two interconnected chambers: an upper atrium and a lower ventricle. The ventricles have thicker walls than the atria, enabling them to pump blood to the rest of the body. The atria and ventricles connect through auriculoventricular valves:
- Mitral Valve: Connects the left atrium and left ventricle (two leaflets).
- Tricuspid Valve: Connects the right atrium and right ventricle (three leaflets).
These valves regulate blood flow, allowing passage from atria to ventricles but not vice-versa.
Blood Flow
Entry Routes (Veins to Atria)
- Left Atrium: Receives blood from four pulmonary veins (two from each lung).
- Right Atrium: Receives blood from two venae cavae (superior and inferior), carrying blood from the body.
Exit Routes (Ventricles to Arteries)
- Right Ventricle: Pumps blood to the pulmonary artery, which branches to carry blood to each lung.
- Left Ventricle: Pumps blood to the aorta, distributing it throughout the body.
Semilunar valves at the base of the arteries control blood flow from the ventricles, opening during ventricular contraction and preventing backflow.
Coronary Circulation
The heart receives its own blood supply via coronary arteries and veins, delivering oxygen and nutrients.
Heart Function
The heart functions as a pump, propelling blood through blood vessels. Its operation involves coordinated contractions (systole) and relaxations (diastole) in the atria and ventricles.
The Cardiac Cycle
The cardiac cycle is the sequence of contractions and relaxations that pump blood. Each cycle comprises:
- Diastole: Blood enters the heart. The right atrium receives blood from the venae cavae, and the left atrium from the pulmonary veins. The atria expand while the mitral and tricuspid valves remain closed.
- Atrial Systole: The atria contract, opening the mitral and tricuspid valves, allowing blood to flow into the ventricles.
- Ventricular Diastole: The ventricles expand to receive blood from the atria. The semilunar valves are closed, preventing backflow from the arteries.
- Ventricular Systole: The ventricles contract, opening the semilunar valves. The mitral and tricuspid valves close to prevent backflow into the atria. Blood is pumped from the left ventricle into the aorta and from the right ventricle into the pulmonary artery. Once blood enters the arteries, the semilunar valves close to prevent backflow.
These coordinated movements ensure continuous blood flow through the heart.