Heart Structure

Heart Structure

• Located in the chest, slightly under the breastbone, roughly the size of a fist
• Enclosed by a double-walled sac (pericardium) containing fluid
• A septum divides the heart into two parallel pumps (left and right)
• Each pump has an atrium (top) and a ventricle (bottom)
• Atria receive blood and pump it into ventricles
• Ventricles pump blood; the right ventricle pumps to the lungs (pulmonary circulation), and the left ventricle pumps to the body (systemic circulation)
• Ventricle walls are thicker than atria walls; the left ventricle is thicker than the right ventricle due to the greater force needed to pump blood to the entire body
• Valves control blood flow in one direction:
  • Semilunar valves (between ventricles and arteries):
    • Pulmonary semilunar valve (right ventricle to pulmonary arteries)
    • Aortic semilunar valve (left ventricle to aorta)
  • Atrioventricular valves (between atria and ventricles):
    • Left AV valve (bicuspid/mitral valve)
    • Right AV valve (tricuspid valve)
    • Chordae tendineae prevent backflow during ventricular contractions

Blood Supply

• The heart needs a significant portion of the blood's oxygen and nutrients (~10%)
• Coronary blood vessels supply the heart with oxygen and nutrients, and remove waste products.
• Coronary arteries branch from the aorta
• Coronary veins merge to form the coronary sinus, which drains into the right atrium

Circulation

• The heart pumps 5 liters per minute at rest, and over 25 liters per minute during maximum output
• Deoxygenated blood enters the right atrium from vena cava.
• The right atrium contracts, and gravity assist blood into the right ventricle.
• The right ventricle contracts to pump blood through pulmonary arteries to the lungs for gas exchange.
• Oxygenated blood returns to the heart's left atrium via pulmonary veins.
• The left atrium contracts and pumps blood to the left ventricle.
• The left ventricle contracts to pump oxygenated blood into the aorta, initiating systemic circulation

Cardiac Cycle

• The cardiac cycle is a complete heartbeat, involving contraction and relaxation of heart chambers.
• Under normal conditions, the cycle lasts ~0.8 seconds.
• Diastole: Heart relaxation and filling with blood
• Systole: Heart contraction and emptying

Heart Sounds

• "Lub-dub" sound is caused by valve closure.
• "Lub": AV valve closure as ventricles contract
• "Dub": Semilunar valve closure as ventricles relax
• Murmurs indicate inefficient valve function, requiring higher heart rate

Regulation of Heart Rhythm

• The heart is myogenic—it can contract and relax on its own.
• Heart rate is regulated by sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) nervous systems.
• The sinoatrial node (SA node) initiates the heartbeat (pacemaker).
• Signal travels through atria, causing contraction.
• Signal reaches the atrioventricular node (AV node)
• Signal travels through the purkinje fibers, causing ventricular contraction from the bottom.

Electrocardiograph (ECG/EKG)

• An ECG measures and records electrical activity of the heart.
• Analysis helps identify abnormal heart conditions
• P wave: atrial depolarization
• QRS complex: ventricular depolarization
• T wave: ventricular repolarization

Explore the intricate structure of the heart, including its chambers, valves, and the circulatory functions of the right and left ventricles. This quiz covers essential aspects such as the role of the pericardium and the differences in wall thickness between atria and ventricles. Test your understanding of how the heart pumps blood throughout the body.