Heart Structure Quiz

Heart Structure

• Located centrally in the chest, beneath the breastbone, roughly the size of a clenched fist.
• Enclosed by a pericardium (double-walled sac) with fluid between its layers.
• A septum separates the heart into two pumps, each with an atrium and a ventricle.
• Atria (upper chambers): Receive and pump blood to ventricles.
• Ventricles (lower chambers): Pump blood out of the heart.
• Right ventricle: Pumps deoxygenated blood to the lungs.
• Left ventricle: Pumps oxygenated blood to the body.
• Ventricle walls are thicker than atria walls (left ventricle thicker than right) due to greater pumping pressures.
• Valves ensure unidirectional blood flow:
  • 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):
    • Bicuspid (mitral) valve (left AV valve, two flaps)
    • Tricuspid valve (right AV valve, three flaps)
  • Chordae tendineae prevent backflow of AV valves during ventricular contraction.

Blood Supply

• The heart requires significant oxygen and nutrients (over 10% of the body's blood supply).
• Coronary blood vessels supply oxygen and nutrients to the heart muscle and remove waste.
• Coronary arteries branch off the aorta.
• Coronary veins drain into the coronary sinus, emptying into the right atrium.

Circulation

• The resting heart pumps approximately 5 liters of blood per minute.
• Maximum output exceeds 25 liters per minute.
• Blood flow pathway:
  • Deoxygenated blood enters the right atrium via superior and inferior vena cava.
  • Right atrium contracts, pushing blood into the right ventricle.
  • Right ventricle contracts, pushing blood to the lungs via pulmonary arteries.
  • Gas exchange occurs in the lungs.
  • Oxygenated blood returns to the left atrium via pulmonary veins.
  • Left atrium contracts, pushing blood into the left ventricle.
  • Left ventricle contracts, pumping blood into the aorta and systemic circulation.

Cardiac Cycle

• Cardiac cycle: Complete heartbeat (contraction and relaxation of heart chambers).
• Typically takes 0.8 seconds at rest.
• Diastole: Relaxation and filling phase.
• Systole: Contraction and emptying phase.

Heart Sounds

• "Lub-dub" sound: Caused by valve closure.
  • "Lub": AV valves closing as ventricles contract.
  • "Dub": Semilunar valves closing as ventricles relax.
• Murmurs: Abnormal sounds from leaking valves, often not life-threatening.

Regulation of Heart Rhythm

• Myogenic heart: Muscle contracts and relaxes independently.
• Controlled by:
  • Sympathetic nervous system (fight-or-flight)
  • Parasympathetic nervous system (rest-and-digest)
• Conduction: Heartbeat initiated by the sinoatrial (SA) node (pacemaker).
• Signal spreads through atria, then to the atrioventricular (AV) node, and finally through Purkinje fibers causing the ventricles to contract from bottom to top.

Electrocardiogram (ECG/EKG)

• Detects and records electrical signals of the heart.
• Provides insights into abnormal heart conditions.
• Components:
  • P wave: Atrial depolarization.
  • QRS complex: Ventricular depolarization.
  • T wave: Ventricular repolarization.