Topics:
Animal Physiology, Animal Refresher
First Heart Sound (Lub) Production
The first heart sound (lub / systolic sound) is produced by:
- Closure of A-V valves — Correct Answer
- Opening of A-V valves
- Closure of semilunar valves
- Opening of semilunar valves
Explanation:
Correct Answer: Closure of A-V valves
The first heart sound (S1 / 'lub' / systolic sound) is produced by the closure of the Atrioventricular (A-V) valves — mitral (bicuspid) valve and tricuspid valve — at the beginning of ventricular systole.
Heart Sound Summary
| Sound | Name | Cause | Timing |
|---|---|---|---|
| S1 (First) | Lub / Systolic sound | Closure of A-V valves (mitral + tricuspid) | Beginning of systole |
| S2 (Second) | Dub / Diastolic sound | Closure of semilunar valves (aortic + pulmonary) | Beginning of diastole |
Cardiac Cycle Key Points
- Natural pacemaker of heart: SA node (sinoatrial node)
- Slowest conduction in heart: AV node (0.05 m/sec) → creates delay for ventricular filling
- Fastest conduction in heart: Purkinje fibers (4 m/sec)
- QRS complex of ECG: Ventricular depolarization
- P-wave: Atrial depolarization; T-wave: Ventricular repolarization
📚 About this Topic — Animal Physiology
This multiple choice question is from Animal Physiology, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Physiology to strengthen your preparation.
