When the doctor listened to Janet's heart, he heard 'lub-hiss, lub-hiss' instead of the normal 'lub-dup' sounds. The hiss is most likely due to _________ . (Explain your answer.) a. a defective atrioventricular (AV) valve b. a damaged pacemaker (SA node) c. a defective semilunar valve d. high blood pressure

Verified step by step guidance

1. Identify the normal heart sounds: The typical heart sounds are 'lub-dup'. The 'lub' (first sound) occurs when the atrioventricular (AV) valves close, and the 'dup' (second sound) occurs when the semilunar valves close.
2. Analyze the abnormal sound: The 'hiss' sound heard in Janet's heart suggests a turbulent or abnormal flow of blood, which is often associated with a heart valve issue.
3. Relate the timing of the sound to valve function: Since the 'hiss' sound follows the 'lub' and replaces the 'dup', it indicates the issue is occurring at the time when the semilunar valves should be functioning.
4. Understand valve defects: A defective semilunar valve can fail to close properly, allowing blood to flow back into the heart chambers (regurgitation), which can create a hissing or whooshing sound.
5. Eliminate other options: A defective AV valve or a damaged pacemaker (SA node) would affect the 'lub' sound or the rhythm of the heart, respectively, and high blood pressure typically does not produce a hissing sound.

Key Concepts

Heart Sounds

The heart produces sounds during its cycle, primarily the 'lub' and 'dup' sounds, which correspond to the closing of the atrioventricular (AV) and semilunar valves, respectively. Abnormal sounds, such as a 'hiss,' can indicate issues with these valves or other cardiac conditions, providing insight into the heart's function and potential problems.

Atrioventricular (AV) Valve Function

The atrioventricular valves, including the tricuspid and mitral valves, separate the atria from the ventricles. A defect in these valves can lead to improper closure, causing abnormal sounds like a 'hiss' due to turbulent blood flow, which is often associated with regurgitation or leakage during the heart's contraction.

Semilunar Valve Function

The semilunar valves, comprising the aortic and pulmonary valves, control blood flow from the ventricles into the arteries. A defect in these valves can also produce abnormal heart sounds, as they may not close properly, leading to backflow or turbulence, which can manifest as a 'hiss' during auscultation.