Chapter 13: Problem 4
The first heart sound is produced at a. the beginning of systole. b. the end of systole. c. the beginning of diastole. d. the end of diastole.
Short Answer
Expert verified
The first heart sound is produced at the beginning of systole.
Step by step solution
01
Understand the cardiac cycle
The cardiac cycle is how the heart functions and is divided into two main phases: systole and diastole. Systole refers to the phase when the heart contracts and pumps blood out into the circulation. Diastole refers to the phase when the heart relaxes and fills with blood.
02
Definition of each option
a. The beginning of systole: This is when the heart starts contracting and blood is pumped out from the heart.
b. The end of systole: This is the point when the pump is complete, and the heart stops contracting.
c. The beginning of diastole: This is when the heart starts relaxing and filling with blood.
d. The end of diastole: This is the point when the heart is fully relaxed and filled with blood, ready for the next systole phase.
03
Identify when the first heart sound is produced
The first heart sound (S1) is produced by the closure of the atrioventricular (AV) valves during ventricular contraction (systole). It is the sound of the blood pressure building up and causing the AV valves to close in response. Therefore, the first heart sound is produced at the beginning of systole.
04
Choose the correct option
Based on our understanding of the cardiac cycle and when the first heart sound occurs, we can confidently choose the correct answer:
a. The beginning of systole.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Heart Sounds
One of the fascinating aspects of the cardiac cycle is the sounds produced by the heart. These sounds are often referred to as "heart sounds," and they provide vital clues about the heart's functioning. When we listen through a stethoscope, the two main audible sounds are the first heart sound (S1) and the second heart sound (S2).
- S1: This sound occurs at the start of systole. It's largely due to the closure of the atrioventricular (AV) valves, which include the mitral and tricuspid valves. This closure prevents the backflow of blood from the ventricles to the atria when the heart contracts.
- S2: Occurring at the beginning of diastole, this sound is attributed to the closure of the semilunar valves, namely the aortic and pulmonary valves. This closure helps stop the backflow of blood into the heart from the aorta and pulmonary artery once the heart relaxes.
Systole
Systole is an essential part of the cardiac cycle where the heart is actively contracting. Its primary purpose is to pump blood out to the body and lungs. Systole is critical for ensuring that oxygen-rich blood reaches all tissues and organs.
During systole:
- The ventricles contract, increasing the pressure within them.
- This pressure prompts the closure of the AV valves, leading to the first heart sound (S1).
- The increased pressure then opens the semilunar valves, allowing blood to flow from the heart into the aorta and pulmonary artery.
Diastole
Diastole is the phase of the cardiac cycle when the heart relaxes after contraction. This relaxation is critical, allowing the heart to fill with blood in preparation for the next systolic phase.
During diastole:
- The heart muscle relaxes after the contraction.
- Blood pressure within the heart drops, causing the semilunar valves to close, which marks the second heart sound (S2).
- The reduced pressure allows the AV valves to open, letting the heart chambers refill with blood.