Guyton Chapter 23: Heart Valves And Heart Sounds

Question 1

What is the lub sound associated with when listening to heart sounds?

Answer 1

The closure of the atrioventricular valves at the beginning of the systole

Question 2

What is the dub sound associated with when listening to heart sounds?

Answer 2

Closure of the semilunar (aortic and pulmonary valves) at the end of systole.

Question 3

What is the main cause of the first heart sound?

Answer 3

Vibration of the taut valves immediately after closure along with vibration of the adjacent walls of the heart and major vessels around the heart.

In generating the first heart sound, contraction of ventricles first causes sudden back flow of blood against the AV valves causing them to close and bulge toward the atria until the cross tendineae abruptly stop the back bulging.

The elastic tautness of the Cordae and valves then causes the back surging blood to bounce forward again into each respective ventricle. This mechanism causes the blood and the ventricular walls to vibrate and causes vibrating turbulence in the blood.

Question 4

What is the duration of each of the heart sounds and why do they differ?

Answer 4

The duration of each of the heart sounds is slightly more than 0,10 seconds with the first sound about 0,14 seconds and the second about 0,11 second. The reason for the shorter second sound is that the semilunar valves are tauter than the AV valves so they vibrate for a shorter time than do the AV valves.

Question 5

When can the third heart sound be heard?

Answer 5

At the beginning of the middle third of diastole.

Question 6

What is the explanatory of the third heart sound?

Answer 6

Oscillation of blood back and forth between the walls of the ventricles initiated by in rushing blood from the atria.

Question 7

What is the fourth heart sound caused by?

Answer 7

Atrial contraction