Physiology Lab (Phsl 3063, Phsl 3701)

Fall 2012












Lesson Summaries

Review Material


 Atlas of Human Cardiac Anatomy


BME Department

Physiology Department

Institute of Technology







Lesson 7 - ECG and Pulse & Lesson 17 - Heart Sounds

Your heart is divided into four chambers - right atrium, right ventricle, left atrium, and left ventricle. Deoxygenated venous blood travels to the right atrium because the right atrium is at a lower pressure than the veins. The blood flows into the right ventricle when enough pressure builds to cause the tricuspid valve to open. As soon as the pressure in the right atrium falls below the pressure in the ventricle, the tricuspid valve closes. When the right ventricle contracts enough so that the pressure of the ventricle exceeds the pressure in the pulmonary system, the pulmonic valve opens and the blood flows into the lungs to get oxygenated. Oxygenated blood flows from the pulmonary system into the left atrium until the pressure in the atrium exceeds that of the ventricle. This causes the mitral or bicuspid valve to open until the pressure in the ventricle is higher than the atrium. After the left ventricle contracts and the pressure exceeds that of the aorta, the aortic valve opens and the blood travels into the aorta. The arteries and especially the aorta have elastic fibers, which allows them to expand enough to accept this high pressure blood volume or stroke volume. This elasticity or compliance allows the arteries to transmit a pressure wave or pulse to the periphery. How fast this pulse travels depends on how compliant the arteries are; the more compliance a vessels has the slower a pulse will conduct to the periphery.

eart Valves

Image from

The open and closing of the heart valves cause the two main heart sounds (there are four heart sounds but only two will be discussed). The first heart sound or S1 is caused by the closing of the atrioventricular valves (tricuspid and mitral) and corresponds to ventricular depolarization. The second heart sound or S2 is caused by the closing of the semilunar valves (pulmonic and aortic) and corresponds to the end of ventricular depolarization. You learned in lab that there are four regions on the chest where you can best hear each valve - aortic, pulmonic, tricuspid, and mitral. Since S1 is caused by the closing of the AV valves, the first heart sound can best be heard in the mitral position. And since S2 is caused by the closing of the semilunar valves, the second heart sound is best heard in the aortic position. In general, in a normal healthy person, you would expect the loudest heart sound to be the second since flow from the ventricles is more forceful than that from the atria.















This page was last updated on August 29, 2007